,transcriber's ,notes ,text transcribed between underscores represents text printed in italics in the source doument4 ,small capitals have been replaced with ,,all ,,capitals4 text and text represent superscript and subscript text resepecively4 ,text between tildes represents marginalia4 ,illustration3 ,,skerryvore ,,lighthouse4 ,,account ,,of ,,the ,,skerryvore ,,lighthouse1 ,,with ,,notes ,,on ,,the ,,illumination ,,of ,,lighthouses2 ,,by ,,alan ,,stevenson1 ,,ll4,b41 ,f4,r4,s4,e41 ,m4,i4,c4,e41 ,,engineer ,,to ,,the ,,northern ,,lighthouse ,,board4 ,illustration3 ,,northern ,,lighthouses ,,in ,,salutem ,,omnium4 8 0 ,inscription on the ,ancient ,pharos of ,alexandria4 ,,by ,,order ,,of ,,the ,,commissioners ,,of ,,northern ,,lighthouses4 ,,adam ,,and ,,charles ,,black1 ,,north ,,bridge1 ,,edinburgh4 ,,longman ,,and ,,co41 ,,london4 ,,mdcccxlviii4 ,,printed ,,by ,,neill ,,and ,,company1 ,,edinburgh4 ,,preface4 ,i am unwilling to dismiss the following pages from my hands without saying a few words in extenuation of the defects which they contain4 ,my chief plea in defence is1 that the preparation of this ,account of the ,skerryvore ,lighthouse1 and the ,notes on the ,illumination of ,lighthouses which follow it1 was not chosen or assumed by me1 but was a task imposed by the express desire of the ,lighthouse ,board1 to whose enlightened and liberal views the ,mariner owes the erection of the ,lighthouse itself4 ,my labours were also continually interrupted by the urgent calls of my official duties2 and1 on several occasions1 ,i was forced to dismiss unfinished chapters from my mind for a period of several months--circumstances which1 ,i hope1 will in some measure account for the desultory character of the performance1 the disproportion of some of its parts1 and more especially for repetitions and perhaps omissions which would otherwise have been quite unpardonable4 ,having said thus much by way of apology for this ,volume1 ,i must acknowledge my many and great obligations to my ,father who preceded me as ,engineer to the ,board of ,northern ,lighthouses1 and of whose experience1 as the ,architect of no fewer than twenty-five ,lighthouses1 including that of the ,bell ,rock1 ,i had the full benefit during the erection of the ,skerryvore ,lighthouse4 ,to the generosity of my esteemed friend1 ,m4 ,,leonor ,,fresnel1 ,i owe all that ,i know of the ,dioptric ,system of ,illumination1 invented by his late illustrious ,brother2 but this general acknowledgment will not supersede the necessity of frequent repetitions of my obligations to him1 as occasion offers1 in the course of these pages4 ,i have also derived much assistance1 as a careful reader will easily trace1 from the valuable little work of ,m4 ,,peclet1 entitled ,trait de l',eclairage4 ,there are1 besides1 many other obligations1 which ,i cannot attempt to acknowledge individually1 but which those1 who kindly conferred them1 well know how much ,i value4 99 99 99 99 99 ,in the ,account of the ,skerryvore ,lighthouse1 which forms the first part of this ,volume1 there is an important omission2 and1 in this short prefatory notice1 ,i gladly embrace the only opportunity1 which now remains1 of supplying the defect4 ,although1 in the course of the ,narrative1 ,i have occasionally noticed some special deliverances from danger1 ,i have altogether neglected to record the remarkable fact1 that1 amidst our almost daily perils1 during six seasons on the ,skerryvore ,rock1 there was no loss of either life or limb amongst us4 ,those who best know the nature of the service in which we were engaged1--the daily jeopardy connected with landing weighty materials in a heavy surf and transporting the workmen in boats through a boisterous sea1 the risks to so many men1 involved in mining the foundations of the ,tower in a space so limited1 and above all1 the destruction1 in a single night by the violence of the waves1 of our temporary barrack on the ,rock1 which had cost the toils of a whole season1 will not wonder that ,i am anxious to express1 what ,i know to have been a general feeling amongst those engaged in the work--that of heartfelt thankfulness to ,,almighty ,,god for merciful preservation in danger1 and for the final success which terminated our arduous and protracted labours4 ,,edinburgh1 ,march #be1 #ahdh4 ,,contents4 ,,part ,i4 ,,account ,,of ,,skerryvore ,,lighthouse4 ,page ,introduction -- ,constitution of the ,lighthouse ,board -- ,lights established since #ahba -- ,improvements in the mode of illumination -- ,dioptric ,lights -- ,beacons and ,buoys1 #i ,,chapter ,i4 ,topographic notice of the ,skerryvore ,rock1 #ai ,,chapter ,,ii4 ,preliminary arrangements and works1 including survey of the rocks1 and opening of quarries from #ahcd to #ahcg -- ,survey of the ,skerryvore rocks -- ,disadvantages of ,tyree -- ,pier and workyard at ,hynish1 ,tyree -- ,quarries at ,hynish -- ,skerryvore ,committee appointed1 #cg ,,chapter ,,iii4 ,on the construction of ,lighthouse ,towers1 #de ,,chapter ,,iv4 ,,operations ,,of #ahch4 ,temporary ,barrack on ,rock -- ,tools and machinery -- ,steam ,tender for the works -- ,employment and wages of workmen -- ,progress of the outfit for the season's operations -- ,embark for ,skerryvore -- ,lay down moorings1 and try to land on the ,rock -- ,driven to ,mull -- ,first day's work on the ,rock -- ,shipment of materials at ,glasgow and ,greenock -- ,reach ,tyree -- ,driven to ,mull -- ,return to ,tyree -- ,first good day's work on the ,rock -- ,sudden gale and great peril to the vessels -- ,reach ,hynish in safety -- ,detained by bad weather four days at ,hynish -- ,return to the ,rock and have six days of good weather -- ,erection of the pyramid of the wooden barrack -- ,mode of determining the length of the beams1 and the sites for their fixtures -- ,pyramid completed -- ,mode of living while erecting the barrack -- ,shoals of ,medus seen -- ,driven by a gale to ,mull -- ,return to ,hynish and are driven to ,coll -- ,return to the ,rock -- ,driven to ,tyree -- ,return to the ,rock -- ,horizontal braces fixed -- ,driven to ,mull -- ,heavy gale -- ,timber cast on ,tyree -- ,return to ,rock and further progress of barrack -- ,last day's work on ,rock this season -- ,precaution for the benefit of shipwrecked seamen -- ,view from top of pyramid -- ,destruction of the barrack during a gale -- ,letter from ,mr ,hogben -- ,proceed to ,skerryvore -- ,state in which the ,rock was found -- ,cause of the destruction of the barrack -- ,preparations for a new barrack -- ,works at ,hynish -- ,hynish quarries1 #ga ,,chapter ,v4 ,,operations ,,of #ahci4 ,shipping station and pier at ,hynish -- ,granite quarries in ,mull -- ,observations on the quarrying of granite -- ,dressing of the ,lighthouse blocks -- ,excavation of foundation for the ,lighthouse ,tower on the ,skerryvore ,rock -- ,fitting up of the second barrack on the ,rock -- ,sudden death of ,george ,middlemiss -- ,wharf and landing-place on the ,rock -- ,ring-bolts1 water-tanks1 and railways -- ,incidents of the season -- ,effects of a gale from the south-west -- ,mutiny of the crew -- ,near approach of the vessels to the ,rock1 and other circumstances shewing the importance of a ,light on the ,skerryvore1 #ajg ,,chapter ,,vi4 ,,operations ,,of #ahdj4 ,hynish workyard -- ,hynish pier -- ,the ,rock -- ,life in the barrack -- ,foundation-pit -- ,landing of the materials on the ,rock -- ,laying the first stone1 #adj ,,chapter ,,vii4 ,,operations ,,of #ahda4 ,hynish workyard -- ,the ,rock -- ,the waves -- ,colours of the breaking waves -- ,the seals1 #aea ,,chapter ,,viii4 ,,operations ,,of #ahdb4 ,state of the ,rock in ,spring of #ahdb -- ,commencement of ,rock operations -- ,last stone -- ,the ,lantern1 #afc ,,chapter ,,ix4 ,,concluding ,,operations ,,and ,,exhibition ,,of ,,the ,,light4 ,harbour works -- ,bo ,pheg beacon -- ,light-keepers' and seamen's houses -- ,concluding works on the ,rock1 such as pointing1 c4 -- ,interior fittings of the ,tower -- ,light-room apparatus1 and first exhibition of the ,light -- ,removal of the barrack from the ,rock -- ,expense1 #afi ,,part ,,ii4 ,,notes ,,on ,,the ,,illumination ,,of ,,lighthouses1 ,,with ,,short ,,notices ,,of ,,their ,,history1 #aha4 ,early history1 #aha -- ,colossus of ,rhodes1 #ahb -- ,pharos of ,alexandria1 #ahc -- ,coruna ,tower1 #ahg -- ,lighthouse at the mouth of the ,quadalquivir1 #ahh -- ,ancient ,phari in ,britain1 #ahh -- ,tour de ,corduan1 #ahi -- ,eddystone1 #ahi -- ,bell ,rock1 #aib -- ,carlingford1 #aid -- ,iron lighthouses1 #aid -- ,early modes of illumination1 #aie -- ,flame1 #aif -- ,drummond and ,voltaic ,lights1 #aii -- ,mr ,gurney's ,lamp1 #bjj -- ,argand ,burners1 #bjj4 ,,catoptric ,,system ,,of ,,lights1 #bjd4 ,application of ,paraboloidal ,mirrors1 #bje -- ,reflection1 #bjg -- ,paraboloidal ,mirrors1 #bji -- ,divergence of ,paraboloidal ,mirrors1 #bab -- ,effect of ,paraboloidal ,mirrors1 #bag -- ,power of ditto1 #bah -- ,manufacture of reflectors1 #bah -- ,testing of mirrors1 #bai -- ,argand ,lamps used in reflectors1 #bbj -- ,arrangements for raising or lowering the ,argand wick1 #bbb -- ,flowing of the lamp1 #bbc -- ,placing the lamp in the focus1 #bbf -- ,distinctions of ,catoptric ,lights1 #bbg -- ,colour as a distinction for lights1 #bbi -- ,arrangement of reflectors on the frame1 #bcj -- ,bordier ,marcet's reflectors1 #bcb -- ,fanal sidral1 #bcb -- ,fanal double effet1 #bcd -- ,fanal double face1 #bcf -- ,mr ,barlow's spherical mirrors1 #bcg -- ,captain ,smith's mirrors in the form of a parabolic spindle1 #bch4 ,,dioptric ,,system ,,of ,,lights1 #bci4 ,early history of ,lighthouse lenses1 ,condorcet1 ,buffon1 ,brewster1 ,fresnel1 #bci -- ,refraction1 #bdb -- ,lenses1 #bde -- ,spherical aberration1 #bdh -- ,fresnel's formul for annular lenses1 #bdi -- ,testing lenses1 #bee -- ,divergence of lenses1 #bef -- ,illuminating power of lenses1 #beg -- ,arrangement of lenses in a ,lighthouse1 #beh -- ,pyramidal lenses and mirrors1 #bei -- ,curved mirrors1 #bfj -- ,cylindric refractors of fixed ,lights1 #bfc -- ,application of crossed prisms to cause flashes1 #bfd -- ,true cylindric form given to refractors1 and other improvements in their construction1 #bfd -- ,catadioptric zones1 the mode of computing their elements1 c41 #bfg -- ,testing of zones1 #bhb -- ,framing of zones1 #bhf -- ,mechanical lamp1 #bhf -- ,height of flame of mechanical lamp1 #bhi -- ,position of flame in reference to focus1 #bij -- ,working of the pumps1 #bia -- ,choice of focal point for various parts of apparatus1 #bib -- ,choice of a focal point for zones1 #bib -- ,application of spherical mirrors to fixed ,dioptric ,lights1 #bic -- ,arrangement of ,dioptric apparatus1 #bic -- ,arrangement of ,dioptric apparatus in ,lightroom1 #bid -- ,power of ,dioptric instruments1 #bih -- ,orders of ,french ,lights1 #bih -- ,distinctions of ,dioptric ,lights1 #bii -- ,comparison of ,dioptric and ,catoptric apparatus for revolving lights1 #cja -- ,comparison for fixed lights1 #cjc -- ,summary of views as to two systems for revolving lights1 #cjf -- ,summary of views as to two systems for fixed lights1 #cjf -- ,advantages and disadvantages of both systems under certain circumstances1 #cjh -- ,distinctions of the ,dioptric ,lights and the application of coloured media1 #caa -- ,captain ,basil ,hall's proposal for fixed lights1 #cac -- ,effects of rapid motion on the power of lights1 #cae -- ,connection of experiments with irradiation1 #cbj4 ,,various ,,general ,,considerations ,,connected ,,with ,,lighthouses1 #cbj4 ,masking ,lights1 #cbj -- ,double ,lights1 #cbb -- ,leading ,lights1 #cbc -- ,distribution of ,lights on a coast1 #cbe -- ,height of ,lighthouse ,tower1 and its relation to range of light1 #cbh -- ,diagonal ,lantern1 #ccj -- ,glazing of ,lantern1 #cca -- ,ventilation of ,lanterns1 #cca -- ,arrangements and ,management of a ,lighthouse1 #ccd -- ,cleansing of apparatus1 #cce -- ,mode of measuring relative power of lights1 #ccf -- ,more accurate comparison of intensity of lights1 #cch -- ,floating ,lights1 #cdf -- ,beacons and ,buoys1 #cdg4 ,,appendix4 #a4 ,table of ,co-ordinates of ,hyperbolic ,column4 #b4 ,notes on the ,making of ,parabolodal ,mirrors4 #c4 ,notes on the ,grinding and ,polishing of ,dioptric ,instruments for ,lighthouses4 #d4 ,table of the ,elements of the ,catadioptric ,zones for ,lights of the first order in the system of ,augustin ,fresnel4 #e4 ,notice to ,mariners of the ,exhibition of the ,skerryvore ,light4 #f4 ,detailed ,account of the ,expense of the ,skerryvore ,lighthouse4 #g4 ,excerpts from ,account of ,experiments on the ,force of the ,waves of the ,atlantic and ,german ,oceans1 by ,thomas ,stevenson1 ,f4,r4,s4,e41 ,civil ,engineer4 #h4 ,annual ,list for #ahdh of ,lighthouses1 ,beacons1 and ,buoys1 in the ,district of the ,northern ,lights ,board4 #i4 ,annual ,report by the ,secretary as to the ,income and ,expenditure of the ,northern ,lights ,board for #ahdf4 #aj4 ,instructions to the ,light-keepers in the ,service of the ,commissioners of the ,northern ,lighthouses4 ,,plates4 ,i4 ,chart shewing the situation of the ,skerryvore ,lighthouse4 ,,ii4 ,chart shewing the position of the ,skerryvore ,rocks and foul ground4 ,,iii4 ,plans of the ,skerryvore ,rock at high and low water of spring tides4 ,,iv4 ,curves for ,lighthouse ,towers -- ,marine ,dynamometer4 ,v4 ,barrack of timber on the ,skerryvore ,rock4 ,,vi4 ,details of fixtures of timbers at the top of the ,timber ,barrack4 ,,vii4 ,elevation of ,skerryvore ,lighthouse4 ,,viii4 ,section of ,skerryvore ,lighthouse4 ,,ix4 ,balance ,crane used at ,skerryvore4 ,x4 ,plan shewing the ,lighthouse ,establishment of ,barracks1 ,harbour1 c41 at ,hynish1 in the ,island of ,tyree4 ,,xi4 ,elevation and ,section entrance to ,dock at ,hynish4 ,,xii4 ,plan and ,section of ,annular ,lens4 ,,xiii4 ,perspective ,elevation of ,revolving ,dioptric ,apparatus of ,first ,order4 ,,xiv4 ,plan of ,revolving ,dioptric ,light of ,first ,order1 with ,mirrors4 ,,xv4 ,vertical ,section of fixed ,dioptric ,lights of ,first ,order1 with ,mirrors4 ,,xvi4 ,elements of ,concave ,mirrors for ,dioptric ,lights of ,first ,order1 and arrangement on the ,frame4 ,,xvii4 ,perspective ,view of ,fixed ,dioptric ,light of ,first ,order1 with ,catadioptric ,zones4 ,,xviii4 ,vertical ,section of ,fixed ,dioptric ,light of ,first ,order1 with ,catadioptric ,zones4 ,,xix4 ,vertical ,section of ,catadioptric ,light of ,fourth ,order1 with ,framing4 ,,xx4 ,elevation of ,mechanical ,lamp for ,dioptric ,lights of ,first ,order4 ,,xxi4 ,enlarged ,views of ,oil-,pumps of ,mechanical ,lamp4 ,,xxii4 ,enlarged ,views of ,oil-,pumps of ,mechanical ,lamp4 ,,xxiii4 ,details of ,clock-work of ,mechanical ,lamp4 ,,xxiv4 ,details of ,clock-work of ,mechanical ,lamp4 ,,xxv4 ,flame of ,mechanical ,lamp of ,first ,order at full size4 ,,xxvi4 ,elevation of ,diagonal ,lantern1 and details of ,astragals4 ,,xxvii4 ,elevation of ,ardnamurchan ,lighthouse4 ,,xxviii4 ,plan of ,ardnamurchan ,lighthouse4 ,,xxix4 ,lines of a ,floating ,light ,vessel belonging to the ,corporation of ,trinity ,house of ,deptford ,strond4 ,,xxx4 ,elevation of ,covesea ,skerries ,beacon4 ,,xxxi4 ,details of ,covesea ,skerries ,beacon4 ,,xxxii4 ,elevations and ,sections of ,stone and ,iron ,beacons4 ,,xxxiii4 ,elevations of ,buoys4 ,,errata4 ,page #eb1 line #h1 for ,redelet read ,rondelet 444 #agh1 line #f1 for ,l4#ic1cjf3h3aj read ,l4#hf1igg3ag3g 444 #bib1 line #cj1 for radius rector read radius vector 444 #bid1 line #ac1 for give read gives 444 #cbi1 line #c1 for earth read sea 444 #cdg1 line #bi1 for ,plate ,,xxxii41 read ,plate ,,xxx41 ,,part ,,first4 ,,account ,,of ,,the ,,skerryvore ,,lighthouse4 ,,introduction4 ,in the course of preparing the account of the building of the ,skerryvore ,lighthouse1 it occurred to me1 that a short ,introduction should be prefixed1 embracing a concise view of the constitution and acts of the ,board of ,commissioners of ,northern ,lights1 more especially from #ahbd1 when my ,father's work on the ,bell ,rock ,lighthouse was published1 up to the present time4 ,this object will be best accomplished1 by presenting to the reader1 in the first place1 an account of the constitution and powers of the ,lighthouse ,board1 chiefly drawn from the 8,introduction to the ,bye-,laws1 ,rules1 and ,regulations of the ,commissioners of ,northern ,lighthouses10 prepared by a ,committee of their number2 and by afterwards briefly noticing the principal works of the ,board since #ahbd1 and stating generally the nature of the changes and improvements made within that period on the mode of illumination1 of which ,i propose1 in a subsequent part of this volume1 to give a somewhat detailed account4 99 99 99 99 99 ,constitution of the ,lighthouse ,board4 ,the trade of ,scotland had begun to increase very soon after the settlement of the civil war in #agde2 but it was not till the year #aghd that the general establishment of ,sea ,lights upon the ,coast appears to have been brought under the notice of the ,legislature4 ,in that year1 the subject was first mentioned at a meeting of the ,convention of the ,royal ,burghs of ,scotland1 by ,mr ,,dempster of ,dunichen1 ,m4,p41 the ,provost of the burgh of ,forfar2 and1 in the year #aghf1 that gentleman brought a bill into ,parliament1 and an ,act was obtained establishing the present ,board of ,northern ,lights4 ,this ,act sets forth1 that 8it would conduce greatly to the security of navigation and the fisheries1 if four ,lighthouses were erected in the ,northern parts of ,great ,britain1 one on ,kinnaird's ,head1 ,aberdeenshire1 one in the ,north ,isles of ,orkney1 one on the point of ,scalpa1 in the ,island of ,harris1 and a fourth on the ,mull of ,kintyre1 ,argyllshire20 and it accordingly authorises the erection of those four ,lighthouses4 ,the ,commissioners appointed for carrying this ,act into execution were1 the ,lord ,advocate and ,solicitor-,general of ,scotland1 the ,lord ,provost and first ,bailie of ,edinburgh1 the ,lord ,provost and first ,bailie of ,glasgow1 the ,provosts of ,aberdeen1 ,inverness1 and ,campbeltown1 the ,sheriffs of the counties of ,edinburgh1 ,lanark1 ,renfrew1 ,bute1 ,argyll1 ,inverness1 ,ross1 ,orkney and ,zetland1 ,caithness1 and ,aberdeen4 ,an ,act was subsequently passed1 which authorised the ,commissioners1 when any new ,lighthouse was established on any part of the coast of ,scotland1 to add to their number the ,provost or ,chief ,magistrate of the nearest ,royal ,burgh1 and also the ,sheriff-,depute of the nearest county2 and1 by the exercise of this power of assumption1 the board now includes the ,sheriffs of the counties of ,ayr1 ,fife1 ,forfar1 ,wigtown1 ,sutherland1 ,kincardine1 and ,kirkcudbright4 ,to enable the ,board to carry on the intended works and to provide the means of maintaining the ,lights1 those ,acts gave power to the ,commissioners to levy a duty of #a;d4 per ton on ,british vessels1 and #b;d4 per ton on foreign vessels2 and liability to pay this duty was incurred by all vessels passing any of the ,lighthouses in the course of a voyage2 but this single payment freed them from any farther exaction1 although they should pass more than one ,lighthouse in the course of the voyage4 ,the ,board held its first meeting at ,edinburgh on #ast ,august #aghf4 ,a ,secretary and ,engineer were appointed1 and a resolution was adopted to borrow ,l4#abjj4 ,for this sum the ,magistrates of the five ,royal ,burghs named in the ,act interposed their security2 and1 at the same time1 assigned1 in farther security1 the duties under the ,act of ,parliament4 ,after appointing a ,committee to prepare matters for a general meeting1 they adjourned till the #bc;d of ,january #aghg4 ,some inconvenience having been felt in conducting the business of the ,board1 particularly in the holding of stock and other property1 by reason of its not being an incorporated body1 an ,act was obtained for erecting the ,commissioners into a body politic1 by the name of the 8,commissioners of the ,northern ,lighthouses40 ,several ,acts have been subsequently passed1 in order to facilitate the erection of particular ,lighthouses1 and for the purpose of granting duties for their support4 ,all those duties1 however1 are now abolished1 and others have been substituted1 the collection of which is regulated by an ,act1 #fth and #gth ,william ,,iv41 cap4 #gi1 intituled1 8,an ,act for vesting ,lighthouses1 ,lights1 and ,sea-marks on the ,coasts of ,england1 in the ,corporation of ,trinity-,house of ,deptford ,strond1 and for making provision respecting ,lighthouses1 ,lights1 ,buoys1 ,beacons1 and ,sea-marks1 and the ,tolls and ,duties payable in respect thereof40 ,this ,act declares1 8,that from the first day of ,january one thousand eight hundred and thirty-seven1 the tolls now payable by or in respect of vessels for or towards the maintenance of the several lighthouses at present under the management of the ,commissioners of ,northern ,lighthouses shall cease to be payable1 and that1 in lieu thereof1 there shall thenceforth for ever be paid to the said ,commissioners of the ,northern ,lighthouses1 for every vessel belonging to the ,united ,kingdom of ,great ,britain and ,ireland 7the same not belonging to his ,majesty1 his heirs or successors1 or being navigated wholly in ballast71 and for every foreign vessel which1 by any ,act of ,parliament1 order in ,council1 convention1 or treaty1 shall be privileged to enter the ports of the said ,united ,kingdom1 upon paying the same duties of tonnage as are paid by ,british vessels 7the same not being vessels navigated wholly in ballast71 which shall pass any of the said lighthouses1 or derive benefit thereby1 the toll of one halfpenny per ton of the burden of every such vessel for each time of passing every such lighthouse1 or deriving benefit thereby1 and of one penny per ton for each time of passing the ,bell ,rock ,lighthouse1 and double the said tolls for every foreign vessel not so privileged40 ,and with regard to any new ,lighthouses to be hereafter erected1 it is provided1 that there 8shall be paid to the ,commissioners by the owner1 or other person having the command of any vessel not belonging to ,his ,majesty1 which shall pass such lighthouse1 or derive benefit thereby1 such reasonable toll as shall have been first approved in that behalf by ,his ,majesty in ,council40 ,before the passing of this ,act1 the ,commissioners had been uncontrolled in the selection of stations for ,lighthouses1 or in choosing the characteristic appearance for the ,lights2 but it being considered desirable to have a systematic arrangement in the three kingdoms1 the ,irish ,lighthouse ,board1 as well as the ,commissioners1 are now required to give notice to the ,corporation of the ,trinity-,house of ,deptford ,strond1 before altering the character of any ,light1 or erecting any new ,lighthouse2 and that ,corporation must1 within the period of six months after receiving such notice1 signify their opinion as to the propriety of the change1 or the utility of any new ,lighthouses submitted for their consideration4 ,the ,act1 however1 provides1 that1 if the ,commissioners are dissatisfied with the opinion of the ,trinity-,house1 they may appeal to the ,privy ,council1 whose determination is final4 ,by this ,act1 also1 an important power is given to the ,commissioners to control the exhibition of all harbour and local ,lights1 or other sea-marks1 and to prevent the exhibition of any ,lights or fires on the sea-coast1 which might be mistaken for the regular ,lights exhibited by the ,board4 ,in the ,appendix ,i have given a copy of the ,annual ,statement of the ,income and ,expenditure of the ,board for the year #ahdf1 prepared by ,mr ,,alexander ,,cuningham1 the ,secretary to the ,commissioners4 99 99 99 99 99 ,lights established since #ahba4 ,since the ,sumburghhead ,lighthouse in ,zetland was lighted in the year #ahba1 with a notice of which the account of the ,bell ,rock ,lighthouse concludes1 the ,commissioners have been engaged in the establishment of seventeen new ,lighthouses1 and the remodelling of several old ones2 and they have1 more particularly1 effected important changes in the mode of illumination1 and have begun to place ,beacons and ,buoys on the coast4 ,they have1 besides1 executed several considerable improvements1 for the purpose of facilitating the communication with the ,lighthouses at ,kintyre in ,argyllshire1 ,cape ,wrath in ,sutherlandshire1 and ,dunnethead in the county of ,caithness1 by the establishment of landing-piers and the formation of roads1 varying in length from three to ten miles1 in connection with those ,stations4 ,of those works1 many interesting details might be given1 were it not desirable that the introduction to an account of a single ,lighthouse should be restricted within a very moderate compass2 and ,i have1 therefore1 thought it sufficient to lay before the reader the most important circumstances of each ,lighthouse ,station belonging to the ,board in a tabular form in the ,appendix4 ,improvements in the mode of illumination4 ,i shall not1 in this place1 enter on any exposition of the general principles which regulate the illumination of ,lighthouses1 and still less will it be proper to discuss the advantages of the different methods of illumination by ,reflection and ,refraction1 as ,i shall1 in the sequel1 find a more convenient opportunity for speaking somewhat in detail on those subjects4 ,it will be enough to present a very brief notice of the improvements in the mode of illuminating ,lighthouses1 which the ,northern ,lights ,board have introduced since #ahbd1 up to which time1 as already mentioned1 a sketch of their works is already before the public4 ,one of the most important changes in ,lighthouse apparatus was1 unquestionably1 the introduction of ,revolving ,lights at the ,tour de ,corduan about the year #aghj1 by which the means of distinguishing one light from another were greatly extended1 and a marked difference in the appearance of contiguous lights was at once simply obtained4 ,the mere variation of the velocity of the revolution is so simple as to afford an obvious source of distinction among lights2 and yet it is remarkable1 that it was only lately that one of its principal advantages was perceived by my ,father1 who first applied it in the year #ahbg as a means of distinction for the ,light of ,buchanness4 ,this distinction consists in giving the frame a greater number of sides or faces1 and a more rapid revolution1 so as to cause a flash in every five seconds of time1 which produces an effect so marked and characteristic as to afford by far the most effective distinction which has been exhibited since the introduction of ,revolving ,lights4 ,under the auspices of the ,board1 this distinction has been since applied at the ,rhinns of ,islay ,lighthouse1 and has given much satisfaction wherever it has been tried4 ,the late ,king of the ,netherlands1 a great patron of the useful arts1 was so much pleased with this device that he presented the author of it with a splendid gold medal1 in token of his approbation4 ,the only other improvement on the ,reflecting ,lights1 which ,i shall notice in this place1 is that called the intermittent light1 which is due to the same officer1 and was by him introduced at the stations of ,mull of ,galloway1 ,tarbetness1 and ,barrahead4 ,it consists of the apparatus of a fixed ,light1 in front of which two cylindric shades are alternately shut and opened by a vertical movement1 so as to produce a sudden extinction and exhibition of the light1 in a manner very difference from the gradual decline and growth of the flash1 which is produced in revolving ,lights by the attenuating effects of divergence on the penumbral portions of the light reflected from the mirror4 ,dioptric ,lights4 ,the introduction of lenticular apparatus into ,lighthouses has been the last great improvement effected in their illumination4 ,so far back as the year #ahbc1 the attention of the ,commissioners was first called by their ,engineer to the invention of the late ,,augustin ,,fresnel1 who had succeeded in building polyzonal lenses of large dimensions1 and in adapting to them a lamp of great power1 having four concentric wicks supplied with oil by a clock-work movement like that of the ,carcel lamp4 ,a committee was appointed to consider this subject2 and under its direction a long train of experiments was made with those instruments and with the paraboloidal mirrors which are generally used in ,british ,lighthouses4 ,the results of the experiments led the ,board1 in the summer of #ahcd1 to send me on a mission to ,france1 with instructions to report my opinion as to the comparative merits of the dioptric and catoptric apparatus for the illumination of ,lighthouses4 ,through the kindness of my friend ,m4 ,,leonor ,,fresnel1 ,secretary of the ,commission des ,phares1 who in the most liberal manner put me in possession of all the information which ,i required1 and afforded me an opportunity of visiting the most important ,lighthouses on the ,french coast1 ,i was enabled on my return to report very fully my views on the various topics whose investigation had been committed to me by the ,lighthouse ,board4 ,the characteristics of the two systems of illumination by ,reflection and ,refraction may be briefly described as follows3 ,in the reflecting apparatus1 the lamp is placed in front of the mirror1 whose surface is so formed that the rays which fall upon it1 and are reflected from it1 must afterwards move in lines parallel to the axis of the mirror2 while in using ,refracting instruments1 the flame is placed behind the lens1 whose action is simply to bend the rays in their passage through it1 in such a manner that they come out from its face parallel to a line drawn from the focus to the centre of the lens4 ,in ,revolving ,lights1 on the reflecting principle1 the mirrors containing the lamps are placed on a frame which revolves on its centre1 and carries them round in succession to the different points of the horizon1 so that each mirror produces a bright flash when it crosses the line drawn from an observer's eye to the centre of the ,lighthouse2 but in ,refracting ,lights1 a single lamp of great power is fixed in the centre of the lightroom1 while the lenses1 placed on a revolving frame1 intercept and modify the rays which fall upon them from the ,lamp1 as they pass in front of it1 and thus produce successive flashes whenever the centre of the lens crosses the imaginary line already noticed1 as joining the observer's eye and the lightroom4 ,in ,fixed ,lights1 on the ,reflecting plan1 the mirrors are ranged around a fixed chandelier in tiers1 one above another1 their centres being placed in spiral lines1 so that each shall subtend an equal arc of the horizon1 and thus distribute the light with as little inequality as is consistent with the application of such an instrument as the paraboloidal mirror to this purpose4 ,this object of distributing the light equally over the horizon1 which1 next to intensity1 is the main object of a fixed light1 and ought1 indeed1 to be strictly co-ordinate with it1 is much better effected by using dioptric instruments4 ,that apparatus consists of successive rings or bent prisms arranged in the form of a hoop or belt1 which may be described as a cylinder1 generated by the revolution of the central section of a polyzonal lens about its focus as a vertical axis1 and which consequently acts only in a vertical direction1 leaving the natural horizontal divergence of the light unchanged1 and thus distributing it with perfect equality in every direction4 ,those two systems of illumination possess advantages and defects peculiar to each4 ,the lenticular instruments insure greater intensity when applied to revolving lights2 but this advantage is in part counterbalanced by the greater duration of the flash caused by the reflectors1 whose divergence is greater2 while in fixed lights1 the refracting instruments not only produce at least an equal intensity of light1 but1 what is of the greatest importance1 afford the same quantity of light in all directions1 a property which fixed ,lights on the reflecting principle employed in ,britain cannot possess4 ,on my return from ,france ,i made a ,report1 which was printed by order of the ,commissioners2 and the views which ,i gave of the superiority of the refracting apparatus1 led the ,board to adopt the resolution of at once converting the revolving light of ,inchkeith from the catoptric to the dioptric system1 as its nearness to ,edinburgh offered good opportunity of observation as to the effect of the change4 ,in ,october #ahce1 the new light was exhibited to the public1 and ,i was forthwith instructed to make a similar change on the fixed light of the ,isle of ,may2 but in carrying this into effect1 ,i introduced an important modification of the form of the refracting part of the apparatus1 with the view of obtaining a still nearer approach to the equal distribution of the light4 ,the only other considerable change in the lightroom apparatus which has since been effected1 is the substitution of catadioptric zones in room of the mirrors hitherto used in the subsidiary parts of the larger ,french lights1 which1 as will appear in the sequel1 was suggested by me in #ahda1 and finally carried into effect in #ahdc1 agreeably to the computations of ,m4 ,,leonor ,,fresnel4 ,a ,table of the ,elements of those zones computed by myself1 and closely verifying ,m4 ,,fresnel',s results1 will be found in the ,appendix4 ,the lenticular apparatus has been applied at the new ,lighthouse stations of the ,little ,ross and the ,skerryvore1 and1 still more recently1 at ,covesea ,skerries1 ,cromarty ,point1 ,chanonry ,point1 ,loch ,ryan1 and ,girdleness4 ,beacons and ,buoys4 ,the establishment of a system of ,beacons and ,buoys on the coast of ,scotland for the purpose of affording additional facilities to navigation1 had long been looked upon as a desirable extension of the operations of the ,northern ,lights ,board2 and the increase of the trade and shipping of the kingdom having1 some years ago1 directed particular attention to the subject1 a committee was named1 on the #abth ,january #ahci1 to take special superintendence of that department4 ,in #ahdj1 the ,engineer reported to the committee upwards of fifty stations for ,beacons1 and nearly a hundred for ,buoys1 as auxiliaries to the navigation in situations where the establishment of a ,lighthouse was either too expensive or not warranted by the wants of the district2 and means were immediately taken for erecting three ,beacons in the ,frith of ,forth1 two in the ,clyde1 one in ,loch ,ryan1 and two in ,cambeltown ,loch4 ,beacons were also erected on the ,iron ,rock or ,skervuile in the ,sound of ,jura1 and on the ,covesea ,skerries in ,morayshire1 in connection with the ,lighthouse of that name4 ,those works1 notwithstanding many obstacles arising from doubts as to the powers of the ,board1 have been carried on with great vigour4 ,in the ,appendix1 ,i have given drawings of three of those ,beacons1 one being of masonry1 and the other two of iron2 and also ,tables which shew the positions of the various ,beacons and ,buoys at present belonging to the ,board4 ,,chapter ,i4 ,,topographic ,,notice ,,of ,,the ,,skerryvore ,,rock4 ,from the great difficulty of access to the inhospitable rock of ,skerryvore1 which is exposed to the full fury of the ,atlantic1 and is surrounded by an almost perpetual surf1 the erection of a ,light ,tower on its small and rugged surface has always been regarded as an undertaking of the most formidable kind4 ,so discouraging was the consideration of expense1 and the uncertainty of the final success of such a work1 that the ,commissioners of the ,northern ,lighthouses1 after successfully completing the arduous and somewhat similar work on the ,bell ,rock1 were induced to proceed with other operations of less magnitude1 but probably1 in some respects1 of no less utility2 and to delay the construction of the ,skerryvore ,lighthouse till the present time1 although the ,act of ,parliament authorising its erection was obtained so long ago as #ahad4 ,the cluster of ,rocks1 of which that called the ,skerryvore is the largest1 has ever been a just cause of terror to the mariner4 ,its dangers have long been known1 and the means of removing these dangers1 by converting its dark horrors into a cheering guide for the benighted mariner1 have often occupied the attention of the ,lighthouse ,board1 and especially of my predecessor in the office of their ,engineer1 with whom it was a constant subject of interest1 from its similarity to his own work on the ,bell ,rock4 ,the first landing that my ,father1 in the course of his annual voyages round the coast1 as ,engineer of the ,northern ,lighthouse ,board1 effected on ,skerryvore1 was in the year #ahjd4 ,in #ahad1 he visited it a second time1 while accompanying a committee of the ,commissioners on a tour of inspection to the ,lighthouses all round the coast1 from the ,frith of ,forth to the ,clyde4 ,on that occasion1 ,sir ,walter ,scott was of the party1 and we find in his diary the following record of his impressions at the time1 expressed in the terse and humorous language by which this interesting relic of the poet is characterised2 and as the hasty observations of that great man seem worthy of a place in a work descriptive of the means which have been taken to obviate the dangers to which he refers1 no apology seems necessary for introducing it in this place4 8,having crept upon deck about four in the morning10 says ,sir ,walter1 8,i find we are beating to windward off the ,isle of ,tyree1 with the determination1 on the part of ,mr ,stevenson1 that his constituents should visit a reef of rocks called ,skerry ,vhor1 where he thought it would be essential to have a ,lighthouse4 ,loud remonstrances1 on the part of the ,commissioners1 who1 one and all1 declare they will subscribe to his opinion1 whatever it may be1 rather than continue the infernal buffeting4 ,quiet perseverance on the part of ,mr ,s41 and great kicking1 bouncing1 and squabbling1 upon that of the yacht1 who seems to like the idea of ,skerryvore as little as the ,commissioners4 ,at length1 by dint of exertion1 come in sight of this long ridge of rocks 7chiefly under water7 on which the tide breaks in a most tremendous style4 ,there appear a few low broad rocks at one end of the reef1 which is about a mile in length4 ,these are never entirely under water1 though the surf dashes over them4 ,to go through all the forms1 ,hamilton1 ,duff1#a and ,i1 resolve to land upon these bare rocks1 in company with ,mr ,stevenson4 ,pull through a very heavy swell with great difficulty1 and approach a tremendous surf dashing over black pointed rocks4 ,our rowers1 however1 get the boat into a quiet creek between two rocks1 where we contrive to land well wetted4 ,i saw nothing remarkable in my way excepting several seals1 which we might have shot1 but1 in the doubtful circumstances of the landing1 we did not care to bring guns4 ,we took possession of the rock in name of the ,commissioners1 and generously bestowed our own great names on its crags and creeks4 ,the rock was carefully measured by ,mr ,s4 ,it will be a most desolate position for a ,lighthouse--the ,bell ,rock and ,eddystone a joke to it1 for the nearest land is the wild island of ,tyree1 at fourteen miles distance4 ,so much for the ,skerry ,vhor40 #a ,the ,sheriffs-,depute of ,lanark and ,edinburgh4 ,notwithstanding those occasional visits1 however1 it was not till the year #ahcd1 that the ,commissioners directed their ,engineer to make a survey of the whole of this extensive reef1 preparatory to taking measures for the erection of a ,lighthouse on that part of it which might be found1 after careful inspection1 to afford the most suitable site2 and1 at the same time1 the shores of part of the ,island of ,tyree were surveyed1 with the view of establishing a ,signal ,tower for communicating with the ,lighthouse1 and of forming a small harbour1 of shelter for the vessels to be employed in attending it4 ,from these surveys the general view of the ,reef which is given in ,plate ,,ii41 and the enlarged plan shewn in ,plate ,,iii4 of the ,skerryvore or principal ,rock1 on which the ,lighthouse has been built1 were constructed4 99 99 99 99 99 ,the ,skerryvore or principal ,rock of this remarkable group1 is situated in ,north ,lat4 #ef #ai #bb1 and ,west ,long4 #g #f #cb4b ,it is about #aa ,nautic miles ,w4,s4,w ,w4 of the island of ,tyree1 which is the nearest land1 #bj miles ,w4,n4,w ,n4 of the island of ,iona1 #cc miles ,s4 ,e4 of the ,lighthouse of ,barrahead1 the most southern of the ,hebrides1 and #ec miles ,n4,e4 by ,n4 of ,mallinhead1 in the county of ,donegal in ,ireland4 ,it may also be added1 that the principal rock is about #ej miles from the nearest point of the main land of ,scotland4 ,the extent of the ,reef1 and its situation in reference to the general position of the coast1 will be best understood by referring to ,plate ,i41 which is a small ,map of the ,british ,isles4 ,from this it will be seen that it lies in an irregular semicircular sea1 inclosed by the southern extremity of the ,hebrides1 the rugged shores of ,argyllshire1 and the northern coast of ,ireland on the one side1 but open on the other to the ,atlantic4 #b ,according to information for which ,i am indebted to ,captain ,yolland1 ,r4,e41 of the ,ordnance ,survey4 99 99 99 99 99 ,the importance of the ,skerryvore as a station for a ,lighthouse is so evident as to require but little comment4 ,although the smaller class of coasting vessels almost invariably sail through the sheltered ,sounds of ,mull1 ,loing1 and ,islay1 to avoid the difficulties and dangers 7,skerryvore among the number7 of the rough navigation of the outward passage1 yet these rocks lie much in the track of the larger vessels bound over seas round the ,north of ,ireland from the ,clyde and the ,mersey4 ,government ,cruisers and ,ships of ,war are also necessarily often within a short distance of its dangers4 ,but for homeward-bound vessels sailing for the ,clyde1 or for any of the ,ports in the ,irish sea1 and directing their course for the ,north ,irish ,channel1 the establishment of a light at this place is of the last importance4 ,when such vessels happened to encounter bad weather before making land1 and so had difficulty in ascertaining their true position in relation to the coast1 they often1 in the event of being driven so far north from their course1 as to miss the lights of ,ireland or that of ,barrahead1 continued their progress onwards in the direction of the ,skerryvore ,rocks2 and thus1 while running in apparent safety1 and probably1 from the state of the weather1 not within sight of ,tyree1 which it is often difficult to see1 they were very liable to encounter some of the many detached rocks and shoals which form this broken reef of nearly seven miles in extent4 99 99 99 99 99 ,in estimating the risks to which vessels were exposed from this cause1 the peculiarly insidious nature of the danger must be kept in view4 ,a headland1 or line of coast1 which rises to some height above the surface of the sea can be seen in most states of the weather1 at a sufficient distance1 even during the night1 to enable the seaman to avoid danger2 but1 in approaching a sunken reef or a low rock1 in the dark1 there is no object to warn the crew of their position1 until their vessel gets unexpectedly among breakers1 after which it is generally too late to bring her round again4 ,and even the very knowledge of the existence of a reef1 such as this1 often causes the seaman1 in ignorance of its exact position1 to give it too wide a berth2 in which case his ship is liable to be carried away by the force of tides or winds1 perhaps on a lee shore1 where1 although the crew may be saved1 the vessel generally goes to pieces4 99 99 99 99 99 ,the exhibition of a ,light1 however1 altogether changes the case4 ,instead of shunning as a danger those dreaded rocks1 vessels will steer boldly on their course1 until checked by the ,light1 availing themselves of which they will be enabled to lie off-and-on during the night1 and so wait the return of daylight1 in perfect confidence as to their position1 and without the necessity of endeavouring to avoid hidden dangers4 ,thus1 that which was formerly an obstruction and a danger1 is rendered an aid and a safety1 to the navigation of the western coasts of our country4 99 99 99 99 99 ,that this source of danger to shipping was by no means imaginary1 and the consequent terror of mariners far from being ill founded1 there is a too melancholy proof in the following list of disasters caused by the ,skerryvore ,rock1 and the neighbouring dangers off the coast of ,tyree3-- ,in #agij4 ,the ,ship ,rebecca of #gjj tons lost2 crew saved4 #ahjd4 ,ship ,brigand of ,nova ,scotia1 ,wright1 master1 of #fjj tons1 lost off ,hough1 in ,tyree2 crew saved4 #ahjd4 ,a ,brig1 ,m#8,iver1 master1 lost off ,hough2 crew saved4 #ahjf4 ,ellen of ,bath1 ,paterson1 master1 of #ij tons1 lost off ,balaphuil1 in ,tyree2 one man drowned4 #ahji4 ,brig ,mary1 ,sanders1 master1 lost off ,balaphuil2 crew saved4 #ahac4 ,sloop1 ,penelope of ,wick1 #fj tons1 lost at ,gott ,bay1 ,tyree2 crew saved4 #ahaj4 ,a ,brig from ,new ,york1 ,greenlees1 master1 lost off ,hynish ,point1 ,tyree2 crew all drowned4 #ahac4 ,a ,sloop1 ,eugene ,m#8,intyre1 master1 lost off ,balaphuil2 one man drowned4 #ahad4 ,brig1 ,betsey of ,leith1 ,ross1 master1 lost off ,hough2 crew saved4 #ahag4 ,a ,brig1 of #djj tons1 foundered off ,kennavarah1 ,tyree2 crew all drowned4 ,numerous casks of butter came ashore4 #ahah4 ,sloop1 ,benlomond of ,greenock1 ,m#8,lauchlan1 master1 lost off ,balaphuil2 crew all drowned4 #ahai4 ,sloop1 ,bee1 ,coice1 master1 of #fj tons1 lost off ,hough2 crew saved4 #ahbj4 ,a ,sloop1 ,m#8,donald1 master1 of #ej tons1 lost in ,reef ,bay1 ,tyree2 crew saved4 #ahbj4 ,ship1 ,masters1 of ,port-,glasgow1 ,martin1 master1 of #gjj tons1 foundered off ,skerryvore ,rocks1 and came ashore at ,clate ,hynish1 in ,tyree2 crew saved4 #ahba4 ,sloop1 ,catharine1 ,m#8,rae1 master lost2 crew saved4 #ahba4 ,a ,sloop1 of #fj tons1 lost off ,hough2 master and three men drowned4 #ahbe4 ,sloop1 ,dan of ,campbelltown1 ,m#8,innes1 master1 of #ej tons1 lost2 crew saved4 #ahbh4 ,sloop1 ,delight1 of #gj tons1 ,stevenson1 ,master1 lost4 #ahbh4 ,an ,irish ,schooner of #ajj tons1 ,montgomery1 master1 lost off ,hough2 crew saved4 #ahbh4 ,jane of ,sligo1 ,collins1 master1 lost off ,balaphuil4 #ahbi4 ,van ,scapan of ,stockholm1 ,fisherton1 master1 of #gjj tons1 lost off ,hough2 fourteen people drowned4 #ahcd4 ,confidence of ,dundee1 ,wesley1 master1 lost off ,hough2 crew saved4 #ahcd4 ,a ,schooner of #gj tons1 lost2 three men drowned4 #ahce4 ,peggy1 ,bitters1 master1 of #ejj tons1 lost off ,beist1 ,tyree2 crew saved4 #ahda4 ,april #b4 ,majestic of ,north ,shields1 ,tait1 master1 of #djj tons1 foundered by a sea off ,boinshly ,rock1 and came ashore at ,gott ,bay2 captain and four men washed overboard and drowned1 and the mate and one seaman had their legs broken when the vessel was struck by the sea4 #ahdb4 ,fleurs of ,liverpool1 ,thomson1 master1 of #cjj tons1 lost off ,kennavarah2 crew saved4 #ahdb4 ,march #ad4 ,two deck beams1 a knee1 and some pieces of deck-plank of a ,north ,american built vessel1 came ashore at ,clate ,hynish4 #ahdb4 ,a ,barra ,boat wrecked1 and four corpses washed ashore2 two men1 a woman and a child4 #ahdb4 ,pieces of wreck were seen in the ,sound of ,coll1 and at the same time the shores of ,tyree were strewed with candles1 mostly of wax1 supposed to be altar candles for the ,west ,indies4 #ahdc4 ,september #b4 ,the ,prussian ,barque ,formosa1 of #cbf tons1 ,p4 ,r4 ,reick1 master1 lost off ,hough2 two seamen drowned4 #ahdd4 ,december #a4 ,the ,hull of a ,sloop of about #gj tons1 was washed ashore off ,clate ,hynish4 ,the ,hull was very much broken up by being in contact with the rocks2 and one of the planks1 apparently off the taffrail1 had the words 8,port of ,dundee0 lettered upon it2 the crew supposed to be all drowned4 ,this list is made up chiefly from data kindly furnished to me by the ,rev4 ,neil ,maclean1 the ,minister of ,tyree and ,coll1 whose long residence on the former island has afforded him ample opportunity for making observations on the subject4 ,it is not to be imagined1 however1 that ,mr ,maclean's list1 which is made up from recollection1 contains a full catalogue of the disasters caused by the ,skerryvore1 within the dates which it cites4 ,very many vessels were wrecked on this dangerous reef whose names could never be learned1 and of which nothing but portions of the drift wood or cargo came ashore2 and there have1 no doubt1 been many shipwrecks of which not a single trace has been left4 ,nothing1 indeed1 is more probable than that many of the foreign vessels whose course lay through the ,north ,irish ,channel1 and whose fate has been briefly and vaguely described1 as 8foundered at sea10 have met their fate on the infames scopuli of the ,skerryvore4 ,it is also well known that the ,tyree ,fishermen were in the constant practice of visiting the ,skerryvore1 after gales1 in quest of wrecks and their produce1 in finding which they were but too often successful4 99 99 99 99 99 ,the natives of ,tyree have many traditions of vessels having struck on the ,skerryvore and gone to pieces2 but1 as might have been anticipated1 few traces of this were to be found on the ,rocks themselves1 the breach of sea which sweeps over them during storms being sufficient to remove any heavy bodies which might be left there after a shipwreck4 ,some relics1 however1 were found during the progress of the works1 and among the rest an anchor which was fished up close to the ,rock1 and which appeared to have belonged to a vessel of about #aej tons burden4 ,it had been wasted to a perfect shadow by the action of the sea1 and was covered with a thick coating of seaweed and barnacles4 ,although1 however1 the ,rocks themselves do not retain the proofs of the disasters of which they have been the cause1 the shores of the neighbouring ,islands1 during the progress of the works1 were frequently strewed with drift wreck in such a manner as clearly to indicate what had taken place on the shoals round the ,skerryvore4 99 99 99 99 99 ,on examining ,plate ,,ii41 it will be seen that what ,i have hitherto denominated the ,skerryvore ,reef1 is a tract of foul ground1 consisting of various small rocks1 some always above the level of the sea1 others covered at high water1 and exposed only at low water1 and others1 again1 constantly under the surface1 but on which the sea is often seen to break after heavy gales from the westward4 ,this cluster of rocks extends from ,tyree in a south-westerly direction1 leaving1 however1 between that island and the rock called ,boinshly1 the first of the great ,skerryvore cluster1 a passage of about five miles in breadth1 and having a depth of thirteen fathoms at low water of spring tides1 but not without hidden dangers1 which line the rugged shores of ,tyree from ,kennavarah to ,ben ,hynish1 and some of which lie farther off than might be expected4 ,this passage is called the passage of ,tyree2 but it is by no means safe during strong and long continued gales1 as the sea which rises between ,tyree and ,skerryvore1 is such that no vessel can live in it4 ,i have myself often seen it one field of white broken water1 the whole way from ,tyree to the ,rock2 and we know that the wreck of the ,majestic1 which occurred in #ahda1 during the progress of the works1 was entirely caused by the heavy seas which she encountered off ,boinshly4 99 99 99 99 99 ,the principal rocks of the group1 are called ,boinshly1 ,bo-rhua1 and ,skerryvore1 while those lying to the westward1 which have been more recently laid down1 have received the names of ,mackenzie1 ,fresnel1 and ,stevenson4 99 99 99 99 99 ,the rock called ,boinshly lies about #c miles from ,skerryvore1 and is of considerable extent4 ,the origin of the names of the different rocks in the vicinity of ,tyree is by no means clear1 and very little assistance or information is to be obtained in this matter from the natives4 ,the name of ,boinshly is probably derived from the ,gaelic words boun1 signifying bottom1 and slighe1 deceitful1 as indicative of the dangers of the place2 but other interpretations have been put on it1 and that which has been now given is by no means certain4 ,in the course of the survey1 several soundings were at considerable risk obtained1 both upon this ,rock itself1 and in its immediate vicinity4 ,the sea in that exposed situation is seldom so tranquil as to warrant an attempt to approach very near this ,rock4 ,the swell1 which1 in a greater or less degree1 almost constantly prevails1 is apt to impel1 or seemingly draw the boat as by a kind of suction1 upon the rock2 and sometimes such accidents cannot be prevented1 even although the greatest caution is used4 ,sudden lifts of the sea1 during an apparent calm1 are common in all the more exposed parts of the coast1 more especially in the ,orkney and ,zetland ,isles1 and on the shores of the most western of the ,hebrides2 and any one much accustomed to the use of boats on these shores1 must have experienced the hazard of encountering such unexpected risings of the sea1 more especially near shelving rocks1 or in rapid tide-ways4 ,in some places the boatmen apply the name of lumps to these sudden waves4 ,this effect is not felt to the same extent in attempting to reach a rock which is partially uncovered at low water1 as a landing can1 in such a case1 often be effected on one side1 at a time when the same rock on the opposite side1 or a sunk rock just topping with the water1 would1 on every side1 be quite unapproachable4 ,from the soundings marked on the plan1 it will be seen that shoal water extends all round ,boinshly to distances varying from a quarter to half a mile4 ,the sea breaks on the rock with great violence1 and its position can easily be discovered from the island of ,tyree by the white foam with which it is almost constantly surrounded1 and which1 in the heavy swells which sometimes accompany a dead calm1 before or after a heavy gale of wind1 rises to a prodigious height in a column or jet1 resembling1 at a distance1 the play of a gigantic fountain4 ,so high1 indeed1 does the sea rise on this shoal after heavy gales1 that it often quite obscures the larger and more distant object of the ,rock and ,tower of the ,skerryvore1 even when viewed from the top of ,ben ,hynish in ,tyree4 ,the wooden barrack erected on the ,skerryvore for the use of the workmen during the progress of the operations1 although about sixty feet in height1 was often lost sight of at ,tyree by the uprising of the sea on ,boinshly1 and could be seen only during the calm that intervenes between returning waves4 99 99 99 99 99 ,the next ,rock that occurs is ,bo-rhua1 a name derived from the ,celtic1 and signifying1 according to the natives1 ,red ,rock4 ,it lies about #b miles from ,boinshly1 and about one mile from the ,skerryvore4 ,the passage between it and ,boinshly is clear1 and has a depth of about fourteen fathoms2 but it is too narrow to be safely navigated except by daylight1 even under the most favourable circumstances1 and then no mariner would run the risk of taking such a passage1 but would prefer1 even at some sacrifice of time1 the fairway of the passage of ,tyree4 ,bo-rhua is completely covered at high1 but is dry at low water4 ,the extent of rock uncovered is about forty feet by twenty feet1 and the highest point of it is about six feet above low water level of spring tides4 ,a small outlying pinnacle1 about ten feet square1 is also uncovered at low water4 ,the depth immediately round ,bo-rhua is considerable1 from three to seven fathoms being found within fifty feet of it2 and in this respect it differs from ,boinshly1 which1 as already mentioned1 is surrounded by shoal water for some distance4 ,between ,bo-rhua and ,skerryvore1 however1 which is a distance of about a mile1 there cannot properly be said to be any clear navigable channel1 as will be distinctly seen by referring to the plan4 ,the whole of this tract may1 in fact1 be termed foul ground4 99 99 99 99 99 ,the ,skerryvore or chief rock1 and the detached rocks immediately surrounding it1 were surveyed with greater minuteness than the others1 as it was at once apparent1 that on this part of the reef alone could a suitable site for a lighthouse be found4 ,the name is derived from the ,gaelic1 and signifies the ,great ,rock4 ,it is very much wasted and cut up2 the number of detached rocks1 sunk and exposed1 in its immediate neighbourhood1 whose positions were determined during the survey1 amounting to no fewer than #acj4 ,the depth of water between those different detached fragments1 which extend over a surface of about a mile in length1 by half a mile in breadth1 is considerable1 varying from #b to #h fathoms at low water of spring tides4 99 99 99 99 99 ,the surface of the main or principal rock1 on which the ,lighthouse has been placed1 measures1 at the lowest tides1 about #bhj feet square4 ,it is extremely irregular1 and is intersected by many gullies or fissures1 of considerable breadth1 and of unlooked for depth1 and which leave it solid only to the extent of #afj feet by #gj feet4 ,the extremity of one of these gullies1 at the south-east corner of the rock1 forms the landing-creek1 which is a narrow track of #cj feet wide1 having deep water2 and1 with the help of some artificial clearing and dressing1 which was executed with much difficulty1 by blasting under water1 while the other works were in progress1 its sides and bottom are now comparatively smooth4 ,at this place a landing can often be effected when the rock is unapproachable from any other quarter1 although great inconvenience is felt from the surge1 which finds its way from the opposite side of the rock1 through the westward opening of the gulley in which the landing-place is situated4 99 99 99 99 99 ,another of the gullies1 immediately to the south-east of the ,lighthouse1 was found1 on examination1 to undermine the rock to the extent of eight or ten feet1 and to terminate in a hollow submarine chamber1 which threw up a spout or jet of water about twenty feet high1 resembling in appearance the ,geyser of ,iceland1 and accompanied by a loud sound like the snorting of some sea monster4 ,the effect of this marine jet d'eau was at times extremely beautiful1 the water being so much broken as to form a snow-white and opaque pillar1 surrounded by a fine vapour1 in which1 during sunshine1 beautiful rainbows were observed4 ,but its beauties by no means reconciled us to the inconvenience and discomfort it occasioned1 by drenching us whenever our work carried us near it4 ,one calm day ,i contrived1 at a very low tide1 by means of ropes and a ladder1 to explore the interior of the cavern1 from which this fountain rose1 and found it to terminate in a polished spherical chamber1 about seven feet in diameter1 its floor filled with boulders1 whose incessant play had hollowed it out of the veined rock1 and rendered its interior beautifully smooth and glassy4 ,as ,i considered that this curious cavern penetrated too far1 and came too close to what ,i had selected as the best foundation1 ,i changed the site of the tower1 so as to avoid any chance of its being undermined4 ,i also deemed it prudent to fill up the cavity1 to prevent its further extension1 and at the same time to rid ourselves of the discomfort of being drenched by the column of water which spouted up from it1 even during fine weather1 when the sea was apparently calm4 ,this gulley affords a good example of the power of pebbles kept constantly in play by the waves to wear down the hardest rock1 and shews what extensive effects so insignificant an agent may effect in the course of time4 99 99 99 99 99 ,before the excavation for the foundation of the tower was made1 a single conical loaf of rock1 about five feet in diameter1 rose to the height of eighteen feet above the level of high water1 the greater part of the rest of its surface being about six feet above the tide mark4 99 99 99 99 99 ,in addition to its shattered and disjointed appearance1 the ,skerryvore ,rock presents1 in another respect1 a striking example of the action of the sea1 which no one1 on first landing on the rock1 can fail to perceive4 ,i allude to the glassy smoothness of its surface1 a feature that existed to so remarkable an extent as to have proved throughout the whole duration of the work1 but more especially at its commencement1 a serious obstacle and hindrance to the operations4 ,it may1 at first sight1 appear strange that this grievance should have been so much felt2 but1 when ,i mention that the landings were often made in very bad weather1 it will be obvious that there was considerable danger in springing ashore from a boat in a heavy surf upon an irregular mass of rock as smooth and slippery as ice4 ,the workmen were1 in that respect1 often sorely tried1 and many inconvenient accidents occurred from falls4 ,it was after one of these trials of patience1 that the foreman of the masons was heard very graphically to describe a landing on the rock as 8like climbing up the side of a bottle40 ,instead of a weather-beaten rock1 whitened by the dung of sea-fowls1 and with marine crustacea adhering to it1 the surface of the ,skerryvore is smoothly polished by the action of the waves1 every projecting angle or point is worn down1 and the whole presents more the appearance of a mass of dark-coloured glass than a reef of gneiss-rock4 ,excepting in some of the more sheltered crevices1 no marine crustacea find shelter2 but different kinds of sea-plants grow upon it1 in great abundance1 at and below the low water mark4 ,these plants are1 doubtless1 enabled to resist the action of the waves in the same way as the sapling1 yielding to the blast1 is preserved during the storm that uproots the aged and more stubborn oak4 99 99 99 99 99 ,the rocks of ,skerryvore have the same characteristics as those of the neighbourhood of ,tyree1 being what we may1 perhaps1 call a syenitic gneiss1 as it consists of quartz1 felspar1 hornblende1 and also mica4 ,it will be seen1 from the narrative of the progress of the works1 that this rock was1 from its hardness1 exceedingly difficult and tedious to excavate4 ,the only variation in the geology of the ,skerryvore1 is the presence of a trap rock1 in the form of a dyke of basalt1 which intersects the strata1 and exhibits a fine specimen of the intrusion of igneous rocks4 ,it is shewn in ,plate1 ,no4 ,,iii41 by a thick black line4 99 99 99 99 99 ,connected with this general view of the appearance and geology of the rock1 it may be interesting also to notice1 that a considerable mass of foreign matter1 somewhat resembling1 in its structure1 a deposit of lime1 was found in different places resting in horizontal layers of various thickness and size4 ,this substance was found in pools or sheltered parts of the rock1 about the level of high water mark1 and1 in some cases1 even a little below it4 ,it was so hard as to admit of a pretty high degree of polish2 and emitted an offensive odour on being burned in the fire1 or rubbed on a stone with water4 ,it gave other clear indications of containing animal matter1 and in other respects resembled the bergmeal and guano4 ,to account for its presence in such a situation1 seems rather a difficult problem4 ,on sending a specimen of this material to my friend the ,rev4 ,dr ,fleming1 ,professor of ,natural ,philosophy in ,king's ,college1 ,aberdeen1 ,i received from him an analysis of the substance1 and a concurrence in the opinion ,i had formed as to its containing animal matter2 and ,dr ,fleming1 indeed1 expressed his belief that the matter in question is the indurated soil of birds1 and had been deposited when the reef was more extensive1 and the resort1 and probably the breeding-place of sea-fowls4#c ,how this singular formation should be found on the verge of the ocean1 and even within the high water mark1 in spite of winds and waves1 or how it should have assumed the stratified structure which seems to indicate the depositation of successive layers in still water1 are matters very difficult to be explained1 without coming to the conclusion1 that the uncovered surface of ,skerryvore ,rock must at some distant period have been much more extensive than at present1 so as to permit the deposit to go on in an interior basin or lagoon1 sheltered from the waves1 and somewhat similar to those which ,dr ,darwin has described as characteristic of the ,coral ,isles of the ,pacific4 ,this supposition seems not at all improbable1 as it does not require a great stretch of fancy to conceive1 that at some period1 the whole of the rocks in the immediate vicinity of ,skerryvore1 and extending perhaps even so far as ,bo-rhua1 may have been connected by a matrix of softer materials1 which have gradually yielded to the action of the sea1 leaving the harder portions to be smoothed and polished by the waves1 and to assume the characteristic features of permanent rocks and sunk reefs which they now possess4 ,there is also some countenance to such a view to be derived from the features of the neighbouring ,island of ,tyree1 which contains numerous small lagoons1 in which such deposits might be formed by the flocks of sea fowl which frequent them4 ,some of these pools are so near the shore1 as to make it no difficult matter to conceive that their walls might be broken by the sea1 and that they might eventually become part of it1 and thus exhibit the phenomenon of deposits apparently lacustrine within the verge of the ocean4 #c ,dr ,fleming has since obtained from ,ichaboe indurated bird-soil or guano1 closely resembling that from the ,skerryvore4 99 99 99 99 99 ,another remarkable feature which ,i observed in the ,skerryvore ,rock1 was a deposit of gravel in the narrow crevices of the rock1 which run nearly from north-east to south-west1 dipping at an angle of #hj to the westward4 ,in almost all of the fissures we found great quantities of small water worn boulders1 less in size than a horsebean1 and generally of the same materials as the rock itself4 ,the boulders bore the appearance of having been forced into the fissures of the rock by some very powerful pressure1 and were wedged hard into the crevices4 ,in some cases a considerable quantity of softer matter containing iron was found1 and in it the pebbles were imbedded4 ,in the upper parts of the rock the crevices swarmed with centipedes of a reddish-brown colour4 ,the rock was covered with sea fowl when first visited1 and during heavy gales seals resorted to it4 99 99 99 99 99 ,about three miles to the westward of ,skerryvore lie ,mackenzie's ,rock1 ,fresnel's ,rock1 and ,stevenson's ,rock1 which1 as will be seen from ,plate ,,ii41 are connected by a tract of foul ground of about a mile and a quarter in length4 ,those rocks are the western limit of what we have already denominated the ,skerryvore ,reef4 ,the passage between them and the ,skerryvore or main rock is clear1 and has a depth of water varying from eleven to twenty-eight fathoms4 99 99 99 99 99 ,mackenzie's ,rock1 which derives its name from the celebrated ,marine ,surveyor1 is uncovered1 at low water1 to the extent of about forty yards1 and consists of scattered patches of rock1 one of which1 at its highest part1 rises about ten feet above high water mark of spring-tides4 ,fresnel's and ,stevenson's ,rocks are always under water2 but the sea is often seen to break violently over them1 as well as over the whole stretch of the sunken reefs which extend between them4 ,the first of those rocks is indebted for its name to the great optical philosopher1 who so greatly improved lighthouses2 and the second bears the name of the surveyor who first laid down the rock1--the late ,engineer of the ,northern ,lights ,board4 99 99 99 99 99 ,during the progress of the survey1 a register of the rise and fall of the tides was regularly kept at ,hynish on the neighbouring ,island of ,tyree2 and from those observations it was determined1 that the rise at that place is between twelve and thirteen feet at high spring tides1 and three feet at dead low neap tides2 and observations subsequently made while the works were in progress1 gave the same results at the ,rock of ,skerryvore4 ,it is high water at the ,rock at full and change of the moon1 at five hours and twenty-five minutes4 ,the tides round the ,skerryvore are not remarkable for their rapidity4 ,in spring-tides the velocity is between four and five miles1 and in neap-tides between two and three miles an hour4 ,the flood sets to the ,n4,n4,e41 and the ebb to the ,s4,s4,w4 ,,chapter ,,ii4 ,,preliminary ,,arrangements ,,and ,,works1 ,,including ,,survey ,,of ,,the ,,rocks1 ,,and ,,opening ,,of ,,quarries1 ,,from #ahcd to #ahcg4 ,survey of the ,skerryvore ,rocks4 ,in this chapter ,i shall very briefly notice those preliminary arrangements which may be said to have been in a great measure preparatory to the commencement of the work itself4 ,it has been already stated1 that the erection of the ,lighthouse was provided for in the ,act of #ahad2 but so formidable did this work appear1 that although it was repeatedly under consideration1 it was not until the ,general ,meeting of the ,board1 on the #hth ,july #ahcd1 that any measures were taken to carry into effect the provisions of the ,act4 ,on that occasion it was moved by the late ,mr ,,maconochie1 ,sheriff of ,orkney and ,zetland1 that the ,engineer should be instructed to make the necessary survey1 and to report as to the expense of erecting the ,lighthouse4 ,in terms of this remit1 the survey of the ,rocks was commenced in the autumn of #ahcd2 but from the broken state of the weather1 little was effected at that time beyond making the triangulation2 and it was not until the summer of #ahce that the survey was completed from which the ,chart1 ,plate ,no4 ,,ii4 was constructed4 ,this survey was attended with much more labour than its extent would lead one to suppose1 in consequence of its embracing the entire range of operations required in a more extensive nautical survey1 and combining with the ordinary details required for a ,chart1 the minute accuracy in regard to surface and levels1 which are always necessary for the purposes of the ,engineer4 99 99 99 99 99 ,the first step was the measurement of a base line in the low lands of the adjoining ,island of ,tyree1 which1 owing to the distance and disadvantageous position of that island1 could not be satisfactorily extended to the ,rock without fixing stations in some of the more distant islands2 and in the course of the work not fewer than twenty land triangles were measured4 ,the calculations of the distances founded on this triangulation agreed with those afterwards obtained from the data of the ,trigonometrical ,survey1 which were kindly furnished to me by ,captain ,yolland of the ,royal ,engineers1 in #ahdc4 ,for the purpose of making the soundings and laying down the sunken rocks1 an entirely separate triangulation1 based upon and connected with that which has already been noticed1 became necessary1 as the land objects were too distant1 and their relative positions were such as to render it difficult by observations from them alone to determine any stations on the sea4 ,buoys were therefore moored at convenient points1 and their positions determined by a subsidiary triangulation1 so as to form a net-work of triangles between the shore and the ,skerryvore ,rock4 ,the distances between these buoys were afterwards used as the bases of imaginary triangles1 having points of sounding or shoals in their apex2 and the angles subtended by those distances being measured by the sextant1 the positions of the shoals or soundings were thence easily deduced and protracted on the ,chart4#d ,in connection also with the soundings whose positions were determined in the way above described1 a complete set of tide observations was made1 extending over a period of about six weeks4 ,those tide observations were connected in point of time1 with the soundings1 and were employed as the means of correcting the observed depths taken with the sounding-line1 so as to give the true depth in reference to the high or low water of a given tide4 ,accurate measurements1 and minute sections1 were also made of the rocks in reference to the tide-level1 and more especially of the main rock1 on which alone it was obvious1 from the first inspection1 that the ,lighthouse ,tower could be erected4 ,in the course of this survey1 the positions of upwards of #adj rocks were determined1 and laid down on the ,chart1 and #ejj soundings were taken1 and their positions protracted4 ,an interesting fact was also noticed regarding the mean level of all the tides which had been watched during the period of about six weeks1 as above noticed1 viz41 that the point half way between the high and low water of every tide is on one and the same level4 ,this fact regarding the tides was1 it is believed1 first detected by my ,father1 in the course of some tidal observations which he made in the ,dornoch ,frith in #ahcj1 and has since been observed in the ,frith of ,forth in #ahcc1 and again on the shores of the ,isle of ,man1 and at ,liverpool4 ,the agreement of so many observations by various persons at places on the opposite shores of the ,kingdom1 seems to imply the universality of this phenomenon in the ,british ,seas2 and the position of ,skerryvore would lead to the belief1 that it is not confined to narrow seas1 but that it exists in the ocean4 ,i cannot dismiss the subject of the survey1 without mentioning the late ,mr ,james ,ritson1 who acted as principal assistant surveyor1 and to whose zeal and intelligence so much of its accuracy is to be attributed4 ,the deep gulley which intersects the main ,rock from ,n4,e4 to ,s4,w41 and across which he one day sprang while it was filled with a breaking wave1 bears his name1 as a memorial of his activity and perseverance4 ,at the close of the survey in #ahce1 the station-pole was left wedged and batted into one of the fissures or crevices of the ,rock1 and a cask of water was firmly lashed to ring-bolts in a cleft of the highest part of the ,rock1 in the hope that it might possibly prove useful to some shipwrecked seamen4 #d ,vide ,stevenson's ,marine ,surveying and ,hydrometry4 ,edinburgh1 #ahdb1 p4 #add4 99 99 99 99 99 ,for the purposes of navigation generally1 a survey merely indicating the position and extent of the foul ground would have been sufficient4 ,but in connection with the work which was about to be commenced1 it was particularly desirable to have exact details of the depths1 rocks1 and shallows of the surrounding sea1 with the nature of the bottom1 accurately laid down2 and our experience during the course of the work1 more than once shewed how essential was the possession of minute topographic information to the safety of the shipping attending the works2 more especially as some of the vessels lay very near the rocks1 and were frequently driven1 by a sudden change of wind1 to seek shelter1 during the darkest nights1 among the neighbouring islands4 99 99 99 99 99 ,until this time the greatest ignorance prevailed amongst seamen as to the extent of the ,reef1 which had never before been minutely surveyed4 ,of this some proofs occurred even during the progress of the survey2 for several vessels came so near the ,rocks as to cause1 in the minds of the surveyors1 who witnessed their temerity1 serious fears for their safety4 ,on one occasion1 in particular1 a large vessel belonging to ,yarmouth1 with a cargo of timber1 was actually boarded between ,mackenzie's ,rock and the main ,rock of ,skerryvore by the surveyors1 who warned the master of his danger in having so nearly approached these rocks1 of the existence of which his chart gave no indication4 ,on another occasion1 a vessel belonging to ,newcastle was boarded while passing between ,bo-,rhua and the main ,rock2 and so little1 indeed1 had the master 7whose chart terminated with the main ,rock1 and shewed nothing of ,bo-,rhua7 been dreaming of danger1 or fancying that he was within a cable's length of the reef1 that he was found lying at ease on the companion1 enjoying his pipe1 with his wife sitting beside him knitting stockings4 99 99 99 99 99 ,disadvantages of ,tyree4 ,much preliminary investigation was necessarily occasioned by the difficulties and disadvantages arising from the remote situation of the island in which a great part of the works was to be carried on4 ,not only is the ,rock itself often inaccessible and dangerous1 being surrounded by numerous shoals1 and visited by the heaviest seas of the ,atlantic2 but what gave rise to no small part of the difficulties which attended this work1 was the nature of the neighbouring ,island of ,tyree4 ,this island is unhappily destitute of any shelter for shipping1 a fact which was noticed as a hinderance to its improvement1 upwards of #adj years ago1 by ,martin1 in his well-known description of the ,western ,islands4#e ,nor is its interior more attractive2 for although some parts of the soil when cultivated are excellent1 the greater part of its surface is composed of sand4 ,it was therefore obvious1 at a glance1 that ,tyree was one of those places to which every thing must be brought2 and this is not much to be wondered at1 as the population1 who1 on a surface not exceeding #bg square miles1 amounted in #ahda to #dfhg souls1 labour under all the disadvantages of remoteness from markets1 inaccessible shores and stormy seas1 and the oft-recurring toil of seeking fuel 7of which ,tyree itself is destitute7 from the ,island of ,mull1 nearly #cj miles distant1 through a stormy sea4 ,it is said that this total absence of fuel in ,tyree is the result of the reckless manner in which it was wasted1 in former days1 in the preparation of whisky2 but1 however this may be1 certain it is that the want of fuel greatly depresses the condition of the people4 ,for our works1 therefore1 craftsmen of every sort were to be transported1 houses were to be built for their reception1 provisions and fuel were to be imported1 and tools and implements of every kind were to be made4 #e ,a ,description of the ,western ,islands of ,scotland1 c41 by ,m4 ,martin1 ,gent4 ,london1 #agjc4 ,vide #b;d ,edition of #agaf1 p4 #bfg4 99 99 99 99 99 ,pier and workyard at ,hynish ,tyree4 ,in the course of the survey1 much attention had been bestowed upon the selection of a convenient place for a workyard in ,tyree for the preparation of materials1 and in examining its rugged shores in quest of the best site for a ,harbour1 for the shipment of the building materials for the ,rock1 and for the all-important purpose of enabling the future attending vessel to lie in safety within sight of signals from the ,rock1 when the ,light should come to be exhibited to the public4 ,the point chosen for this establishment was ,hynish1 which1 though twelve miles distant1 is1 nevertheless1 the nearest creek to the ,skerryvore ,rock1 and which1 however exposed it may be1 if compared with creeks elsewhere dignified with the name of ,harbour1 certainly affords as good prospect of shelter as any other part of the ,island of ,tyree1 and is1 in this respect1 greatly to be preferred to any other place within sight of the ,rock4 ,a deputation of the ,commissioners visited the ,skerryvore in the month of ,july #ahcf1 and concurred with the ,engineer in regard to his choice of ,hynish as a site for the ,harbour and establishment4 99 99 99 99 99 ,quarries at ,hynish4 ,another most important point of inquiry was regarding the materials for building the ,lighthouse2 and on this subject the suggestions in a ,report by the ,engineer1 of the #cast ,december #ahce1 were followed1 which proposed the opening of quarries among the gneiss rocks around ,hynish4 ,much facility was afforded by the liberality of the late ,duke of ,argyll1 the proprietor of ,tyree1 who granted to the ,commissioners free permission 8to quarry materials for the purpose of the ,lighthouse1 on any part of the ,argyll estates40 ,this freedom was generously continued by the present ,duke1 who has all along taken a lively interest in the success of the works4 ,in terms1 therefore1 of the ,engineer's recommendations contained in the above noticed ,report1 ,mr ,james ,scott and fourteen quarriers were employed1 during the summers of #ahcf and #ahcg1 in opening quarries1 with very promising appearances of final success1 among the gneiss rocks near ,hynish ,point4 ,in the summer of #ahcg1 ,mr ,scott and his party turned out about #chjj cubic feet of rock1 capable of being applied to the purposes of squared masonry1 and a very large quantity of stones fit for rubble work4 ,this produce1 although small1 if contrasted with that of established quarries1 is by no means despicable1 when the force employed and all the disadvantages of the situation are considered2 and if the nature of the material1 which is full of rents and fissures 7technically called dries and cutters71 the frequent deceptions attending the opening of new quarries1 the excessive hardness and unworkable nature of the rock1 the quality and size of the blocks required to entitle them to claim a place in a marine tower1 and the great loss of time1 caused by the badness of the weather1 be considered1 it will not appear that ,mr ,scott and his party had been eating the bread of idleness4 99 99 99 99 99 ,in the mean time1 measures had been taken for obtaining from his ,grace the ,duke of ,argyll a feu of fifteen acres of ground at ,hynish1 for carrying on the works1 with a view to its being finally occupied as an establishment for the crew of the vessel which was to attend the ,lighthouse1 and the families of the four lightkeepers1 as well as for the site of the harbour4 ,to this was added a lease of thirty acres1 for the various purposes connected with a workyard1 and such an establishment as seemed necessary for carrying on the work4 ,a subject of anxious deliberation with the ,board1 was the construction of the harbour at ,hynish for the vessels engaged in the service of the work2 and the ,commissioners1 on the #bdth ,may #ahcg1 authorized the ,engineer to make arrangements for commencing the formation of the ,pier4 ,the work was1 accordingly1 undertaken1 in terms of his ,reports of the #cast ,december #ahce1 and #bgth ,february #ahcf2 and the summer of #ahcg was chiefly occupied in preparing a wharf1 mostly composed of pierres-perdues1#f and in the opening of the quarry already noticed4 ,such may serve as a brief and somewhat desultory notice of the work during the seasons of #ahcf and #ahcg1 after which it appeared to the ,board that the operations must soon assume such an aspect as to require the superintendence of a committee of their number1 as well as that of an ,engineer specially entrusted with the management of the work4 #f ,blocks rough from the quarry1 which are dropt or thrown promiscuously into the sea4 99 99 99 99 99 ,skerryvore ,committee appointed4 ,at the meeting of the ,board1 on the #hth ,december #ahcg1 a ,committee of their number was accordingly named1 to superintend the erection of the ,lighthouse4 ,this ,committee consisted of--,,robert ,,bruce1 ,esq41 ,sheriff of ,argyllshire2 ,,andrew ,,murray1 ,esq41 ,sheriff of ,aberdeenshire2 ,,robert ,,thomson1 ,esq41 ,sheriff of ,caithness2 and the late ,,james ,,maconochie1 ,esq41 ,sheriff of ,orkney and ,zetland2 and1 shortly after its appointment1 the ,committee1 on the motion of ,mr ,,bruce1 the ,chairman1 appointed me ,engineer for the work4 99 99 99 99 99 ,among the first matters which engaged the attention of this ,committee1 was a ,report from the ,engineer1 dated the #cjth ,january #ahch1 in which the necessity of erecting a wooden barrack1 as a place of shelter for the workmen on the ,rock1 was pointed out2 the general arrangements for carrying on the operations were described2 and the building of a steam-tender1 to act as a towing vessel for the stone lighters between the workyard in ,tyree and the ,rock1 was also recommended4 ,the ,report was accompanied by a detailed requisition or estimate for the operations of the ensuing season1 amounting to ,l4#ae1jjj 3 #c 3 #c2 of which sum it was proposed to expend about one-third in building a steam-tender1 and the rest in erecting the wooden barrack on the ,rock1 and in providing tools and materials for the work1 as well as in the wages of men to be employed in preparing the foundation of the ,lighthouse ,tower1 and in building the ,pier1 and dressing stones at ,hynish4 99 99 99 99 99 ,the ,committee1 after considerable deliberation1 sanctioned the various items of the estimate1 but hesitated to embark in the expense of building a steamer1 until a fruitless correspondence with various ports of the kingdom1 with the view of purchasing an old vessel1 satisfied them of the necessity of building a tender expressly for the purpose4 99 99 99 99 99 ,offers were immediately received from various parties at ,greenock for the preparation of the wooden barrack1 which was soon afterwards commenced by the late ,mr ,john ,fleming1 house-carpenter1 who was the successful competitor4 ,,chapter ,,iii4 ,,on ,,the ,,construction ,,of ,,lighthouse ,,towers4 ,in this chapter ,i purpose1 in the first place1 to make a few observations regarding the construction of ,lighthouse ,towers in situations which are exposed to the assault of the waves1 and afterwards to give a short notice of the design which ,i adopted for the ,tower on the ,skerryvore ,rock4 ,in making a design for a ,lighthouse ,tower in an exposed situation1 numerous considerations at once present themselves to the ,engineer2 and it is difficult to assign to any one of them a priority in the train of thought which eventually conducts him to the formation of his plan4 ,these considerations1 however1 may be conveniently divided into two classes3--#ast1 ,those which refer to elements common to ,lighthouses in all situations1 and differ only in amount1 such as the height of the ,tower necessary for commanding a given visible horizon1 and the accommodation required for the ,lightkeepers and the ,stores2 and1 #b;d1 ,those which are peculiar to ,towers in exposed situations1 and which refer solely to their fitness to resist the force of the waves which tend to destroy them4 ,the first class of considerations is so extremely simple1 as to require few remarks in this place4 ,the distance at which it is desirable that a light should be visible being ascertained1 with reference to the nature of the surrounding seas and the extent to which any dangerous or foul ground lies seaward of the proposed ,lighthouse1 the height of the ,tower is at once determined by means of the known relations which subsist between the spheroidicity of the earth1 the effects of atmospheric refraction1 and the height required for an object which is to be seen from a given distance4 ,the question regarding the space to be provided in the interior of the ,tower1 can only be properly answered by a person who has a minute practical acquaintance with the peculiar wants and the internal economy of ,lighthouses4 ,the accommodation required for ,lighthouses in exposed situations must1 in a considerable degree1 depend upon the greater or less facility of access to them1 and the opportunities for replenishing the stores of all kinds which are in daily consumption4 ,in such places1 also1 the risk of accidents naturally leads to the precaution of retaining additional ,lightkeepers1 and of having duplicates or even triplets of those parts of the apparatus that are liable to be injured4 ,of such circumstances1 corresponding extension of the space devoted to the reception of ,stores and the accommodation of the ,lightkeepers1 is the necessary consequence4 ,in the long nights of a ,scotch winter1 when the lamps are kept burning for about seventeen hours1 during which time they are never left for a moment without the superintendence of at least one ,keeper1 the care of the light1 even in the most favourable situations1 necessarily occupies at least two persons2 but in places like the ,eddystone1 the ,bell ,rock1 and the ,skerryvore1 where it sometimes happens that six or eight weeks elapse without its being possible to effect a landing1 it has been thought necessary that there should never be fewer than three ,keepers on duty4 ,this addition to the ordinary establishment of a ,lighthouse calls for a greater number of sleeping-cabins1 and1 at the same time1 involves a corresponding increase in the supply of water1 fuel and other provisions1 requiring much additional stowage4 ,so far1 therefore1 a ,light ,tower in an exposed situation1 differs from one on shore only in the extent of its internal accommodation4 ,the second class of considerations1 which must guide the ,engineer in framing a design for a ,light ,tower which is exposed to the force of the waves1 refers solely to the stability of the building4 ,the first observation which must occur to any one who considers the subject is1 that we know little of the nature1 amount and modifications of the forces1 on the proper investigation of which the application of the principle which regulates the construction must be based4 ,when it is recollected1 that1 so far from possessing any accurate information regarding the momentum of the waves1 we have little more than conjecture to guide us1 it will be obvious1 that we are not in a situation to estimate the power or intensity of those shocks to which ,sea ,towers are subject2 and much less can we pretend to deal with the variations of these forces which shoals and obstructing rocks produce1 or to determine the power of the waves as destructive agents4 ,no systematic or intelligible attempt has been made practically to measure the force of the waves1 so as to furnish the ,engineer with a constant to guide him in his attempts to oppose the inroads of the ocean4 ,the only experiments1 indeed1 on the subject1 with which ,i am acquainted1 are those of ,mr ,thomas ,stevenson1 ,civil-,engineer1 who had long entertained the idea of registering the force of the impulse of the waves1 and lately contrived an instrument for the purpose1 which he has applied at various parts of the coast4 ,i therefore gladly avail myself of the present opportunity1 to give a brief statement of the results indicated by it1 as contained in a paper by the inventor1 which appeared in the ,transactions of the ,royal ,society of ,edinburgh of #bjth ,january #ahde1 and of which a digest will be found in the ,appendix1 as any attempt to throw light upon this most obscure1 but highly important subject1 cannot fail to be interesting1 not merely to the philosopher1 but to the ,marine ,architect4 ,it would naturally be expected1 that the force of the waves should vary according to the season of the year1 and the nature of the exposure1 and this expectation is fully justified by the indications of the ,marine ,dynamometer4 ,thus it appears1 that during five summer months of #ahdc and #ahdd1 the average indications registered at different places near ,tyree and ,skerryvore1 gave #faa lb4 of pressure per square foot of surface exposed to the waves2 while the average for the winter months for the same places during those two years1 gave #bjhf lb4 per square foot1 or upwards of three times that of the summer months4 ,it also appears1 that the greatest result as yet obtained at ,skerryvore ,rock was #dcce lb4 per square foot2 while that observed on the ,bell ,rock was #cjac lb41 or one-fourth part less than that of ,skerryvore4 ,but these experiments have not been continued long enough as yet to render them available for the ,engineer4 ,in the present state of our information1 therefore1 we cannot be said to possess the elements of exact investigation1 and must consequently be guided chiefly by the results of those numerous cases which observation collects1 and which reason arranges1 in the form which constitutes what is called professional experience4 ,this kind of experience can only be acquired by long habit in carefully observing the appearance and effects of waves in different situations1 and under various circumstances4 ,we must attend to their magnitude and velocity1 their level in regard to the rocks on which they break1 the height of the spray caused by their collision against the shore1 the masses of rock which they have been able to move1 and those which have successfully resisted their assault2 as also1 where such exist1 the slopes of the shores produced by the waves1 viewed in connection with the nature of the materials composing the beach1 with many other transient features which an experienced eye seizes and fixes in the mind as elements of primary importance in determining the power of the sea to produce certain effects4 ,such phenomena1 with all their features and circumstances1 we may carry in our recollection2 and by comparing them with what has been observed at places where we know that artificial works have resisted the shocks of the waves1 we may in some cases successfully arrive at a conclusion as to what works will1 at all events1 be within the bounds of safety4 ,we must not1 however1 in any case1 venture to approach too near the limit of stability1 so long as we continue to labour under our present disadvantages of defective information on some of the most important elements in the inquiry4 ,if it be asked1 therefore1 how the size and form of buildings exposed to the shock of the waves are to be determined1 the answer must be1 that1 in any given case1 the problem is to be solved chiefly by the union of an extensive knowledge of what the sea has done against man1 and how1 and to what extent1 man has succeeded in controlling the sea2 together with a cautious comparison of the circumstances which modify and affect any given case which has not been the object of direct experience2 nor does it seem possible as yet to found the art of ,engineering1 in so far as it refers to this class of works1 upon any more exact basis4 ,the uncertainty which must ever attend such reasoning can only1 it is obvious1 be dispelled by actual experience of the result2 and time only can test the success of our schemes in cases of difficulty4 99 99 99 99 99 ,a primary inquiry1 in regard to ,towers in an exposed situation1 is the question1 whether their stability should depend upon their strength or their weight2 or1 in other words1 on their cohesion1 or their inertia8 ,in preferring weight to strength1 we more closely follow the course pointed out by the analogy of nature2 and this must not be regarded as a mere notional advantage1 for the more close the analogy between nature and our works1 the less difficulty we shall experience in passing from nature to art1 and the more directly will our observations on natural phenomena bear upon the artificial project4 ,if1 for example1 we make a series of observations on the force of the sea1 as exerted on masses of rock1 and endeavour to draw from these observations some conclusions as to the amount and direction of that force1 as exhibited by the masses of rock which resist it successfully and the forms which these masses assume1 we shall pass naturally to the determination of the mass and form of a building which may be capable of opposing similar forces1 as we conclude1 with some reason1 that the mass and form of the natural rock are exponents of the amount and direction of the forces they have so long continued to resist4 ,it will readily be perceived1 that we are in a very different and less advantageous position when we attempt1 from such observations of natural phenomena1 in which weight is solely concerned1 to deduce the strength of an artificial fabric capable of resisting the same forces2 for we must at once pass from one category to another1 and endeavour to determine the strength of a comparatively light object which shall be able to sustain the same shock1 which we know1 by direct experience1 may be resisted by a given weight4 ,another very obvious reason why we should prefer mass and weight to strength1 as a source of stability1 is1 that the effect of mere inertia is constant and unchangeable in its nature2 while the strength which results1 even from the most judiciously disposed and well executed fixtures of a comparatively light fabric1 is constantly subject to be impaired by the loosening of such fixtures1 occasioned by the almost incessant tremor to which structures of this kind must be subject1 from the beating of the waves4#g ,mass1 therefore1 seems to be a source of stability1 the effect of which is at once apprehended by the mind1 as more in harmony with the conservative principles of nature1 and unquestionably less liable to be deteriorated than the strength1 which depends upon the careful proportion and adjustment of parts4 #g ,it was chiefly on these grounds that the ,commissioners of ,northern ,lights1 after consulting a ,committee of the ,royal ,society of ,edinburgh1 and ,messrs ,cubitt and ,rennie1 ,civil ,engineers1 rejected the design of ,captain ,sir ,samuel ,brown1 ,r4 ,n41 who volunteered a proposal to build an ,iron ,pillar at the time that the erection of the ,skerryvore ,lighthouse was determined on in #ahce4 99 99 99 99 99 ,having satisfied himself that weight is the most eligible source of stability1 the next step of the ,engineer is to inquire what quantity of matter is necessary to produce stability1 and what is the most advantageous form for its arrangement in a tower4 ,the first question1 which respects the mass to be employed1 is1 as already stated1 one of the utmost difficulty1 and can be solved by experience alone1 directed by that natural sagacity which ,smeaton1 in his account of his own thoughts on the subject1 with much navet1 terms #8feelings1' in contradistinction to that more accurate process of deduction which he calls #8calculation4' ,it is very difficult1 for example1 to conceive that the waves could displace a cylindric block of granite1 #be feet in diameter and #aj feet high1 which would contain about #chj tons1 and we almost feel that they could not do so4 ,if1 in order to test the soundness of this expectation1 we appeal to such experience as we possess1 and apply to the largest vertical section of such a solid1 the greatest force yet indicated by my brother's ,marine ,dynamometer1 which1 as already stated1 is #dcce lb4 per square foot1 we shall obtain a pressure of #dhd tons1 which1 being reduced by one-half#h for the loss of force occasioned by the convexity of the opposing cylindric surface1 gives #bdb tons1 as the greatest force of the waves tending to displace the cylinder4 ,but in the extreme case we have now supposed the solid will be entirely immersed in the water1 and its efficient weight will thus be reduced by #adj tons1 or the weight of an equal bulk of sea-water2 and the remaining weight of #bdj tons1 by which it will resist the force of the waves1 will be almost exactly equal to the pressure which they exert4 ,this imaginary cylinder may1 however1 be regarded as still within the limits of safety1 because the waves could not overturn it1 unless their pressure exceeded the weight of the block in a ratio greater than that of its diameter to its height1 which in this case is that of #be to #aj1 or #b times4 ,in order1 therefore1 to endanger the stability of the solid by overturning it1 the pressure1 instead of being #bdj tons1 must be #fjj tons4#i ,we have thus seen1 that the cylinder is secure from the chance of being overturned2 but we have yet to consider how far it is exempt from the risk of being displaced by the pressure of the waves1 causing it to slide along the surface of the ,rock1 owing to deficiency of friction between the two surfaces in contact4 ,the block1 for our present purposes1 may be regarded as monolithic1 either being really so or as a mass composed of parts so united by joggles1 treenails and mortar1 as to be free from any tendency to disintegration by the force of the waves2 and in this case the stability of the cylinder will depend upon the amount of friction opposing the pressure of the waves which tends to produce a sliding movement4 ,it appears1 by some experiments of ,m4 ,rondelet1#aj that the friction of a block of stone sliding on a chiselled floor of rock is equal to ths of its own weight2 and we should thus obtain in the present instance #afh tons1 as the amount of friction tending to resist the pressure of the waves1 which would therefore exert a power superior to that resistance by #gd tons4#aa ,but this excess of force would be easily neutralized by the adhesion of the mortar and the abutment of the block against the sides of the foundation pit into which ,lighthouse ,towers in such exposed places are generally sunk in the solid rock4 ,when1 in addition to these considerations1 we learn that the solid frustum1 or lower part of the ,eddystone ,tower1 which has weathered so many storms for the last ninety years1 does not greatly exceed in mass the imaginary cylindric block which ,i have spoken of1 our confidence in the stability of the cylinder is greatly increased4 ,our belief receives a still farther confirmation from the fact1 that the strongest instance recorded of the power of the waves1 falls considerably short of the case which we have just imagined4 ,the instance alluded to is given in ,mr ,lyell's ,geology1 on the authority of the ,reverend ,george ,low1 of ,fetlar1 in ,zetland1 who mentions1 that a block1 whose dimensions seem to give us reason to estimate its weight at nearly #cjj tons 7or about one-fifth less than that of the cylinder71 was moved over a point1 and thrown into the sea2 and it must be remembered1 that the form of this block1 which was only #e feet thick and about #dj feet long1 rendered it very susceptible of a sliding motion1 and must have greatly aided its transport4 ,we may therefore not unreasonably conclude1 that1 in designing such a tower1 it is safe to assume a mass which our own judgment and recorded facts seem to concur in pronouncing beyond the power of the greatest waves1 as fixing the lowest limit to which the contents of the proposed edifice may be reduced4 #h ,this reduction seems to be warranted by the results of some experiments of ,bossut4 #i ,this is the product of #bdj tons1 by the ratio of #be4 #aj ,l'art de btir4 #aa ,the number #afh is ths of #bdj1 which is the weight of the cylinder1 reduced by the weight of an equal bulk of salt water2 and #gd is the excess of #bdb tons1 the pressure of the waves1 above #afh1 the amount of friction4 99 99 99 99 99 ,there are several circumstances1 however1 which tend to increase or diminish the stability of the same mass exposed to the same forces4 ,of these a very prominent one is the form of the mass1 which may be so modified as to offer more or less resistance to the forces which assault the building4 ,thus a parallelopiped would be a much less suitable form for a sea tower than a cylinder1 and so proportionally of all the polygonal prisms which may occur between these two extremes4 ,i remember having heard it proposed1 in the course of conversation1 by a non-professional friend1 that ,lighthouse ,towers might be formed in such a manner1 that each horizontal section should be a wedge with its narrow end directed to the greatest assaulting force4 ,this notion is in itself not destitute of ingenuity2 for1 if the circumstances to which it is to be adapted were constant1 we should thereby present the form of least resistance1 and1 at the same time1 the greatest depth and strength of the building to the line of greatest impulse4 ,but the notion is wholly impracticable1 because the direction of the winds and waves is so variable1 as to render it almost certain that a ,tower so constructed would1 on some occasion1 be assaulted in the line of its thinnest section2 and thus1 what might in one case be an advantage1 would1 in the event of such a change in the point of attack1 become a great source of weakness1 as the flat side of the wedge would then be opposed to the force1 thereby presenting to the direct assault of the waves the largest surface1 with1 at the same time1 the most disadvantageous disposition of the resisting matter4 ,there seems little reason1 therefore1 for any doubt as to the circular section being practically the most suitable for a ,tower exposed in every direction to the force of the waves4 99 99 99 99 99 ,next to this1 and hardly to be separated from it1 inasmuch as it involves the question regarding the form of the ,tower1 is the position of the centre of gravity4 ,the stability of any solid will1 in general1 greatly depend upon its centre of gravity being placed as low as possible2 and the general sectional form which this notion of stability indicates is that of a triangle4 ,this figure revolving on its vertical axis1 must1 of course1 generate a cone as the solid1 which has its centre of gravity most advantageously placed1 while its rounded contour would oppose the least resistance which is attainable in every direction4 ,whether1 therefore1 we make strength or weight the source of stability1 the conic frustum seems1 abstractly speaking1 the most advantageous form for a high ,tower4 ,but there are various considerations which concur to modify this general conclusion1 and1 in practice1 to render the conical form less eligible than might at first be imagined4 ,of these considerations1 the most prominent theoretically1 although1 ,i must confess1 not the most influential in guiding our practice1 is1 that the base of the cone must in many cases meet the foundation on which the ,tower is to stand1 in such a manner1 as to form an angular space in which the waves may break with violence4 ,the second objection is more considerable in practice1 and is founded on the disadvantageous arrangement of the materials1 which would take place in a conic frustum carried to the great height which ,lighthouse ,towers must generally attain1 in order to render them useful as sea-marks4 ,towards its top1 the ,tower cannot be assaulted with so great a force as at the base1 or1 rather1 its top is entirely above the shock of heavy waves2 and1 as the conoidal solid should be prolate in proportion to the intensity of the shock which it must resist1 it follows that1 if the base be constructed as a frustum of a given cone1 the top part ought to be formed of successive frusta of other cones1 gradually less prolate than that of the base4 ,but it is obvious1 that the union of frusta of different cones1 independently of the objection which might be urged against the sudden change of direction at their junction1 as affording the waves a point for advantageous assault1 would form a figure of inharmonious and unpleasing contour1 circumstances which necessarily lead to the adoption of a curve osculating the outline of the successive frusta composing the ,tower2 and hence1 we can hardly doubt1 has really arisen in the mind of ,smeaton the beautiful form which his genius invented for the ,lighthouse ,tower of the ,eddystone1 and which subsequent ,engineers have contented themselves to copy1 as the general outline which meets all the conditions of the problem which they have to solve4 ,and here ,i cannot help observing1 as an interesting1 and by no means unusual1 psychological fact1 that men sometimes appear to be conducted to a right conclusion by an erroneous train of reasoning2 and such1 from his 8,narrative10 we are led to believe1 must have been the case with ,smeaton in his own conception of the form most suitable for his great work4 ,in that 8,narrative0 7 #ha71 he seems to imply1 that the trunk of an oak was the counterpart or antitype of that form which his 7 #bdf7 8feelings1 rather than calculations10 led him to prefer4 ,now1 there is no analogy between the case of the tree and that of the ,lighthouse1 the tree being assaulted at the top1 and the ,lighthouse at the base2 and although ,smeaton goes on1 in the course of the paragraph above alluded to1 to suppose the branches to be cut off1 and water to wash round the base of the oak1 it is to be feared the analogy is not thereby strengthened2 as the materials composing the tree and the tower are so different1 that it is impossible to imagine that the same opposing forces can be resisted by similar properties in both4 ,it is obvious1 indeed1 that ,smeaton has unconsciously contrived to obscure his own clear conceptions in his attempt to connect them with a fancied natural analogy between a tree which is shaken by the wind acting on its bushy top1 and which resists its enemy by the strength of its fibrous texture and wide-spreading ligamentous roots1 and a tower of masonry1 whose weight and friction alone enable it to meet the assault of the waves which wash round its base2 and it is very singular1 that1 throughout his reasonings on this subject1 he does not appear to have regarded those properties of the tree which he has most fitly characterized as 8its elasticity10 and the 8coherence of its parts40 ,one is tempted to conclude that ,smeaton had1 in the first place1 reasoned quite soundly1 and arrived by a perfectly legitimate process at his true conclusion2 and that it was only in the vain attempt to justify these conclusions to others1 and convey to them conceptions which a large class of minds can never receive1 that he has misrepresented his own mode of reasoning4 ,in the paragraph preceding that which refers to the tree 7 #hj71 he has1 in point of fact1 clearly developed the true views of the subject2 and1 with the single exception of the allusion to the oak1 he has discussed the question throughout in a masterly style4 99 99 99 99 99 ,in a word1 then1 the sum of our knowledge appears to be contained in this proposition--,that1 as the stability of a sea-tower depends1 cteris paribus1 on the lowness of its centre of gravity1 the general notion of its form is that of a cone2 but that1 as the forces to which its several horizontal sections are opposed decrease towards its top in a rapid ratio1 the solid should be generated by the revolution of some curve line convex to the axis of the tower1 and gradually approaching to parallelism with it4 ,and this is1 in fact1 a general description of the ,eddystone ,tower devised by ,smeaton4 99 99 99 99 99 ,illustration3 ,no4 #a4 ,it is deserving of notice1 as one of the many proofs which the records of antiquity afford of the similarity of the results of human thought in all ages1 and of the truth of the ,wise ,man's saying1 that 8there is nothing new under the sun10 that the ancient ,egyptians appear to have had the same conceptions of the solid of stability that were present to the mind of the modern ,engineer of the ,eddystone ,lighthouse4 ,in the admirable work recently published by ,sir ,j4 ,gardner ,wilkinson on the ,manners and ,customs of the ,ancient ,egyptians1 he gives1 in the first volume of his second series1 at page #bec1 a wood-cut1 shewing the figure of the deity ,pthah1 under the symbol of stability1 according to ,egyptian conceptions4 ,this symbol so closely and strikingly resembles the general appearance of the ,eddystone1 that ,i willingly give it a place in the text1 7,no4 #a7 denuded1 however1 of the arms and head-dress of the deity whom it shrouds4 99 99 99 99 99 ,in applying these general notions to the design of a ,tower for the ,skerryvore ,rock1 ,i was1 of course1 guided by numerous circumstances1 which modified my views and produced the individual form of ,tower which ,i have adopted4 ,since the days of ,smeaton1 when his magnificent ,tower was lighted by common candles1 the application of optical apparatus to ,lighthouses has greatly altered the state of the case2 and the improvement of the system in modern times has1 in most instances1 rendered a greater altitude of ,tower desirable1 in order to extend1 as much as possible1 the benefit of a system capable of illuminating the visible horizon of any ,tower which human art can reasonably hope to construct4 ,in the particular case of the ,skerryvore1 also1 the great distance of the outlying rocks 7some of which1 as will be seen from the chart1 are #c miles right seaward of the ,lighthouse7 concurs with the improvement of the ,lights1 in making it desirable that the ,tower should be of considerable height1 and that the light should command an extensive range4 ,it was1 therefore1 from the first consideration of the subject1 determined that the ,light should be elevated about #aej feet above high water of spring tides1 so as to illuminate a visible horizon of not less than #ah miles of radius2 and1 after much deliberation1 and a full consideration of the infrequency of communication with the proposed ,lighthouse from the great difficulty of landing on the ,rock1 and the consequent uncertainty of keeping up the supplies1 ,i found that1 for the convenient accommodation of the ,lightkeepers and the suitable stowage of the stores1 a void space of about #ac1jjj cubic feet would be required4 ,these elements being fixed1 the general proportions of the ,tower came next to be considered4 99 99 99 99 99 ,in the ,eddystone the radius of the base1 at the level of high water of spring tides1 is somewhat less than one-fifth of the height of the ,tower above that level2 while in the ,bell ,rock1 at the same level1 it is little more than one-seventh of the height4 ,if1 again1 we suppose the curve of the ,eddystone to be continued downwards to the level of low water1 the radius 7in so far as we may judge from sketching the continuation of a curve undefined by any geometrical property7 would be rather more than one-fourth of the whole height above that level2 while in the ,bell ,rock the proportion1 in reference to the same level1 is a little more than one-fifth4 ,viewing the whole height of the ,skerryvore ,tower above high water of spring tides as equal to #adb feet1 and finding that1 in the cases of the ,eddystone and the ,bell ,rock1 the radius of the horizontal section at that level is respectively one-fifth and one-seventh of the whole height2 and again1 viewing the extreme height of the ,skerryvore ,tower above low water of spring tides as equal to about #aee feet1 and considering the proportionate radii of the ,bell ,rock and ,eddystone 7in so far as the latter is ascertainable7 as respectively one-fifth and one-fourth of the heights of the top of the masonry above the level of low water1 ,i finally decided upon giving the ,tower at the ,skerryvore such dimensions as would not be widely discordant with these general proportions4 ,in this view1 ,i determined that the radius of the base should not exceed #bb feet1 on the level of about #d feet above the high water mark1 where ,i expected to obtain a solid foundation--a base which bears to the whole height of the ,tower a proportion somewhat less than that of the ,bell ,rock1 which is one-fifth4 ,it so happens1 that the diameter adopted is nearly the greatest which the ,rock affords2 for1 although a glance at the accompanying plan of the ,rock at high water 7,plate1 ,no4 ,,iii47 would lead one to suppose that a more extended base might have been obtained1 ,i found1 after many careful examinations of the gullies and fissures which intersect it1 that some of the concealed fissures run much farther into the ,rock than might at first be imagined4 ,the adoption of a much larger base1 even had it been otherwise advisable1 would therefore have involved some risk of the external ring of stones of the lowest course giving way by the yielding of an unsound part of the outer portion of the ,rock to the pressure of the superincumbent mass1 and might eventually have led to the destruction of the ,tower4 ,illustration3 ,no4 #b4 ,the height of the ,pillar having been finally fixed at #ache feet1 and the radius of the base1 at the level of about #d feet above high water1 at #ba feet1 ,i next proceeded to consider the details of its proportions4 ,of the whole height of #ache feet1 #ah were to be absorbed in a suitable capital for the ,pillar1 consisting of a parapet for the ,lantern1 an abacus1 a cavetto1 and a belt separating these from the shaft4 ,the internal void ,i determined should be #ab feet in diameter1 as the size most suitable for the reception of the lantern and apparatus2 and this1 combined with the choice of about #ac1jjj cubic feet of void already mentioned1 fixed the height of the solid frustum at the base of the ,tower at about #bf feet above the foundation4 ,having farther decided that the thinnest part of the walls1 immediately under the belt-course which separates the capital from the shaft1 should not be less than #b feet thick1 as necessary to give due solidity and strength to the walls1 and prevent1 by the breadth of the joints1 the percolation through the walls of the water which might be furiously dashed against them in storms1 ,i had nothing farther to do but to determine the nature of the line which should connect the extremities of the top and bottom radii of the ,pillar4 ,as ,i had already concluded that this line must1 as in the ,eddystone and ,bell ,rock1 be a curve line1 concave to the sea1 ,i next proceeded to try the effects of various curves traced between these points1 in giving a convenient and advantageous disposition of the materials1 with regard to both the thickness of the walls and the mass of the solid frustum at the base of the ,tower4 ,these two points1 as will be better understood by means of the accompanying diagram 7,no4 #b71 are separated from each other vertically #abjbe feet1 and are horizontally distant from each other #ac feet1 which is the excess of the bottom radius over that of the top of the shaft1 or the consequent amount of what may be called the aggregate slope of the wall4 ,the solid generated by the revolution of some curve line about the vertical axis of the building then becomes the shaft of the pillar4 ,for this purpose ,i tried four different curves1 the ,parabola1 ,logarithmic1 ,hyperbola1 and ,conchoid1 figures of which1 upon the same scale1 will be found in ,plate1 ,no4 ,,iv41 with the position of the centre of gravity1 which was carefully calculated1 marked on each4 ,the logarithmic curve ,i at once rejected1 from its too near approach to a conic frustum1 and the excessive thickness of the walls which such a figure would produce1 where the hollow cylindric space for the internal accommodation commences at the level of #bf feet above the base4 ,the parabolic form displeased my eye by the too rapid change of its slope near the base2 and ,i had some difficulty in reconciling myself to the condition of the exterior ring of stones at the base1 too much of the outer portion of each stone being left without the advantage of direct pressure from the superincumbent mass of the wall above4 ,the two remaining pillars1 derived from the hyperbolic and conchoidal#ab frusta1 are nearly identical in form2 and of these two curves ,i preferred the former1 which gives the most advantageous arrangement of materials1 in regard to stability1 of all the four forms4 ,this quality of advantageous proportion exists in these forms1 in the ratio of the numbers in the last column of the following table3#ac which shews a slight superiority of the ,hyperbolic over any of the other forms4 ---------------------------------------- --------------------- ,volume ,distance ,height ,diameter of of of the solid centre of ,economic ,tower at at ,tower ,gravity ,advantage4 in ,base ,top in cubic from ,h ,g,m4 ,hypothetical feet4 in in feet4 ,base4 - ------ ,towers4 7,h47feet4feet4 ,m4 ,g4 ,g ,g,m4 ---------------------------------------- -------------------- ,hyperbolic1 #abj #db #af #fb1iae #dabbg #biaa #ajjjjj ,conchoidal1 #abj #db #af #fb1ihd #daccf #bijc #jiifbg ,parabolic1 #abj #db #af #fc1fje #dcdjj #bgfe #jicifc ,logarithmic1 #abj #db #af #gd1gdb #dbdfj #bhbf #jhafjh ,conical1 #abj #db #af #hd1gcg #dcbhj #bggc #jgjgbe ---------------------------------------- -------------------- #ab ,the solid1 in this case1 would have been formed by the revolution of the interior conchoid of ,nicomedes about its directrix2 and its co-ordinates were kindly calculated for me by my late revered preceptor1 ,dr ,,wallace1 ,professor of ,mathematics in the ,university of ,edinburgh1 who employed so many hours of his latter years in labours of kindness among his friends4 ,this act of the ,professor was the result of a conversation ,i had with him on the subject4 ,before ,i received his friendly communication1 however1 ,i had resolved to adopt the rectangular hyperbola1 whose co-ordinates ,i had myself determined with this view some time before2 and when ,i found that the conchoid and the hyperbola1 traced between the two fixed points by means of the calculated co-ordinates1 were so nearly coincident1 that it was difficult to prevent their running into each other1 even when drawn out on a large scale1 ,i determined to adhere to my original purpose of adopting the latter curve as my guide4 #ac ,the last column of this table is derived as follows3--,assuming that the economic advantage of any proposed tower of given height and diameter at base and top1 is inversely as the mass and the height of the centre of gravity above the base1 and denoting these quantities by ,m and ,g respectively1 the fraction #a --- ,g,m may be taken as an indication of the economic advantage of the proposed tower4 ,let #a ----- ,g,m express the economic advantage of another tower2 then the advantage of the second tower1 compared to that of the first1 taken as unity1 will be ,g,m -----1 ,g,m by which expression1 the last column in the table was calculated4 ,the shaft of the ,skerryvore ,pillar1 accordingly1 is a solid1 generated by the revolution of a rectangular hyperbola about its asymptote as a vertical axis4 ,its exact height is #abjbe feet1 and its diameter at the base #db feet1 and at the top #af feet4 ,the ordinates of the curve1 at every foot of the height of the column1 were carefully determined in feet to three places of decimals2 and the ,appendix contains a tabular view of the co-ordinates from which the working drawings were made at full size4 ,the first #bf feet of height is a solid frustum1 containing about #bg1aaj cubic feet1 and weighing about #aiij tons4#ad ,immediately above this level the walls are #ieh feet thick1 whence they gradually decrease throughout the whole height of the shaft1 until at the belt they are reduced to #b feet in thickness4 ,above the shaft rests a cylindric belt #ah inches deep2 and this is surmounted by a cavetto #f feet high1 and having #c feet of projection4 ,the contour of this cavetto is that resulting from a quadrant of an ellipse revolving about the centre of the tower1 with a radius of #h feet on the level of its transverse axis2 and the moulds for this curve were drawn at full size from co-ordinates calculated for the purpose4 ,the cavetto supports an abacus #c feet deep1 the upper surface of which forms the balcony of the tower1 and above it rest the parapet-wall and lantern4 #ad ,at the rate of #acfb cubic feet of granite to a ton4 ,it may1 perhaps1 be not uninteresting to the reader to examine the woodcuts 7,no4 #c71 which shew1 on one scale1 the elevations of the ,lighthouses of the ,eddystone1 the ,bell ,rock1 and the ,skerryvore1 and exhibit the level of their foundations in relation to high water4 ,they will also serve to give some idea of the proportionate masses of the three buildings4 ,the position of the centre of gravity1 as calculated from measurements of the solids1 is also marked by a round black dot on each tower2 and in the table following1 ,i have given the cubic contents of each of these towers1 the height of the centre of gravity above the base and the ratio of that quantity to the height of the tower4 ,illustration3 ,no4 #c4 ,,eddystone4 ,,skerryvore4 ,,bell ,,rock4 ---------------------------------------- ---------- ,height of ,distance ,tower of above centre of first gravity entire,contents ,diameter in feet ,h course4 of at at from ,base4 - ,lighthouse4 7,h7 ,tower4 ,base4,top4 7,g7 ,g ---------------------------------------- --------- ,eddystone1 #fh #ac1cdc #bf #ae #aeib #dbg ,bell ,rock1 #ajj #bh1ecj #db #ae #bcei #dbd ,skerryvore1 #ache #eh1ehj #db #af #cdie #cif ---------------------------------------- --------- ,i come now to notice the few subordinate points in which the design of the ,skerryvore ,tower may be regarded as differing from those of the ,eddystone and the ,bell ,rock4 ,in glancing at the contrasted figures of the three buildings1 it will be at once observed that the outline of the ,skerryvore approaches more nearly to that of a conic frustum than the other two4 ,to the adoption of this form1 various considerations induced me2 and these ,i shall very briefly detail4 ,in the first place1 it seemed to me that1 in both the ,bell ,rock and the ,eddystone1 the thickness of the walls had been reduced to the lowest limits of safety towards the top2 and the effects of the sea and wind acting upon a heavy cornice1 cause a degree of tremor which ,i felt satisfied would not occur in a building with thicker walls4 ,the effect of thickening the walls at the top1 is1 of course1 cteris paribus1 to diminish the projection of the base1 and thus to produce less concavity of figure1 and consequently a nearer approximation to the contour of a conic frustum4 ,i have already stated1 that this excess of the bottom radius over that of the top1 is in the ,skerryvore ,tower #ac feet1 and that the height of the shaft is #abjbe feet4 ,the quotient resulting from the division of the height by the excess of bottom radius over that at the top is #ibg2 and1 if the figure had been conical1 this number would have given a measure of the slope of the walls throughout4 ,there can be little doubt that the more nearly we approach to the perpendicular1 the more fully do the stones at the base receive the effect of the pressure of the superincumbent mass as a means of retaining them in their places1 and the more perfectly does this pressure act as a bond of union among the parts of the ,tower4 ,this consideration materially weighed with me in making a more near approach to the conic frustum1 which1 next to the perpendicular wall1 must1 other circumstances being equal1 possess the property of pressing the mass below with a greater weight1 and in a more advantageous manner1 than a curved outline in which the stones at the base are necessarily farther removed from the line of the vertical pressure of the mass at the top4#ae ,this vertical pressure operates in preventing any stone being withdrawn from the wall in a manner which1 to my mind1 is much more satisfactory than an excessive refinement in dovetailing and joggling1 which ,i consider as chiefly useful in the early stages of the progress of a work1 when it is exposed to storms1 and before the superstructure is raised to such a height as to prevent seas from breaking right over it4 #ae ,it is most satisfactory to find that the views expressed above1 regarding the eligibility of the conical form1 seem to have the sanction of the late ,dr ,thomas ,young1 who appears to have connected his preference of this form with its greater efficiency as a source of friction among the parts of a building4 ,in his syllabus of ,lectures1 under the section 8,architecture10 he thus speaks3 8,for a ,lighthouse where a great force of wind and water was to be resisted1 ,mr ,smeaton chose a curve convex to the axis4 ,in such a case1 the strength depends more on weight than on cohesion1 and also in a considerable degree on the friction which is the effect of that weight4 ,perhaps a cone would be an eligible form40 ,if these views be substantially correct1 it may not1 perhaps1 be altogether inadmissible 7without1 however1 venturing to enunciate any general law7 to conclude1 that1 in the three ,lighthouses of the ,eddystone1 the ,bell ,rock1 and the ,skerryvore1 this source of union among the outer stones of the lower courses must bear some proportion to the numbers #gec1 #fei1 and #ibg1 which are the quotients of the height of the column1 divided by the difference of the top and bottom radii of the shaft in each case respectively4 ,this consideration seems too important to be entirely overlooked2 and ,i conceive that1 by following out this view1 ,i have been enabled to depart with perfect safety from the intricate and elaborate work required for the connection of the materials by means of dovetailing and joggling1 which the adoption of a more concave outline 7in which the vertical pressure could not have been so advantageously transmitted to the outer stones of the base71 would perhaps have rendered advisable4 ,in the case of the ,bell ,rock1 however1 whose construction1 in regard to this property1 is the least advantageous of the three buildings1 it must be borne in mind that the ,tower is covered to the depth of #ae feet at spring tides1 and that this principle of vertical pressure could not have been safely appealed to during the whole time which intervened between the commencement of the building and the attainment of a height sufficient to render it available1 which1 in a ,tower having so great a part submerged1 was of necessity much prolonged4 ,the stones were thus exposed to the full effect of heavy seas1 at all levels1 during two entire winters1 and could not therefore have been safely left1 without being kept together by numerous ties and dovetails4 ,it also seemed important1 in designing that ,tower1 with reference to the rise of tide1 to give its lower part a sloping form1 as the least likely to obstruct the free passage of the waves4 ,the outer stones of the lower courses were also selected of unusual length inwards1 so as to bring them more under the influence of the vertical pressure of the upper wall4 ,before leaving this subject1 ,i may remark1 that it is quite possible to construct a ,tower of a curved form1 in such a manner1 that the pressure of the upper part of the pillar shall be distributed to the greatest advantage on every stone1 by building the outer walls as inverted arches1 so that the section of each stone shall be that of a voussoir1 with joints perpendicular to the successive tangents of the curve4 ,this arrangement of the stones is1 in fact1 practised in sea walls of various kinds1 and has even been recommended for circular ,towers in an ingenious paper in the ,transactions of the ,royal ,scottish ,society of ,arts4 ,but in many situations1 and at ,skerryvore in particular1 this mode of transmitting the pressure1 so as to throw it perpendicular to the beds of the stones1 is inadmissible1 as conducing to or involving a greater evil4 ,the evil has already been noticed1 and consists in the thrust of the lowest stone 7which is of course inclined to the horizon7 having a tendency to push out the sides of the ,rock on which the ,tower is built4 ,this fear1 where the ,towers are to be placed on small steep rocks or pinnacles1 and more especially when these ,rocks are traversed by veins nearly vertical1 is by no means visionary2 and there is good reason to apprehend1 that the pressure thus resulting in a line considerably inclined to the plane of cleavage1 might throw outwards a thin portion of rock1 which1 under the more conservative influence of a vertical pressure1 might continue to retain its connection with the rest of the ,rock unimpaired for ages4 ,another method of1 in some degree1 increasing the resistance of a ,sea ,tower to a horizontal thrust1 if such aid be required1 is to give the line of courses a continuous spiral form1 instead of building them in successive horizontal layers4 ,were there reason to fear that the entire dislocation of the building might take place in a plane nearly horizontal1 this method seems more calculated to counteract the danger than the use of dowels or joggles passing from the course below to the course above2 but1 as this is one of the accidents least to be apprehended1 there does not seem any good ground for resorting to a mode of structure which would lead to considerable intricacy of workmanship1 and would1 in practice1 be attended with difficulty in obtaining a proper vertical bond or union among the several stones4 ,the only remaining point1 in which the example furnished by the ,eddystone and ,bell ,rock ,lighthouses has been at all materially departed from1 is 7as has already been hinted at by an unavoidable anticipation7 the mode of uniting the different parts of the masonry together4 ,in both these ,towers the stones were dovetailed throughout the buildings1 chiefly 7at least in the case of the ,bell ,rock where the foundation was so much below the tide7 with the view of preventing the sea from washing away the courses which might be left exposed to the winter storms before the weight of the superstructure had been brought to bear upon them4 ,in the upper part of the ,bell ,rock my father also introduced a kind of band joggle1 which consists of a flat ribband of stone raised upon the upper bed of one course1 and fitting into a corresponding groove cut in the under bed of the course above2 and this system of tying the adjoining courses together also forms a chief feature in his design for a ,lighthouse on the ,wolf ,rock4#af ,when the great pressure of the superstructure of these ,towers1 however1 and the effect of the mortar are considered1 there seems little probability of one course being dislocated1 in defiance of the friction resulting from the weight of the column4 ,an impulse sufficient to produce such an effect would tend to overset the whole superstructure from mere deficiency in weight1 and in this case the joggle would have little effect4 ,but if joggles be thought necessary for this purpose1 the ribband form certainly produces a better arrangement than that of the cubic joggles employed by ,smeaton for connecting the adjoining courses of his building together1 as the sectional strength of these scattered square joggles is very small compared to the effect of a shock which could be supposed capable of moving the whole mass of a ,tower4 ,in the lower parts of the ,skerryvore ,tower1 ,i entirely dispensed with dovetailing and joggles between the courses1 and thus avoided much expensive dressing of materials4 ,the stones were retained in their places during the early progress of the work1 chiefly by common diamond joggles1 and the courses were temporarily united to each other by wooden treenails1 like those used in the ,eddystone and ,bell ,rock4 ,these treenails had split ends1 with small wedges of hardwood loosely inserted1 which being forced against the bottom of the holes in the course below1 into which the treenails were driven1 expanded their lower ends until they pressed against the sides of the holes2 while their tops were made tight by similar wedges driven into them with a mallet4 ,i have1 however1 adopted the ribband-joggle in the higher part of the ,tower1 where the walls begin to get thin in the very same manner as at the ,bell ,rock1 where it was used1 partly that it might counteract any tendency to a spreading outwards of the stones1 and partly that it might operate as a kind of false joint to exclude the water which1 when pressed with great violence against the ,tower1 is apt to be forced through a straight or plain joint4 ,the stones in the higher courses throughout each ring are also connected at the ends by double dovetailed joggles1 which unite the two adjoining stones2 and the walls are1 besides1 tied together at various points by means of the floor stones1 which are all connected by dovetails let into large circular stones which form the centres of the floors4 ,i also ventured to leave out the metallic ties at the cornice1 which consisted1 at the ,eddystone1 of chains1 and1 at the ,bell ,rock1 of copper rings4 ,the reasons which induced me to adopt this change ,i need not here enlarge upon4 ,it is sufficient to state1 that ,i believe ,i have nearly balanced the forces which would have tended to throw the cornice outwards1 had a greater disproportion existed in the weight of the outer and inner parts of the cavetto1 and to point out 7,plate ,,vii47 that the ,lightroom or highest floor occurs1 at such a level1 as of itself to answer all the ends which metallic ties could have served4 #af ,account of the ,bell ,rock ,lighthouse1 ,plate ,,xxi4 ,,chapter ,,iv4 ,,operations ,,of #ahch4 ,temporary ,barrack on ,rock4 ,the hazardous nature of the anchorage1 and the consequent difficulty of mooring a vessel in the neighbourhood of the ,skerryvore ,rock1 induced me1 from the first1 to consider it as a matter of great importance1 even at a large expenditure of time and money1 to erect some temporary dwelling on the ,rock for the accommodation of the people engaged in the work1 with the view of rendering the operations less dependent on the state of the sea1 which varied with every wind4 ,so important1 indeed1 did this object appear to me1 that ,i was at times apt to look upon it as an indispensable step towards ultimate success4 ,that opinion was amply confirmed during our first season's operations1 by the experience of the oft-recurring difficulty of returning to the moorings when driven away by stress of weather1 together with the daily risk and loss of time in landing the workmen in small boats1 even in weather when they could be profitably occupied if once placed on this small terra firma4 ,with this view1 ,i naturally turned to the same plan which had been adopted at the ,bell ,rock1 where the temporary barrack stood the test of five winters4 ,that structure1 which is represented in ,plate ,no4 ,v41 and is particularly described in the ,appendix to my father's ,account of the ,bell ,rock ,lighthouse1 consisted of an open framework of six logs1 about #dg feet long and #ac inches square1 assembled in such a manner as to form by their union a hexagonal pyramid1 on the top of which rested a wooden turret2 the whole erection rising to the height of about #fj feet above the rock4 ,this pyramidal framework was strongly trussed and tied2 and1 being open at the lower part1 offered little resistance to the waves4 ,the upper part contained a gallery for keeping various stores and such materials as could not be safely left on the ,rock1 even in the finest weather2 but it was framed of lighter materials1 so as to admit of its yielding easily to any extraordinary waves1 without involving injury to the principal part of the structure1 by offering great resistance to the sea4 ,the turret on the top was in the form of a twelve-sided prism1 #ab feet in diameter1 and #cj feet high1 and was securely attached1 by means of the ties and braces shewn in the drawing1 to the apex of the pyramid1 which entered into the lower part of it4 ,the small space which the turret afforded was1 with the utmost economy of room1 divided into three storeys1 of which the lower was entirely taken up by the kitchen and the bread-store1 a great deal of room being occupied by the main beams of the pyramid which passed through its centre4 ,the next storey was subdivided into two chambers1 of which one was appropriated to the foreman of the works and the landing-master1 while the other was set apart for myself2 and the top storey1 which was surmounted by a small lantern and ventilator1 formed a barrack room1 capable of containing #cj people4 ,of the comforts and discomforts of this habitation ,i shall at some future time have occasion to speak4 ,i merely draw attention to its erection at present1 as an operation1 which it was most desirable should precede every other work on the ,rock4 ,one of the first proceedings1 therefore1 was to obtain estimates for the preparation of this log-house1 which1 in order to avoid loss of time in making adjustments on the ,rock1 was to be carefully fitted up in the workyard of the contractor before being shipped4 ,drawings and a specification were accordingly prepared1 and submitted to several carpenters in ,greenock1 who gave in offers for the work2 and it was finally commenced in the month of ,march1 by the late ,mr ,john ,fleming1 who was the successful offerer4 ,tools and ,machinery4 ,it was also necessary to provide a large assortment of quarriers' and masons' tools of every kind2 and many cranes1 crabs1 anchors1 mooring buoys and other implements were ordered1 according to detailed specifications and drawings4 ,these preparations necessarily occupied the early part of the year #ahch4 ,steam ,tender for the ,works4 ,from the extent of the foul ground round the ,skerryvore1 and the absence of good harbours in the neighbourhood1 it was foreseen at the outset that the operation of landing about #fjjj tons of materials on the ,rock could not be accomplished by means of sailing vessels with that degree of certainty or regularity which was desirable1 in order to obtain the full benefit of the short working season which the climate of the ,western ,hebrides affords2 and the necessity for providing a steam tender was1 therefore1 generally admitted4 ,it has already been stated1 that1 in order to avoid the expense attending the building of a vessel for this purpose1 application was made at the principal ports of the kingdom1 with the view of purchasing a suitable vessel2 but1 although twenty-four vessels of nearly the required dimensions were offered for sale1 not one of them was considered fit for such a service1 the great majority being light craft1 such as are generally used in river and port navigation4 ,it was therefore found necessary to build a steamer2 for which purpose1 specifications and drawings were prepared1 and after receiving various tenders from respectable parties1 a contract was entered into with ,messrs ,menzies and ,sons1 shipbuilders1 and ,messrs ,j4 ,b4 ,maxton and ,co41 engineers1 both of ,leith1 for building a steamer of #aej tons1 with two engines of #cj horse power each4 ,the use of a steamer1 at the very outset of the works1 would doubtless have proved of the greatest service in the erection of the barrack on the ,rock1 and would have materially lightened our cares and toils2 but ,i am not sure that ,i should have acquired so thorough an acquaintance with the difficulties and dangers of the ,skerryvore1 or that ,i should have been so well prepared for all the obstacles that presented themselves in the after parts of the work1 had the first season's operations been conducted under those advantages which are always derived from the use of steam-power4 ,as it was1 we had much to bear from the smallness of the ,lighthouse ,tender1 named the ,pharos1 a vessel of #cf tons1 new register1 which was all the regular shipping attendance we possessed during this first season2 and the inconvenience arising from her heavy pitching1 was1 to landsmen1 by no means the least evil to be endured4 ,but the frequent loss of opportunities1 of which we might easily have availed ourselves1 if we had possessed the command of steam-power1 and the danger and difficulty of managing a sailing vessel in the foul ground near the ,rock1 and between it and ,tyree1 were1 perhaps1 even more felt by the seamen than by the landsmen2 and if the experience of a single year's work can form any ground for an estimate of the length of time required for building the ,skerryvore ,lighthouse1 with a sailing vessel1 ,i should say1 we must still 7even in #ahde7 have been engaged in the masonry part of the work1 which was finished on the #beth ,july #ahdb4 ,employment and ,wages of ,workmen4 ,about the middle of ,april1 arrangements were made with ,mr ,charles ,neilson1 a builder in ,aberdeen1 to select granite masons for the works at the ,skerryvore1 as it was expected that the operation of dressing stones for the ,tower would be begun in the ensuing summer2 and it was also obvious1 that their services would be required in excavating seats for the supports of the ,barrack-house on the ,rock4 ,masons were accordingly selected1 and engaged on the terms stated in the following letter to ,mr ,james ,scott1 the ,foreman1 who was sent to ,aberdeen to assist in choosing the men3--8,although it is difficult to fix the precise number of men who may be required1 during the progress of the works1 as this must1 in some measure1 depend upon the produce of the quarries at ,hynish1 and of those to be opened in ,mull1 you may1 in the mean time1 engage thirty masons or stone-cutters1 twelve quarriers1 and three or four smiths1 for two years of certain employment4 ,with regard to the rate of wages to be paid to the men1 this will1 in some measure1 depend upon the demand for the season at ,aberdeen2 it is1 at all events1 expected1 that they will on no account exceed the rate of #cs4 #aj;d4 per day for masons1 and #bs4 #f;d4 per day for quarriers1 as paid last season during the long day1 or from the #ast of ,february till #cast of ,october2 and for the short day during the remaining three months1 #cs4 for the masons1 and #bs4 for the quarriers1 from #ast ,november till #cast ,january4 8,it is intended that subsistence money shall be paid to such of the families or relatives of the workmen as may require it2 and that their wages shall be fully settled monthly1 deducting the subsistence money advanced to their relatives4 ,a ,store will be kept at the works by the ,lighthouse ,board1 from which provisions will be served out at stated periods1 to be fixed by the storekeeper2 and these provisions shall be sold to the workmen at the cost prices at which such stores are laid in4 ,barrack accommodation or lodgings1 with cooking1 will also1 as formerly1 be allowed to the men free of expense40 ,progress of the outfit for the season's operations4 ,early in the month of ,may the preparation of the wooden barrack for the ,rock had been completed1 and the whole had been set up in the workyard at ,greenock2 and when ,i visited it for the last time about the #eth of that month1 ,i found it all ready for shipment1 excepting some additional iron ties1 which ,i ordered for securing the turret to the top of the pyramid1 which were to be applied at the level of the floor of the upper or barrack-room storey4 ,i also found that the moorings1 including the mushroom anchors and chains1 and the workyard materials1 consisting of several cranes1 trucks1 a janker for the transport of timber1 and a ,woolwich sling-cart for carrying stones to the various sheds1 were in the course of preparation4 ,a large assortment of masons' and quarriers' tools was at the same time ready for shipment at ,aberdeen4 ,early in ,june1 a vessel called the ,duke of ,montrose was chartered to carry coals to ,tyree1 both for household purposes and for the work2 and two small portable smiths' forges were prepared for use on the ,rock4 ,embark for ,skerryvore4 ,in providing the means of efficiently carrying on so many complicated operations in a situation so difficult and remote1 it is impossible1 even with the greatest foresight1 to avoid omissions2 while delay of a most injurious kind may result from very trivial wants4 ,even the omission of a handful of sand1 or a piece of clay1 might effectually stop for a season the progress of plans1 in the maturing of which hundreds of pounds had been expended4 ,accordingly1 although ,i had bestowed all the forethought which ,i could give to the various details of the preparation for the season 7of which ,i found it absolutely indispensable to be personally aware1 even to the extent of the cooking dishes71 new wants were continually springing up1 and new delays occasioned1 so that it was not until the evening of the #bc;d of ,june that ,i could embark at ,tobermory in the ,pharos ,lighthouse ,tender1 commanded by ,mr ,thomas ,macurich1 with all the requisites on board for commencing the season's operations4 ,next morning we moored off ,hynish ,point about three o'clock1 and1 from the roughness of the passage1 were not unwilling to land at that early hour4 ,here ,i found that ,mr ,scott1 the foreman of the workyard1 had1 notwithstanding the unworkable nature of the ,rock1 more particularly afterwards noticed1 procured about sixty fine blocks of gneiss1 as the produce of the ,tyree quarries1 which had been wrought for upwards of #ae months2 and had at the same time completed the masonry of a range of buildings for stores and barracks1 capable of containing upwards of #ajj men1 and had built about #ajj feet in length of a landing-pier1 reaching nearly to low-water mark4 ,a magazine for gunpowder1 of which a considerable stock was required for quarrying purposes1 had also been built2 and a piece of garden ground had been inclosed and stocked for the use of the people to be employed at the works4 ,measures had also been taken for inclosing the ground1 which had been feued by the ,board from the ,duke of ,argyll4 ,this day being ,sunday1 nothing was done at ,hynish1 and we waited until next morning before sailing for the ,rock4 #beth ,june4--,sailed in the ,pharos from ,hynish ,bay this morning about six1 with ,mr ,scott1 the foreman of the workyard1 and one or two masons on board2 but1 having a foul wind during the early part of the day1 and the weather falling afterwards calm1 it was not until three in the morning of the #bfth that we reached the ,rock4 ,lay down ,moorings1 and try to land on the ,rock4 #bfth ,june4--,our first step was to lay down moorings for the tender as near the ,rock as seemed to be consistent with safety4 ,the position chosen by ,mr ,macurich1 who commanded the vessel1 was to the ,s4,s4,e4 of the ,rock1 about a quarter of a mile off1 and in #ac fathoms water1 on an irregular rocky bottom4 ,about half-past five ,i attempted a landing on the ,rock1 but there was a great deal too much sea4 ,the vessel was pitching the bowsprit under at her moorings1 and the surf broke into the creek where landings are generally made1 in such a manner as to render it quite impossible to get near the ,rock4 ,after hanging on our oars in the boat for nearly an hour1 in the hope of a smooth lull between the heavy seas1 we returned to the vessel1 and1 as the wind still freshened from the ,s4,e41 we reefed the mainsail and set the first jib1 and steered for the ,mull shores1 where1 about ten at night1 we came to an anchor in ,loch ,loich1 not far from the ,island of ,iona4 ,driven to ,mull4 #bgth ,june4--,next day also being unsuitable for attempting to reach the ,skerryvore1 the vessel lay in ,north ,bay1 and the early part of the day was spent in a careful examination of the granite ,rocks of the district called ,ross of ,mull1 with the view of establishing quarries there2 as our experience of the unsatisfactoriness of working the ,tyree quarries during fifteen months had frequently led me to anticipate the necessity of soon seeking a supply of materials in some other quarter4 ,in this district an almost inexhaustible supply of flesh-coloured granite was found1 not certainly of the hardest description1 but singularly equal and homogeneous in its texture4 ,i therefore made a general survey of the neighbouring localities1 with a view to select the best position for opening quarries and establishing a landing place or wharf for shipping the materials1 as well as for erecting barracks for the workmen4 ,in the afternoon1 ,i embarked at the call of ,mr ,macurich1 to attempt another landing on the ,skerryvore2 but as the wind soon fell calm1 we did very little good until evening1 when some progress was made in stretching across towards the ,rock4 ,first day's work on the ,rock4 #bhth ,june4--,at nine this morning1 we reached our moorings at the ,rock1 but there was still so much surf that a landing could not be attempted till mid-day1 when ,i went with ,mr ,macurich in the boat1 and with some difficulty contrived to spring on the ,rock1 after which the boat returned to the vessel for the rest of the party4 ,while left alone on this sea-beaten ,rock1 on which ,i had landed with so much difficulty1 and as ,i watched the waves1 of which every succeeding one seemed to rise higher than the last1 the idea was for a few minutes forcibly impressed on my mind1 that it might1 probably1 be found impracticable to remove me from the ,rock1 and ,i could not avoid indulging in those unaccountable fancies which lead men to speculate with something like pleasure upon the horrors of their seemingly impending fate4 ,these reflections were rendered more impressive by the thought that many human beings must have perished amongst those rocks4 ,a consideration1 however1 of the rarity of an opportunity of landing on the ,rock1 and the necessary shortness of our stay1 soon recalled me to my duty1 and before the boat returned with a few of the workmen1 ,i had projected some arrangements as to the first step to be taken in erecting the framework of the barrack-house4 ,the second landing was more easily effected1 as the tide had fallen1 and the landing-place was more sheltered1 so that we were the more emboldened to make a fair commencement of operations4 ,it was a day of great bustle and interest1 the work consisting in chalking out and marking on the ,rock with paint1 the sites of the ,lighthouse-,tower1 and the wooden barrack1 and the positions for cranes1 crabs1 and ring-bolts for guys and other tackling1 as well as ascertaining such dimensions as would enable me at once to proceed to fit up the log-house1 or barrack1 at our next landing4 ,in that way1 we spent four hours on the ,rock1 much to the annoyance of the seals and the innumerable sea-fowl1 which we drove from their favourite haunts4 ,during the whole day1 the sun had great power2 and the smell from the cast-away feathers and the soil of the sea-fowl was extremely disagreeable4 ,i was amazed to find that those animals should select1 as their place of repose1 a rock in the ,atlantic1 intersected by deep gullies which are never dry1 with only one pinnacle1 about #e feet in diameter1 raised about #af feet above the sea4 while the greater part is only #e feet above high water4 ,yet1 in a crevice of this ,rock1 ,i found an egg resting on a few downy feathers1 which the first wave must have infallibly washed away6 ,after the day's work on the ,rock1 we sailed for ,tyree1 but did not reach the workyard till next morning at nine2 and a long day of bustle and hurry was spent there in preparing provisions1 timber1 ring-bolts1 chains and all sorts of tackling for the operations connected with the erection of the barrack on the ,rock4 ,on the evening of the #cjth ,june1 ,i sailed for ,greenock1 whence ,i trusted soon to return to the ,skerryvore with the whole of the materials1 to commence operations4 ,shipment of all the materials at ,glasgow and ,greenock4 ,reach ,tyree4 ,driven to ,mull4 ,return to ,tyree4 ,it seldom happens that human expectations are fully realised1 especially in matters which excite a strong interest in the mind1 and thus lead one to desire a more rapid progress than usual4 ,but this is peculiarly true in all arrangements which depend on the co-operation of many persons2 and so ,i experienced on my visit to ,greenock and ,glasgow1 where ,i had given orders for shipping all the machinery and apparatus required for carrying on the works1 such as cranes1 trucks1 boats1 blocks and tackle1 anchors1 coals1 grindstones1 stucco1 pavement1 mats and fascines for blasting1 clay for puddling1 shear-poles1 and innumerable small utensils1 some of no great value1 but all necessary to the success of the work4 ,the great bulk of those materials were despatched by a vessel called the ,new ,leven1 and part by the ,mary ,clark1 on the #bdth ,july2 but it was not until the #cjth that the ,pharos ,lighthouse tender was fully loaded1 on the morning of which day ,i again embarked at ,greenock for the ,skerryvore ,rock4 ,the weather proving somewhat unfavourable1 we were forced 7being very heavily laden7 to pass through the ,crinan ,canal1 instead of going round the ,mull of ,kintyre1 so that it was not till the morning of the #dth ,august that we landed at ,hynish1 in ,tyree4 ,here ,i found some farther progress had been made in building the barracks for the men1 some of the houses being already roofed and slated4 ,the quarries1 too1 had turned out stones sufficient for about four of the lowest courses of the ,tower1 a quantity which might be estimated at about #gibj cubic feet4 ,next day 7,august #eth71 the wind blowing strong from the ,s4,s4,w41 we were forced to leave ,hynish ,bay1 and retreat before a very heavy sea to ,tobermory4 ,we immediately sailed again1 and made for ,loch ,erin1 a small creek in the ,island of ,coll1 as being nearer to ,hynish and better adapted for enabling us to take advantage of any sudden improvement in the weather4 ,on our arrival at this singular natural haven1 at nine in the evening1 ,i was glad to find the ,new ,leven1 before mentioned as having loaded materials at ,greenock lying already there1 waiting a favourable change of wind4 ,next morning we weighed anchor1 and sailed along with that vessel for ,hynish1 where she was immediately discharged of her cargo1 which was chiefly intended for the workyard there1 and took in materials for the erection of the barrack on the ,skerryvore ,rock4 ,first good day's work on the ,rock4 #gth ,august4--,we this morning took on board various tools and implements for the ,rock1 together with workmen to the number of four carpenters1 sixteen masons and quarriers1 and a smith1 along with ,mr ,george ,middlemiss1 as foreman4 ,having sailed with a northerly wind1 we made a landing about noon1 and had what may be called our first entire day of work on the ,rock4 ,our work was by no means easy1 as we had to erect shear-poles and fix crabs for landing the materials1 and to lash every article that was landed1 with great care down to ring-bolts on the ,rock1 which a few of the masons were fixing1 while the rest of the people were discharging the vessel4 ,all this was attended with a good deal of trouble1 and it required my constant attention to keep everything going on in a fair train1 so as to prevent one party of workmen requiring to wait for another2 but1 after eight hours of very hard work1 ,i had the satisfaction of seeing all the materials which had been landed left in a secure state4 ,the extreme smoothness of the surface of the ,rock greatly impeded the landing of materials2 for as yet we had no tramways on which wheeled trucks could be moved1 and the transport by hand of heavy materials over so irregular and slippery a surface was attended with considerable danger4 ,a short trial was this day made of boring one of the holes for the stancheons or bats1 by which the timbers of the ,barrack were to be secured to the ,rock2 and ,i found1 that with a jumper of #c inches diameter1 a depth of about #c inches was bored in one hour4 ,the commencement of the operations involved much labour and considerable discomfort2 but it invariably happened throughout the work1 that in spite of all the fatigue and privation attending a day's work on this unsheltered ,rock1 the landsmen were for the most part sorry to exchange it for the ship1 which rolled so heavily as to leave few free from sea-sickness1 and to deprive most of the workmen of sleep at night1 even after their unusually great exertions during the day4 ,on leaving the ,rock at night we had the greatest difficulty in boarding the ,pharos with two boats containing upwards of thirty-two persons1 as the vessel rolled so heavily1 that there was great danger of the boats being thrown right upon her deck4 ,next morning 7#hth ,august7 we landed1 with some sea running1 about nine o'clock1 before which hour it was impracticable1 owing to the surf in the landing creek4 ,our first work was to prepare the tackling for landing the heavy materials from the ,new ,leven1 which came up about eleven o'clock1 and was made fast by a warp to the ,pharos4 ,we next took means for fixing the smith's forge on the ,rock and preparing the fixtures for the crab1 which stood on the point of rock to the westward 7see ,plate ,,iii471 and served chiefly for raising the beams of the log-house into their places4 ,the greater part of the day1 till half-past eight in the evening 7when it became dark71 was spent in lining off with accuracy the site of the supports of the wooden barrack1 and in landing and fixing by strong lashings to the ,rock1 all the principal timbers and iron fixtures4 ,the spot in which the framework of the first barrack was placed1 will be seen by reference to ,plate ,,iii4 ,the ,rock was at this place a good deal lower than the site afterwards adopted for the barrack4 ,the high water of spring-tides rose #b feet upon the legs or main beams2 but this site had many advantages1 as it left more room for operations at or near the ,tower itself than could have been obtained in any other position4 ,sudden gale1 and great peril to the vessels4 ,reach ,hynish in safety4 ,we also made some progress in erecting a wooden shed round the smith's forge1 to protect him and his fire from the wind and the spray of the sea4 ,as we left the ,rock in the boats1 speculating on the prospect of getting the whole of the materials discharged in the course of next day1 it was remarked that the northern sky was very clear1 and that the wind had entirely fallen4 ,the great and sudden stillness of the air1 which permitted every ripple on the ocean to be heard1 was regarded by ,mr ,macurich and the seamen generally1 as the forerunner of a change2 and the moon1 which rose red and fiery1 confirmed their fears of a gale4 ,nor were they wrong in their forebodings4 ,about midnight there was a stiff breeze from the ,s4,e41 which induced the master of the ,new ,leven to hoist sail1 cast loose from us1 and run2 and had not the seaman on watch on the deck of the ,pharos fallen asleep in consequence of excessive fatigue1 there can be little doubt we should have been at once called to follow her example1 if1 indeed1 we had not led the way4 ,no sooner1 however1 did ,mr ,macurich become aware of the state of the wind1 which was blowing very strong at ,s4,s4,e4 right into the landing place1 than he roused me about two o'clock4 ,at this time there was a very heavy sea2 the little vessel was pitching her forecastle under1 and we had to contend with a strong tide combined with the wind against us in working clear of the ,rock1 from which our moorings were not more than a quarter of a mile to windward2 while from the place where we lay1 half of the horizon was foul ground1 all lying to our leeward4 ,we soon set sail1 but in vain tried to weather the sunk rock ,bo-,rhua1 whose large black mass 7after having imagined ourselves past it7 we discovered encircled by a wreath of white foam within less than a cable's length of us4 ,the heavy seas we encountered had greatly deceived us as to our progress1 and thick blinding showers of rain made it difficult to see far beyond the vessel's head4 ,such was the precarious and dangerous position of the vessel1 that had an attempt been made to tack her amidst the surf which came rolling off the ,rock1 she would most probably have missed stays1 the consequence of which would have been the inevitable loss of the vessel and of every soul on board4 ,in this dilemma we were obliged to resort to a less dangerous expedient1 by wearing the ship and running her through the narrow passage between ,bo-,rhua and the sunk rocks1 about #cjj yards to the ,w4,n4,w4 of it1 although this was a most hazardous attempt1 as we had then little or no knowledge of that dangerous and intricate passage4 ,a more anxious night ,i never spent2 there being upwards of thirty people on board1 with the prospect1 during several hours1 of the vessel striking every minute4 ,and here ,i must award due praise to ,mr ,macurich for the coolness and intrepidity which he on this occasion displayed1 and the calmness with which he gave his orders to the crew2 and as ,i stood in the companion1 telling him the time at intervals of five minutes1 so as to enable him the better to judge of the vessel's way through the water1 ,i could not but remark the necessity for silence on the part of the master of a vessel in cases of difficulty4 ,the workmen were told to be getting ready for landing1 but we did not make them aware of the full extent of the danger2 and to avoid confusion1 they were not permitted to come on deck4 ,we had no sooner cleared the sunk rocks already alluded to1 than we were in fear of the great reef of ,boinshly1 and the heavy seas which were breaking over the foul ground all round it4 ,in this way we spent a night of almost uninterrupted anxiety until daylight1 and at eight in the morning we came to the moorings in ,hynish ,bay1 after a hard struggle against wind and tide and a very heavy sea1 which made us hang dead a long time off ,hynish ,point4 ,at one time ,i feared we should have been forced1 as ,i had been1 when returning from my first unsuccessful and discouraging attempt to land on the ,skerryvore in #ahcf1 to go round the west side of ,tyree and ,coll1 which is a very foul coast2 and when we did round ,hynish ,point1 it was almost at the expense of our boat1 which the heavy sea had nearly swept away from us4 ,after all this anxiety about our safety and discomfort from rain1 wind1 and spray1 during five or six hours1 we were not sorry to set foot even on the wild shores of ,tyree2 and ,i trust there were none who did not gratefully acknowledge the protecting care of ,almighty ,god1 in preserving us through such peril4 ,detained by bad weather four days at ,hynish4 ,return to the ,rock1 and have six days of good weather4 ,it was not until ,monday the #acth that a landing was again effected on the rock1 as the wind continued to blow strongly from the south2 and the intervening four days were spent in ,hynish ,bay1 landing in the morning1 and again returning to the vessel in the evening4 ,during this time ,i was engaged in making drawings of some of the lower courses of the ,lighthouse ,tower1 with a view to fix finally upon dimensions1 from which working drawings and wooden moulds for cutting the stones could be made4 ,the only alleviation of my impatience at being detained at ,hynish was the satisfaction of seeing some #bj feet of the pier founded at low water4 ,late in the evening of the #acth ,august we again landed on the ,rock1 when we found time1 before dark1 to complete the fixture of the smith's forge1 which ,i had been forced to leave unfinished4 ,even the short period of work this evening was curtailed by a very heavy shower1 which drenched us to the skin--a great evil1 where there are many people to be accommodated in a small vessel1 without room for much spare clothing1 or the means of getting any thing quickly dried4 ,after this we had an uninterrupted tract of good weather for six days2 and as we landed every morning at four o'clock1 and remained on the ,rock until eight1 taking only half an hour for breakfast1 and the same time for dinner1 we had thus the work of twenty-eight persons for about ninety hours4 ,erection of the ,pyramid of the wooden ,barrack4 ,after carefully setting out the radial directions in which the six legs1 or main beams were to stand1 our next step was to lay off their approximate distances from the centre of the ,barrack1 and to clear a space in the solid ,rock of sufficient extent to admit of adjusting the exact positions of the bats before boring the holes4 ,this operation involved the necessity of blasting parts of the ,rock by very small shots1 the bores being about #a inch diameter1 and #ae inches in depth1 and so directed as to have the effect of throwing off a thin superficial crust without shaking the solid part below4 ,the materials thus quarried in forming the seats for each post were thrown1 by means of tackle1 into the deepest pools1 to prevent their being driven by the sea against the timbers of the barrack1 and so injuring them4 ,illustration3 ,no4 #d4 ,illustration3 ,no4 #e4 ,mode of determining the length of the ,beams1 and the sites for their fixtures4 ,for ascertaining the exact length of each of the six beams1 which formed by their union a pyramid of about #ba #cj of inclination1 and1 at the same time1 for determining its exact place1 in reference to the centre of the hexagon1 both of which elements necessarily varied with the level of the irregular surface of the ,rock1 ,i used the following simple arrangement3--,each beam being of the greatest length that could be required1 the level and distance from the centre were ascertained for the longest beam1 which1 of course1 had the lowest seat or rest1 by means of a wooden frame1 shewn in the diagram 7,no4 #d71 in which a a is a vertical rod of iron firmly batted into the rock1 so as to coincide with the centre of the pyramid to be formed by the main beams1 and of sufficient length to exceed the greatest variation of level between the different points where the beams are likely to stand2 c c is a horizontal board which can be freely turned about a a horizontally1 and resting upon a small shoulder d1 and which is equal in length to the radius of the hexagon1 on the horizontal plane at the level of the lowest beam4 ,on this board is a spirit-level s1 which regulates its horizontality2 e e is the approximate position of the lower end of the beam2 f f is a pitched board1 representing the section of the permanent beam1 on a vertical plane passing through the axis of the pyramid1 and also shewing its inclination towards the centre of the pyramid4 ,as this pitched board is capable of being moved up or down by sliding through a groove at g1 it may be successively applied to the rough surface at e e in the course of cutting it down1 and thus be made truly to represent the position of the beam1 and1 at the same time1 give the inclination of the surface e e1 which must be at right angles to the axis of the beam f f4 ,in this way1 by repeated trials1 the surface was truly dressed to its proper inclination1 and the length ascertained which required to be cut from the beam1 so as to make it rest on that surface when in its true position4 ,hence1 also1 in the case of all the other beams1 the length which the pitch-board f f was moved upwards through the groove g1 beyond the level c c1 indicated the quantity to be cut from the end of any given beam4#ag ,the surface of the ,rock1 dressed for the seat of the beam1 being thus brought to its proper inclination1 the sliding-board correctly set and the centre line a a of the beam carefully marked on the ,rock1 a square board 7see fig4 ,no4 #e7 representing the cross section of one of the beams1 was then put down at the proper distance1 so as to cover the space indicated by the pitch-board as the site of the beam1 and with its centre coinciding with the radius already traced on the dressed seat or bed4 ,when so placed1 the small round knobs1 or ears1 d d 7,no4 #e7 on this board1 shewed the position of the holes to be bored for the bats or side fixtures1 which1 as afterwards shewn in figure 7,no4 #h1 p4 #hh71 spread outwards from the axis of the beam1 and thus formed a kind of dovetail4 ,in order to make the holes capable of receiving the bats and1 at the same time1 embracing the timbers of the barrack1 a quoin of wood 7,nos4 #f and #g7 e1 was put down1 with bevelled faces or grooves g1 cut in it for directing the motion of the jumper or boring iron i1 thus3-- ,illustration3 ,no4 #f4 ,illustration3 ,no4 #g4 ,these holes were bored with jumpers1 #c inches in diameter1 and were sunk #b feet deep in the rock4 ,the boring of each hole took upwards of eight hours1 in consequence of the hardness of the material1 which is gneiss1 a stone considerably more difficult to bore than even the granite of ,aberdeenshire4 ,the bats or stancheons1 although very accurately forged1 were occasionally found not to fit truly1 owing to unavoidable twists in the holes1 which arose from dries or veins in the ,rock crossing the line of the hole1 and thus disturbing the motion of the jumper4 ,this gave us much trouble1 and shewed that1 had we determined1 as ,i at first contemplated1 to cut a lewis-hole1 swelling towards the base1 the work would have been almost impracticable4 ,the mode which ,i had proposed for executing this operation was to bore a number of very small holes1 inclined at the proper angle1 all round the outside of this lewis chamber1 and then to cut out between them2 but this1 as our after experience in cutting the foundation of the ,tower proved1 would have occupied an extent of time which we should have been very unwilling to bestow upon a merely temporary erection like the wooden barrack4 ,even as it was1 and with all the retrenchments that could be safely adopted1 the preparation of the seats for the six outer or main beams1 and those for the six inner braces1 employed twelve men for four days4 #ag ,the accented letters e1 c1 f1 g1 o1 s1 in the figure 7,no4 #d71 page #he1 denote the various parts of the gauging-rule1 when applied to the beam1 opposite that to which the letters e1 c1 f1 g1 o1 s1 in the text1 refer4 ,illustration3 ,no4 #h4 ,after the seats for the timbers had been dressed in this manner1 the carpenters were employed cutting the beams to their respective lengths1 the piece to be cut off being measured1 as already stated1 by the length through which the sliding-board f f 7,no4 #d1 p4 #he7 had been raised above its position on the level platform on which the pyramid had been erected in the workyard at ,greenock4 ,at the same time1 the stancheons 7k k7 in the figure 7,no4 #h1 p4 #hh71 and the glands or collars e e 7in figure ,no4 #h71 were let into grooves in the beam1 and the holes admitting the screwed bolts a a1 to pass through the two stancheons and the beam between them1 were bored with an auger1 and widened with a red hot iron4 ,the tops of the beams b b 7see fig4 ,no4 #i71 having been already fitted in the workyard at ,greenock1 so as to meet a hexagonal quoin of hardwood e1 round which they were assembled as shewn in the figure 7,no4 #i71 straps of iron d d1 were made to pass over the top of the whole1 and were secured to the beams with bolts1 and a spike at a was driven into the centre to wedge the timbers tightly up1 so as to fill a ring which embraced the exterior of the whole4 ,it was obvious1 that if the sliding-board 7described on p4 #he7 had indicated the true inclination of the seat on the ,rock for the end of the beam to rest on1 as well as its radial distance from the centre of the pyramid and the corresponding length of the beams1 the top of each beam must necessarily meet in its exact place around the central hexagonal quoin4 ,the operation of determining the positions and lengths of such beams on a rugged rock1 and placing them with the accuracy requisite1 to insure their mitering truly at the top1 was attended with a good deal of trouble2 and ,i have judged it advisable to give these details1 as they may prove useful to others who may have a similar work in hand4 ,illustration3 ,no4 #i4 ,after a good deal of trouble1 owing to the lowness of the ,rock and the smallness of its surface1 the six main beams1 each nearly #ej feet long1 were raised on end by means of shear-poles1 and the iron straps which passed over the top of them1 and the ring which embraced the whole so as to secure them at the top1 were fixed with much care4 ,the temporary guys were removed on the afternoon of the #ahth ,august4 ,a plummet suspended from the centre of the quoin1 after all the six beams were in their places and the stancheons had been run up with lead1 came within half-an-inch of the centre bar1 which was about #dj feet below the point of suspension1 thus indicating an angular deviation of less than #d4 ,this is a very good approximation1 under all the circumstances with which we had to contend2 and it is chiefly to be imputed to the very accurate measures pursued in the workyard of the contractor at ,greenock1 by ,mr ,george ,middlemiss1 foreman of the carpenters 7who then acted as superintendent of the contract works71 and whose intelligence and zeal made him1 at all times1 able and ready to do full justice to all my suggestions for incurring as little loss of time on the ,rock as possible4 ,the operation of fixing these six beams1 which formed1 by their union1 a hexagonal pyramid of about #dd feet high1 and about #cd feet in diameter at the base1 occupied only six days1 including the cutting of the seats and the boring of the holes in the ,rock4 ,much labour and time were consumed in the mere moving of beams1 each weighing about #ac cwt41 over the rugged surface of the ,rock1 for which purpose we could only use a small set of shear-poles1 with crabs and blocks1 and tackle purchase2 and it sometimes happened1 that merely for the purpose of moving a beam1 it was necessary to place a special ring-bolt for holding a snatch-block for a few minutes1 in spite of all the care and forethought which had been bestowed1 in selecting the most advantageous positions for placing them1 before the work of raising the beam was begun4 ,nor was the necessity for securing every loose material by means of lashings to the ,rock1 before leaving for the night1 an insignificant source of delay2 for we were sometimes forced by the waves or the darkness1 which drove us from our work1 to lower a beam which was just ready for being fixed and to replace it in a safe situation4 ,pyramid completed4 ,on ,saturday the #ahth ,august1 the pyramid having been successfully erected1 the men were busied for two hours1 before embarking for the vessel1 in collecting and lashing all the loose materials to the ,rock1 for the sky gave some indications of a change4 ,as we took to the boats1 ,i looked at the result of our labours with some satisfaction1 not unmingled with gratitude4 ,mode of living while erecting the ,barrack4 ,during the week1 while we had been engaged in fitting up the main timbers of the barrack1 the weather had been very fine2 and except the long hours of toil and the sea-sickness on board the vessel1 there was nothing to complain of2 but the economy of our life while moored for days off the ,rock1 was somewhat singular4 ,we landed at four o'clock every morning to commence work1 and generally breakfasted on the ,rock at eight1 at which time the boat arrived with large pitchers of tea1 bags of biscuit1 and canteens of beef4 ,breakfast was despatched in half an hour and work again resumed1 till about two o'clock1 which hour brought the dinner1 differing in its materials from breakfast only in the addition of a thick pottage of vegetables1 and the substitution of beer for tea4 ,dinner occupied no longer time than breakfast1 and like it1 was succeeded by another season of toil1 which lasted until eight and sometimes till nine o'clock1 when it was so dark that we could scarcely scramble to the boats1 and were often glad to avail ourselves of all the assistance we could obtain from an occasional flash of a lantern and from following the voices4 ,once on the deck of the little tender and the boats hoisted in1 the materials of breakfast were again produced under the name of supper2 but the heaving of the vessel damped the animation which attended the meals on the ,rock1 and destroyed the appetite of the men1 who1 with few exceptions1 were so little sea-worthy as to prefer messing on the ,rock even during rain1 to facing the closeness of the forecastle4 ,as ,i generally retired to the cabin to write up my notes1 when that was practicable1 and to wait the arrival of my own refection1 ,i was sometimes considerably amused by the regularity with which the men chose their mess-masters1 and the desire which some displayed for the important duties of carving and distributing the rations4 ,even the short time that could be snatched from the half-hour's interval at dinner1 was generally devoted to a nap2 and the amount of hard labour and long exposure to the sun1 which could hardly be reckoned at less than #af hours a-day1 prevented much conversation over supper3 yet1 in many1 the love of controversy is so deeply rooted1 that ,i have often1 from my small cabin1 overheard the political topics of the day1 with regard to ,church and ,state1 very gravely discussed on deck1 over a pipe of tobacco4 ,perhaps the great heat below1 where upwards of twenty people were confined1 might in some measure account for this wakefulness on board the ,tender4 ,shoals of ,medus seen4 ,one beautiful morning1 during our stay of six days at the ,rock1 we had a visit from a shoal of small fish1 whose novel appearance made me take them for a fleet of some species of ,nautilus4 ,those animals came in such numbers1 that the pale blue silky membranes or sails1 which wafted them before a gentle breeze over the glassy surface of the ocean1 literally covered the water as far as we could see4 ,one of those animals ,i sent in a small phial to my friend1 ,professor ,fleming1 then of ,king's ,college1 ,aberdeen1 who assigns to it the ,linnean name of ,medusa velilla1 and says it is noticed by ,dr ,walker and ,mr ,pennant1 as a native of ,scotland4 ,driven by a gale to ,mull4 ,return to ,hynish1 and are driven to ,coll4 ,return to the ,rock4 ,the threatening of the previous night was fully verified by the succeeding ,sunday morning1 as a strong southerly wind with heavy showers1 forced us to part from our moorings at the ,rock at break of day1 and make sail for ,hynish ,bay1 where we anchored at seven4 ,on ,monday ,i landed at ,hynish2 but as the wind1 which had increased to a strong gale1 was still rising and inclining more to ,e41 ,mr ,macurich summoned me to the boat1 when1 with much difficulty1 and at the expense of shipping several seas1 we reached the vessel which was pitching the bowsprit under4 ,this soon forced us to run for the ,sound of ,mull1 where we were detained until ,saturday the #beth1 on the morning of which day we again made ,hynish ,bay2 but the wind1 which had been less violent when we started from ,tobermory the night before1 again commencing to blow strong from the same unpropitious quarter1 we had only time to land at ,hynish1 and take on board a salted sheep 7which proved a rather unpalatable addition to our provisions71 when we were forced to seek shelter in our old quarters at ,loch ,erin in ,coll4 ,as we entered ,loch ,erin1 we saw the ,regent 7the ,general ,lighthouse ,tender7 leave the ,sound of ,mull1 and again put back to ,tobermory4 ,next day 7the #bfth ,august7 we left ,loch ,erin1 and boarded the ,regent2 but the weather proving boisterous1 we were again forced into our old anchorage1 while the ,regent proceeded with the ,engineer1 who was then on his annual voyage1 to ,barrahead ,lighthouse1 without attempting to go near the ,skerryvore4 ,from this date the weather did not prove favourable for a landing until the #cjth1 when the wind being ,n4,w41 we sailed from ,loch ,erin at daybreak1 and reached the ,skerryvore at ten4 ,we now discharged all the remaining materials which had been shipped for the ,rock with a view to complete the pyramid of the barrack1 which it was intended should stand the test of a winter1 deferring the fixing of the habitable part till next spring4 ,driven to ,tyree4 ,return to the ,rock4 ,horizontal braces fixed4 ,driven to ,mull4 ,heavy gale4 ,timber cast on ,tyree4 ,return to ,rock1 and farther progress of barrack4 #cast ,august4--,the last day of ,august was one of considerable discomfort4 ,our landing at four in the morning was attended with great difficulty and some danger2 and throughout the day we were a good deal incommoded by a thick drizzling rain1 which continued without intermission4 ,about mid-day the sea rose so much as to render it no longer prudent to delay leaving the ,rock1 and we therefore embarked4 ,after lying at our moorings until half-past two1 in what1 to landsmen1 was a most distressing sea1 we slipped and ran for ,hynish ,bay1 which we reached at #e ,p4,m4 ,the weather continued boisterous until next evening 7#ast ,september71 when the wind went round to the north1 and at eight all the men were summoned on board2 but although we sailed at daybreak1 we could not reach the moorings with daylight2 and it was not till the morning of the #dth ,september1 about four o'clock1 that we could again land on the ,rock4 ,we succeeded1 in spite of a very unfavourable day1 in remaining till three o'clock1 during which time we fixed the whole of the horizontal braces1 and got everything which we had not been able to secure in its place firmly lashed to the ring-bolts on the ,rock1 after which we were forced to leave it for ,mull4 ,the gale continued to blow very hard1 without any intermission1 for some days2 and on the #fth1 some wreck-timber1 covered with goose-barnacles1 came ashore among the surf at the beach at ,hynish1 but no trace of its history was ever found1 nor did any rumour reach us of a shipwreck having occurred on this coast4 ,it was not till the #hth that we could again attempt to reach the ,skerryvore2 when1 sailing from ,mull with a fair wind1 and taking on board at ,hynish nine masons1 and ,mr ,c4 ,barclay1 foreman of the quarriers1 we again landed on it at #b ,p4,m4 ,we succeeded in getting up the mortar gallery 7see ,plate ,v471 and in fixing some of the diagonal braces1 and left the ,rock about eight4 ,a marrot perched on the vessel's side this afternoon1 much fatigued and evidently desirous to get on board2 but the sailors1 from some superstitious dread1 would not admit the poor bird4 #ajth ,september4--,we landed at four o'clock1 and had a long and good day's work until daylight left us4 ,we were now within twenty-four hours at most of completing all that could be expected to be done this season2 and it was with no small anxiety that ,i observed a change of wind from ,n4,e4 to ,s4,s4,w41 accompanied by a fall of the sympiesometer2 as in the event of a change of weather at that season1 it seemed very uncertain when we might again land1 and still more uncertain whether our work1 in its incomplete state1 could resist the winter's seas4 ,last day's work on ,rock this season4 ,precaution for the benefit of shipwrecked seamen4 ,view from top of pyramid4 #aath ,september4--,this was our last day's work on the ,rock this season4 ,we landed at four o'clock with very great difficulty1 and some danger of having our boats swamped2 and we were forced1 owing to the heavy sea which broke upon it1 to leave the ,rock at high water2 but1 about one o'clock1 we were enabled to return1 as the sea fell a little4 ,by dint of great exertions1 we got the last of the diagonal braces fixed1 and the bats run up with lead and painted1 for their protection against corrosion4 ,we also contrived to remove the greater part of the tools from the ,rock1 but some we were forced to leave to their fate4 ,to the upper part of the pyramid we lashed a water-tight chest1 containing biscuits and a cask of water1 to serve as a means of support to any shipwrecked mariners who might chance to reach the ,rock4 ,i also caused some spars to be lashed at various levels1 by way of testing the effects of the sea2 but to how little purpose1 the sequel will shew4 ,before leaving the ,rock1 ,i climbed to the top of the pyramid1 from which ,i now1 for the first time1 got a bird's eye view of the various shoals which the stormy state of the sea so well disclosed2 and my elevation above the ,rock itself decreased the apparent elevation of the rugged ledge so much1 that it seemed to me as if each successive wave must sweep right over its surface1 and carry us all before it into the wide ,atlantic4 ,so loud was the roaring of the wind among the timbers of the barrack1 and so hoarse the clamour of the waves1 that ,i could not hear the voices of the men below2 and ,i1 with difficulty1 occasionally caught the sharp tinkle of the hammers on the ,rock4 ,when ,i looked back upon the works of the season1 upon our difficulties1 and1 ,i must add1 dangers1 and the small result of our exertions--for we had only been #afe hours at work on the ,rock between the #gth ,august and the #aath ,september--,i could see that1 in good truth1 there were many difficulties before us2 but there was also much cause for thankfulness1 in the many escapes we had made4 ,after a somewhat precarious embarkation in the boats1 and shipping several seas in our way1 we reached the vessel1 and immediately set sail with three cheers1 rejoicing to have thus concluded our season's work4 ,destruction of the barrack during a gale4 ,letter from ,mr ,hogben4 ,after spending a few days at ,hynish in making various arrangements for the operations of the next season1 which were to embrace the extension of the pier1 the completion of the barracks and the erection of sheds and workshops for carrying on the dressing of the materials for the ,lighthouse ,tower1 ,i left ,tyree with the pleasing belief that the successful termination of our first season's labours might be taken as an omen of future success4 ,but how uncertain are even the most rational sources of satisfaction which ,time can furnish6 ,on the #abth ,november1 ,i received from ,mr ,hogben1 the clerk and store-keeper at ,tyree1 the unwelcome intelligence that the ,barrack-house had been destroyed1 as was supposed1 by the heavy sea of the #c;d ,november2 and as his letters contain all the facts of the case in so far as they could be collected at the time1 ,i cannot do better than quote them at full length3--8,skerryvore ,lighthouse ,works1 ,tyree1 #eth ,november #ahch4--;,dear ,sir1--,i am extremely sorry to inform you1 that the barrack erected on ,skerryvore ,rock has totally disappeared4 ,it was seen on the #cast of ,october1 when ,i observed no change in its appearance4 ,on the two following days the weather was showery1 with haze1 so that the ,rock was not seen2 and on the #c;d it rained almost all day1 with strong breezes4 ,in the evening the wind increased to a gale1 with a great swell1 and an extraordinary high tide4 ,yesterday 7,sunday the #dth7 the weather was moderate1 but the swell prevented the ,rock being seen from the low ground4 ,mr ,scott and ,charles ,barclay1 however1 having gone to the top of ,ben ,hynish1 got a momentary glimpse of the ,rock through the spray1 and both were of opinion that the barrack was gone4 ,this was not credited by the workmen who had been employed at it1 but this morning we found it to be the case2 the ,rock was pretty clearly seen1 but no trace of the barrack4 ,from the circumstance of the yard of a large vessel1 and also a piece of a boom1 having come ashore in the direction of the ,rock1 we think it is not improbable that some wreck has happened1 and that some part of it has been thrown upon the barrack by the force of the sea4 ,should any opportunity occur for going out to the ,rock1 we shall take advantage of it1 in order to give you farther information on the subject4 ,i remain1 c4 7,signed7 ,,wm4 ,s4 ,,hogben40 ,a subsequent letter from ,mr ,hogben is of the following tenor3--8,skerryvore ,lighthouse ,works1 ,tyree1 #ajth ,november #ahch4--;,dear ,sir1--,this morning1 ,charles ,barclay1 with a boat and four men1 went out to the ,rock to view the site of the barrack2 and1 the weather being moderate1 he got a good landing4 ,the following is the state in which he found everything3--,the whole barrack timbers had been carried away1 excepting the long beam next the place where the crab stood which drew up the beams1 and about seven feet of the long beam opposite the place where the other crab stood4 ,the former of these beams had fallen in the direction of the highest part of the ,rock1 and had drawn one of the iron stancheons #af inches4 ,the latter was all in splinters1 with one of the iron stancheons broken1 and the other bent4 ,the rest of the stancheons were broken at the point between the round and the flat1 and some of them were drawn about #i inches4 ,the iron hoop which bound the top of the beams was lying at the distance of about the length of the beams to the eastward of the centre of the barrack1 having one of its screws broken4 ,five large wooden knees were remaining1 a ladder partly broken1 some moulds for taking the angle of the beams1 and most of the quarry and masons' tools4 ,the grindstone was thrown from the top of the ,rock into a deep hole on the side next ,tyree1 a distance of about #ab yards1 apparently whole4 ,the smith's forge had disappeared1 and the anvil had been thrown about #h yards to the ,n4,e4 of the place1 where it was left2 it was brought ashore1 along with the hoop which encircled the top of the barrack4 ,the iron posts which supported the bellows were standing4 ,the crab on the ,s4,w4 side was thrown from its place to the east side of the site of the barrack1 a distance of about #ae or #bj yards1 and was dashed to pieces1 excepting the axle1 handles1 pinion1 and the trunk of the barrel4 ,the other crab was thrown from its place to the ,n4,e41 over a part of the rock #e or #f feet high1 to a distance of about #f yards1 and was found in a similar state to the former4 ,a stone measuring three-fourths of a ton was found near the seat of one of the beams2 it had been thrown up from the hole where it had been deposited while cutting the seats for the barrack timbers4 ,one of the ring-bolts near the top of the ,rock to which the chain binding the wood had been made fast1 was broken close by the surface of the ,rock1 and the wood was all gone4 ,the mooring buoy has also disappeared4 ,the barrack was seen from the top of ,ben ,keen-na-vara1 by some men on ,saturday1 #c;d ,november1 so that the succeeding night1 which was truly awful1 must have done the damage4 ,i may mention1 that many of the islanders say that they have not seen such a swell as on that evening for about sixteen years4 ,i am happy to say that no damage has been done to the works on shore here1 as on that evening the wind was about ,s4,w41 and we are pretty much sheltered from the wind in that direction4 ,the shore on the ,s4,w4 side of the island is strewed with sea-weed1 which has been carried up far beyond the usual reach of the tide4 ,hoping that the above information will suffice1 ,i remain1 c4 7,signed7 8,,wm4 ,s4 ,,hogben40 ,proceed to ,skerryvore4 ,state in which the ,rock was found4 ,on the day on which ,i received this discouraging intelligence1 ,i requested a special meeting of the ,committee1 for the purpose of deliberating as to the best course to be pursued1 when ,i received instructions to proceed to the ,rock1 and for that purpose to hire a steamer at ,glasgow4 ,i accordingly started that very evening for ,skerryvore1 with the intention at the same time of removing such of the men from ,tyree as were not to be employed during the winter4 ,i left ,greenock in the steamer ,tobermory1 accompanied by ,mr ,macurich of the ,lighthouse tender1 at midnight of the #adth ,november1 after some delay in repairing a leak in the boiler1 which was discovered in time before starting1 and reached ,hynish at #aa on the forenoon of the #afth1 having got a good passage round the ,mull of ,kintyre4 ,the weather was1 however1 in every other respect most unfavourable for the purpose2 and having merely touched1 in passing ,tyree1 at the workyard at ,hynish1 to inquire whether any thing farther had transpired1 and to take on board ,mr ,charles ,barclay1 who had visited the ,rock after the loss of the barrack1 we at once proceeded and reached ,skerryvore about #d o'clock in the afternoon4 ,the sea ran very high1 and there was not the most remote chance of landing1 but1 having got into the boat1 ,i approached near enough to the ,rock to enable me to survey the melancholy remains of our labours1 which seemed to be in the same state in which they were described by ,mr ,hogben4 ,the beam which lay back on the inclined ledge still kept its place1 having been firmly lashed by ,mr ,charles ,barclay to a ring which was near it when he landed on the #ajth ,november2 and ,i could see the remains of some of the stancheons and of the crabs which the sea had left4 ,after waiting1 in the hope of a change in the state of the sea1 until it was nearly dark1 we again turned towards ,tyree1 in all the gloom of a stormy night1 and depressed by mingled disappointment and sad forebodings1 occasioned by the fate of our intended asylum from the waves4 ,owing to the heavy sea1 and a strong gale against us1 we hung for a long time off ,hynish ,point1 and did not reach the ,bay till midnight4 ,next morning about #g1 we came off ,hynish1 in order to take in the men who were to go home for the winter4 ,the ground was deeply covered with snow1 which made the embarkation of so many persons and so much baggage a tedious and uncomfortable operation2 and when we sailed1 we experienced all the inconveniences of a strong gale and a heavy sea1 with the concomitant of a deck covered with passengers1 all very sick and much dispirited4 ,many of the men1 indeed1 seemed to be as deeply concerned for the loss we had sustained as ,i myself was4 ,to add to our difficulties1 the vessel1 under the care of a native pilot1 had touched slightly on a rock off ,hynish ,point1 and gave some indications of leaking4 ,we1 however1 reached ,oban in safety4 ,illustration3 ,no4 #aj4 ,cause of the destruction of the barrack4 ,various conjectures were made as to the cause of the destruction of the barrack4 ,those who saw it erected were so confident of its stability1 that they could not avoid connecting its failure with some injury received from the wreck-timber1 which had come ashore on the island of ,tyree1 two days after the supposed date of the accident4 ,in this opinion they were strengthened by the total destruction of the cranes and other objects on the rock1 forgetting that the timber of the barrack itself1 when once let loose1 must of necessity have proved even a more powerful agent of destruction than the driftwood of the wreck4 ,but whatever doubt may exist as to the first cause of the injury1 there seems good reason to suppose that the dismemberment of the parts of the structure had commenced with the removal of the horizontal braces1 and that the beams1 having thus more liberty for play and tremor1 had gradually shaken loose the fixtures at the top1 which consisted of straps c c1 passing right over the tops a a1 of the beams and b b1 the hexagonal quoin of hardwood already noticed at p4 #hh1 which were secured by means of a central bolt d1 and finally girt outside by a ring1 e e1 as shewn in the annexed woodcut 7,no4 #aj47 ,the moment this dismemberment occurred1 the beams would be free to work their own destruction2 and the enormous leverage which they exerted1 when dashed to and fro by the breakers1 would soon snap the iron stancheons at the base1 and throw all loose to the waves4 ,the only remaining beam was that which was supported against a ledge of rock1 and which had received the sea from the opposite direction to that in which it was found lying4 ,that beam1 however1 although firmly lashed to the rock by the men who first visited it after the accident1 along with ,mr ,charles ,barclay1 also disappeared in the course of the winter4 ,as a proof how severely these beams had been dashed by the waves1 ,i may state1 that the only remaining part of a beam which ,i saw attached to the iron stancheons1 when ,i landed in the following spring1 was so thoroughly riven and shaken as to be quite like a bundle of lathwood4 ,preparations for a new barrack4 ,illustration3 ,no4 #aa4 ,these circumstances by no means shook my belief in the suitableness of the plan adopted for obtaining a temporary dwelling on the rock2 but they induced me1 as soon as ,i received authority from the ,commissioners1 whose confident expectation of final success was not damped by the unhappy issue of our season's labours1 to examine very carefully the whole details of the ties and fastenings4 ,in preparing a similar structure for next season1 ,i resolved to strengthen the ties at the top1 where ,i imagined the former failure to have occurred1 by adding six strong stancheons a1 a 7,plate ,v471 one to each beam1 with heads passing through a centre-plate 7,h71 which united them in one as a cap and to which they were secured by strong screws and keys4 ,the nature of those fixtures will be more easily understood by a reference to the figures 7#a7 and 7#b7 in ,plate ,,vi41 which shew an elevation and plan of the upper part of the beams4 ,in the elevation only the beams ,a1 ,b1 ,c1 are shewn2 but in the plan1 all the six beams appear mitering at their heads n1 n1 to the central beam or tie o1 o 7see also ,plate ,v471 which was introduced to counteract the tendency of the heavy seas that might burst inside the pyramid1 and by exerting a powerful force in the vertical direction1 might separate the beams at the top4 ,in the ,plate 7,,vi471 a1 a1 are strong stancheons of iron attached to the outside of the beams by bolts1 and also by collars r1 r1 attached to ears g1 g4 ,these stancheons being bent into the vertical direction and rounded at the top1 passed through the malleable iron plate ,h1 which was held down1 and1 as already stated1 bound the beams together by nuts c1 c1 and wedges b1 b4 ,through a hole in the centre of this plate1 a large spike p was driven1 which produced an expansion of the central beam1 and thus wedged up or tightened all the joints formed by the mitering of the seven timbers4 ,on each of those stancheons1 snugs were formed at e1 capable of receiving and retaining in its place against any tendency to move upwards1 a strong metallic ring g1 which was tightly keyed by wedges at k4 ,additional ties of iron ,d1 ,e1 ,f1 were also provided1 which connected the six beams together in pairs4 ,each end of those ties was attached to the timbers by three spikes2 one tie1 ,d1 is shewn a little fore-shortened2 another1 ,e1 is seen only on the end2 while the third ,f1 is shewn as cut off at the middle4 ,lastly1 an important change was made1 by the substitution of malleable iron for wooden braces 7see ,plate ,v47 b1 b1 b1 b1 in the horizontal direction4 ,fixtures of this kind held the whole more firmly together2 and their construction was such that they might firmly embrace each beam1 without requiring any means of attachment beyond wedging tightly up2 and thus the entire strength of the timbers was unimpaired by the driving of spikes or bolts4 ,those braces 7,no4 #aa71 a1 a1 had1 at each end1 double knobs1 and were pushed up along the beams1 until they squeezed the timbers x1 x1 x between them2 plates p1 p 7having holes in them through which the double knobs of the braces were made to pass71 were then put on and keyed and screwed1 as shewn in the figure1 so that each beam was quite enclosed by fixtures1 which were thus independent of spikes or bolts4 ,thin hardwood wedges were afterwards driven in1 wherever they could be inserted between the iron and the timber2 and those wedges were 8stitched0 to the beams with common nails1 merely to prevent their dropping downward1 after any temporary contraction of the timber from the state of the atmosphere4 ,in all this1 ,i have anticipated what more properly belongs to the works of the season #ahci2 but ,i consider it best1 for the sake of clearness1 to connect this account of the new with the destruction of the old ,barrack4 99 99 99 99 99 ,works at ,hynish4 ,while the operations already described were in progress at the ,rock1 various works were going forward at the workyard in ,tyree4 ,about #af masons1 #ab quarriers1 and #d carpenters1 were employed in building the barracks for the workmen and in erecting smiths' and carpenters' shops4 ,a large room1 paved with a stone floor1 for drawing out at full size the courses of the ,tower and making the moulds for dressing the stones1 was also provided2 and a platform of squared masonry was set in the workyard1 on which the courses were to be laid1 before being shipped for the ,rock4 ,during the season1 the pier had also been carried out #bef feet1 to a point #ae feet within the low-water mark4 ,it was also necessary to provide depositories for the security of tools and other implements1 as well as a large coal-shed for the supply of the ,steamer which was then in the course of being built4 ,it had1 as already noticed1 been determined that the stores were to be served out at the cost prices of the ,greenock market1 to be paid for once a month1 at the same time that the wages of the men were paid4 ,that arrangement had been carried into effect on a small scale1 from the very beginning of the works2 but this season it became necessary1 owing to the increased number of men1 to conduct it on a more extended and systematic plan2 and1 for that purpose1 a person was required to act as storekeeper and clerk4 ,in order also to preserve the provisions from injury by damp and to secure them from the inroads of the needy ,celts and from innumerable rats which overrun that part of ,tyree1 it was found necessary to set apart1 as a storehouse1 a large room on the second storey of one of the workshops4 ,the chief articles served out in the store were meal1 molasses1 sugar1 coffee1 tea1 tobacco and butter4 ,the establishment of the store entailed a great deal of trouble1 and led to some expense for carriage and packages1 as well as to occasional trifling losses in serving out the allowances or from injury sustained in the transport of the goods2 but the inhospitable nature of the country1 and the remoteness of ,tyree from the ordinary steam-boat traffic1 made the adoption of some such plan unavoidable4 ,amongst other inconveniences which attended the store1 not the least may be reckoned the frequent importunities1 on the part of the native labourers whom we employed1 to be permitted to purchase provisions at the workyard2 but that was never acceded to1 except in cases where dearths 7which are of frequent occurrence in the island7 rendered the call irresistible4 ,had their entreaties easily prevailed1 we should soon have had the whole population of ,tyree as our regular customers at the ,store4 ,hynish ,quarries4 ,the quarries at ,hynish1 as already stated1 were by no means productive4 ,the great proportion of the materials which had been quarried1 was found to be applicable only to the building of the pier and the inclosing walls1 and to the various erections in the workyard2 and not more than one-tenth of the whole could be dressed as blocks for the ,tower4 ,during the numerous occasions on which ,i had been driven by stress of weather to the neighbouring coasts1 ,i had visited the quarries around ,oban and in various parts of ,morven and ,mull4 ,when so forced to leave what ,i might more especially call my post1 ,i had an opportunity of seeing the quarries at ,ardentallen near ,oban1 which contain the old red sandstone strongly impregnated with clay4 ,that stone is by no means suitable for the face-work of a marine building1 in such a situation as the ,skerryvore2 while the comparatively small quantity of hearting which could be admitted into such a work1 made it inexpedient to seek such materials at so great a distance4 ,in this way1 the ,ardentallen quarry seemed completely excluded from the field4 ,at another time1 in passing through ,inverary1 ,i devoted a day to the examination of the quarries which had lately been opened at that place and in which a beautiful porphyry is wrought2 but ,i saw no appearance of very large blocks1 or1 at all events1 nothing that could favour the expectation of a considerable supply4 ,but after carefully weighing the matter1 the great masses of granite at the ,ross of ,mull finally determined my choice in favour of that locality2 and the ,duke of ,argyll having1 with the greatest liberality1 ratified his predecessor's grant of liberty to the ,lighthouse ,board to quarry stones from any part of the ,argyll estates1 it was resolved to take measures early in the spring of #ahci for opening quarries at ,north ,bay1 in ,mull1 where an excellent station for shipping had been discovered1 close to the place where we saw the most promising appearance of rock4 ,this measure seemed the more indispensable1 as the last part of the quarry terred#ah or laid bare at ,hynish1 had greatly disappointed our expectations4 ,the unworkable nature of gneiss rock also and its extreme uncertainty with regard to quality1 farther concurred to make a change most desirable4 ,granite1 indeed1 is a material in many respects superior to sandstone1 gneiss1 or porphyry4 ,the first it greatly excels in durability and weight2 and1 as a stone for the workyard1 it is superior to the other two1 from its property of being fissile1 or easily split in any direction4 ,in this respect it resembles certain parts of some sandstone strata which are commonly called liver rock1 of which ,craigleith quarry1 near ,edinburgh1 furnishes an excellent example4 ,porphyry1 and1 ,i think1 all other igneous rocks 7excepting granite71 gneiss also1 and most of the other primary rocks1 have not this property1 being fissile only in one plane1 so that quarries of those rocks generally turn out very uncouth or irregular stones1 which1 though they may in some favourable cases possess good natural beds1 will always be found to have ragged and irregular joints1 which1 for the most part1 are incapable of being properly dressed4 #ah ,this term in ,scotland denotes the removal of the soil and unsolid material1 in order to lay bare the rock previous to working the quarry1 and seems obviously to be derived from the ,latin 8terra10 perhaps through the medium of some old charter4 ,the quantity of terring very much affects the profitable working of a quarry4 ,,chapter ,v4 ,,operations ,,of #ahci4 ,shipping ,station and ,pier at ,hynish4 ,during the winter months which intervened between ,november #ahch and ,march #ahci1 a small detachment of men1 consisting of three masons1 nine quarriers1 and one smith1 were left at ,hynish under the superintendence of ,mr ,charles ,barclay1 to clear the landing-place of several patches of rock which encumbered the entrance4 ,they were also to build some walls of inclosure1 and to quarry and dress stones for the pier and other buildings at ,hynish4 ,the provision of accommodation for shipping at that place was now naturally regarded as of more urgent necessity than formerly1 because the importation of stones from ,mull1 which the failure of the ,tyree stone had rendered unavoidable1 led to the necessity of a reshipment of all the materials at ,hynish1 where they were dressed before being sent to the ,rock4 ,it may1 perhaps1 be naturally enough imagined1 that instead of importing the materials to be dressed at ,tyree and there reshipped in order to be carried to the ,rock1 they might have been prepared in ,mull1 and sent directly to the ,skerryvore2 but many things concurred to render this inexpedient1 if not altogether impracticable4 ,the advantage of being able1 by means of a good telescope1 in some measure to ascertain the state of the sea at the ,rock1 the comparative shortness of the passage1 which gave the prospect of several cargoes being landed on it in one day during fine weather1 and the convenience of communicating with the ,rock by signal1 were circumstances in themselves quite sufficient to determine my choice in favour of ,hynish1 as the place from which the materials must be shipped for the ,rock1 even if there had been no other considerations leading to the same conclusion4 ,but in addition to all this1 ,i could not fail to perceive that ,hynish was the only place for the permanent station of the vessel attending on the future ,lighthouse2 and that on that account alone the construction of a ,harbour there was unavoidable4 ,that the arrangement1 by which the future station for the ,tender was used as the workyard for the operations1 was the most judicious that could have been adopted1 was fully proved by my subsequent experience of the advantage of assembling all our materials and all our force at a point as near to the ,rock as possible1 so that we might be at all times ready to supply defects or omissions1 and take advantage of every favourable change of the sea or sky4 ,in the middle of ,march the ,regent conveyed from ,aberdeen a detachment of twenty-nine masons and quarriers and five smiths1 and the foreman of the workyard1 who1 together with the men already at ,hynish and the native labourers1 were to be employed during the season of #ahci1 in the various departments of the work4 ,on their arrival the men were separated into two small bands1 of which the one1 consisting of six masons1 twelve quarriers1 one smith and a foreman1 was stationed at ,north ,bay in ,mull1 where the new quarries were to be opened2 while the other had its head quarters at ,hynish1 and1 when not engaged in the work on the ,rock itself1 was subdivided into smaller parties1 varying in number with the nature of the particular operations in which the men were occupied4 ,granite quarries in ,mull4 ,on the afternoon of the #aith ,april ,i sailed from ,greenock in the ,regent1 for ,north ,bay in ,mull1 where the quarries were to be opened4 ,we had on board the whole materials of the new ,barrack1 which was to supply the place of that which had been destroyed in the preceding month of ,november2 and we had also a party of carpenters who came to fit up the ,barrack in a temporary manner at ,north ,bay1 as a residence for the masons who were to be engaged in preparing more permanent dwellings for the quarriers and in forming a landing-wharf for the shipment of the stones for ,tyree4 ,it was not till the #beth1 after a tedious passage of six days1 that we anchored at ,north ,bay2 and next morning we had the satisfaction of seeing the steamer1 the ,skerryvore 7by which name she was specially set apart for the service of the works71 arrive in the ,bay with a party of masons and quarriers1 who had been appointed to meet us in order to begin the work4 ,the necessary arrangements with the ,duke of ,argyll's tenants at the ,ross of ,mull 7in which district ,north ,bay is situated7 having been already made1 no time was lost in erecting the wooden ,barrack2 and1 in seven days after our arrival1 the masons and quarriers entered their new habitation under the charge of ,mr ,charles ,stewart1 whom ,i left as foreman of the ,north ,bay works4 ,mr ,stewart and his party1 following the example of diligence thus set to them1 were not less expeditious in proceeding with the work which had been assigned to them2 and by the beginning of ,august a range of barracks1 capable of accommodating forty persons1 had been erected1 a landing wharf had been built1 and various storehouses had been provided1 although the quarry had to be opened1 and the blocks of stone required for those various works were still in situ at the time of our landing at ,north ,bay three months before4 ,the landing wharf is placed on a small projecting face of rock in a depth of #ab feet at high water of ordinary spring tides4 ,it presents a face of #dj feet in length1 and was provided with wooden fenders for the protection of the vessels loading stones4 ,landward of it a considerable space was levelled1 by cutting and filling1 to serve as a yard for storing the quarried materials1 so as to be ready for shipment4 ,the quarry itself was opened in the face of a hill1 so steep as almost to deserve the name of a cliff2 but advantage was taken of a deep gully which intersected it and in it an inclined plane was formed communicating directly with the landing-place4 ,this gully was partly cleared by excavation of the rock and partly1 where necessary1 its inequalities were smoothed down by filling it with stone shivers2 and along its bed thus prepared1 longitudinal sleepers of timber were laid1 to which edge-rails were attached4 ,at the top of the incline two iron drums or barrels were set1 and round them were wound1 in opposite directions1 the chains by which the trucks or wagons1 loaded with stones from the quarry1 were lowered to the wharf below4 ,a powerful break apparatus was attached to those barrels1 to check the velocity of the descending wagons1 which was also in part counteracted1 by making their gravity act as a power to raise the empty wagons in the same manner as is usually practised in coal-mines4 ,the quarry itself1 as already stated1 was opened in the face of the cliff1 at a point where the successive beds of solid rock seemed to promise the fairest prospect of success4 ,the preliminary operation was to remove a very thin alluvial cover which scarcely concealed from view a large mass of most beautiful granite1 whose reddish colour is said to have given the name of ,ross#ai to that part of ,mull1 the shores of which everywhere exhibit massive slopes of that fine rock4 ,the granite is separated very abruptly from the basalts of the surrounding district1 so as to leave the ,ross purely granitic2 but in no part of the whole coast1 which abounds with creeks and bays1 does the rock appear to be of equal quality1 or so conveniently situated for shipping1 and so easily accessible to quarriers1 as at the spot we had chosen4 ,i know of no instance of a quarry so fully answering the most sanguine expectations as that of the ,ross of ,mull2 and ,i have never seen a granite quarry of equally great resources1 as regards both the quantity and the quality of the material produced4 ,the rock in general yielded easily before well-directed shots1 and was separated into large masses1 capable of being advantageously cut1 with little loss of material1 into shapely blocks1 by means of wedges1 which work remarkably well in that rock4 ,a few weeks after the quarrying operations had been commenced1 a single shot detached #aej tons of excellent stone1 in the cutting of which into blocks for the ,lighthouse ,tower little loss of material occurred2 and in the course of the season of #ahci1 although the summer was chiefly spent in the preliminary works above noticed1 the ,mull quarries produced nearly as much workable material for the ,lighthouse ,tower as the ,hynish quarries had done in three years4 ,in the course of the future working of the quarry1 when it came to be more fully opened1 its resources were so great1 that on one occasion a single shot shook about #egj tons1 while another shot detached a mass of #dfj tons4 ,in that way1 between ,april #ahci and ,june #ahdj1 material had been quarried in that single spot1 sufficient to supply #dcjj selected blocks1 varying in weight from ton to #b tons each4 ,the average monthly produce of the quarries was about #djj tons1 and there were generally employed in them #bf quarriers1 #c labourers1 and #b smiths4 ,the quantity of gunpowder consumed in the quarry was small1 as it was almost exclusively employed in great bores about #aa feet deep1 for the purpose of detaching large masses which had no open side and could not be removed by means of the pinch or crow-bar4 ,when a mass of rock had been thus removed1 it was cut up into various portions by means of wedges1 and finally subdivided into blocks1 hammer 7or as it is called quarry7 dressed1 according to rough moulds1 whose dimensions exceeded those of the stones of the various courses of the building by a quantity which was considered sufficient to cover any casualty in the final dressing of the block by the masons at ,hynish1 and which allowance was generally equal to a film of rock about #a inch in depth4 ,the blocks thus roughly formed were shipped for ,hynish1 distant about #bf miles1 through a tempestuous sea1 open to the full reach of the ,atlantic towards the south-west1 sometimes in a small vessel called the 8,queen10 belonging to the ,commissioners1 and sometimes in undecked boats of #af tons1 belonging to the adventurous men of ,tyree4 ,the freight usually paid was #es4 a ton1 and yet the whole of the blocks for the ,lighthouse ,tower1 and many of those used in the pier at ,hynish1 were laid down to the number of about #ejjj1 at the rate of #bs4 #a;d4 per cubic foot1 including all the expense of building barracks1 opening quarries1 freight of stones1 and the expense of building and maintaining the small vessel called the 8,queen10 above noticed4 ,the stone of the ,mull quarries is a reddish or flesh-coloured granite1 in which felspar predominates4 ,about #acff cubic feet weigh a ton1 and it is not quite so hard as the granite of ,aberdeen4 #ai ,whether from any inflection of the ,celtic ,rhua1 or ,roy1 or directly from the ,italian ,rosso1 it would1 perhaps1 be impossible to determine4 ,observations on the quarrying of granite4 ,as ,i am not aware that any professional work contains a detailed description of the quarrying of granite1 some observations on that subject may not be unacceptable in this place2 and ,i therefore propose1 at the risk of appearing somewhat prolix1 to give a pretty minute account of the mode of opening and working a granite quarry1 more especially as practised by us at ,north ,bay4 ,having laid bare the rock of earth1 gravel1 or other loose matter 7which operation1 as ,i have elsewhere mentioned1 is in ,scotland technically called terring71 and having swept or washed clean the surface of the rock so as to have a good view of the natural seams or joints which traverse it1 the next step is to fix the best place for putting in a bore or mine4 ,in selecting the position of the bore1 the direction of the seams and veins of the rock must be duly considered1 with a view to employ the force of the explosion to the greatest advantage in separating the natural joints or beds of the rock1 instead of shattering the solid masses or posts 7as they are called in the language of the quarry7 into shivers or fragments4 ,one thing to be strictly borne in mind is1 that the bore should never be in the centre of a fine or large block1 but should be placed within a few inches of its back so as not to break the finer rock into small and useless fragments2 and care must1 at the same time1 be taken to keep the bore clear of cracked or unsound rock1 as the jumper1 in passing through such material1 is liable to be jammed by the cracks and fissures before it can be driven to the proposed depth4 ,it is not possible to lay down precise rules for guiding the quarrier in choosing the place of the bore1 as his plan must be regulated chiefly by the circumstances of each case2 but it may be observed1 that having first determined the depth of the hole1 it will seldom be found advantageous to keep the bore farther back from the face of the rock than about four-fifths of that depth4 ,the depth itself1 also1 to which the mine should be carried1 is a point for deliberation with the skilful and experienced quarrier1 who will take great care not to go so deep as to pass through the solid rock in which he is boring and thus to touch a bed1 unless indeed he shall think it advisable to attempt to raise more than one post of rock by a single mine1 in which case he will carry the bore through the first post into the second or third as the case may be4 ,but in all cases the boring must be stopt at two inches before coming to the bed or seam of the post in which the mine is to terminate1 lest the exploding powder should escape by the bottom of the bore1 and thus leave the top of the rock altogether undisturbed4 ,in endeavouring to procure large materials1 the bores should in general be as deep as possible4 ,it is only experience1 however1 which teaches the quarrier to form a sound prognosis as to the direction and level of the beds of the rock at any particular spot1 and enables him to choose the most advantageous position and depth for the mines4 ,in the blasting of granite there are a few general rules which 7although it may not be necessary to follow them in every case7 may be considered as constituting the best practice4 ,if the bore be a vertical one of the depth of #f feet1 #b inches diameter at the top1 diminishing to #b inches at the bottom1 may be considered a proportionate caliber4 ,if the bore be a deep one 7perhaps of #ad feet71 its diameter will require to be #c inches at the top1 and should diminish to #b inches at the bottom2 and the quantity of powder required for the charge will in most cases be about as much as is required to fill ths of the hole4#bj #bj ,miners and quarriers1 who always work by empirical rules1 disregard entirely the line of least resistance as a measure for the charge1 and invariably refer to the depth of the bore4 ,the patent fusee having been inserted among the powder1 with its end about the centre of the charge1 and the upper part of the bore having been filled up with dried clay1 well forced down with a wooden rammer faced with copper1 a length of #c or #d inches of the fusee should be left outside the bore1 to which the match is to be attached4 ,having cleared away every thing near the blast which can receive any injury and covered up the machinery of the cranes with strong planks1 the mine may be said to be ready for being fired2 and1 on a signal given1 by blowing a horn1 all hands retreat to a safe distance1 with the exception of the fireman1 who then lights the match1 and follows the others as fast as possible4 ,if1 as already stated1 the object in quarrying be to obtain large materials1 the bores should1 if possible1 be deep2 and1 in that case1 the rock will seldom be thrown down in fragments by the blast1 but will merely be cracked1 and intersected by rents about one inch in width4 ,recourse must therefore be had to what1 in quarry language1 is called a ,bull1 which consists in running a quantity of loose powder into the crack which has been made by the blast1 at that part where its explosion seems most likely to throw out the cracked or broken mass in various fragments and disengage them from their place in the rock4 ,in bulling1 perhaps twice as much powder as was used in the bore is loosely poured into the crack1 care being at the same time taken to get as much of it to go under the bottom of the rock as possible4 ,after enough of powder has been poured into the crack1 a quantity of dried smithy ashes1 or dry sand1 is run in over the powder1 so as completely to cover it1 except so much as is required to fire it by2 and that coating1 which is merely superficial1 is employed partly to keep down the powder1 and partly for security against its being accidentally fired before all things are ready4 ,the fireman having seen every thing cleared away1 gives notice to sound the alarm1 when all hands escape to a distance in the direction which is supposed to be the safest4 ,the match is then applied1 and the fireman retires1 as fast and as far as he can1 yet so as if possible to keep in view1 during his retreat1 the progress of the match4 ,the operation of bulling is far more dangerous than the firing of a bore1 as the charge is much greater1 and not so well confined1 so that many splinters are thrown off1 and the direction in which they fly varies continually with the direction of the cracks which the original bore may have produced4 ,as might be expected1 by far the greater part of the accidents which occur to firemen in granite quarries1 arise from that practice4 ,illustration3 ,no4 #ab ,should it happen1 as it sometimes does1 that after having gone through those operations1 the quarrier fails in getting the cracked mass thrown down to the bottom of the quarry1 he varies his mode of attack1 and proceeds to bore a row of plug-holes on the face of the rock in such a line as to cut off a part from one end of the shaken mass2 and for that purpose he is often obliged to hang a scaffold over the face of the rock on which to stand while boring the holes4 ,those plug-holes should be slightly inclined1 so that1 when the wedges1 called plugs#ba and feathers1 are driven into them1 they may rend the rock in such a direction that the piece intended to be cut off may be a little narrower on the inner than the outer face1 so that1 thus resting on an incline it may be more easily taken out4 ,the plug-holes should be cut at one foot asunder1 and bored with a jumper #a inch diameter to the depth of #i inches2 and if the plug-holes be deep1 and some difficulty in driving be expected1 the plugs should be carefully greased or oiled previously to being driven4 ,having cut off a block as above described1 an attempt may be made1 if the mass be great1 to throw it down by means of bulling2 but if it be of lesser dimensions1 and there be reason to expect that it may be removed in the ordinary way1 the power of the crane may be applied to draw it down4 ,for that purpose1 the quarrier employs an instrument called a ,dog1 which is a strong short hook1 armed like a pick on the point with steel1 and having a ring in the end of it for the hook of the crane-chain to pass through4 ,having cut a small hole with a pick1 on the upper part of the block which is meant to be removed1 the steeled point of the dog is inserted into it1 in such a manner that the weight of the crane-chain may retain it steadily in its place4 ,five or six men then heave on the crane a strain just as much as they suppose it may bear1 without danger of carrying away any of its fixtures2 and as many men as can find room are1 at the same time1 employed at the top of the rock1 working with crow-bars behind the block1 so as to shake it and loosen its hold4 ,the two parties continue their work reciprocally1 leading and following1--the men at the crane1 still keeping up the strain1 and taking care not to heave so much as to break any of the chains1 while those on the top continue to shake the block by means of the crow-bars1 or throw in stones into the opening1 which is always getting wider between the block and the cliff1 so as to prevent the loosened mass from falling back into its old place4 ,when the block has been drawn as far forward as to appear just ready to fall over the cliff1 one of the most expert men at the crane stands carefully watching the movement of the block2 and whenever the stone begins to fall1 he instantly throws the crane out of the gear1 so as to prevent the wheelwork being pulled to pieces by the tumbling mass getting entangled in the chains1 on which it frequently falls and breaks them to pieces4 ,the operation of taking down large blocks from a great height is very tedious1 and is often attended with much danger1 as the stone1 when it falls on the bottom of the quarries1 makes the shivers among which it alights fly in all directions with a force which nothing can withstand4 #ba ,the plug 7fig4 #ab1 c c71 and feathers 7fig4 #ab1 d d71 are flat pieces of malleable iron1 slightly tapered1 and forming together a kind of compound wedge1 the two feathers being first inserted into the hole1 and the plug being driven between them by a series of gentle blows1 from malls of the weight of from #cj lb4 to #ce lb4 ,an opening being made in the manner above described1 by getting one piece brought down1 the same process is continued by cutting off and taking down pieces of eight or ten tons weight1 until there be as many blocks in the floor of the quarry as can be easily managed at one time4 ,those masses are then arranged by means of the crane in convenient positions for being cut up into blocks of the requisite sizes2 and as all of them are within range of the crane1 they can with its assistance be easily turned over or set in any position4 ,while some of the men are employed in cutting up those blocks1 others are clearing away the rubbish1 and others are boring holes or making ready for a fresh blast4 ,illustration3 ,no4 #ac4 ,if those blocks1 which we have supposed to be brought down to the quarry floor and to be ready for cutting1 exceed seven feet in depth of cut1 their farther subdivision will require the use of the plugs and feathers already described2 but if their depth or thickness fall short of that1 the ordinary iron wedges will answer4 ,if the cut be of the depth of about #f feet1 the wedges must be placed about #c inches apart from side to side2 but if the depth of cut be less1 they may be set #d or #e inches asunder4 ,the method of setting in those wedges is as follows3--,the person who cuts the wedge-holes generally works in a sitting posture1 and if the block will admit of it1 he prefers to bestride it1 with a stone1 as a stool1 under each foot4 ,he works with a pick of #af lb4 weight1 having a handle only #af inches long1 with which he cuts the first hole generally about #c inches from the end of the block4 ,the holes are for the most part about #b inches deep1 and #c inches long1 and must be well cleared out at the bottom with a sharp pick2 and the wedges must be set in a line as fair and straight as possible4 ,cutting wedges of that kind are of iron1 from #g to #i inches long1 and #b inches broad1 and weigh about #g lb4 weight each4 ,when in good order they must not be sharp in the mouth1 but about of an inch thick1 to prevent their grounding in the bottom of the hole2 for if they but touch the bottom of the hole1 they fly out at the first touch of the mall4 ,when the wedges have been all properly arranged for a cut1 the workman proceeds to give each of them in succession a gentle tap1 so as to make them all fast2 and for that purpose he uses a mall about #cj lb4 weight 7fig4 ,no4 #ac71 and having a handle #b feet #i inches long4 ,he then goes over all the wedges1 giving each of them a smart blow in regular1 yet not too rapid succession1 but allowing a little time for the parts of the stone to separate gradually4 ,if the wedges be forced too quickly1 there is great danger of the cut being spoiled by its flying out obliquely at one side1 and thus not reaching throughout the whole depth of the block4 ,the blocks1 when thus subdivided by means of the wedges1 are generally nearly of the size required by the rough moulds sent from the workyard1 and are fit to be carried to the stone-cutter's shed4 ,illustration3 ,fig4 #ad4 ,as a conclusion to the above account of quarrying1 it may perhaps be thought desirable to give some notion of the probable time required to perform certain parts of that sort of work4 ,in boring holes of #a inch to #a inch in diameter1 it may be observed that they are generally done with the hand mall 7fig4 ,no4 #ad71 one and the same person striking with the mall with one hand1 and turning the boring tool for himself with the other2 and in most cases a man will bore #i or #aj inches an hour in granite rock4 ,if the bore be #a inch diameter1 as for plugs1 three men will generally bore two plug holes in one hour1 each hole being about #i inches deep4 ,if the bore be for blasting and of #b or #b inches diameter1 three men will bore1 at the rate of one foot per hour1 to the depth of #f or #g feet2 but if the bore be for a large blast of #ac or #ad feet deep1 the hole must be #c inches in diameter at the top 7diminishing to #b inches at bottom71 and will employ three men working hard between two and three days4 ,bores of that sort1 indeed1 cannot be made 7at least by hand7 to a greater depth than #ad or #ae feet1 as the weight of a rod of iron1 #ag feet in length1 and #b inches in diameter1 makes it quite unmanageable for one man either to turn or to lift2 while1 from its great mass1 the strokes of the mall produce little effect on it4 ,the malls used in boring holes1 which require three men1 are #g or #h lb4 weight1 having handles #c feet long 7fig4 ,no4 #ae71 and are swung over the shoulder1 while striking for down bores1 in the same manner as a smith's forehammer is used4 ,an expert cutter with the wedges will make good wages by cutting holes at the rate of #b;d4 for a dozen of holes1 taking light and heavy cuts as they come to hand4 ,illustration3 ,no4 #ae4 ,what has been said above of boring and blasting refers only to downright or vertical bores2 but1 in the lower parts of a quarry1 it is often necessary to have recourse to what are called breast-bores1 from their running in a nearly horizontal direction and piercing the front or breast of the rock4 ,those bores are not so easily made as the downright bores and1 in general1 are only used where the rock is low1 or in taking up bottom rock4 ,they can seldom be carried to a greater depth than about #i or #aj feet1 owing to the difficulty of turning the jumper1 and can never be bored quite horizontally1 but require as much dip as will retain a little water in the hole to keep the jumper moving4 ,instead of throwing the mass outward1 as is done by down-bores1 those breast-bores generally only cut or break the stone in the direction or line of the bore1 so that the block always requires to be afterwards removed by bulling1 in the manner already described4 ,dressing of the ,lighthouse blocks4 ,the dressing of the blocks for the ,lighthouse ,tower1 as already mentioned1 was one of the most important operations in the workyard at ,hynish2 and as no writer with whom ,i am acquainted has given any account of the mode now practised of dressing granite1 ,i hope ,i shall be excused for attempting1 in this place1 to give some idea of the method employed by the masons of ,aberdeenshire1 whose skill in that department of workmanship is well known both in our own and in other countries4 ,as the whole of the materials for the ,tower were to be dressed in such a manner as to avoid the necessity of any fitting on the ,rock1 by the introduction of what are technically called closers1 the greatest accuracy in the formation of the moulds from which the stones were to be shaped became necessary4 ,with that view1 ,i had a trainer or radius made with a moveable vernier1 capable of sliding along it1 so as to give the differences between the readings of the feet1 as far as to the thirtieth part of an inch2 and ,i was thus enabled to lay off the batter or slope on each course 7according to the quantities in the ,table of ,co-ordinates in the ,appendix7 with great nicety1 and so to trace very distinctly the contour of the intended column4#bb ,on the stone floor of an apartment in one of the workshops1 the quadrant of each course of the building was carefully drawn out1 at full size1 and divided into the sectors which were required for preserving a due bond among the joints of the adjoining courses4 ,the form of each stone in the tower having been thus determined by those full-sized draughts1 moulds1 representing the beds and sides of each stone1 were prepared according to them1 of seasoned timber1 well shielded at the angles with sheet-iron1 to prevent their being injured4 ,those moulds having been marked with reference to the number of the course1 and the position of the stones in the wall1 were given to the foreman of the workyard1 who regulated the work of each of the stone-cutters1 often to the number of #gj men4 ,a proper block having been selected for each stone1 leaving about #a inch all round the extremity of the moulds when applied to its several faces1 it was conveyed1 by means of the sling-cart1 to the shed where it was to be dressed4 ,the shed for dressing granite stones differs in no respect from an ordinary mason's shed1 except in its greater height2 but1 as the stone cutter1 in order to wield his tools to advantage1 must1 at certain parts of the work1 stand on the top of the block1 it has been found1 that a height of about #ae feet is required for the back-wall of a granite mason's shed4 ,each man also requires1 for large blocks1 a space of about #aj feet 7measured along the front of the shed71 as his peculiar territory4 #bb ,such nicety1 ,i would observe1 was by no means superfluous1 because the arrangements of the ,tower precluded the possibility of using a trainer in building2 and as the whole was done by means of plumb-templets1 the greatest accuracy in tracing the curve of the ,tower became necessary1 as the only true basis of good workmanship on the ,rock4 ,when a block has been brought to the shed1 the first thing to be done1 if it is a large stone of #a or #b tons weight1 is to lay it nearly level on the ground1 with the side which is to be first dressed uppermost4 ,the form or plan is then sketched upon it according to the mould1 and the stone is blocked out with a large hammer weighing #cj or #ce lb4 7fig4 ,no4 #af71 which is the most suitable weight for ordinary men1 although a stout man will manage one of #dj lb4 well enough1 if the block be lying in an advantageous position4 ,when the stone has been thus rudely blocked out1 it is set upon its edge with a gentle inclination to one side1 so that the mason1 who mounts on the top of it1 may conveniently use a pick of #ah lb4 weight1 having a handle three feet long1 to dress off very roughly the most prominent parts of its irregular surface4 ,in doing that he makes a great many deep ruts in a downward direction1 at the same time taking care that none of them shall be so deep as to fall below the general surface of the stone when finished4 ,when he has in that style dressed as far down the surface of the stone as he can conveniently reach1 7and that is generally about half way17 the stone is then thrown over and set up on the opposite edge1 when he again mounts upon it1 and goes over the rest of the surface in the same manner1 until the whole shall be reduced to one rough plane1 so that in spite of numerous partial inequalities1 the general face may be straight1 or what is technically termed out of winding4 ,a stone in that state is also said to be well opened4 ,illustration3 ,no4 #af4 ,illustration3 ,no4 #ag4 ,illustration3 ,no4 #ah4 ,the next step is to raise the stone so that it may incline at about #cj or #dj with the horizon2 after which the mason1 standing at the higher side1 commences to put on the draughts or guide-lines all round the edge of the face which he has just opened4 ,for that purpose he first employs a pick of about #ab lb4 weight1 having a handle about #b feet in length 7fig4 ,no4 #ag71 with which he dresses a band of about #c inches broad1 taking care that this band or draught be straight and out of winding4 ,he then1 with the pick1 goes over the whole face between the draughts1 dressing off all the ridges which still remain between the ruts which he had made while the stone was standing on edge1 as before noticed1 so that the whole surface will present the appearance of a pretty regularly dabbed face4 ,having arrived at that stage1 he next proceeds to put on the true draughts 7as round the edges of the stone1 as in the case of the guide-lines71 with the cast-steel chisel or punch 7a1 a1 fig4 ,no4 #ah71 and a small iron-mall of #c lb4 weight2 and afterwards with the axe1 he carefully axes a band about #b inches broad1 so as to be quite out of winding1 and as straight as possible all round4 ,the dressing is then completed between those bands4 ,if the block be a broad one1 the mason will probably be able to take in only one half of the face at a time2 and1 in that case1 the stone must be let down at the high side1 and the other one raised as high as may be necessary to enable him to work to advantage4 ,if the surface thus dressed1 which is in this case supposed to be the largest side1 be intended for the bed of a stone1 the knobs or high points between the pick-dabs are merely roughly dressed down with a blunt axe1 so as to be all as low as the axed lines or draughts round the extremities1 and thus to present no convexity on which the stone1 when laid1 could rock2 but if the surface should be meant for a fine face1 the dressing must be commenced with a bluntish axe1 taking care that all the axe marks be made quite across the stone1 at right angles to the side where the workman stands4 ,the whole face having been once gone over in that manner with a blunt axe1 a sharper and well ground axe is next used for crossing the first axing in such a manner that all the second axe-marks may be inclined at an angle of #de1 or thereby1 with the first4 ,the whole face having been thus brought to a smoother and more uniform surface1 the third and last axing follows2 and then the mason uses his shortest and lightest axe1 which must1 for that work1 be well ground and sharp4 ,that axing must be done right across the block1 or in the same direction as the first axing had been done1 and in that state the surface of the stone may be supposed to be fine enough for most kinds of work used in housebuilding or in public works2 but for very fine work1 such as some sepulchral monuments1 or for surfaces which are afterwards to be polished1 it is not unusual to axe four or even five times1 care being always taken that how often soever that operation may be performed1 the axing should never be made twice consecutively in the same direction1 for by that precaution alone can a true and even surface be obtained4 7,the form of the axe is shewn in fig4 ,no4 #ai47 ,illustration3 ,no4 #ai4 ,illustration3 ,no4 #bj4 ,the dressing of the first face being finished in the manner described1 the block is laid flat on the ground1 and the plan or form of the stone is then accurately drawn on it1 according to the mould1 with some substance that makes a bright or good mark1 such as a piece of tile ground sharp1 or a thin splinter of logwood4 ,if there be much waste to be taken off beyond the lines so drawn1 a hammer1 whose weight must be in proportion to the piece to be struck off1 is applied2 but care must be taken not to come too near the lines with the hammer1 and it is generally safe to leave at least an inch outside of them4 ,the piece which is left gives a good hold for the chipper or pincher 7fig4 ,no4 #bj71 which is next carefully applied along the line1 being steadily held within one hand1 and with the other sharply struck with a small iron mall of #c lb4 weight1 having a short handle about #h inches in length4 ,while the chipper receives sharp strokes in succession with the mall1 it must be slowly moved several times along the line from one end of the stone to the other1 till the piece projecting beyond the line1 or a part of it1 breaks off4 ,such is the power of this small instrument1 that it not infrequently cuts down to a depth of #i or even #ab inches1 thereby doing more execution and to greater purpose1 than a heavy hammer can generally accomplish1 even in the hands of a skilful workman4 ,the chipper is a tool lately introduced2 but has now become a most important article in every hewer's kit4 ,it makes a regular and clean cut1 and leaves little to be done by the punches and chisels 7fig4 ,no4 #ah1 in p4 #abb71 in preparing the arris of the next face of the stone4 ,the block is now raised a little from the ground1 and the workman standing at its higher side1 the axing of which he has just finished1 puts on with the punches and chisel a fine band or draught along the side next to that just dressed4 ,he then applies to the finished face the square or bevel1 according to the inclination of the faces1 and dresses a band across the stone at each end of the block2 and1 finally1 joins those two cross bands by means of another band along the back4 ,in that way the external draughts on the second side are completed4 ,he then with the pick and axe dresses away the material between those draughts until the second face is finished2 and the same process is repeated for each side of the block which requires to be dressed4 ,if the block be a large one1 and it require to be dressed on all its sides1 it will1 lastly1 be cut to the proper thickness or height1 which is regulated by means of a gauge1 known1 in the technical language of the shed1 as 8a grippers0 7fig4 ,no4 #ba71bc from its embracing the stone on three sides4 ,it is simply a three-sided iron templet1 having one long and one short tail 7at right angles to the connecting piece71 the space between the two tails shewing the thickness of the stone4 #bc ,the figure shews 8a grippers0 for a stone #ad inches thick4 ,illustration3 ,no4 #ba4 ,the practical reader will readily see1 that what has been said above about the hewing of granite1 is chiefly applicable to the dressing of the large stones used in public works1 such as docks1 bridges1 or marine towers2 and it may be proper to add1 that such heavy materials are always dressed on the ground1 and that a piece of wood is placed under each end of the stone as a necessary precaution to prevent its being split by the blows of the mall4 ,in dressing the lighter materials for house building1 where a good deal of fine work is generally required1 the stones are laid on what is called a banker1 similar to that which is used in hewing freestone4 ,the banker is a bench of stone #b or #c feet long1 and #b feet broad1 and is raised about #b feet above the ground1 so as to suit the workman's convenience4 ,in dressing one of the outside stones of the first or lowest courses of the ,skerryvore ,tower1 a mason was occupied eighty-five hours 7see ,plans of courses1 ,plate ,,viii472 and in dressing one of the largest of the hearting or inner stones of the same courses1 fifty-five hours4 ,but as the work proceeded1 owing to the greater readiness which the men had acquired in the application of the moulds1 gauges and bevels1 the time occupied1 gradually decreased to the extent of about ten hours for each stone1 until the work had been carried on as far as to the thirteenth course1 where the number of outside stones was reduced to twenty-four1 at which stage of the work1 the time required for dressing increased to about one hundred and twenty hours for each outside stone4 ,from that point upwards1 the time again gradually decreased till we reached the sixty-fourth course1 where it may be stated1 that1 on an average1 a man was employed sixty-three hours in dressing each stone2 but the time gained in the last instance seemed to depend less on the readier application of the implements1 than on the gradual diminution in the size of the stones1 which1 from that level upwards1 decreased along with the thickness of the wall4 ,but above the sixty-fourth course1 a very marked increase in the time of dressing took place1 owing to the introduction of the ribband or ring joggles 7shewn in the ,plans of the #hdth and #idth courses1 ,plate ,,viii472 and to the substitution of the dovetailed joggles in the place of the square or diamond joggles1 which were used in the lower parts of the building4 ,the time required for dressing a stone of the sixty-fifth course was ninety-three hours of one man1 a circumstance which strikingly shews1 that a small1 and1 apparently1 trifling alteration in the style of workmanship may sometimes increase to a considerable extent1 the expense of a great work4 ,each radiating stone of the eighty-fourth course1 which forms the floor that goes quite through the wall1 required one hundred and sixty-one hours for its completion2 and the other radiating floor-stones1 which did not pass quite through the wall to the outside1 occupied one man about one hundred and twenty hours4 ,each centre stone of the floors into which the others were dovetailed1 required about three hundred and twenty hours of one man's time4 ,the time of a labourer occupied in cutting a hole for the dovetailed ,lewis bats1 by which the stones were raised1 was about three hours4 ,the tools necessary fully to equip a granite mason are as follows3--,one dressing hammer about #af or #ah lb4 weight2 #f dressing picks1 from #ab to #bj lb4 weight2 one small hand-mall1 or mash-hammer1 about #d lb4 weight2 #c stone axes about #g lb42 #af or #ah cast-steel punches and chisels1 with one or two chippers or pinchers of #b lb4 weight4 ,one large blocking-hammer of #cj or #cb lb41 may very well serve for eight men4 ,the value of a granite mason's kit may be estimated1 when in good working order1 at about ,l4#g4 ,a very great revolution has taken place during a few years in the method of working granite4 ,the most important change is the substitution of the hand-mall and chisel in the operation of putting the drafts or bands on the stones1 in place of arris-picks1 which made the workmanship clumsy1 tedious and imperfect1 by slowly grinding down the stone at a great expense of labour to the hewer1 who was forced to remain bent forward in an irksome posture1 without the relief which is obtained by occasionally shifting his position1 a change1 which1 every one who has been long employed in any laborious occupation1 knows well how to value4 ,the introduction of the chipper may also be regarded as one of the most important modern improvements in the art of working granite2 and had it not been for those changes1 the actual expense of dressing the blocks for the ,skerryvore ,tower1 as ascertained from the journals of the works1 would have been exceeded by a sum of between ,l4#djjj and ,l4#ejjj2 and it may even be questioned whether it would have been at all practicable with such tools to cut the dovetailed spaces of the floors out of the solid stone4 ,excavation of ,foundation for the ,lighthouse ,tower on the ,skerryvore ,rock4 ,the excavation of the foundation of the ,lighthouse ,tower was the first operation which engaged my attention at ,skerryvore ,rock1 at the beginning of the season of #ahci4 ,it was commenced on the #fth of ,may1 and was continued up to the last hour of our remaining on the ,rock1 on the #c;d of ,september4 ,a more unpromising prospect of success in any work than that which presented itself at the commencement of our labours1 ,i can scarcely conceive4 ,the great irregularity of the surface1 and the extraordinary hardness and unworkable nature of the material1 together with the want of room on the ,rock1 greatly added to the other difficulties and delays1 which could not fail1 even under the most favourable circumstances1 to attend the excavation of a foundation-pit on a rock at the distance of #ab miles from the land4 ,the ,rock1 as already noticed1 is a hard and tough gneiss1 and required the expenditure of about four times as much labour and steel for boring as are generally consumed in boring the ,aberdeenshire granite4 ,after a careful survey of the ,rock1 and having fully weighed all the risks of injuring the foundation1 ,i determined at once to enter upon a horizontal cut1 so as to lay bare a level floor of extent sufficient to contain the foundation pit for the ,tower4 ,the very rugged and uneven form of the ,rock made this an almost necessary precaution1 in order to prevent any misconception as to its real state1 for it was traversed by numerous veins and bands inclined at various angles1 on the position and extent of which the stability of the foundation in no small degree depended4 ,that operation occupied #cj men for #ajb days1 and required the firing of no fewer than #bdf shots1 chiefly horizontal1 while the quantity of material removed did not greatly exceed #bjjj tons4 ,it was a work of some hazard2 for the small surface of the ,rock confined us within #cj1 and sometimes within a dozen yards of the mines1 while its form afforded us no cover from the flying splinters4 ,the only precautions we could adopt were to cover the mines with mats and with coarse nets1 which ,i had caused to be made during the previous winter1 of the old ropes of one of the ,lighthouse ,tenders1 and in each blast to apportion very carefully the charge of powder to the work that was to be done4 ,that was managed with great skill by ,charles ,barclay1 the foreman of the quarriers1 who charged all the bores1 and1 along with myself1 fired all the shots4 ,so completely did the simple expedient of covering the bores with nets and mats check the flight of the stones1 that1 except on one or two occasions1 none of the splinters reached us1 and all the damage done was a slight injury to one of the cranes4 ,perhaps1 also1 our safety may1 in some measure1 be attributed to a change which ,i introduced into the mode of charging the horizontal shots1 by which all the risk of pushing home the powder in the ordinary mode with the tamping rod is avoided4 ,that change consisted in using a kind of shovel1 formed of a rod1 armed with a hollow half-cylinder of sheet copper1 which contained the powder1 and being inverted by giving the rod half a turn round its axis1 made the powder drop out when the cylinder reached the bottom of the bore4 ,it was1 in all respects1 excepting size1 the same as the charging-rod used for great guns4 ,the amount of materials removed by blasting1 as nearly as ,i could ascertain1 was only about #ajjj cubic yards2 and1 taking all the circumstances into account1 it may be doubted whether there be any instance in modern engineering of an operation of so small an extent occupying so much time1 and involving so great risk4 ,the blasting of the ,rock1 however1 was not the only difficulty with which we had to contend1 for it also became necessary to remove the quarried materials1 amounting to about #bjjj tons1 into the deep water round us1 to prevent their being thrown by the waves upon the ,rock1 and so endangering the future temporary ,barrack4 ,that was rather a laborious work1 and occupied two cranes1 with temporary runs and trucks1 during the greater part of the time we spent on the ,rock4 ,i am well aware that the quantity of materials which ,i have just mentioned1 will be apt to produce a smile from those who have been chiefly conversant with the gigantic but simple operations which generally characterize the great railways of this country2 but if it be remembered that we were at the mercy of the winds and waves of the wide ,atlantic1 and were every day in the expectation of a sudden call to leave the ,rock1 and betake ourselves to the vessel1 and on several occasions had our cranes and other tools swept into the sea1 the slowness of our progress will excite less surprise2 and still less will those who duly weigh the dangers of our daily life1 both in our little vessel and on the ,rock1 and who1 at the same time1 reflect on the many striking proofs which we almost every hour experienced of the care of an ,almighty hand1 be disposed to withhold their sympathy from the heartfelt expressions of gratitude which often went round our little circle in the boats1 as we rowed in the twilight from the ,rock to the ship4 ,isolation from the world1 in a situation of common danger1 produces amongst most men a freer interchange of the feelings of dependence on the ,almighty1 than is common in the more chilly intercourse of ordinary life4 ,with a view to lessen the dangers of blasting in such a situation1 ,i had provided a galvanic battery on the plan proposed by ,mr ,martyn ,roberts1 but ,i used it less frequently than ,i intended4 ,the attachments of the wires were very liable to be broken from various causes1 where there were many men congregated in a small space2 and as we could not venture to leave the apparatus on the ,rock1 the frequent re-shipment of it in a heavy sea was another cause of the derangement of its parts4 ,i soon1 therefore1 laid it aside1 and only had recourse to it when any work was to be done under water1 or in cases where the simultaneous firing of several mines 7for which it is admirably adapted7 was of importance in effecting any special purpose4 ,when the floor had been roughly levelled ,i again carefully surveyed the ,rock1 with the view of fixing precisely the site of the foundation-pit1 and of taking advantage of its form and structure to adopt the largest diameter for the ,tower of which the ,rock would admit4 ,in some places ,i found that parts of the ,rock1 apparently solid1 had been undermined by the constant action of the waves1 to the distance of #ac feet inward from its face2 but none of those cavernous excavations reached the main nucleus1 so that1 after much deliberation and repeated examinations of all the veins and fissures1 ,i was enabled to mark out a foundation-pit #db feet in diameter1 on one level throughout4 ,that was a point of no small importance2 and although it had cost great labour at the very outset1 much time was saved by it in the subsequent stages of the work4 ,not only was the labour thereby avoided of cutting the rock into separate terraces1 and fitting the blocks to each successive step1 as was done by ,smeaton at the ,eddystone2 but the certainty that we had a level foundation to start from1 enabled us at once to commence the dressing of stones without regard to any irregularities in the surface of the ,rock2 and the building operations1 when once commenced1 continued unimpeded by the necessity for accommodating the courses to their places in the foundation-pit1 so that the ,tower soon rose above the level1 at which there was the greatest risk of the stones being removed by the waves before the pressure of the superincumbent building had become great enough to retain them in their places4 ,the outline of the circular foundation pit1 #db feet in diameter1 having been traced with a trainer on the rock1 numerous jumper-holes were bored in various places1 having their bottoms all terminating in one level plane1 so as to serve as guides for the depth to which the basin was to be excavated4 ,the depth did not exceed #ae inches below the average level1 already laid bare by the cutting of the rough horizontal floor which has just been described2 and before the close of the season of #ahci1 about one-third of the area of the circle had been cleared1 and was ready for the final pick-dressing which prepared it for the reception of the first course4 ,the excavation of this circular basin was conducted with the greatest caution1 and few shots were permitted to be fired lest the foundation should in any place be shaken by the action of the gunpowder on any of the natural fissures of the ,rock4 ,the work was chiefly done by means of what are called plugs and feathers1 the form of which has already been shewn in the woodcuts 7,no4 #ab1 p4 #aae74 ,in that part of the work the bores were nearly horizontal1 and the action of the plug and feathers was to throw up a thin superficial shelf or paring of rock of from #f to #ab inches in depth1 and not more than #b feet square4 ,by that painful process an area of about #adjj superficial feet was cleared4 ,the chief trouble connected with that operation was cutting1 by means of the pick1 a vertical face for the entrance of the horizontal jumpers or boring rods2 and wherever advantage could be taken of natural fissures it was gladly done4 ,another considerable source of labour was the dressing of the vertical edges of the basin1 as that implied cutting a square check1 #ae inches deep and about #acj feet long1 in the hardest gneiss rock2 and the labour attending which1 can only be fully estimated by a practical stone-cutter who has wrought in such a material4 ,the plan employed was to bore all around the periphery of the circle1 #a inch vertical jumper-holes1 #f inches apart1 to the required depth1 and to cut out the stone between them4 ,the surface thus left was afterwards carefully dressed1 so as to admit vertical and horizontal moulds1 representing truly the form of the masonry which the check was intended to receive4 ,the experience of the labour attending that operation gave me great reason for congratulation on having adopted a foundation on one level throughout1 instead of cutting the rock into several terraces1 at each of which the same labour of cutting angular checks must necessarily have been encountered4 ,the cutting of the foundation occupied #bj men for #bag days in all1 whereof #afh days were in the season of #ahci1 and the rest in the summer of #ahdj4 ,fitting up of the ,second ,barrack on the ,rock4 ,sudden death of ,george ,middlemiss4 ,the minute details given in my account of the destruction of the first ,barrack1 have entirely superseded the need for any particular description of the fitting up of the second ,barrack on the ,rock2 and ,i shall therefore confine myself to a brief notice of the work in the chronological order in which it occurred4 ,on the #ast of ,july1 after the level floor for the foundation of the ,tower had been roughly cleared1 and all risk of injury from the firing of mines was past1 the boring of holes for the fixtures of the second ,barrack was begun2 and so great were our exertions1 that in the short period of fourteen days1 the pyramidal frame-work on which the ,barrack-house was to stand 7see ,plate ,v471 consisting of #ac beams1 of about #ej feet in length1 with all their braces1 ties and stancheons1 and the malleable iron cap which secured their union at the top1 was firmly fixed on the ,rock4 ,after the pyramid was completed1 the ,barrack-house 7which had previously been removed from ,north ,bay1 where1 as already noticed1 it had served as a temporary abode for the men who opened the quarries there71 was transported1 piece-meal1 from ,hynish to the ,rock as required2 for it was not considered prudent1 after the experience of last year1 to trust1 even in the finest part of the season1 a great quantity of timber to lashings on the ,rock4 ,the fitting-up of the ,barrack-house was completed on the #c;d ,september and occupied only eleven days2 so that the whole work extended to only twenty-five days1 a remarkably short time for such a work1 in such a situation4 ,that despatch1 indeed1 was only obtained by working 7as we did both during the excavation of the foundation and the erection of the ,barrack71 at all times when the weather would permit1 from four o'clock in the morning till eight1 and even nine in the evening1 with an interval of only half-an-hour for breakfast and the same for dinner4 ,the erection of the ,barrack was a work of great difficulty and anxiety2 for1 as every thing depended on the exact union of all its parts1 the slightest error in any dimension would have stopped the work until it could be remedied1 a delay which1 in such a situation1 would1 at certain stages of its progress1 have proved fatal to the whole structure4 ,i cannot1 therefore1 omit this opportunity of paying a tribute1 in passing1 to the memory of the late ,mr ,george ,middlemiss1 the foreman of the carpenters who fitted up the ,barrack1 whose zeal for the completion of the work was very conspicuous4 ,poor ,middlemiss died very suddenly at ,hynish1 about a fortnight after the completion of his labours on the ,rock4 ,he had received some instructions from me1 so late as #aa o'clock1 on the night of the #bjth ,september2 and when one of the men went to call him next morning at #f o'clock1 he was found dead1 and in such a state as led ,mr ,moxey1 the surgeon attached to the works1 after a careful examination1 to conclude1 that he had died of paralysis of the heart1 about three hours before he was found1 or not more than four hours after ,i had seen him1 to all appearance1 in perfect health6 ,wharf and ,landing-place on the ,rock4 ,no inconsiderable part of the labour of this season was devoted to the clearing of the landing-place1 which was formed in a natural creek 7see ,plate ,,iii47 and in excavating the rocks in front of the line of wharf1 so as to admit the vessels carrying the building materials to come alongside of it4 ,that work could only be done at certain times of tide and during very fine weather1 and was1 therefore1 tedious as well as hazardous4 ,after two entire days spent in cutting with a sickle1 mounted on a long pole1 the thick cover of gigantic sea-weed1 which hid the true form of the ,rock from view1 we were able to mark out the line of the wharf2 and after all the mines were bored and charged and the tide had risen1 and every one had retired from the spot1 the whole were fired at the same instant1 by means of the galvanic battery1 to the great amazement and even terror of some of the native boatmen1 who were obviously much puzzled to trace the mysterious links which connected the drawing of a string at the distance of about #ajj yards1 with a low murmur1 like distant thunder1 and a sudden commotion of the waters in the landing-place1 which boiled up1 and then belched forth a dense cloud of smoke2 nor was their surprise lessened1 when they saw that it had been followed by a large rent in the rock2 for so effectually had the simultaneous firing of the mines done its work1 that a flat face for a quay had been cleared in a moment1 and little remained to be done1 to give the appearance of a regular wharf and to fit it for the approach of a stone lighter1 except attaching wooden fenders and a trap ladder4 ,ring-bolts1 ,water-,tanks1 and ,railways4 ,a good deal of time was also spent in fixing a great many ring-bolts on various parts of the ,rock and its outlyers1 for the use of the shipping1 which we expected to carry stones to the ,rock the next season and in clearing a line for a permanent iron railway1 about #ej yards long1 from the landing wharf to the ,tower1 the position of which is shewn in ,plate ,,iii4 ,the railway was used for the conveyance of materials from the stone-lighters to the building1 and is now the highway for all the stores which pass from the wharf to the ,tower4 ,means were also taken for laying down two cast-iron water-tanks on the ,rock in tolerably sheltered positions1 as shewn in ,plate ,,iii4 ,one of those tanks was completed and filled with water1 but the sole-plate only of the other was fixed1 as unfortunately one of the plates dropped from the vessel's side into the water1 while the seamen were lowering it into one of the boats1 a loss which prevented the second tank from being finished till the next year4 ,those tanks1 together1 held about #ijj gallons1 and contained our chief supply of water during the whole subsequent progress of the works1 when there were often about fifty men on the ,rock4 ,incidents of the ,season4 ,i shall conclude this ,chapter1 by noticing a few incidents which occurred during the season of #ahci1 serving1 in some degree to throw light upon the peculiar difficulties we had to encounter1 or tending to shew the importance of the work in which the ,commissioners had engaged4 ,effects of a gale from the ,s4,w4 ,on the #ith of ,august a strong gale suddenly sprang up from the ,s4,w41 which1 while it lasted1 caused us much alarm and anxiety at ,hynish1 whither we had been driven from our station at the ,rock to seek shelter at the commencement of the storm4 ,several small pieces of timber1 which we had left on the ,rock when we were forced to leave it1 came ashore in ,balaphuil ,bay2 and it was generally reported in the ,island that the ,barrack had1 for the second time1 been destroyed4 ,that report ,i did not credit1 as ,i had great confidence in the fixtures which attached it to the ,rock2 but my anxiety to ascertain the true state of the case1 led me to examine the south-eastern shore of ,tyree1 when all that could be discovered was a few pieces of loose timber1 and one of the smith's cooling tubs1 which had been washed from the ,rock4 ,next day1 however1 the smith's bellows came ashore in the same ,bay1 and so little injured1 that we had them repaired and put in use again on the ,rock4 ,on the #abth of ,august1 when the weather permitted us to return to our station at the ,skerryvore1 we found all the timbers which had been lashed down with chains to the ,rock scattered in every direction around the beams of the ,barrack1 the smith's forge overturned1 the bellows of course gone2 one of the cranes also which had been used for the removal of the excavated materials had been swept away1 and not a vestige of it left1 except a small piece of one of the wooden stays1 which the force of the waves had broken4 ,but that which most of all surprised us1 and gave us the greatest concern1 as an alarming proof of the force of the sea and a source of great inconvenience and hazard during the rest of the season1 was the disappearance of our moorings1 which had been lost by the foundering of the cask buoy in the heavy surf which the gale had raised4 ,during all the rest of our stay at the ,rock that season1 we were forced to ride at anchor in foul rocky ground of the worst and most irregular description1 over which the vessel frequently drifted to a considerable distance1 occasioning us no small fear for our safety4 ,that was the second set of moorings which had disappeared at ,skerryvore2 and a stronger proof of the very great power of the western swell can hardly be imagined1 as nothing of the kind had happened during the whole time the ,bell ,rock works were in progress4 ,that circumstance also convinced us of the necessity of adopting vessels of small burden for landing the materials4 ,so great1 indeed1 was the difficulty of hanging even the boats at the ,rock1 that on two occasions 7on the nights of the #dth ,may and #abth ,july7 we had both the boats half filled by the sea1 and nine or ten men thrown out on the ,rock by the kanting of one of the boats at the recoil of the wave4 ,the landing department was indeed1 throughout the whole season1 attended with great difficulty1 and was to me a source of constant anxiety2 for1 in the daily transport to and from the vessel and the ,rock of #cj men1 unaccustomed to boating1 during a period of four months1 it was more than could have been expected that we should have been preserved from the loss of either life or limb4 ,on the night of the #c;d ,september1 when we left our anchorage at the ,skerryvore for the season1 every heart was full of rejoicing1 and many cordial expressions of gratitude to our ,almighty ,protector were uttered in deep whispers by the more seriously disposed men1 whose number bore a goodly proportion to our whole band4 ,i cannot omit saying1 in this place1 that both ,mr ,macurich1 who acted as landing-master on the ,rock1 and the late ,mr ,heddle1 the master of the steam-tender1 conducted the boating department in a most masterly style4 ,mutiny of the ,crew4 ,as an aggravation of our difficulties1 we were occasionally much annoyed by the unprincipled and cowardly conduct of a few of the seamen1 who1 despite the contempt of their comrades1 fearing or pretending to fear the risk of lying all night so near the face of the ,rock1 spared no pains to spread alarm1 and made several attempts1 by threatening desertion1 to extort a rise of wages4 ,they even spoke of leaving the vessel at the ,rock1 which they could easily have done by some of the native boats which called in passing to see the progress of the works2 and ,mr ,heddle1 the master of the steamer1 was forced to dismiss the mutineers on the first occasion when the vessel was driven for shelter to the land1 and to rely during the rest of the season on the native boatmen to supply their place4 ,that firm conduct had1 for some time afterwards1 the desired effect on those who remained2 but the spirit of disaffection having spread pretty widely1 we had subsequently several other instances of sudden desertion from the service4 ,near approach of ,vessels to the ,rock1 and other circumstances shewing the importance of a ,light on the ,skerryvore4 ,in the course of my residence for four months on board the tender moored off the ,rock1 ,i had opportunities of witnessing many proofs of the great necessity which existed for a ,light on the ,skerryvore2 and if ,i had ever entertained any doubt as to the beneficial effects of such an establishment1 the experience of the season of #ahci must have entirely removed it4 ,it often happened that for several days successively1 not fewer than five or six vessels of large size1 both outward and homeward bound1 were visible at distances varying from #c to #f miles from the ,rock2 and much anxiety was often felt by us for the safety of those vessels1 several of which approached so near the outlying rocks as to keep us for some time in the most painful suspense4 ,on two occasions1 more especially1 ,i was about to direct the steam to be raised1 in order that the ,skerryvore tender might be sent to warn the masters of vessels of their danger1 or if too late for that1 to afford them assistance in case of accident4 ,on the #bith of ,may a large schooner1 and on the #acth of ,june a large brig ran right down upon the western outlyers1 called ,,fresnel',s ,rocks 7which were covered at the time71 and just put about in time to avoid striking2 and on the #abth ,june1 a fine foreign barque 7apparently a ,prussian7 passed so close to ,bo-,rhua as to leave us for a short time in doubt whether or not she had struck on it4 ,on the #bast of ,june1 also1 a large brig came very near the rocks which lie off ,tyree1 at the base of ,ben-,hynish1 in trying to avoid ,boinshley ,rock1 which lies about #e miles to the ,n4,w4 of the ,skerryvore4 ,those circumstances1 together with the list of shipwrecks already given at page #bc1 afford strong proofs that the ,skerryvore ,rock occupies a most fatal position in a great fairway much frequented by large vessels bound to or from ports in the ,irish ,sea and in the ,clyde4 ,there cannot be a doubt that many vessels have been wrecked on the ,skerryvore and its numerous outlyers1 being borne down upon the reef by the strong tide which runs at the rate of between four and five miles an hour at the height of spring tides2 and the natives of ,tyree have many stories about chains and anchors and hidden treasures1 with which their fancy has filled every nook of the ,rocks4 ,to what extent those stories1 which are often most circumstantially told1 may be true1 it is not easy to determine2 but in the end of ,july #ahci1 we succeeded1 under the guidance of a native boatman1 in raising from a creek in one of the detached shelves to the south-west of the main ,rock1 an anchor worn by the action of the sea to a mere skeleton1 a circumstance which so far corroborates the truth of their traditions4 ,,chapter ,,vi4 ,,operations ,,of #ahdj4 ,in describing the progress of the works during the season of #ahdj1 ,i shall speak of the various departments separately1 as in the last chapter1 beginning with the workyard at ,hynish4 ,hynish ,workyard4 ,during the preceding winter months1 the establishment at ,hynish was reduced to about fifty persons1 of whom twenty-seven were masons employed chiefly in dressing blocks for the ,lighthouse1 in laying the stone platform in the workyard 7on which each course was adjusted previously to its being shipped for the ,rock1 to prevent the occurrence of mistakes which might not be easily remedied there71 and in building some additional barracks1 masons' sheds and a limekiln for the summer of #ahdj4 ,the quarriers and labourers formed a party of about eighteen1 and were engaged in cutting blocks in the ,tyree quarries1 which1 although unfit for the ,lighthouse ,tower1 were very suitable for the completion of the ,pier at ,hynish2 while nine carpenters had full occupation in making moulds for dressing the ,lighthouse blocks1 preparing oaken treenails to be used in the lower courses of the ,lighthouse ,tower1 and in dressing handles for the masons' and quarriers' tools4 ,in the month of ,april1 a reinforcement of thirty-seven masons from ,aberdeen arrived at ,hynish2 and the greater number of them were at once employed in the dressing of stones for the ,tower2 while a few assisted in building the dressed materials in a temporary manner on the stone platform in the workyard already mentioned4 ,the number of masons in the workyard1 during the summer months1 varied considerably1 according to the state of the works on the ,rock1 where seldom fewer than thirty men were stationed throughout the whole working season4 ,but the dressing of the stones for the ,tower proceeded with considerable vigour2 and notwithstanding the inroads necessarily made upon the men's time1 by their being frequently required to assist in the landing of materials from ,mull1 a work for which few of the ,tyree men were fit1 from their awkwardness in the management of cranes and all kinds of machinery or tackling1 and also by the constant detachment of a considerable number both of men and of tools for the laborious work of dressing the foundation-pit at the ,rock1 upwards of #bj1jjj cubic feet of granite had been dressed and fitted on the platform1 when ,i left ,hynish in the end of ,october #ahdj4 ,hynish ,pier4 ,during the whole of the summer1 the traffic at the pier at ,hynish was so great in landing materials from the ,mull quarries1 and in shipping stones for the ,rock1 that much inconvenience was felt from want of room4 ,nearly #djjj tons were shipped and discharged at the quay1 independently altogether of the ballasting of each vessel which discharged at the pier1 and the receiving1 storing1 and finally supplying coals to the steamer1 which formed no inconsiderable item of the labour4 ,every exertion was made to extend the pier1 so soon as the works at the ,rock were closed for the season and the stone trade with ,mull had ceased2 and by great perseverance on the part of ,mr ,james ,scott1 the foreman of the workyard1 whom ,i always found ready1 night and day1 to second and even to anticipate my wishes in regard to the progress of the works1 an additional length of #cf feet was added to the berthage of the quay before the winter had set in4 ,the ,rock4 ,the first landing on the ,rock1 for the purpose of resuming the work in #ahdj1 was on the #cjth ,april1 when all things connected with the ,barrack were found in nearly the same state in which we had left them seven months before4 ,the red paint with which we had coated it had become nearly white1 partly by a covering of sea-salt1 and by blanching of the paint itself1 but chiefly towards the top by the soil of the numerous sea-fowl which had perched on the roof4 ,the timbers1 also1 bore the signs of being wave-washed1 and in the more sheltered parts were tufted with the finer kinds of seaweed2 the iron-work was much rusted and entirely divested of paint4 ,the door had been firmly secured with lashings and bolts1 and some difficulty was experienced in forcing an entrance into the interior1 about the state of which1 as our future abode1 much curiosity was naturally felt by the men1 who were desirous to know how it had weathered a seven months' exposure to the waves of the ,atlantic4 ,it was with no small pleasure1 therefore1 that1 when the door was opened and the windows unbarred and the sunshine admitted to dispel its gloom and chilly damp1 we found1 that although the water had forced its way through some of the imperfect seams in the window-frames1 the interior shewed evident signs of the stability of the fabric1 and was in some places so dry1 that the greater part of the biscuits which we had left the year before1 as a store for shipwrecked seamen who might find their way to the ,rock1 although some of them were wet and pulpy on the side nearest the outer walls1 admitted of being dried1 and when a little toasted at the fire1 were palatable enough to hungry men1 so that1 in fact1 we consumed the greater part of that stock before we entered on our new supply4 ,the most important change which had occurred during the winter1 was the removal of a mass of rock in the neighbourhood of the foundation-pit1 which had been shaken by the effects of the blasting operations of the previous year4 ,that mass1 the moving of which shewed that a great weight of water had passed over the ,rock1 weighed about five tons1 and had been detached from its bed during a heavy gale from the ,n4,w41 in the month of ,march1 and carried right across the foundation-pit to the ,barrack1 against one of the beams of which it had rested1 and had partially injured the iron collars or glands by which the beam was secured4 ,the stone was broken into small fragments by a party of men1 who had been appointed to visit the ,rock after heavy gales1 and had landed on the #bgth of ,march1 to see the state of the ,barrack4 ,the men1 in their anxiety to break down the block1 which they feared might injure the ,barrack1 if thrown against it by the waves1 and allured by the smoothness of the sea1 most imprudently remained all night1 mooring their boat in the landing creek1 and trusting to the scanty stock of provisions which they had brought out1 with the intention of at once returning to ,hynish4 ,the risk involved in such a proceeding1 we afterwards had many opportunities of knowing during our stay on the ,rock1 as we were often forced to make fast all our materials1 to prevent their being washed away by the sudden rising of the waves1 especially about the time of high-water in spring-tides4 ,the discomforts1 however1 experienced by the men on that occasion while in the ,barrack1 without fire1 light or bedding1 in a cold dark night of spring were such1 that several of them did not afterwards much affect the ,rock as a residence even in summer4 ,life in the ,barrack4 ,owing to the great difficulty of landing on the ,rock in the early part of ,may1 few opportunities occurred of preparing the ,barrack as a habitation2 and it was not until the #adth of that month that we were enabled to take up our quarters in it2 and even then we were most uncomfortably lodged1 as many of the smaller fittings which are essential to a wind-and-water-tight habitation had not been completed4 ,during the first month we suffered much from the flooding of our apartments with water1 at times when heavy sprays lashed the walls of the ,barrack with great violence and also during rainy weather2 and in northerly gales we had much difficulty in keeping ourselves warm4 ,on one occasion1 also1 we were fourteen days without communication with the shore or the steamer2 and during the greater part of that time we saw nothing but white fields of foam as far as the eye could reach1 and heard nothing but the whistling of the wind and the thunder of the waves1 which were at times so loud as to make it almost impossible to hear any one speak4 ,for several days1 the seas rose so high as to prevent our attempting to go down to the ,rock2 and the cold and comfortless nature of our abode reduced all hands to the necessity of seeking warmth in bed1 where 7rising only to our meals7 we generally spent the greater part of the day listening to the howling of the winds and the beating of the waves1 which occasionally made the house tremble in a startling manner4 ,such a scene1 with the ruins of the former barrack not #bj yards from us1 was calculated only to inspire the most desponding anticipations2 and ,i well remember the undefined sense of dread that flashed across my mind1 on being awakened one night by a heavy sea which struck the ,barrack1 and made my cot or hammock swing inwards from the wall1 and was immediately followed by a cry of terror from the men in the apartment above me1 most of whom1 startled by the sound and tremour1 immediately sprang from their berths to the floor1 impressed with the idea that the whole fabric had been washed into the sea4 ,the alarm1 however1 was very short and the solemn pause1 which succeeded the cry1 was soon followed by words of reassurance and congratulation4 ,towards the end of the fourteen days ,i began to grow very uneasy1 as our provisions were drawing to a close2 and when we were at length justified1 by the state of the sea on the rock1 in making the signal to those on shore 7at the hour fixed for pointing the telescope at ,hynish on the ,barrack71 that a landing could be effected1 we had not more than twenty-four hours' provision on the ,rock1 so that when the steamer came in sight she was hailed by all hands with the greatest joy6 ,the construction of the ,barrack has already been very fully described1 and a glance at ,plate ,v4 will be sufficient to give a pretty correct idea of the nature of our singular dwelling4 ,immediately under the wooden tower was an open gallery1 the floor of which was removed at the end of each season1 so as to allow free space for the passage of the sea during the storms of winter1 but on which1 during the summer1 we kept the stock of coals1 the tool-chests1 the beef and beer casks1 and other smaller materials which we could not1 even at that season1 safely leave on the ,rock itself4 ,next came the kitchen and provision store1 a six-sided apartment about #ab feet in diameter and somewhat more than #g feet high1 in which small space1 curtailed as it was by the seven beams which passed through it1 stood a caboose1 capable of cooking for forty men1 and various cupboards and lockers1 lined with tin1 for holding the biscuits1 meal1 flour1 barley and other things needful for the sustenance of the human frame4 ,that apartment1 for protection against fire1 was coated1 partly with tin and partly with sheet-lead1 which latter1 although not in all respects the most desirable material to come in contact with that element1 was found to be the only one which we could in some parts conveniently apply4 ,the next storey was divided into two apartments1 whereof one was shared by ,mr ,thomas ,macurich1 who superintended the landing of all the materials and ,mr ,charles ,stewart1 the foreman of the builders1 and the other was allotted to myself4 ,the apartments thus occupied consisted of a twelve-sided narrow space twisted around a centre pyramid1 whose bevelled faces formed1 as will in part be seen by inspecting ,plate ,v41 their sloping walls on one side4 ,the half of that space constituted my apartment1 which1 ,i think1 would be generally pronounced not over commodious2 and when it is added that it contained my bed1 desk1 chair and table1 and a stock of groceries1 it will readily be imagined ,i had little room to spare for myself4 ,so much attention was paid to economy of space1 that the recesses of the pyramid formed by the meeting of the beams were boarded over and made into cupboards2 while my cot1 or framed hammock 7which1 during the night1 rested upon brackets which could be folded close to the wall when not required71 was1 during the day1 hoisted by pullies to the roof of the apartment1 so as to leave me as much space to move about in as a prisoner could expect4 ,the cornice of the apartment consisted of a narrow shelf adorned with books1 which ,i found very needful helps to solitary life4 ,the highest apartment was also twelve-sided1 surmounted by a pyramidal roof and a small six-sided lantern or ventilator1 and was lined round the sides with four tiers of berths1 capable of accommodating thirty people4 ,the closeness of that room was most intolerable1 especially during the heat of fine weather in summer1 at which time several of the men preferred taking a nap on the rock1 with the clear blue sky for a canopy4 ,the economy of our life on the ,rock was strange enough4 ,at half-past three in the morning we were called1 and at four the work commenced1 continuing till eight1 when half-an-hour was given for breakfast3 after which it was carried on till two1 when another half-hour was given for dinner2 and the work was again resumed and continued till seven1 eight1 and even nine o'clock1 when anything urgent was in hand4 ,supper was then produced and eaten with more leisure and comfort in the cool of the evening4 ,such protracted exertion produced a continual drowsiness1 and almost every one who sat down fell fast asleep4 ,i have myself repeatedly fallen asleep in the middle of breakfast or dinner2 and have not unfrequently awakened1 pen in hand1 with a half-written word on the paper6 ,yet life on the ,skerryvore ,rock was by no means destitute of its peculiar pleasures4 ,the grandeur of the ocean's rage1 the deep murmur of the waves1 the hoarse cry of the sea-birds1 which wheeled continually over us1 especially at our meals1 the low moaning of the wind1 or the gorgeous brightness of a glassy sea and a cloudless sky1 and the solemn stillness of a deep blue vault1 studded with stars1 or cheered by the splendours of the full moon1 were the phases of external things that often arrested our thoughts in a situation where1 with all the bustle that sometimes prevailed1 there was necessarily so much time for reflection4 ,those changes1 together with the continual succession of hopes and fears connected with the important work in which we were engaged1 and the oft-recurring calls for advice or direction1 as well as occasional hours devoted to reading and correspondence1 and the pleasures of news from home1 were more than sufficient to reconcile me to1 nay1 to make me really enjoy1 an uninterrupted residence1 on one occasion1 of not less than five weeks on that desert ,rock4 ,foundation-pit4 ,during the first half of the season #cj men were engaged #ad hours a day in the preparation of the foundation-pit1 which1 as already said1 was a work of the greatest labour4 ,the ,rock1 indeed1 was in many places so hard as often to make it seem hopeless that tools could make any impression on it4 ,the time employed in the excavation and the number of tools expended on it1 were very great1 as a pick seldom stood more than three strokes in the harder quartzose veins2 but our perseverance was at length amply rewarded by obtaining a foundation so level and so fairly wrought throughout the whole area of a circle #db feet in diameter1 as to present to the view the appearance of a gigantic basin of variegated marble2 and so much pleased were the workmen themselves with the result of their protracted toil1 that many of them expressed serious regret that the foundation must soon be covered up so1 as 7we trusted71 never to be seen again4 ,in the dressing of the ,rock much inconvenience arose from the small splinters which flew out before the tools1 sometimes rising to the height of #dj feet1 and coming in at the windows of the ,barrack2 and after several injuries had been sustained1 ,i at length found it necessary to send to ,glasgow for fencing masks to protect the men's faces4 ,in all our work1 nothing was more grudged than the occasional loss of half a day in baling out the water from the foundation-pit after it had been filled by a heavy sea4 ,landing of materials on the ,rock4 ,before we had made an actual trial of landing stones on a ,rock at the distance of #ab miles from the nearest shore1 exposed to the incessant beating of ,atlantic waves1 there was much room for doubt as to the measure of success to be expected2 and1 as the time approached1 ,i naturally looked to the attempt with increasing anxiety1 as to an experiment in a great measure decisive of the future complexion of our operations4 ,four small vessels1 carrying from #af to #ai tons1 had been built at ,leith and ,dumbarton1 for the purpose of carrying the stones on their decks1 so as to admit of their being easily lifted by the crane1 and so to avoid the risk which would have been incurred by any attempt to raise stones by a crane from the hold of a vessel moored to a rock in the open sea and moving about with every wave4 ,had that been attempted1 the crane would1 on many occasions1 have been pulled down before the stone could be cleared from the hold4 ,the vessels were very similar to those which were used for the same purpose at the ,bell ,rock2 and ,i therefore beg leave to refer the reader to page #eji1 and to ,plate ,,xi4 of my ,father's account of that work1 for a description of them4 ,being decked all over1 to give room for cargo 7for they carried nothing in the hold but empty casks for the purpose of floating them in the event of their sustaining any injury71 they were towed between ,hynish and the ,rock by the steamer1 and being cast off as near the landing-place as possible1 were taken by the boats to the creek1 and moored with warps to the fenders at the quay4 ,the first trial of the lighters in landing stones on the ,rock was made on the #bjth of ,june1 on which occasion both the steamer and the stone craft were decorated with flags2 and due honour was done to the occasion of landing the first stone1 by firing a salvo shot and drinking success to the works4 ,the landing service throughout the whole progress of the works was one of much difficulty and anxiety and many narrow escapes were made2 but it was managed with great prudence1 and at the same time with unremitting energy1 by ,messrs ,macurich and ,heddle1 in their several departments1 both ashore and afloat4 ,on many occasions the men who steered the lighters ran great risks2 and it was often found necessary to lash them to the rails1 to prevent their being thrown overboard by the sudden bounds of the vessels1 or being carried away by the weight of water which swept their decks as they were towed through a heavy sea4 ,sometimes1 also1 we were forced1 owing to the rush of the sea into the creek1 which threatened to lift the vessels on the top of the ,rock1 to draw out the loaded lighters from the wharf without landing a single stone1 after they had been towed through a stormy passage of #ac miles2 and one day1 during the very best part of the season1 so sudden was the bounding of the vessel before the sea1 that eight large warps were snapped like threads as the lighter was carried violently before a crested wave which rolled unexpectedly into the creek1 while those who stood on her deck were thrown flat on their faces and imagined that the vessel had been laid high and dry on the top of the ,rock4 ,during the whole season1 however1 in the course of landing #hjj tons of masonry on the ,rock1 too often in that dangerous manner1 none of the dressed stones received any great damage1 nor was any other injury of importance sustained4 ,building the first stone4 ,the building of the ,tower was commenced on the #dth ,july2 but it was not till the #gth that the ceremony of laying the foundation-stone was performed by ,his ,grace the ,duke of ,argyll1 who1 as proprietor of the adjacent ,island of ,tyree1 took a great interest in the success of the works1 and on that day visited the ,skerryvore with the ,duchess of ,argyll1 the ,marquis of ,lorne1 ,lady ,emma ,campbell1 and a party of friends1 in the ,toward ,castle steamer4 ,on that occasion ,his ,grace expressed himself much pleased with the works and kindly left with me a donation of ,l4#aj for the workmen4 ,the building operations in #ahdj were entirely carried on by means of two cranes with moveable jibs1 of which one was fixed just beyond the foundation1 at the place shewn in ,plate ,,iii41 between the landing quay and the ,tower1 and was chiefly used in bringing forward the materials2 and the other1 placed in the centre of the ,tower1 served for laying the stones1 and was raised along with the rise of the building4 ,so perfectly had the stones been dressed in the workyard at ,tyree1 that no alteration or paring of the beds or joints was required2 and such was the facility afforded by the building apparatus1 that by working #ad hours1 we occasionally set1 through the activity of ,mr ,charles ,stewart1 the foreman builder1 so many as #he blocks in a day4 ,the first course of masonry was laid by means of a wooden trainer2 but the place of all the subsequent stones was1 as already noticed1 regulated by the use of plumb-templets1 whose inner faces were arcs of the generating hyperbola4 ,by those means we succeeded in setting1 in a most perfect manner1 six courses1 which carried the building to the height of #h feet #b inches1 and contained a mass equal to #aj1ghj cubic feet4 ,that quantity is not greatly less than the whole materials of the ,eddystone ,lighthouse ,tower1 which1 according to my computations from the drawings of ,,smeaton1 do not exceed #ac1cjj cubic feet1 and is somewhat more than one-third of the contents of the ,bell ,rock ,tower1 which are about #bh1ejj cubic feet4 ,that frustum was also nearly equal to one-fifth part of the whole mass of the proposed building1 which is about #ef1jjj cubic feet4 ,of the six courses1 the first three are of ,hynish gneiss1 and the rest are of granite from the ,ross of ,mull4 ,the comparative merits of those two materials may be stated as follows3--,the ,hynish stone is harder1 and susceptible of finer workmanship1 and perhaps its most perfect blocks are more durable2 but it requires much more labour in dressing than the ,mull granite1 which is more homogeneous in its structure and is not intersected by hard veins1 like those which occur in the gneiss of ,tyree4 ,there is good reason also for concluding that the ,mull stone is sufficiently durable1 because it contains but a small proportion of micaceous matter1 and in its texture closely resembles some of the blocks of ,st ,oran's chapel in the neighbouring ,island of ,iona1 which have resisted the action of the weather1 it is believed1 for more than #fjj years and still retain the marks left by the tools of the workmen4 ,i had also carefully compared the density of the ,hynish and ,mull stones1 by weighing blocks of known dimensions1 and found that it requires #acaf cubic feet of the former1 and #acff cubic feet of the latter to weigh one ton1 a difference much less than the appearance of the stone would lead one to expect4 ,a ,tower of the dimensions of that at ,skerryvore1 built entirely of ,hynish stone1 would have weighed about #dcjh tons1 while the same mass of ,mull stone would weigh #dbeb tons1 leaving a difference of not more than #aef tons in favour of the ,hynish stone4 ,the mortar employed in the building was composed of equal parts of ,aberdda lime and ,pozzolano earth1 and was therefore identical1 in its composition1 with that used by ,smeaton at the ,eddystone4 ,not having been able1 after searching the neighbouring islands1 to obtain good sand1 ,i found it inexpedient to adopt the proportion of equal parts of lime1 sand1 and ,pozzolano1 which were so successfully used at the ,bell ,rock2 but so perfect was the adhesion of the mortar used at the ,skerryvore1 that in that mass of #hjj tons only two small leaks were discernible1 which being ripped or opened with an iron1 and allowed to run dry1 were afterwards carefully repointed1 and have never since shewn the slightest symptoms of leaking4 ,,chapter ,,vii4 ,,operations ,,of #ahda4 ,hynish workyard4 ,the workyard at ,hynish presented a very busy scene during the summer and winter of #ahdj2 and the desolation and misery of the surrounding hamlets of ,tyree seemed to enhance the satisfaction of looking on our small colony1 where about #aej souls were collected in a neat quadrangle of cleanly houses1 conspicuous by their chimnies and windows amongst the hovels of the poor ,hebrideans1 who generally make no outlet for the smoke in their gloomy dwellings1 but permit it to escape by the doors4 ,the regular meals and comfortable lodgings and the cleanly and energetic habits of the ,lowland workmen1 whose days were spent in toil and their evenings1 most generally1 in the sober recreations of reading and singing1 formed a cheering contrast to the listless1 dispirited1 and squalid look of the poor ,celts1 who have none of the comforts of civilized life and are equally ignorant of the value of time and the pleasures of activity4 ,the number of masons employed in #ahda1 varied from #fj to #hd and they were chiefly engaged in dressing blocks for the ,lighthouse-,tower1 in discharging the cargoes of vessels loaded with stone from ,mull and also in shipping stones for the ,rock1 in which operation1 their acquaintance with the handling of dressed materials and their readiness in working the cranes1 made them very useful in directing and also in working along with the native labourers1 who1 partly from incapacity and partly from excessive indolence1 could not be trusted for a moment to themselves4 ,during that year1 upwards of #ch1jjj cubic feet of granite were dressed into blocks with straight beds and joints1 and with faces of double curvature1 so as to suit the contour of the ,tower1 when arranged in the wall4 ,the blocks were also fitted with stone joggles1 for retaining them in their places1 and with lewis-holes for raising them in the manner usually practised in building materials of that description4 ,of those materials upwards of #gj blocks were floor-stones 7see ,plans of #hdth and #heth courses1 ,plate ,,viii471 dovetailed on the heads1 checked on the joints and having a plain surface on the upper and a concave one on the under bed4 ,the necessity of preserving throughout their entire joints a perfect uniformity of bearing1 made the dressing of those materials a work of great nicety2 and each stone1 as before noticed1 being cut according to moulds1 was fitted temporarily in its place on the platform at ,hynish1 previously to its being laid aside as ready for transport to the ,rock4 ,those various operations were conducted with great care2 and the stones1 which were regularly arranged and numbered according to a schedule1 formed1 at the time ,i left the workyard in the end of ,october1 a considerable pile1 bearing ample testimony to the diligence and zeal of ,mr ,james ,scott1 the foreman of the workyard and leader of the party ashore4 ,the ,rock4 ,owing to the uncertain and stormy weather in spring1 it was not till the #acth of ,may1 that the first landing was effected on the ,rock4 ,the result of our visit1 however1 was most satisfactory4 ,we found the ,barrack quite as we had last seen it six months before2 and not one joint of the pile of masonry1 which we had left exposed to the waves1 had been shaken or started4 ,the ,railway and ,landing ,wharf1 although much exposed to the breach of the sea1 had survived the winter's storms with no greater damage than the loss of one of the sleepers or beams1 on which the rails rested1 which had been torn by the waves from its fixtures to the rock4 ,it was not till a week after our first landing that we were enabled again to take up our quarters on the ,rock2 for we had few landings in the mean time1 and some of them1 owing to the heavy surf which played round the ,rock1 were of no very satisfactory kind4 ,our first experience of this season was indeed far from inviting4 ,so difficult was the first landing1 that we were forced to direct all our endeavours to laying in a small stock of provisions in the ,barrack1 before being left on the ,rock2 and1 considering the scanty nature of the supplies which the weather permitted us to secure1 it was thought prudent to restrict the number of men to eight masons and myself1 with as many tools as we could land1 to enable them to make the necessary repairs and arrangements before fairly commencing for the season the works of a more strictly progressive character4 ,the vessel then returned to ,tyree with the rest of the men and all the heavy apparatus which we could not land2 and1 to add to the unpleasantness of being left in such a position1 with the improbability of a visit from the vessel for several days1 one of the masons took alarmingly ill soon after the steamer was too far off for a signal1 and suffered so acutely during the whole night1 that his piercing cries in the spasms which accompanied his disorder1 combined with the howling of a strong north-wester and the incessant lash of the waves1 deprived the whole party of sleep during the first night4 ,in this uncomfortable predicament1 until the steamer returned on the #bb;d1 we spent two days exposed to winds piercingly cold and in apartments soaked with spray1 which found its way through inlets which had been made by the winter's storms4 ,we were not sorry1 at the same time1 to have an opportunity of removing the poor man to the care of ,dr ,campbell1 the surgeon who was attached to the workyard at ,hynish and of reinforcing our stock of provisions and the detachment of men4 ,we also succeeded in landing the cranes and other building apparatus1 which1 owing to the heavy surf on the #bjth1 we had not been able to accomplish4 ,the few first days after getting fairly established in our habitation for the season1 were occupied in extending the railway to a point on the northern part of the ,rock1 somewhat sheltered during certain seas 7see ,plate ,,iii471 where a crane for stowing the materials previously to building them had been erected2 and thus it was not till the #beth of ,may that the first cargo of stones was landed4 ,next day a crane 7then thirty-four years old71 which had been used in the building of the ,bell ,rock ,lighthouse1 was placed on the top of the masonry1 and the more cheering operations of mixing the mortar and of setting stones were begun4 ,in spite of the unfavourable state of the weather and the continual distraction of our exertions1 occasioned by storms and the landing of materials1 we continued our operations with such vigour as to complete the solid part of the masonry of the ,tower on the #hth ,july4 ,until the building had reached to the level of #ae feet1 the work was carried on by the use of two jib-cranes1 one on the ,rock and the other on the ,tower1 by means of which latter the stones were set1 after being brought to hand by the first4 ,but above that level1 shear-legs similar to those used at the ,eddystone1 were employed4 ,those shear-legs were about #ej feet high1 and were erected in the situation1 at the side of the ,tower1 shewn in ,plate ,,iii4 ,they consisted of two spars attached at the base to jointed sockets batted into the ,rock1 and connected at the top by means of a crosshead of timber4 ,the jointed sockets permitted the shears to hang forward at any angle suited to the level and distance of the part of the ,tower to be reached2 and chain guys both in front and behind1 secured them from falling either backwards or forwards4 ,at the crosshead hung an iron sheave with a chain1 one end of which was provided with a hook for raising stones1 while the other was wound around the barrel of a crab machine well batted down to the rock1 by working which the blocks were raised to such a level as to be within reach of the building crane on the top of the masonry4 ,the shear-poles were used1 until the building of the ,tower was completed1 to raise the stones the first lift of forty feet above the ,rock4 ,in the later stages of the work1 the stones1 instead of being taken by the building cranes directly from the shear-poles1 were raised from storey to storey by means of crabs placed inside the ,tower1 which worked chains1 reeved through sheaves hanging from the end of beams projecting from the windows4 ,such beams are called needles1 and are described at page #ejd1 and shewn in ,plate ,,ix41 fig4 #c1 of my ,father's ,account of the ,bell ,rock ,lighthouse1 where they were used for the same purpose4 ,the ,waves4 ,colours of breaking ,waves4 ,during the early part of the season the weather was intensely cold1 with showers of sleet and heavier showers of spray1 which dashed round us in all directions1 to the great discomfort of the poor masons1 whose apartments did not admit of a large wardrobe1 while they had not the benefit of much room for drying their clothes at the small coboose or cooking-stove in the ,barrack4 ,for days together1 also1 the men were left without building materials1 owing to the impossibility of landing them1 or1 what was worse1 without the power of building what we had on hand in consequence of the violence of the winds4 ,during such times we often felt much anxiety about the safety of the stones which we had piled on the rock ready for being built2 and it took no small trouble1 by the occasional application of the crane1 to save them from being swept into the sea by the surf4 ,nothing struck me more than the illusive effect produced on the mind by the great waves which rolled past the rock4 ,the rapidity of their movements1 and the noise which accompanied their passage through the gullies and rents of the rugged reef1 seemed to give them the appearance of being much larger than they really were2 and1 even when viewed from the ,tower1 after it had risen to the height of #cj feet1 they seemed1 on approaching the rock1 to be on the eve of washing right over the top of the building and sweeping all before them into the sea4 ,it was a long time before1 by continually watching the waves and comparing their apparent height with the results of their impact on the rock1 we were enabled to correct our notions of their magnitude1 so as to mark the approach of their crested curling heads with composure2 and some of the party never became sufficiently familiarized with those visitors1 to avoid suddenly looking round when the rush of a breaker was heard behind them1 or recoiling a few paces when they saw its towering crest apparently about to burst in a torrent over their heads4 ,it was only after a long residence on the rock and continual experimental observation1 that ,i acquired confidence to approach within a few feet of the point which ,i expected the breakers to reach4 ,i occasionally suffered for my temerity1 by being thoroughly drenched with spray2 but by long perseverance1 ,i attained considerable skill in predicting the limits of their influence1 though ever and anon an extraordinary wave overthrew all our confidence1 by bursting far above the boundaries which we had assigned in our minds4 ,that1 however1 did not generally occur in calm weather1 but after strong gales from the ,n4,w41 when the waves had assumed the larger and more flattened form known by the name of the ground-swell4 ,to gauge the height of those waves by means of a vertical rod1 graduated with large divisions1 so as to be read at a little distance1 as the waves washed it in passing1 was an object ,i had long in view2 but ,i found it utterly impossible to apply any fixture in the deep water1 in a situation fitted for the purpose4 ,by making numerous comparisons1 however1 of the waves1 with various known points of rock near the main ,rock1 and by availing myself of the observations of some of the more intelligent of the masons1 ,i was led to conclude1 that the greatest elevation of an unbroken wave1 measuring from the hollow to the crest1 does not1 in the sea around the ,skerryvore1 exceed #ae feet2 but the sailors1 perhaps from their being less accustomed to accurate measurement1 generally estimated it at #cj or even #dj feet4 ,i was often much interested1 while ,i sat watching the waves that boiled round us on every side1 to observe the peculiar tints which they assumed at the moment of breaking1 passing as they did from the bluish-green colour of solid water by very rapid changes1 to a delicate and very evanescent blush of rose colour1 which invariably accompanied their greatest state of comminution or disintegration4 ,those appearances ,i have often observed in other places1 and ,i supposed them to be produced by reflection from the thin plates of water2 and took them for indications of the perfect homogeneousness of the sea-water1 in regard to density1 and also of the similarity of its condition at the moment of breaking4 ,the ,seals4 ,amongst the many wonders of the 8great deep10 which we witnessed at the ,skerryvore1 not the least is the agility and power displayed by the unshapely seal4 ,i have often seen half a dozen of those animals round the ,rock1 playing on the surface or riding on the crests of curling waves1 come so close as to permit us to see their eyes and head1 and lead us to expect that they would be thrown high and dry at the foot of the ,tower2 when suddenly they performed a somersault within a few feet of the ,rock1 and diving into the flaky and wreathing foam1 disappeared and as suddenly reappeared a hundred yards off1 uttering a strange low cry1 as we supposed1 of satisfaction at having caught a fish4 ,at such times the surf often drove among the crevices of the ,rock a bleeding cod1 from whose back a seal had taken a single moderate bite1 leaving the rest to some less fastidious fisher4 ,the latter part of the season1 although not so stormy as the first1 was far from being favourable for the building operations which1 on one occasion1 even during the month of ,july1 were suspended for five days by a violent gale1 which made it unsafe to attempt standing on the ,tower4 ,happily the wind was from the ,n4,e41 a quarter from which it has comparatively little power in raising heavy seas1 otherwise we should infallibly have lost a large part of the dressed materials which lay piled on the ,rock1 and1 in all probability1 should have had our work thus prematurely cut short in the middle of summer4 ,after building a few courses above the level of the solid part of the ,tower1 the jib-crane could no longer be conveniently used1 and recourse was had to a balance-crane1 which1 during the previous winter1 ,i had caused to be constructed at ,edinburgh1 in the workshop of ,mr ,james ,dove4 ,that apparatus1 which1 except as to its greater size and strength1 in order to suit the greater dimensions of the ,tower1 was almost identical with that which was used at the ,bell ,rock1 is shewn in ,plate ,,ix42 and it is only necessary1 in this place1 to notice its general construction and mode of working1 which is also shewn in ,plate ,,xvii4 of my ,father's ,account of the ,bell ,rock ,lighthouse4 ,in the hollow of the ,tower1 a cast-iron pipe or pillar was erected1 susceptible of being lengthened as the ,tower rose1 by means of additional pieces of pillar let in by spigot and faucet joints2 and on the pillar a frame of iron was placed capable of revolving freely round it1 and carrying two trussed arms and a double train of barrels and gearing4 ,on the one arm hung a cylindric weight of cast-iron1 which could be moved along it by means of the gearing1 so as to increase or diminish by leverage its effect as a counterpoise2 and on the other was a roller4 ,the roller was so connected with the weight on the opposite arm1 as to move along with it1 receding from1 or approaching to1 the centre pillar of iron in the same manner as the weight did4 ,from the roller hung a sheave1 over which a chain moved1 with a hook at the end for raising the stones4 ,when a stone was to be raised1 the weight and the sheave were drawn out to the end of the arms of the crane1 which projected over the outside of the walls of the ,tower1 and they were held in their places by simply locking the gearing which moved them4 ,the second train of gearing was then brought into play to work the chain which hung over the sheave1 and so to raise the stone to a height sufficient to clear the top of the wall4 ,when in that position1 the first train of gearing was slowly unlocked and the slight declivity inwards from the end of the arms formed an inclined plane1 along which the roller carrying the sheave was allowed slowly to move 7one man using a break on the gearing to prevent a rapid run71 while the first train of gearing was slowly wound by the others1 so as to take up the chain which passed over the sheave1 and thus to keep the stone from descending too low in proportion as it approached the centre of the ,tower4 ,when the stone so raised had reached such a position as to hang right over the wall1 the crane was made to turn round the centre column in any direction that was necessary1 in order to bring it exactly above the place where it was to be set2 and by working either train of gearing1 it could be moved horizontally or vertically in any way that was required4 ,the men who wrought the crane1 stood on two small stages of planks attached to either side of the framework1 and moving round the shaft along with it4 ,the balance-crane was safely landed on the ,rock on the #bjth ,july and on the #beth it was erected in working order on the top of the masonry4 ,on the afternoon of that day1 ,i had the satisfaction of seeing it put to a severe trial in raising a stone of nearly two tons weight and drawing it from the shear-poles already noticed to the top of the building4 ,as that trial was made at an earlier stage of the works than was originally intended1 the ,tower was of larger diameter than was quite suited to the arrangements of the crane1 which was consequently subjected to the weight of the stone at the very point of the jib4 ,i felt no small anxiety as to the result1 and had taken the precaution to relieve the centre pillar or shaft1 on which the crane swung1 from part of its burden1 by means of a guy attached to a lewis-bat on the top of the building2 yet even with that aid1 the point of the jib was depressed #f or #h inches on a length of #ad feet4 ,that test1 however1 having been successfully passed and not the slightest trace of any injury having been discoverable in any part of the crane1 we continued to work it with perfect confidence and in the most satisfactory manner throughout the whole season until the close of the ,rock operations for the year on the #agth of ,august4 ,the mass of masonry built during the season was #cj1cjj cubic feet1 a quantity considerably more than double that contained in the ,eddystone and somewhat more than the mass of the ,bell ,rock4 ,the whole was very carefully set and when gauged at the upper bed of each course was found to preserve the diameter due to the height1 according to the calculated dimensions1 within a fraction rarely exceeding th of an inch4 ,the height of the mass also1 when measured1 exceeded the specified height only by half an inch4 ,the mortar employed was composed of equal parts of lime from the ,halkin ,mountain in ,north ,wales and ,pozzolano2 and ,i consider it if possible superior to that produced from the lime of ,aberdda4 ,when we left the ,rock this season1 two apartments were covered in and the third was nearly completed1 as will appear from the section 7,plate ,,iii47 7on which the progress of the several seasons is marked71 and only about one-third of the whole ,tower remained to be built4 ,our last work on the ,rock before leaving it for the season on the #agth ,august1 was to cover the balance-crane with a strong tarpaulin in order to protect it as much as possible from the weather and also to make a temporary lightning-conductor from the top of the building to the sea4 ,the extent of work done during the season of #ahda at the ,rock1 must in a great measure be attributed to the advantage of steam attendance1 without which numerous favourable opportunities of landing materials must necessarily have been lost1 from the uncertainty which pervades all the movements of sailing craft4 ,the number of lighters towed out and discharged at the ,rock was #abj2 and it is remarkable that no accident of importance occurred1 although many risks were run1 from the breaking of warps while the craft lay moored to the landing quay during heavy seas4 ,i cannot omit in this place to record my sense of the services rendered to the works by the late ,mr ,james ,heddle1 who commanded the steamer and who died from some consumptive disease soon after the close of the season's operations4 ,mr ,heddle's health had been somewhat enfeebled towards the latter part of the autumn2 and his excessive exertions and continued exposure during his arduous service1 in some measure1 ,i fear1 hastened the crisis of his disease1 which at length terminated suddenly by the rupture of an abscess in the lungs4 ,of his anxiety to forward the work1 and his unwearied exertion in the discharge of his harassing duty at ,skerryvore1 which frequently allowed him less than twenty hours sleep in a week1 ,i cannot speak too highly1 as ,i consider his intrepidity and zeal to have been one of the most efficient causes of our success ever since the commencement of the works on the ,rock in #ahci4 ,mr ,heddle possessed attainments superior to those generally found among persons in his walk of life and was in every respect a most estimable man4 ,,chapter ,,viii4 ,,operations ,,of #ahdb4 ,state of the ,rock in ,spring of #ahdb4 ,on the #agth of ,april #ahdb1 ,i made my first landing on the ,skerryvore1 for the season1 and found traces of very heavy seas having passed over the ,rock during the preceding winter4 ,its surface was washed quite clean from all the scattered materials which were left lying on it at the end of the last season2 and the building1 to the height of #f or #h feet from the foundation1 was covered with a thick coating of green sea-weed4 ,the railway had suffered considerably from large stones having been thrown upon it2 and several blocks of about half a ton in weight were found wedged into the deep fissures of the ,rock1 and lying among the main timbers of the ,barrack4 ,heavy sprays had been playing over the ,tower1 in the upper uncovered apartment of which a great number of water-worn pebbles or boulders were found4 ,those stones had been raised by the heavy surf and deposited on the floor of the apartment and on the top of the wall at a height of no less than #fj feet above high watermark2 but the balance-crane1 which had stood all winter on the top of the ,tower1 had sustained no damage1 although the canvass cover was torn to shreds by the action of the weather4 ,in the ,barrack every thing was in good order except the smoke-funnel1 which1 from the effects of the sea-water1 was riddled full of holes and required to be completely renewed4 ,commencement of ,rock operations4 ,as ,i had resolved to keep1 during the summer of #ahdb1 a complement of about eighteen or twenty seamen on the ,rock1 in addition to the usual detachment of masons1 in order to work the crabs for raising the materials to the top of the ,tower by successive stages2 my first step was to set about preparing additional accommodation in the ,barrack1 by converting the open gallery 7called store for coals1 c41 in ,plate ,v471 immediately below the cook-house1 into a covered apartment for lodgings for the additional hands4 ,i accordingly landed on the #bjth of ,april1 with a stock of provisions1 water and fuel and a party of joiners and a smith1 to prepare that apartment by simply flooring over the joists of the gallery and closing the triangular1 or rather trapezodal1 spaces between the uprights of the ,barrack1 with double planking1 protected on the seams with painted canvass1 so as to render them impervious to the heavy sprays which1 even in summer1 dashed forcibly on the lower parts of the ,barrack4 ,windows were formed on the sides least exposed to the intrusion of the sea2 but1 with all our precautions1 we could not succeed in keeping dry even the cots or hammocks1 which were suspended there2 and it must be admitted that the addition to the ,barrack proved1 in bad weather1 but a comfortless retreat1 the inconveniences of which few but seamen would have patiently endured4 ,those discomforts1 however1 were to a certain extent1 counterbalanced by some advantages which that singular abode possessed in hot weather2 for1 at such times1 its inhabitants enjoyed more room1 freer air1 and more tolerable temperature1 than any of their neighbours in the highest storey could obtain1 owing to the greater number of persons in that part of the ,barrack and its exposure to the heat of the cook's stove4 ,during the remainder of the month of ,april and the commencement of ,may we had frequent stiff gales2 and it often happened that the men could not venture out of the ,barrack1 owing to the heavy sea which swept over the ,rock4 ,the crane1 too1 which had been erected at the wharf for unloading the stones1 although its top stood about #h feet above the ,rock1 was often buried in the breakers and seemed in hourly danger of being carried away1 an event which we were the more ready to fear from our experience in a former season1 when the crane disappeared during a heavy westerly gale4 ,the sea on those occasions also broke so heavily on the ,barrack1 that the windows of my apartment1 which were about #ee feet above the sea1 were often darkened by the sheet of water which flowed over them after the house had been struck by a wave4 ,from those causes it was not till the #ahth ,may that we were enabled to occupy the ,rock in full force2 and on the day following we commenced building the #chth course on the top of the last year's work4 ,after that period we had a long continuance of north-easterly winds1 which always brought both smooth water for landing materials and dry weather for building2 so that by the #bc;d of ,may our work had made such progress and the ,tower had risen so high1 that the chain of the balance-crane1 which had been raised along with the building1 by sliding it upwards on the cast-iron pillar or shaft placed in the centre of the ,tower1 could not reach the top of the shear-poles1 by which the stones were raised to the level of about #dj feet above the ,rock2 and it was found necessary to rig from the lowest window a beam or needle 7in the manner described at page #aee1 and as also shewn in ,plate ,,ix4 of my ,father's ,account of the ,bell-,rock ,lighthouse71 as an intermediate stage between the top of the ,tower and the shear-poles on the ,rock4 ,the needle1 as already noticed1 projected horizontally from the window and the stones were raised by a chain which passed over the sheave at its outer end and was wrought by means of a crab placed in the interior of the ,tower4 ,in that manner we continued for about six weeks1 with little interruption from the weather1 to raise the blocks of stone to the top of the ,tower by successive needles from storey to storey2 while the mortar1 lewis-bats and other lighter materials were raised at once by means of a line wrought by a windlass placed on the ,rock4 ,on the night of ,saturday the #ith of ,july1 however1 a heavy sea1 caused by a combination of high tides and strong gales1 threw down some of the stones of the belt course which lay piled up round the base of the ,tower ready to be raised for building2 and they were with great difficulty1 but most happily1 saved from the insatiable deep4 ,the loss of any of the stones of that course would have been a serious obstacle to the progress of the works and might have prevented our completing the erection of the lantern until next year2 and indeed1 as that course formed a prominent feature of the ,tower1 any slight injury even to the arris or corners of the outer face would have been much to be regretted4 ,it was with great satisfaction1 therefore1 that it was found on examination next morning that none of the stones had sustained the slightest damage4 ,last ,stone4 ,on the #bast ,july the last stones of the ,tower were safely landed on the ,rock1 under a salute from the steamer1 as an expression1 no doubt1 of the satisfaction which the commander ,mr ,kerr and his crew naturally felt at having successfully brought out not fewer than #ge lighter loads1 or about #aejj tons1 of stone during the season1 as well as in some measure of their joy at the prospect of a speedy and happy termination of our arduous labours4 ,the process of landing1 indeed1 owing to the fine weather that prevailed throughout the season1 was very easy1 compared with that of former years2 in proof of which1 ,i may state1 that in #ahda1 there were often as many as five warps broken at a single landing1 while in #ahdb1 not a single rope was broken in the discharging of the stones4 ,on the #beth ,july the last stone of the parapet or top-course was built2 and immediately thereafter we proceeded to remove from the ,tower1 the balance-crane and the cast-iron pillar on which it was swung1 and to make way for the erection of the ,lantern4 ,in looking back upon the works we found great cause for thankfulness for the successful conclusion of the building operations1 without loss of life1 or even the occurrence of any serious accident1 excepting the destruction of the first ,barrack in ,november #ahci4 ,it also gave me great satisfaction to reflect that1 however difficult a rigid adherence to scrupulous accuracy of workmanship may be in such a situation as the ,skerryvore1 it had nevertheless1 from the exactness with which the stones were dressed1 on no occasion been necessary1 throughout the execution of the whole work1 to deviate from the rule which ,i had laid down of carefully gauging the diameter of each course and of admitting no variation from the true form materially exceeding inch4 ,every part of the stone work1 indeed1 was fitted in an accurate manner and the floor stones1 in particular1 which serve as ties across the building1 were finely dressed and carefully set4 ,all opportunities were also embraced1 whenever it was practicable1 to grout each course over night that the recent masonry might be in a state fit for building upon in the morning2 and by those precautions and the peculiar properties of the mortar used1 any disadvantages from very rapid building were entirely avoided4 ,even the elliptic cavetto which forms the cornice and which projects no less than three feet from the face of the wall1 although bearing a very heavy entablature or plinth1 never gave any signs of settling outwards2 and when ,i examined it from a stage hung from the end of the balance-crane just before it was removed1 there was no appearance of any change in the thickness of the joints1 although the outer heads of the stones had been purposely kept a little high to allow for any tendency to settlement4 ,the effect of the cornice is very bold and striking and is quite in accordance with the simple and almost severe style of the pillar itself4 ,the masonry of the ,tower is #acg feet #aa inches in height and it contains #eh1ehj cubic feet or about #dcjh tons4 ,the ,lantern4 ,the day after landing the last stone of the parapet1 the steamer started from ,tyree for ,greenock1 with two lighters in tow1 for the transport of the ,lantern2 and by the #ajth of ,august the whole was landed on the ,rock4 ,no time was lost in preparing the beds for the sole-plates of the ,lantern1 and that operation had been nearly completed when my ,father1 in the course of his annual tour of inspection1 as ,engineer for the ,northern ,lights1 visited the ,rock1 two days after the iron work had been landed4 ,by the #afth the whole of the sashes and the frame of the roof were to their places2 and on the same day the fixtures of the lightning-conductor were completed4 ,on the #ahth of ,august ,mr ,bruce1 the ,sheriff of ,argyll1 and some gentlemen who accompanied him and had spent the preceding night at ,hynish1 visited the ,rock2 and1 after breakfasting at the base of the ,tower1 ascended to the top and minutely inspected every part of the work4 ,they afterwards returned to ,hynish1 whither ,i accompanied them and had an opportunity of pointing out to ,mr ,bruce the various works in progress there4 ,the party sailed for ,oban in the afternoon of the same day4 ,from want of room on the ,rock it was found necessary to build the roof of the ,lantern in separate pieces instead of rivetting together the sheets of which it was composed on the ground1 and raising the whole to the top in one mass1 as is usually done2 but1 in spite of that disadvantage1 the work was brought to a close for the season on the #adth ,september1 on which day the glazing of the ,lantern was completed and the glass was covered with a framework of timber to protect it from the sea-fowls which frequent in myriads the ,rock and the ,tower4 ,the workmen were1 on the same day1 removed from the ,rock1 although with much difficulty1 owing to the heavy surf which broke over the landing-place and rendered the embarkation more perilous than almost any ,i had before experienced at the ,skerryvore4 ,,chapter ,,ix4 ,,concluding ,,operations ,,and ,,exhibition ,,of ,,the ,,light4 ,harbour ,works4 ,the shores of ,tyree1 as already often noticed in these pages1 and as deplored by ,martin #adj years ago1 in his ,account of the ,hebrides1 afford few places of safety fit even for boats4 ,it had therefore been determined1 by the ,commissioners1 that any attempt at the construction of a harbour should be strictly confined to the provision of a place of shelter for the vessel which was to attend the ,lighthouse4 ,much attention had been bestowed on the subject1 not merely by myself during my five years' acquaintance with ,tyree1 but also by ,mr ,thomas ,stevenson1 who succeeded me in the charge of the works at ,hynish1 at the time when ,i was appointed ,engineer to the ,lighthouse ,board in ,january #ahdc1 after the completion of the masonry of the ,tower4 ,a small sandy beach at ,hynish1 which lies embayed between rugged rocks1 had been selected as the fittest place for the pier2 and all the materials had been landed and shipped there1 so that we naturally looked to it as the site for the projected harbour1 not only as presenting works already finished1 which might be made available as part of a more extended plan1 but as a place which1 during an experience of some years1 had justified our anticipations as to its being less frequently disturbed during stormy weather than most of the neighbouring creeks4 ,all that was contemplated in the proposed plan1 was to form a small basin in which the vessel could lie sheltered in all states of the weather1 and from which she could find an easy departure in any condition of the sea which would permit a landing to be made on the ,rock4 ,the ,skerryvore ,steamer having been sold and a small vessel of #ce tons1 named the 8,francis10 having been purchased at ,deal1 the dock accommodation at ,hynish was1 for the sake of economy1 laid out with reference to the shelter of that vessel4 ,it was calculated that a basin #ajj feet in length and #ej feet wide1 would afford sufficient room for such a vessel2 and as her draught of water is between #g and #h feet1 it was thought sufficient to provide for a depth of about #ab feet at high water of spring-tides1 which1 it was expected1 would render the dock accessible during good springs at about three quarters flood4 ,the exposure of the shore at ,hynish1 to the effects of heavy westerly swells1 made it desirable to avoid carrying the entrance of the basin so far seaward1 as1 under more favourable circumstances1 would undoubtedly have been done2 and it was accordingly determined that the landing pier should be extended to about #dj feet seaward of low-water mark1 and terminated in a round head1 as shewn in ,plate ,x41 having a talus wall on its seaward face1 composed of rough blocks1 arranged in courses regularly receding1 so as to form a slope of #de of inclination1 as shewn in ,plate ,,xi4 ,the inner face of that pier1 being nearly vertical and guarded by fenders of timber1 had served as the quay for landing and shipping stones and other stores and it now forms one side of the basin or dock4 ,the other side consists of a shorter talus wall1 built about #fj feet to the westward of the first1 and1 together with the crossheads projecting from each wall and containing the gateway1 completes the inclosure of the basin4 ,in the gateway1 booms are employed1 as the shifting nature of the sand and the heavy seas render gates inadmissible4 ,the space contained between those walls was left completely dry at low water of spring-tides1 and was chiefly composed of rock1 covered with a thin layer of shifting sand1 which varied in depth with the state of the wind and sea4 ,the rocky matter1 consisting of decomposed gneiss1 was excavated to the extent of about #ejjj tons1 in three separate compartments1 protected by successive dams of rubble masonry1 built with ,pozzolano mortar1 and presenting an aggregate area of #gcci square feet4 ,those dams1 two feet thick1 proved so water-tight1 that by the aid of a small hand-pump1 the excavation and the building of the entrance heads of the booms went regularly forward without any delay1 although the men worked in the bottom of the pit1 surrounded on all sides by the sea1 which1 at high water of spring-tides1 rose #ag feet above them4 ,the dams were sheltered from the action of the swell by a temporary breakwater of heavy blocks1 which formed a convenient roadway for the transport of the materials during the progress of the works1 and which were removed at the close of the operations4 ,the talus wall for protecting the seaward side of the harbour1 has about #fj feet of its foundation laid in a depth of water varying at low spring-tides from #ah inches to #c feet4 ,the mode of its construction1 as already stated1 is shewn in ,plate ,,xi4 ,it is surmounted by a strong parapet of rustic masonry of ,mull granite1 and is altogether a most substantial piece of work4 ,the idea of a tide-basin with boom-gates facing the breach of ,atlantic waves is somewhat novel and was not very hastily entertained by me at first2 but the most complete success has attended the plan4 ,during my occasional visits to the works in the course of the summer #ahdc1 our attention had been often occupied with considering the probability of the sand shutting up the basin2 and as a single tide during heavy winds from the ,n4,w41 made great changes on the appearance of the beach1 we feared that the vessel might often be imprisoned within the boomgates by a bank of sand heaped against them by the sea4 ,to such an extent did the accumulation go before the harbour was fully opened1 that on many occasions there was not water for a rowboat to pass between the boom-heads even at the highest spring-tides4 ,the only remedy for such an evil1 was obviously to attempt some mode of artificial scouring2 and for that purpose1 it was proposed to divert several small streams which run from ,ben ,hynish and the neighbouring hills through the grounds at ,hynish1 into one feeder1 and pen them up in a pond1 so as to afford the means of scouring the entrance to the basin from the incumbrance of the loose sand which might choke it4 ,those streams were repeatedly gauged during the summer and were found to deliver from #ac to #ej cubic feet of water per minute1 according to the state of the weather1--a supply which seemed ample for the purpose in view4 ,the sand at ,hynish is of a light nature and is easily acted on by currents of very feeble power4 ,it consists of comminuted shells and requires about #be cubic feet to make a ton1 instead of #bd feet1 which is the common allowance for silicious sand4 ,the leave of the ,duke of ,argyll and also of the ,farmer at ,hynish1 having been obtained1 various cuts were made and the stream was diverted into a pond capable of containing about #age1jjj cubic feet and provided with a waste-weir and with sluices for opening the communication between the pond and the scouring tunnel1 from which the water flows in a stream of about #i square feet of area1 at the rate of about #bfj feet per minute for a period of #a hour4 ,the operation of scouring is performed at low water and is generally found quite sufficient for the purpose of clearing a passage down to the bare rock in a single tide4 ,nothing can be more satisfactory than to witness the effect of that process in opening the entrance to a basin apparently inaccessible2 and but for such an arrangement1 the dock must have remained permanently choked with sand and sea-weed4 ,the position of the various works is marked in ,plate ,x41 which shews the ground at ,hynish4 ,on the side of the dock stands a crane1 which is used for various purposes connected with the shipment and discharging of materials4 ,it also serves for raising the booms1 by means of a double hook1 which can be attached to the chain and which embraces the pegs in the centre of each boom1 shewn in ,plate ,,xi4 ,the two tiers of booms are firmly lashed down by means of chains passing through ring-bolts in the manner shewn in the section 7,plate ,,xi471 so as to prevent their rising with the tide4 ,the necessity of providing somewhere in the neighbouring island of ,tyree for the proper accommodation of the vessel which was to wait upon the ,lighthouse 7if it could ever have been a matter of doubt71 was abundantly demonstrated by the experience of #ahdc1 and more especially by that of the months of ,november and ,december4 ,owing to the shortness of the day and the distance of any place of shelter from the ,skerryvore1 together with the difficulty of landing on the ,rock and the extreme variableness and uncertainty of the climate1 the ,regent ,tender1 although constantly waiting on the coast and making trials on every occasion that seemed to offer any prospect of success1 could not effect any communication with the people who had been left on the ,rock1 during a period of no less than seven long weeks4 ,the poor seamen who were living in the ,barrack passed that time most drearily1 for not only had their clothes been literally worn to rags1 but they suffered the want of many things dearer to them than clothes1 and amongst others of tobacco1 the failure of the supply of which they had despondingly recorded in chalk on the walls of their prison-house1 with the date of the occurrence6 ,unless1 therefore1 the vessel had been stationed near the rock1 the few casual and uncertain opportunities which occur at intervals1 during the short days of winter1 would often have been lost1 and the future maintenance of the ,light rendered excessively precarious4 ,the experience of subsequent years1 during which the relief of the ,light-keepers has been kept up with considerable regularity1 shews that the small ,harbour at ,hynish forms a most important integral part of the ,establishment of ,skerryvore1 than which ,i believe no ,lighthouse on the coast is more comfortable as a residence4 ,bo ,pheg ,beacon4 ,in connection with the ,harbour at ,hynish1 ,i naturally notice the erection of a ,beacon on a rock called ,bo ,pheg1 which is dry only at low water of spring tides4 ,it lies about one mile ,,ne4 from ,hynish ,point1 7,see ,plates ,,ii4 and ,x47 right in the track of the ,tender in its passage to and from the ,lighthouse4 ,from the great difficulty of landing on that small rock1 over which the sea almost continually breaks1 even in very fine weather1 the shortness of the time during which the men could remain at work1 and the want of room on its irregular surface of about #af yards square1 the erection of a beacon proved to be a work of great difficulty4 ,the ,beacon consisted of an open frame-work of iron1 7somewhat on the same plan as that which is described in the ,appendix7 and calculated to offer little opposition to the free passage of the waves2 but before all the fixtures could be completed1 the heavy storms of the winter of #ahdd1 acting on its unfinished base 7the bats of which were only partially secured71 destroyed it piecemeal1 at a season when no landing could be effected1 nor any effort made to save almost any part of it from the sea4 ,in the ensuing summer1 a second ,beacon1 consisting of a hollow cone1 composed of iron plates1 united together by strong flanges and attached to the rock by webbed flanges round its base with strong bats passing through them1 was fixed down to the rock2 and in order to increase its weight1 the interior was filled with concrete gravel4 ,that structure also has since yielded to the force of the waves1 after giving slight indications of movement1 an effect which ,i attribute chiefly to the smallness of the base1 which the narrow limits of the rock unhappily prescribe4 ,lightkeepers' and ,seamen's ,house4 ,another necessary part of the ,establishment at ,hynish1 was the provision of dwelling-houses for the families of the ,lightkeepers and ,seamen and of ,storehouses of various kinds4 ,those were partly built on purpose and partly consisted of altered forms of the buildings which had been found necessary as barracks for workmen and stores for materials1 during the progress of the works4 ,concluding works on the ,rock1 such as pointing1 c4 ,on landing on the ,rock1 on the #bith of ,march #ahdc1 the ,resident ,engineer had the satisfaction of finding the whole building perfectly water-tight and saw not the slightest trace of a defective joint4 ,the outside joints of the building were therefore carefully 8ripped10 and repointed with mortar1 composed of equal parts of ,halkin lime and ,pozzolano4 ,that operation1 from the difficulty of employing many men1 where suspended scaffolds were necessary and from the care with which it requires to be executed1 occupied a great deal of time4 ,interior fittings of the ,tower4 ,another tedious operation was the fitting up of the interior of the ,tower with wainscot lining and forming the various stories into apartments separate from the staircase4 ,much work was also expended in providing the fire-places with proper flues1 in fitting up water tanks1 coal stores1 and oil tanks1 and also in conveying the air-tubes between the ,lightroom and the several apartments by which the signal bells are rung for summoning the keepers to mount guard4 ,the keeper on duty is1 by the rules of the ,service1 forbidden1 under penalty of instant dismissal1 to leave the ,light-room1 on any pretext1 until relieved by the next who mounts guard1 and who is summoned by means of a bell placed inside his cot or sleeping berth1 which is rung by means of a small piston1 propelled by simply blowing into a mouth-piece in the ,light-room4 ,the keeper in bed answers this signal by a 8counter-blast10 which rings another bell in the ,light-room1 and informs the keeper there that his signal has been heard and will be obeyed4 ,arrangement of the several apartments4 ,the general arrangement of the ,tower1 may be seen in the ,section ,plate ,,viii42 and the details of its subdivision are very similar to those shewn in ,plate ,,xvi4 of my ,father's ,account of the ,bell ,rock ,lighthouse4 ,the ascent to the outside door is by a ladder or trap of gun metal1 #bf feet high4 ,the first apartment on the level of the entrance door1 is chiefly appropriated to the reception of iron water-tanks1 capable of holding a supply of #abea gallons4 ,the next story is set aside for coals1 which are stowed in large iron boxes4 ,the third apartment is a workshop2 the fourth is the provision store2 and the fifth is the kitchen4 ,above are two stories1 each divided into two sleeping apartments1 for the four ,light-keepers4 ,over them is the room for the ,visiting ,officers2 then follows the oil store1 and lastly comes the ,lightroom1 making in all twelve apartments4 ,the nearness of the oil store to the ,lightroom is a great convenience to the ,keepers1 who are thus saved the trouble of carrying the daily supply of oil to the ,lightroom1 up a long flight of steps4 ,the passage from story to story is by oaken trap ladders1 passing through hatches in each floor and partitioned off from each apartment in order to prevent accidents and to check cold draughts4 ,lightroom ,apparatus1 and first exhibition of the ,light4 ,the light of ,skerryvore was exhibited to the mariner on the night of the #ast ,february #ahdd1 in terms of the ,statutory ,notice1 which will be found in the ,appendix4 ,the light is revolving1 appearing in its brightest state once in every minute of time4 ,it is elevated #aej feet above the sea1 and is well seen as far as the curvature of the earth permits2 it is also frequently seen as a brilliant light from the high land of ,barra1 a distance of #ch miles4 ,the apparatus consists of eight annular lenses 7of the first order1 in the system of ,,augustin ,,fresnel71 of #cfbb inches focal distance1 revolving round a lamp with four concentric wicks1 and producing a bright blaze when each lens passes between the lamp and the eye of a distant observer4 ,above those lenses are placed eight pyramidal lenses of #aifh inches focal distance1 inclined at #ej with the horizon and combined with eight plane mirrors1 inclined in the opposite direction at #ej with the horizon4 ,by this arrangement1 that part of the light from the lamp which would otherwise escape uselessly beyond the great lenses1 upwards into the sky1 being parallelized in its passage through the smaller lenses and falling on the mirrors1 is finally projected forwards in horizontal beams1 so as to aid the effect of the light4 ,those lenses and mirrors1 however1 instead of having their axes in the same vertical plane with the axes of the principal lenses1 are inclined about #g horizontally to the right hand1 and by that deviation produce small premonitory blazes1 which1 blending with the beams of the larger lenses1 tend in some measure to lengthen the duration of the impression on the eye4 ,so far the apparatus of the ,skerryvore ,lighthouse is identical in its general arrangements with that of the ,tour de ,corduan1 and differs only in the superior workmanship of the lenses and the machinery1 which the experience of more than twenty years has brought about1 since ,,fresnel designed that light in #ahbb4 ,instead1 however1 of employing curved mirrors1 as has been done at ,corduan1 to collect the light which would otherwise escape below the lenses and1 at the same time1 to send it to the horizon1 ,i determined to put in practice a plan which ,i had long contemplated1 of placing totally reflecting zones below the lenses1 similar in construction to the zones of the small ,harbour ,light ,apparatus of the fourth order1 which was also invented by ,,fresnel4 ,this was finally carried into effect1 agreeably to the design of ,m4 ,,leonor ,,fresnel1 his brother1 with whom ,i had corresponded on the subject4 ,in the subsequent pages of this volume1 ,i intend to make some observations explanatory of the principles and arrangement of the various optical instruments employed in ,lighthouses2 and as that will afford me a more convenient opportunity of describing the nature and properties of the totally reflecting zones1 ,i shall forbear in this place to enter into further details as to the construction or action of the apparatus at the ,skerryvore4 ,it is right1 however1 that ,i should mention here that the lenses1 mirrors and zones are from the works of ,m4 ,,fran,,ois of ,paris1 whose name ,i shall afterwards have occasion to notice2 and that the machinery was constructed to my entire satisfaction1 and in a manner worthy of his reputation as a mechanician1 by ,mr ,,john ,,milne of ,edinburgh4 ,removal of the ,barrack from the ,rock4 ,in such a situation as the ,skerryvore1 new wants were discovered every day2 and each summer brought its round of smaller works1 which the experience of the preceding winter had suggested4 ,the ,barrack was found very useful as a place of residence for the workmen1 who were engaged in such needful works2 and it was not until the summer of #ahdf1 that it was taken to pieces and removed from the ,rock1 after having kept its place for six years4 ,its removal1 however1 was then thought advisable1 as some of its fixtures1 by the continual action of the weather1 had become very loose and precarious2 and1 although a very small outlay would have made it almost as stable as at first1 it was considered inexpedient to attempt to perpetuate a structure confessedly temporary in its nature1 and the sudden destruction of which by the waves1 seemed to involve some risk of injury to the ,tower itself4 ,expense4 ,the expense of erecting the ,skerryvore ,lighthouse1 including the opening of quarries and forming wharfs at the quarries in ,mull and also the ,harbour in ,tyree1 was1 as appears from the ,account in the ,appendix1 ,l4#hf1igg 3 #ag 3 #g4 ,in the course of the ,summer of #ahdd1 a marble tablet1 bearing an inscription in letters of gold1 was1 by order of the ,commissioners1 placed over one of the windows in the ,visiting ,officers' ,room4 ,with a representation of the ,tablet and the ,inscription1 which1 after acknowledging the hand of ,almighty ,god in the success which attended the work1 briefly sets forth the beneficent purposes for which the ,lighthouse was erected and records the laying of the foundation-stone by his ,grace the ,duke of ,argyll1 ,i willingly close this most defective narrative of the work4 ,illustration3 ,,in ,,salutem ,,omnium ,,northern ,,lighthouses ,a4 ,d4 ,o4 ,m4 ,,auctoritate 4 ,,et 4 ,,conciliis ,,pharorum 4 ,,scotiae 4 ,,collegii ,,haec 4 ,,structa 4 ,,fuit 4 ,,pharos ,,cujus 4 ,,directi 4 ,,flamma ,,nautae ,,infamibus 4 ,,his 4 ,,scopulis 4 ,,adhuc 4 ,,merito 4 ,,deterriti ,,optatum 4 ,,portum 4 ,,rectius 4 ,,advenirent4 ,,joannes 4 ,,dux 4 ,,de 4 ,,argyll ,,insularum 4 ,,adjacentium 4 ,,dominus ,,lapidem 4 ,,auspicalem 4 ,,rite 4 ,,statuit ,,die 4 ,,iv 4 ,,mensis 4 ,,julii 4 ,,anno 4 ,,iv 4 ,,vict4 ,,reg4 ,m 4 ,d 4 ,c 4 ,c 4 ,c 4 ,x 4 ,l 4 ,,operum 4 ,,magistro 4 ,,alano 4 ,,stevenson 4 ,l4,l4,b4 ,engraved by ,w4 ,a4,k4 ,johnston ,,part ,,second4 ,,notes ,,on ,,the ,,illumination ,,of ,,lighthouses4 ,,part ,,second4 ,,notes ,,on ,,the ,,illumination ,,of ,,lighthouses1 ,,with ,,short ,,notices ,,of ,,their ,,early ,,history4 ,early ,history4 ,the early history of ,lighthouses is very uncertain2 and some ingenious antiquaries1 finding the want of authentic records1 have been anxious to supply the deficiency by conjectures based upon casual and obscure allusions in ancient writers1 and by vague hypotheses drawn from the heathen mythology4 ,some writers have gone so far as to imagine1 that the ,cyclopes were the keepers of lighthouses2 whilst others have actually maintained that ,cyclops was intended1 by a bold prosopopia1 to represent a lighthouse itself4#bd ,a notion so fanciful deserves little consideration2 and accords very ill with that mythology of which it is intended to be an exposition1 as seems sufficiently plain from a passage in the ninth ,odyssey1 where ,homer 7who flourished about #ijg ,b4 ,c471 after describing the darkness of the night1 informs us that the fleet of ,ulysses actually struck the shore of the ,cyclopean island1 before it could be seen4#be #bd ,this spirit of etymological conjecture has converted ,cyclops1 ,proteus1 ,cneph1 ,phanes1 ,canobus1 ,chiron1 ,tithonus1 ,thetis1 ,amphitrite1 ,minotaurus1 ,chronus1 ,phrontis1 and other demigods1 into celebrated lighthouses1 or1 at all events1 has imagined that those mythological personages were worshipped under the emblem of fire or light in buildings1 which1 at the same time1 served as guides to the benighted mariner4 ,on the faith1 also1 of similar obscure and finely drawn etymologies1 various places1 such as ,calpe and ,abyla1 the opposite points of ,africa and ,europe1 at the ,straits of the ,mediterranean1 have been unhesitatingly recognized as the sites of celebrated light-towers2 and the ,latin words turris and columna have been supposed primarily to signify a lighthouse1 the first being written ,tor-is1 the ,tower of fire1 and the ,col-on1 the ,pillar of the ,sun4 #be ' ' 4 ,odyss41 ix41 #adf4 ,nor does there appear any better reason for supposing1 that under the history of ,tithonus1 ,chiron1 or any other personage of antiquity1 the idea of a lighthouse was conveyed2 for such suppositions1 however reconcileable they may appear with some parts of mythology1 involve obvious inconsistencies with others4 ,it seems1 indeed1 most improbable1 that1 in those early times1 when navigation was so little practised1 the advantages of beacon lights were so generally known and acknowledged as to render them the objects of mythological allegory4 ,it must not1 however1 be imagined1 that ancient writings are entirely destitute of allusions to the subject of ,beacon ,lights for the guidance of the ,mariner4 ,the venerable poet1 already noticed1 in speaking of the shield of ,achilles1 has beautifully described the flash of a beacon-light in some solitary place1 as seen by seamen leaving their friends1 in those lines1 which contain ample proof of the existence of such a provision for the safety of the mariner in ,homer's time3-- ' 1 ' 1 ' ' 4 ,il41 xix41 #cge4 ,in the ,holy ,scriptures the word ,beacon occurs but once1 and that in ,prophecies of ,isaiah 7xxx4 #ag471 who lived above #bjj years later than ,homer2 but it is obvious that the original term1 which the ,septuagint translate by the word 1 merely imports a flagstaff or perch and does not at all imply the knowledge of beacon-lights among the ,hebrews1 who were not a maritime people4 ,colossus of ,rhodes4 ,about #cjj years before the ,christian era1 ,chares1 the disciple of ,lysippus1 constructed the celebrated brazen statue1 called the ,colossus of ,rhodes4 ,it was of such dimensions as to allow vessels to sail into the harbour between its legs1 which spanned the entrance4 ,there is considerable probability in the idea that this figure served the purposes of a lighthouse2 but there is no passage in any ancient writer1 where this use of the ,colossus is expressly mentioned4 ,many inconsistencies occur in the account of this fabric by early writers1 who1 in describing the distant objects which could be seen from it1 appear to have forgotten the height which they assign to the figure4 ,it was partly demolished by an earthquake1 about eighty years after its completion2 and so late as the year #fgb of our era1 the brass of which it was composed was sold by the ,saracens to a ,jewish merchant of ,edessa1 for a sum1 it is said1 equal to ,l4#cf1jjj4 ,pharos of ,alexandria4 ,little is known with certainty regarding the ,pharos of ,alexandria1 which was regarded by the ancients as one of the seven wonders of the world4 ,it was built in the reign of ,ptolemy ,philadelphus1 about #cjj years before the ,christian era2 and ,strabo relates that ,sostratus1 a friend of the royal family1 was the architect4 ,he describes it as built in a wonderful manner in many stories of white stone1 on a rock forming the promontory of the island ,pharos 7whence the ,tower derived its name71 and says that the building bore the inscription--8,sostratus of ,cnidos1 the son of ,dexiphanes1 to the ,gods1 the ,saviours1 for the benefit of seamen40 ,he concludes his brief notice of it by describing the neighbouring shores as low and encumbered with shoals and snares1 and as calling for the establishment of a lofty and bright beacon1 a sign to guide sailors arriving from the ocean into the entrance to the haven4#bf #bf ,the passage from which the above description is drawn will be found in the ,oxford edition of ,strabo1 #ahjg1 page #aabc4 ,it is as follows3 1 1 1 1 1 1 1 4 1 1 1 1 ' 4 ,strabo's account of the position of the island of ,pharos at once leads to the conclusion of its having formed part of the harbour of ,alexandria 7as is abundantly testified by ,josephus1 ,pliny1 and other writers71 and cannot be easily reconciled with that of ,homer 7fourth ,odyssey1 l4 #ced71 who describes the island as a day's sail with a fair wind from the mainland4 ,his words are as follows3-- 7 k7 ' ' 1 4 ,odyssey1 iv41 l4 #ced4 ,pliny1 however1 does not scruple to identify the ,pharos of ,homer's time with that of his own day4 8,pharos10 says he1 8quondam diei navigatione distans ab gypto1 nunc turri nocturnis ignibus cursum navium regens40 ,hist4 ,nat41 v4 #ca2 see also ,hist4 ,nat41 ii4 #hg1 and xiii4 #ba4 ,the accounts which have come down to us of the dimensions of this remarkable edifice are exceedingly various2 and the statements of the distance at which it could be seen are clearly fabulous4 ,that of ,josephus 7who likens it to the second of ,herod's three ,towers at ,jerusalem1 called ,phasael1 in honour of his brother7 is the least removed from probability2 yet even he informs us1 that the fire which burnt on the top to enable seamen to anchor in sight of it1 before coming near the shore1 and so to avoid the difficulty of the navigation by night1 was visible at a distance equal to about thirty-four ,english miles4 ,such a range for a lighthouse on the low shores of ,egypt1 would require a tower about #eej feet in height6#bg ,ammianus ,marcellinus#bh and ,pliny#bi are both very circumstantial in their notices of the ,pharos as a beacon-light to guide seamen in approaching the coast of ,egypt and port of ,alexandria4 ,the latter adds the interesting fact1 that the cost of the ,tower was reckoned at a sum equal to about ,l4#cij1jjj of our money2#cj and both of them agree in stating that a light was shewn from it at night4 ,ammianus ,marcellinus differs from all the other writers1 in attributing the erection of the ,tower to ,queen ,cleopatra4 ,pliny mentions in passing1 that there were also lighthouses at ,ostia and ,ravenna4 #bg ,bell4 ,judaic4 iv41 cap4 #aj1 sec4 #e4 7,havercamp's ,josephus1 tom4 ii41 p4 #cji4 ,amsterdam1 #agbf47 1 1 1 1 4 ,and again1 in the sixth ,book of the same ,history 7v4 #d1 sec4 #c1 tom4 ii41 p4 #ccj71 he says1 ' 4 ,the height of the ,tower in the text proceeds on the idea of the observer's eye being ten feet above the sea4 #bh ,ammianus ,marcellinus1 l4 xxii41 c4 #af4 7,leipsic #ahjg1 tom4 i41 p4 #cjf47 ,hoc littus cum fallacibus et insidiosis accessibus affligeret antehac navigantes discriminibus plurimis1 excogitavit in portu ,cleopatra turrim excelsam1 quae ,pharos a loco ipso cognominatur1 praelucendi navibus nocturna suggerens ministeria2 cum1 quondam ex ,parthenio pelago venientes aut ,libyco1 per pandas oras et patulas1 montium nullas speculas vel collium signa cernentes1 harenarum inlisae glutinosae mollitiae frangerentur4 #bi ,plinii ,hist4 ,nat41 xxxvi4 #ah4 7,paris1 #agbc1 p4 #gci47 ,magnificatur et alia turris a rege facta in insula ,pharo portum obtinente ,alexandriae1 quam constitisse octingentis talentis tradunt2 magno animo 7nequid omittamus7 ,ptolemai regis1 quod in ea permiserit ,sostrati ,guidii ,architecti structur ipsius nomen inscribi4 ,usus ejus1 nocturno navium cursu ignes ostendere ad praenuncianda vada portsque introtum3 quales1 jam compluribus locis flagrant1 ut ,ostiae ac ,ravennae4 ,periculum in continuatione ignium1 ne sidus existimetur1 quoniam longinquo similis flammarum aspectus est4 #cj ,supposing1 as is most probable1 that ,pliny means the ,egyptian talent2 the ,attic talent was about one-half the value of the other4 ,if the reports of some writers are to be believed1 this ,tower must have far exceeded in size the great ,pyramid itself2 but the fact that a building of comparatively so late a date should have so completely disappeared1 whilst the ,pyramid remains almost unchanged1 is a sufficient reason for rejecting1 as erroneous1 the dimensions which have been assigned by most writers to the ,pharos of ,alexandria4 ,some have pretended that large mirrors were employed to direct the rays of the beacon-light on its top1 in the most advantageous direction2 but1 in so far as ,i know1 there is no definite evidence in favour of this supposition4 ,others1 with greater probability1 have imagined that this celebrated beacon was known to mariners1 simply by the uncertain and rude light afforded by a common fire4 ,in speaking of the ,pharos1 the poet ,lucian1 on most occasions sufficiently fond of the marvellous1 takes no notice of the gigantic mirrors which it is said to have contained4 ,he thus speaks of this celebrated lighthouse as having indicated to ,julius ,csar his approach to the ,pharos of ,egypt on the seventh night after he sailed from ,troy3 ,septima nox1 ,zephyro nunquam laxante rudentes1 ,ostendit ,phariis gyptia littora flammis4 ,sed prius orta dies nocturna lampada texit1 ,quam tutas intraret aquas4 ,pharsal41 ix41 #ajjd4 ,it is true that1 by using the word 8lampada10 which can only with propriety be applied to a more perfect mode of illumination than an open fire1 he appears to indicate that the 8flammis0 of which he speaks1 were not so produced4 ,the word lampada may however1 be used metaphorically2 and flammis would1 in this case1 not improperly describe the irregular appearance of a common fire4 ,perhaps1 also1 the opinion that some kind of lamp was used in the ,pharos1 may seem to receive countenance from the remarkable words of ,pliny1 in the passage above cited--8,periculum in continuatione ignium1 ne sidus existimetur1 quoniam longinquo similis flammarum aspectus est40 ,the fear he expresses lest the light viewed from a distance should be mistaken for a star1 could hardly be applicable to the diffuse1 oscillating1 lambent light derived from an open fire1 and certainly gives some reason for imagining that1 even at that remote time1 the art of illuminating lighthouses was better understood than in the early part of the present century4 ,before leaving the subject of the ,pharos of ,alexandria1 ,i wish to vindicate the memory of its architect ,sostratus from the calumny of ,lucian1 who1 in his ,treatise on the art of writing history1 with his usual acrimony1 accuses the builder of the ,pharos of a fraud1 in cutting his own name on the solid walls of the ,tower1 and covering the inscription with plaster1 on which he carved the name of his royal master ,ptolemy4#ca ,against this assertion ,i would oppose the testimony of ,strabo1 who calls ,sostratus the 8friend of the ,kings0 7see the quotation at the foot of page #ahc71 and the direct evidence of ,pliny1 who1 in the passage above cited1 expressly states1 as a proof of ,ptolemy's magnanimity1 his giving the architect liberty to inscribe his own name on the ,tower4 ,the only other notices of the ,pharos which ,i have been able to find in ancient writers are from ,csar's ,commentaries1 ,valerius ,flaccus1 and ,pomponius ,mela4#cb ,at ,alexandria1 there is a modern lighthouse called the ,pharos1 which is maintained by the ,pacha of ,egypt4 #ca ,lucian1 in his ,treatise 7,amsterdam1 #agdc1 vol4 ii41 p4 #fh47 1 thus details the merit and fraud of ,sostratus4 1 2 1 1 ' 1 1 1 1 1 1 1 4 1 1 1 4 1 1 1 1 1 1 4 1 444 #cb ,csar de ,bell4 ,civil41 iii4 #ih 7,lond4 #agab1 p4 #cee74 ,pharus est in insula turris1 magna altitudine1 mirificis operibus extructa1 quae nomen ab insula accepit4 ,valerius ,flaccus very distinctly sets forth the great advantage of lighthouses to the seaman1 and especially speaks of those at ,alexandria and ,ostia in these lines-- ,non ita ,tyrrhenus stupet ,ioniusve magister1 ,qui portus1 ,tyberine1 tuos1 claramque seren ,arce ,pharon prceps subiit3 ,argonaut1 vii41 v4 #hd4 ,pompon4 ,mela1 ii4 cap4 #g4 ,corua ,tower ,mr ,moore1 in his ,history of ,ireland1 vol4 i41 p4 #af1 speaks of the ,tower of ,corua1 which he says is mentioned in the traditionary history of that country1 as a lighthouse erected for the use of the ,irish in their frequent early intercourse with ,spain4 ,in confirmation of this opinion1 he cites a somewhat obscure passage from thicus1 the cosmographer4 ,this in all probability is the tower which ,humboldt mentions in his ,narrative under the name of the ,iron ,tower1 which was built as a lighthouse by ,caius ,saevius ,lupus1 an architect of the city of ,aqua ,flavia1 the modern ,chaves4#cc ,a ,lighthouse has lately been established on this headland1 for which ,dioptric apparatus was supplied from the workshop of ,m4 ,,letourneau of ,paris4 #cc 8,the traditionary history10 says ,mr ,moore1 8of the latter country 7,ireland7 gives an account of an ancient ,pharos or lighthouse erected in the neighbourhood of the port now called ,corua1 for the use of navigators on their passage between that coast and ,ireland4 ,there is a remarkable coincidence between this tradition and an account given by thicus1 the cosmographer1 of a lofty ,pharos or lighthouse standing formerly on the sea-coast of ,gallicia1 and serving as a beacon in the direction of ,britain4 ,secundus ,angulus intendit ubi ,brigantia civitas sita est ,galliciae1 et altissimum ,pharum et inter pauca memorandi operis ad speculum ,britanniae4 ,whether the translation ,i have given of the last three words of this passage convey their real meaning1 ,i know not2 but they have been hitherto pronounced unintelligible4 ,the passage is thus noticed by ,casaubon1 in a note on ,strabo1 lib4 iii4 #8thicus in ,hispaniae descriptione altissimi cujusdam ,fari meminit4'0 ,the passage in ,strabo above referred to is on page #agi of the first volume of the ,oxford folio edition of #ahjg1 where the geographer speaks of ,cape 1 which ,casaubon distinctly identifies with the ,cabo de ,finisterra of modern seamen4 ,lighthouse at the mouth of the ,guadalquivir4 ,there is also a record in ,strabo of a magnificent lighthouse of stone at ,capio1 or ,apio1 near the ,harbour of ,menestheus 7the modern ,mesa ,asta1 or ,puerto de ,sta4 ,maria71 which he describes as built on a rock nearly surrounded by the sea1 as a guide for the shallows at the mouth of the ,guadalquivir1 in terms almost identical with those used by him in speaking of the ,pharos of ,alexandria4 ,i am not aware of any other notice of this great work1 for such it seems to have been1 to have deserved the praises of ,strabo4#cd #cd ,the words of ,strabo are 7,oxon4 #ahjg1 p4 #ahd71 7vel 7 1 1 1 4 ,ancient ,phari in ,britain4 ,in ,camden's ,britannia1 a passing notice is taken of the ruins called ,csar's ,altar1 at ,dover1 and of the ,tour d',ordre1 at ,boulogne1 on the opposite coast2 both of which are conjectured to have been ancient lighthouses4 ,pennant describes the remains of a ,roman ,pharos near ,holywell1 but cites no authorities for his opinion as to its use4 ,there were likewise remains of a similar structure at ,flamborough-head4 ,a very meagre and unintelligible account is also given of a lighthouse at ,st ,edmund's ,chapel1 on the coast of ,norfolk1 in ,gough's additions to ,camden1 by which it might seem that the lighthouse was erected in #abgb4ce #ce ,gough's ,camden's ,britannia1 vol4 i41 #cah1 and vol4 ii41 p4 #aih2 ,batcheller1 in his ,dover ,guide 7#ahde1 p4 #aaa71 says1 that the ,dover ,pharos was built 8during the lieutenancy of ,aulus ,plautius and ,ostorius ,scapula1 the latter of whom left ,britain1 ,a4 ,d4 #ec40--,pennant's ,history of ,whiteford and ,holywell1 p4 #aab4 ,such seems to be the sum of our knowledge of the ancient history of lighthouses1 which1 it must be admitted1 is neither accurate nor extensive4 ,our information regarding modern lighthouses is of course more minute in its details and more worthy of credit4 ,the greater part of it is drawn from authentic sources2 and much of what is afterwards stated is the result of my own observation1 during my visits to the most important lighthouses of ,europe4 ,tour de ,corduan4 ,the first lighthouse of modern days that merits attention1 is the ,tour de ,corduan1 which1 in point of architectural grandeur1 is unquestionably the noblest edifice of the kind in the world4 ,it is situated on an extensive reef at the mouth of the river ,garonne1 and serves as a guide to the shipping of ,bordeaux and the ,languedoc ,canal1 and indeed of all that part of the ,bay of ,biscay4 ,it was founded in the year #aehd1 but was not completed till #afaj1 under ,henri ,,iv4 ,it is minutely described in ,belidor's ,architecture ,hydraulique4 ,the building is #aig feet in height1 and consists of a pile of masonry1 forming successive galleries1 enriched with pilasters and friezes1 and rising above each other with gradually diminished diameters4 ,those galleries are surmounted by a conical tower1 which terminates in the lantern4 ,round the base is a wall of circumvallation1 #acd feet in diameter1 in which the light-keepers' apartments are formed1 somewhat in the style of casemates4 ,this wall is an outwork of defence1 and receives the chief shock of the waves4 ,the tower itself contains a chapel1 and various apartments2 and the ascent is by a spacious staircase4 ,the first light exhibited in the ,tour de ,corduan was obtained by burning billets of oak-wood1 in a chauffer at the top of the tower2 and the use of coal instead of wood1 was the first improvement which the light received4 ,a rude reflector1 in the form of an inverted cone1 was afterwards added1 to prevent the loss of light which escaped upwards4 ,about the year #aghj1 ,m4 ,,lenoir was employed to substitute parabolodal reflectors and lamps2 and in #ahbb1 the light received its last improvement1 by the introduction of the dioptric instruments of ,,augustin ,,fresnel1 the celebrated ,french ,academician4 ,eddystone4 ,the history of the famous ,lighthouse on the ,eddystone ,rocks is well known to the general reader1 from the narrative of ,,smeaton the ,engineer4 ,those ,rocks are #i miles from the ,ram-,head1 on the coast of ,cornwall2 and from the small extent of the surface of the chief ,rock and its exposed situation1 the construction of the ,lighthouse was a work of very great difficulty4 ,the first erection was of timber1 designed by ,mr ,,winstanley2 and was commenced in #afif4 ,the light was exhibited in ,november #afih4 ,it was soon found1 however1 that the sea rose upon that tower to a much greater height than had been anticipated2 so much so1 it is said1 as to 8bury under the water0 the lantern1 which was sixty feet above the ,rock2 and the ,engineer was therefore afterwards under the necessity of enlarging the ,tower1 and carrying it to the height of #abj feet4 ,in ,november #agjc1 some considerable repairs were required1 and ,mr ,,winstanley1 accompanied by his workmen1 went to the ,lighthouse to attend to their execution2 but the storm of the #bfth of that month1 carried away the whole erection1 when the ,engineer and all his assistants unhappily perished6 ,the want of a light on the ,eddystone1 soon led to a fatal accident2 for not long after the destruction of ,mr ,,winstanley',s lighthouse1 the ,winchilsea man-of-war was wrecked on the ,eddystone ,rocks1 and most of her crew were lost4 ,three years1 however1 elapsed1 after this melancholy proof of the necessity for a light1 before the ,trinity-,house of ,london could obtain a new ,act of ,parliament1 to extend their powers2 and it was not till the month of ,july #agjf1 that the construction of a new lighthouse was begun under the direction of ,mr ,,john ,,rudyerd of ,london4 ,on the #bhth of ,july #agjh1 the new light was first shewn1 and it continued to be regularly exhibited till the year #agee1 when the whole fabric was destroyed by accidental fire1 after it had stood forty-seven years4 ,but for this circumstance1 it is impossible to tell how long the lighthouse might1 with occasional repair1 have lasted1 as ,mr ,,rudyerd seems to have executed his task with much judgment1 carefully rejecting all architectural decoration1 as unsuitable for such a situation1 and directing his attention to the formation of a tower which should offer the least resistance to the waves4 ,the height of the tower1 which was of a conical form and constructed of timber1 was #ib feet1 including the lantern2 and the diameter at the base1 which was a little above the level of high water1 was #bc feet4 ,the advantages of a light on the ,eddystone having been so long known and acknowledged by seamen1 no time was permitted to elapse before active measures were taken for its restoration2 and ,,smeaton1 to whom application was made for advice on the subject1 recommended the exclusive use of stone as the material1 which1 both from its weight and other qualities1 he considered most suitable for the situation4 ,on the #eth of ,april #agef1 ,,smeaton first landed on the ,rock and made arrangements for erecting a ,lighthouse of stone and preparing the foundations1 by cutting the surface of the rock into regular horizontal benches1 into which the stones were carefully dovetailed or notched4 ,the first stone was laid on #abth ,june #ageg and the last on the #bdth of ,august #agei4 ,the ,tower measures #fh feet in height and #bf feet in diameter at the level of the first entire course2 and the diameter under the cornice is #ae feet4 ,the first #ab feet of the ,tower form a solid mass of masonry2 and the stones of which it is composed are united by means of stone joggles1 dovetailed joints1 and oaken treenails4 ,it is remarkable that ,,smeaton should have adopted an arched form for the floors of his building1 instead of employing the floors as tie-walls formed of dovetailed stones4 ,to counteract the injurious tendency of the outward thrust of those arched floors1 he had recourse to the ingenious expedient of laying1 in circular trenches or grooves cut in the stones which form the outside casing1 tie-belts of chain1 which were heated before being set in the grooves by means of an application of hot lead and became tight in cooling1 after they were fixed in the wall4 ,the light was exhibited on the #afth ,october #agei2 but such was the state of lighthouse apparatus in ,britain at that period1 that a feeble light from tallow candles was all that decorated this noble structure4 ,in #ahjg1 when the property of this lighthouse again came into the hands of the ,trinity-,house1 at the expiry of a long lease1 ,argand burners1 and parabolodal reflectors of silvered copper1 were substituted for the chandelier of candles4 ,bell ,rock4 ,the dangerous reef called the ,inch ,cape1 or ,bell ,rock1 so long a terror to mariners1 was well known to the earliest navigators of ,scotland4 ,its dangers were so generally acknowledged1 that the ,abbots of ,aberbrothwick1 from which the ,rock is distant about twelve miles1 caused a float to be fixed upon the ,rock with a bell attached to it1 which being swung by the motion of the waves1 served by its tolling to warn the mariner of his approach to the reef4 ,from this circumstance1 which formed the groundwork of ,,southey',s striking ballad of ,sir ,ralph the ,rover1 the ,rock is said to have derived its name4 ,amongst the many losses which occurred on the ,bell ,rock in modern times1 one of the most remarkable is that of the ,york1 seventy-four1 with all her crew1 part of the wreck having been afterwards found on the ,rock and part having come ashore on the neighbouring coast4 ,during the survey of the ,rock also1 several instances were discovered of the extent of loss which this reef had occasioned2 and many articles of ships' furnishings were picked up on it1 as well as various coins1 a bayonet1 a silver shoe-buckle1 and many other small objects4 ,impressed with the great importance of some guide for the ,bell ,rock1 ,captain ,brodie1 ,r4,n41 set a small subscription on foot and erected a beacon of spars on the ,rock1 which1 however1 was soon destroyed by the sea4 ,he afterwards constructed a second beacon1 which soon shared the same fate4 ,it was not1 therefore1 until #ahjb1 when the ,commissioners of ,northern ,lights brought a bill into ,parliament for power to erect a lighthouse on it1 that any efficient measures were contemplated for the protection of seamen from this ,rock1 which1 being covered at every spring-tide to the depth of from twelve to sixteen feet1 and lying right in the fairway to the ,friths of ,forth and ,tay1 had been the occasion of much loss both of property and life4 ,in #ahjf1 the bill passed into a law2 and various ingenious plans were suggested for overcoming the difficulties which were apprehended1 in erecting a lighthouse on a rock twelve miles from land1 and covered to the depth of twelve feet by the tide4 ,but the suggestion of ,mr ,,robert ,,stevenson1 the ,engineer to the ,lighthouse ,board1 after being submitted to the late ,mr ,,rennie1 was at length adopted2 and it was determined to construct a tower of masonry1 on the principle of the ,eddystone4 ,on the #agth of ,august #ahjg1 ,mr ,,stevenson accordingly landed with his workmen and commenced the work by preparing the ,rock to receive the supports of a temporary pyramid of timber1 on which a barrack-house for the reception of the workmen 7similar to that which has already been described in a preceding part of this volume7 was to be placed2 and during this operation1 much hazard was often incurred in transporting the men from the ,rock1 which was only dry for a few hours at spring-tides1 to the vessel which lay moored off it4 ,the lowest floor of this temporary erection1 in which the mortar for the building was prepared1 was often broken up and removed by the force of the sea4 ,the foundation for the tower having been excavated1 the first stone was laid on the #ajth ,july #ahjh1 at the depth of sixteen feet below the high water of spring-tides2 and at the end of the second season1 the building was five feet six inches above the lowest part of the foundation4 ,the third season's operations terminated by finishing the solid part of the structure1 which is thirty feet in height2 and the whole of the masonry was completed in ,october #ahaj4 ,the light was first exhibited to the public on the night of the #ast of ,february #ahaa4 ,the difficulties and hazards of this work were chiefly caused by the short time during which the ,rock was accessible between the ebbing and flowing tides2 and amongst the many eventful incidents which render the history of this work interesting1 was the narrow escape which the ,engineer and thirty-one persons made from being drowned1 by the rising of the tide upon the ,rock1 before a boat came to their assistance1 at a time when the attending vessel had broken adrift4 ,this circumstance occurred before the ,barrack-house was erected1 and is narrated by ,mr ,,stevenson1 in his ,account of the work1 published at the expense of the ,lighthouse ,board in #ahbd1 to which ,i would refer for more minute information on the subject of this work and the other lighthouses on the coast of ,scotland4 ,the ,bell ,rock ,tower is #ajj feet in height1 #db feet in diameter at the base1 and #ae at the top4 ,the door is #cj feet from the base and the ascent is by a massive copper ladder4 ,the apartments1 including the light-room1 are six in number4 ,the light is a revolving red and white light2 and is produced by the revolution of a frame containing sixteen ,argand lamps1 placed in the foci of parabolodal mirrors1 arranged on a quadrangular frame1 whose alternate faces have shades of red glass placed before the reflectors1 so that a red and white light is shewn successively4 ,the machinery1 which causes the revolution of the frame containing the lamps1 is also applied to tolling two large bells1 to give warning to the mariner of his approach to the ,rock in foggy weather4 ,the erection of the ,bell ,rock ,lighthouse cost ,l4#fa1cca 3 #i 3 #b4 ,carlingford4 ,the most remarkable ,lighthouse on the coast of ,ireland is that of ,carlingford1 near ,cranfield ,point1 at the entrance of ,carlingford ,lough4 ,it was built according to the design of ,mr ,,george ,,halpin1 the ,inspector of the ,irish ,lights2 and was a work of an arduous nature1 being founded #ab feet below the level of high-water1 on the ,hawlbowling ,rock1 which lies about two miles off ,cranfield ,point4 ,the figure of the ,tower is that of a frustum of a cone1 #aaa feet in height1 and #dh in diameter at the base4 ,the light1 which is fixed1 is from oil burned in ,argand lamps1 placed in the foci of parabolodal mirrors4 ,it was first exhibited on the night of ,december #bj1 #ahcj4 ,iron ,lighthouses4 ,there are various other ,lighthouses1 which1 in themselves1 are sufficiently deserving of a separate notice1 were it not that they have more or less something in common with those already described1 which are unquestionably the most remarkable edifices of the kind4 ,the first design for an ,iron ,lighthouse1 is that by my ,father for the ,bell ,rock1 in the year #ahjj4 ,the invention of ,mr ,,mitchell of ,belfast1 for applying the principle of the screw to the erection of ,lighthouses on soft foundations1 deserves a longer notice than is consistent with the nature of these notes4 ,it must therefore be sufficient to say1 that the principal ,lighthouses on this plan 7those of the ,maplin1 ,fleetwood1 and ,belfast ,lough7 consist of piles or of hollow pillars of cast-iron1 grouped together in the form of a truncated pyramid1 and closely resembling1 in the general arrangement of their parts1 the ,beacon shewn in ,plate ,,xxx41 and that erected on the ,carr ,rock in #ahba4 ,the lower end of each pillar is furnished with a flat screw or worm and a sharp point1 which is screwed into the sand1 clay1 or gravel1 or other soft subsoil4 ,mr ,,alexander ,,gordon of ,london also fitted up a ,lighthouse1 composed of cast-iron plates1 which was erected at ,morant1 in the ,west ,indies1 a style of building in itself by no means eligible1 and which seems suitable only where stone cannot be easily obtained1 or conveniently applied4 ,both those plans 7except in so far as the screw is concerned1 which is indeed the distinguishing feature of ,mr ,,mitchell',s ingenious plan7 are to be found in one of my ,father's designs for the ,bell ,rock ,lighthouse 7see his ,account1 at ,plate ,,vii41 figs4 #b1 #c1 #d1 and #e1 and pp4 #dii1 #ejj74 ,dr ,,potts has also invented a method of driving piles by means of atmospheric pressure1 which has been used at the ,south ,galliper ,beacon1 on the ,goodwin ,sands4 ,early modes of ,illumination4 ,having thus hastily described the most interesting and celebrated ,lighthouses1 ,i proceed to the proper object of these ,notes1 which are chiefly intended to make known the various methods now in use for the illumination of ,lighthouses4 ,there can be little doubt1 that down to a very late period1 the only mode of illumination adopted in the ,lighthouses1 even of the most civilized nations of ,europe1 was the combustion of wood or coal in chauffers1 on the tops of high towers or hills4 ,it consists with the personal knowledge of many persons now living1 that the ,isle of ,may ,light1 in the ,frith of ,forth1 previous to its being assumed by the ,commissioners of the ,northern ,lights in #aghf1 was of that kind2 and1 even in ,england1 the art of illumination had made so little progress1 that the magnificent ,tower of the ,eddystone1 for about forty years after it came from the hands of ,,smeaton1 could boast of no better ,light than that derived from a few miserable tallow candles4 ,such methods were most imperfect1 not only in point of efficiency and power1 but also as respects the distinction of one light from another1 an object which1 on a difficult and rugged coast1 may be considered as of almost equal importance with the distance at which the ,light can be seen4 ,flame4 ,solid substances which remain so throughout their combustion1 are only luminous at their own surface1 and exhibit phenomena1 such as the dull red heat of iron1 or of most kinds of pit-coal1 and are therefore more suited for the purpose of producing heat than light4 ,but by using substances which are formed into inflammable vapours1 at a temperature below that which is required for the ignition of the substances themselves1 gas is obtained and flame is produced4 ,much light is thus evolved at a comparatively low temperature4 ,the gas necessarily rises above the combustible substance from which it is evolved1 owing to its being formed at a temperature considerably higher than that of the surrounding air1 than which it is necessarily rarer4 ,of this description are the flames obtained by the burning of the various oils1 which are generally employed in the illumination of lighthouses4 ,in the combustion of oil1 wicks of some fibrous substance1 such as cotton1 are used1 into which the oil ascends by capillary action1 and being supplied in very thin films1 is easily volatilized into vapour or gas by the heat of the burning wick4 ,the gas of pit-coal has been occasionally used in lighthouses2 it is conveyed in tubes to the burners1 in the same manner as when employed for domestic purposes4 ,there are certain advantages1 more especially in dioptric lights1 where there is only one large central flame1 which would render the use of gas desirable4 ,the form of the flame1 which is an object of considerable importance1 would thus be rendered less variable1 and could be more easily regulated1 and the inconvenience of the clock-work of the lamp would be wholly avoided4 ,but it is obvious1 that gas is by no means suitable for the majority of lighthouses1 their distant situation and generally difficult access rendering the transport of large quantities of coal expensive and uncertain2 whilst in many of them there is no means of erecting the apparatus necessary for manufacturing gas4 ,there are other considerations which must induce us to pause before adopting gas as the fuel of lighthouses2 for1 however much the risk of accident may be diminished in the present day1 it still forms a question1 which ought not to be hastily decided1 how far we should be justified in running even the most remote risk of explosion in establishments such as lighthouses1 whose sudden failure might involve consequences of the most fatal description1 and whose situation is often such1 that their re-establishment must be a work of great expense and time4 ,gas is1 besides1 far from being suitable in catoptric lights1 to which1 in many cases 7especially when the frame is moveable1 as in revolving lights71 it could not be easily applied4 ,the oil most generally employed in the ,lighthouses of ,england is the sperm oil of commerce1 which is obtained from the ,south ,sea whale 7,physeter macrocephalus74 ,in ,france1 the colza oil1 which is expressed from the seed of a species of wild cabbage 7,brassica oleracea colza71 and the olive oil are chiefly used2 and a species of the former has lately been successfully introduced into the ,lighthouses of ,great ,britain4 ,of all these oils1 the purified sperm oil has hitherto been generally considered the most advantageous for lighthouse purposes2 but there is every reason for anticipating that the late adoption of the colza oil in many of the ,british ,lights1 on the suggestion of ,mr ,,joseph ,,hume1 ,m4,p41 while chairman of a select committee of the ,house of ,commons on ,lighthouses1 will lead to an important saving1 as its combustion produces an equal quantity of light at somewhat more than one-half of the expense for spermaceti oil4 ,careful trials have been made of this oil2 and on the #ajth of ,march #ahdg1 ,i was enabled to report the results to the ,commissioners of ,northern ,lighthouses in the following terms3 8#a4 ,the colza oil possesses the advantage of remaining fluid at temperatures which thicken the spermaceti oil so that it requires the application of the frost lamp4 8#b4 ,it appears1 from pretty careful photometrical measurements of various kinds1 that the light derived from the colza oil is1 in point of intensity1 a little superior to that derived from the spermaceti oil1 being in the ratio of #ajef to #a4 8#c4 ,the colza oil burns both in the ,fresnel lamp and the single ,argand burner with a thick wick during seventeen hours without requiring any coaling of the wick or any adjustment of the damper2 and the flame seems to be more steady and free from flickering than that from spermaceti oil4 8#d4 ,there seems 7most probably owing to the greater steadiness of the flame7 to be less breakage of glass chimneys with the colza than with the spermaceti oil4 8#e4 ,the consumption of oil1 in so far as that can be ascertained during so short a period of trial1 seems in the ,fresnel lamp to be #aba for colza1 and #aad for spermaceti2 while in the common ,argand1 the consumption appears to be #iaj for colza1 and #ijb for spermaceti4 8#f4 ,if we assume the means of these numbers1 #eae for colza1 and #ejh for spermaceti1 as representing the relative expenditure of these oils1 and if the price of colza be #cs4 #i;d41 while that of spermaceti is #fs4 #i;d4 per imperial gallon1 we shall have a saving in the ratio of #a to #agee1 which1 at the present rate of supply for the ,northern ,lights1 would give a saving of about ,l4#cbff per annum4 8,of these conclusions1 the three last may be considered as more or less conjectural1 being founded on data derived from too short a trial2 but the striking agreement of the results obtained at the six lights in which the experiments were made1 tends in some measure to supply the place of a longer period of trial2 and ,i have no hesitation1 therefore1 in recommending the ,board at once to introduce the use of the colza oil into all the dioptric lights1 except that of ,skerryvore1 where some special reasons induce me to defer the change for another season4 ,in the catoptric lights1 the only reason for not making an equally extensive trial is the necessity for renewing all the burners1 which require to be so constructed as to receive thick wicks of brown cotton2 and it may perhaps be considered prudent to proceed with some caution in changing the apparatus1 so as to suit it for burning a patent oil1 the circumstances attending the regular and extensive supply of which are not yet fully known4 ,i may remark1 that ,i have burnt the colza oil in the solar lamp alluded to in my last report2 but ,i disapprove of it as tending to elongate the flame vertically1 and thus to decrease its horizontal volume4 ,the elongated form of flame increases the divergence vertically where the light is lost1 and so far circumscribes its horizontal range where it is most required4 ,i have therefore substituted the thick wick burner for the solar lamp1 whereby an equally complete combustion is obtained1 and the proper form of the flame is at the same time preserved40#cf #cf ,since the above report was written1 the price of colza oil has risen2 and other circumstances have occurred to justify the caution as to the universal adoption of that oil4 99 99 99 99 99 ,drummond and ,voltaic ,lights4 ,the application of the ,drummond and ,voltaic lights#cg to lighthouse purposes is1 owing to their prodigious intensity1 a very desirable consummation2 but it is surrounded by so many practical difficulties that1 in the present state of our knowledge1 it may safely be pronounced unattainable4 ,the uncertainty which attends the exhibition of both these lights1 is of itself a sufficient reason for coming to this conclusion4 ,but other reasons unhappily are not wanting4 ,the smallness of the flame renders them wholly inapplicable to dioptric instruments1 which require a great body of flame in order to produce a degree of divergence sufficient to render the duration of the flash in revolving lights long enough to answer the purpose of the mariner4 ,m4 ,,fresnel made some experiments on the application of the ,drummond light to dioptric instruments1 which completely demonstrate their unfitness for this combination4 ,he found that the light obtained by placing it in the focus of a great annular lens was much more intense than that produced by the great lamp and lens2 but the divergence did not exceed #cj2 so that1 in a revolution like that of the ,corduan ,light1 the flashes would last only #a second1 and would not1 therefore1 be seen in such a manner as to suit the practical purposes of a revolving light4 ,the great cylindric refractor used in fixed lights of the first order1 was also tried with the ,drummond light in its focus2 but it gave coloured spectra at the top and bottom1 and only a small bar of white light was transmitted from the centre of the instrument4 ,the same deficiency of divergence completely unfits the combination of the ,drummond light with the reflector for the purposes of a fixed light1 and even if this cause did not operate against its application in revolving lights on the catoptric plan1 the supply of the gases1 which is attended with almost insurmountable difficulties1 would1 in any case1 render the maintenance of the light precarious and uncertain in the last degree4 #cg ,the ,drummond light is produced by the ignition or combustion of a ball of lime 7 inch diameter7 in the united flames of hydrogen and oxygen gases1 and is equal to about #bfd flames of an ordinary ,argand ,lamp with the best ,spermaceti oil4 ,it derives its name from the late ,,lieut4 ,,drummond1 ,r4 ,e41 who first applied it in the focus of a parabolod for geodetical purposes1 and afterwards proposed it for ,lighthouses4 7,see his ,account of the ,light in the ,phil4 ,trans4 for #ahbf1 p4 #cbd1 and for #ahcj1 p4 #chc47 ,the ,voltaic light is obtained by passing a stream of ,voltaic electricity from a powerful battery between two charcoal points1 the distance between which requires great nicety of adjustment1 and is the chief circumstance which influences the stability and the permanency of the light4 ,the ,voltaic light greatly exceeds the ,drummond light in intensity1 as ascertained by actual comparison of their effects2 but the ratio of their power has not been accurately determined4 ,it was first exhibited in the focus of a reflector by ,mr ,,james ,,gardner1 formerly engaged in the ,ordnance ,survey of ,great ,britain4 ,mr ,gurney's ,lamp4 ,in #ahce1 ,mr ,,gurney proposed the combination of a current of oxygen with the flame of oil1 in order to obtain a powerful light of sufficient size to produce the divergence required for the illumination of lighthouses4 ,the ,trinity-,house of ,london entertained the proposal1 and made some experiments on this important subject2 but the plan was finally rejected as disadvantageous in practice4 ,argand ,burners4 ,until the invention by ,,argand 7about the year #aghd71 of the lamp with a double current of air1 the art of illumination seems to have received no improvement1 and to have occupied very little attention from the time of ,,cardan1 or at all events of ,dr ,,hook1 who1 about the year #afgg1 in a monograph entitled 8,lampas10 made some important observations on the constitution of flame1 so as to make one wonder that he should have stopped short of the discoveries of later inventors4 ,before ,,argand',s time1 every wick consisted of a solid cord1 whose flame was fed only by the current of air on its outside2 and the consequence of this arrangement is1 that the stream of vapour or smoke1 especially from the centre of thick wicks1 escapes unburnt1 because1 before it reaches the height at which the combustion of the central stream can take place1 its temperature has become too low to admit of its ignition4#ch ,the chief improvements which had been made1 consisted in varying the level of the oil in the cistern1 or in attempts to render that level constant1 by mechanical means1 and in lessening the thickness of the wick1 by spreading its substance into a flat form1 thus reducing the stream of gas which escapes from the centre of a thick cylindric wick without being burnt1 and thereby causing a more complete combustion1 and producing less smoke and a whiter flame4 ,to ,,argand belongs the great merit of having first formed the wick into a hollow cylinder1 thus supplying the flame with two currents of air1 one of which1 as in the case of the solid wick1 envelopes the flame1 and the other1 passing through the centre of the wick1 is enveloped by the flame itself4 ,he also added a chimney1 which served to defend the flame from irregular draughts of air1 and to regulate the proportion between the velocities of the currents of air and the stream of gas4 ,this was indeed a most important step in the art of illumination1 and causes the great difference between the incomplete combustion1 which1 owing chiefly1 as we have seen1 to a defect in the supply of air1 always takes place with a solid wick 7from which much unburnt gas escapes in the form of smoke71 and that more perfect combustion in which passage is given for a free current of air through the centre of the wick4 ,the invention of ,,argand came nearly perfect from his hands2 and but a few slight modifications of his original arrangement have been introduced4 ,the ,argand burner consists of two concentric tubes or cylinders1 separated by a small annular space1 which is shut at the bottom1 and communicates by a pipe with the oil fountain1 whose level ought to be a little below the level of the upper edge of the cylinders4 ,in this annular space1 partly filled with oil from the fountain1 stands a cylindric wick of cotton1 loosely wove1 into which the oil rises freely by capillary action4 ,the wick has its lower edge fixed to a metallic ferule or ring1 called a wickholder1 which 7by means of a peculiar arrangement1 to be afterwards described7 gives the power of raising or depressing the wick to any convenient level with regard to the burner4 ,a cylinder of glass1 of greater diameter than the burner1 rests on a gallery or ring which hangs from the burner and surrounds it4 ,this glass cylinder1 or chimney as it is generally called1 should stand vertically with its axis coincident with that of the burner itself4 ,the effect of this arrangement is obvious1 and has already in part been indicated4 ,the flame is thus necessarily bounded on all sides by two conical concentric surfaces1 one external and concave1 and the other internal and convex1 both of which receive a free current of air4 ,the flame is therefore very thin in every direction2 and1 as a consequence of the mutual radiation of its different parts on each other1 it is throughout its entire surface of more equal temperature than can ever be attained in the thick solid wick or the narrow flat one4 ,the glass cylinder also increases the force of the two currents which pass outside and inside of the flame2 and the union of so many favourable circumstances produces a greater amount of pure light than has yet been obtained by any other method4 ,the contraction of the glass chimney 7known by the technical name of the shoulder7 at a point a little above the level of the wick1 tends to direct the current of air inwards on the flame1 thereby causing a more perfect combustion and the evolution of more light4 #ch ,that the form of a flame is necessarily conoidal1 and that its height is determined by the relation subsisting between its diameter and the continually varying velocities of the currents of gas and air1 may be easily shewn2 and the combustion of each annular film of the stream of gas from the wick can take place only at a level determined by1 and continually varying with1 the ratio of the velocities of the streams of gas and air4 ,i am unwilling to offer this explanation in my own words1 when those of ,m4 ,peclet1 in his excellent work1 ,trait de l',eclairage1 are at hand1--8,let us conceive10 says he1 8a very thin film or layer of inflammable gas placed horizontally1 and which rises into the air parallel to itself1 with a uniform motion4 ,we shall suppose that it cannot be burnt1 except at its circumference1 and that the top and bottom of the film are1 by some means1 preserved from combustion 7they are so preserved in ordinary flames1 by the films which precede and follow them74 ,if the circumference is at a high enough temperature it will burn2 at each instant the film or layer of air1 which has assisted the combustion and also the products of that combustion1 being very hot1 will rise very rapidly1 and will make room for other layers or films of air1 which will rise in their turn2 and as the diameter of the film of gas is continually diminishing1 it is obvious that its combustion will offer the appearance of a series of circles continually growing smaller1 and terminating at length in a point4 ,if we trace in thought the series of circles which the combustion has successively developed1 we shall form a cone whose length will depend on the ratio of the velocities of the films of gas and of air which escape after combustion4 ,if1 for example1 the velocity of the current of air were very great1 compared to the velocity of the cylinder of gas1 the entire combustion would take place1 while the film of gas passes over a very small space2 and the cone formed by the succession of luminous circles would1 consequently1 be very short4 ,if1 on the contrary1 there were but a very small difference between these velocities1 the luminous circles would only appear at considerable intervals from each other2 for the air which had served for combustion1 being unable to feed it longer1 the surface of the cylinder could not become luminous until the difference of velocity had freed it from the air which had served for the preceding combustion4 ,if1 then1 we imagine a set of similar films succeeding each other1 each of them would give rise to the same series of coloured rings2 and as there would be a film in each section of the cone in a state of combustion at the same instant of time1 the cone would1 of course1 appear luminous throughout its height40--,peclet1 ,trait de l',eclairage1 p4 #ea4 ,great as the improvement of ,,argand undoubtedly was1 the value of the lamp alone as a means for the illumination of lighthouses must be regarded as comparatively small4 ,the primary object of a lighthouse is to give early notice to the mariner of his approach to the coast1 and it is therefore necessary that the light be of such a kind that it may be seen at a great distance4 ,every one is practically acquainted with the fact that the rays proceed in all directions from a luminous body in straight lines2 and if we could obtain a ball equally luminous in every part of its surface1 it would give an equal share of light to every part of the inner surface of a hollow sphere1 whose centre coincided with the centre of the ball4 ,again1 if an opaque body were placed between the luminous ball and the hollow sphere1 the part opposite that body would be deprived of the light by the interception of the rays1 and no light would emerge from a hole bored in that part of the surface of the hollow sphere4 ,the bearing of these facts is obvious2 and no one can fail to perceive that in the case of a lighthouse illuminated by a single unassisted burner1 a seaman could only receive the benefit of that small portion of light which emerges from the lamp in a line joining his eye and the centre of the flame4 ,the other rays would be occupied partly in making the light visible in other parts of the horizon1 and but a very small portion of them would be usefully employed for that purpose1 while all the rest would be lost by escaping upwards into the sky1 or downwards below the plane in which seamen can see a lighthouse4 ,this state of matters would be little improved by increasing the number of burners1 as the effective part of the light would only be augmented by the addition of an equally trifling portion of light from each burner4 ,the small pencils of rays thus meeting at the eye of a distant observer1 would form a very minute fraction of the whole quantity of light uselessly escaping above and below the horizon1 and also at the back of each flame2 and the wasteful expenditure of light would be enormous4 ,by such a method no practically efficient sea-light could ever be obtained4 ,,catoptric#ci ,,system ,,of ,,lights4 #ci ,from the ,greek 1 a mirror2 a compound of 1 opposite to1 and 1 ,i see4 ,for those defects a simple remedy is found in the well known power possessed by most bodies1 of reflecting or throwing back from them the light which falls upon them4 ,this property is not possessed by all reflecting bodies in an equal degree1 some absorbing more and some less of the incident light4 ,perhaps the earliest attempts to apply this property as a corrective for the direction of the rays from a ,lighthouse1 would be confined to placing plane mirrors behind each lamp2 yet this would prove but a partial remedy1 as it would still leave the greater part of the light to stray above and below the proper direction4 ,hollow mirrors of a spherical form might next be tried2 and if properly placed with reference to the flame1 would constitute a very great improvement in lighthouse illumination4 ,but those steps in the march of improvement are more imaginary than real2 and ,i am not aware of any well authenticated records of such gradual attempts having preceded the adoption of the right mode of applying reflection as a means of rectifying the direction of the rays emerging from a lighthouse4 ,there is1 on the contrary1 distinct evidence that the impulse given by ,,argand',s invention1 led to an immediate adoption of the most perfect form of reflecting instruments4 ,application of ,parabolodal ,mirrors into ,lighthouses4 ,the name of the inventor of parabolodal mirrors and the date of their first application to ,lighthouses1 have not been accurately ascertained4 ,the earliest notice which ,i have been able to find1 is that by ,mr ,,william ,,hutchinson1 the pious and intelligent author of a quarto volume on 8,practical ,seamanship0 7published at ,liverpool in #agia71 who notices 7at p4 #ic7 the erection of the four lights at ,bidstone and ,hoylake1 in the year #agfc1 and describes large parabolic moulds1 fashioned of wood and lined with mirror-glass1 and smaller ones of polished tin-plate1 as in use in those ,lighthouses4 ,mr ,,hutchinson seems to have understood the nature1 properties1 and defects of the instruments which he describes1 and has shewn a good acquaintance with many of the most important circumstances to be attended to in the illumination of ,lighthouses4 ,many claims to inventions rest on more slender grounds than might be found in ,mr ,,hutchinson',s book for concluding him to have first invented the parabolodal mirror and applied it to use in a ,lighthouse2#dj but1 in the absence of any statement as to the date when the mirrors were really adopted1 the merit of the improvement must1 in justice1 be awarded to others4 #dj ,mr ,,hutchinson seems also 78,practical ,seamanship10 p4 #aih7 to have tried speculum metal as a material for ,lighthouse reflectors4 ,m4 ,,teulere1 a member of the ,royal ,corps of ,engineers of ,bridges and ,roads in ,france1 is1 by some1 considered the first who hinted at the advantages of parabolodal reflectors2 and he is said1 in a memoir dated the #bfth ,june #aghc1 to have proposed their combination with ,argand lamps1 ranged on a revolving frame1 for the ,corduan ,lighthouse4 ,whatever foundation there may be for the claim of ,m4 ,,teulere1 certain it is that this plan was actually carried into effect at ,corduan1 under the directions of the ,,chevalier ,,borda2 and to him is generally awarded the merit of having conceived the idea of applying parabolodal mirrors to lighthouses4 ,these were most important steps in the improvement of lighthouses1 as not only the power of the lights was thus greatly increased1 but the introduction of a revolving frame proved a valuable source of differences in the appearance of lights1 and1 in this way1 has since been the means of greatly extending their utility4 ,the exact date of the change on the light of the ,corduan is not known2 but as it was made by ,,lenoir1 the same young artist to whom ,,borda1 about the year #aghj1 entrusted the construction of his reflecting circle1 it has been conjectured by some that the improvement of the light was made about the same time4 ,the reflectors were formed of sheet-copper1 plated with silver1 and had a double ordinate of #ca ,french inches4 ,it was not long before these improvements were adopted in ,england1 by the ,trinity-,house of ,london1 who sent a deputation to ,france to inquire into their nature4 ,in ,scotland1 one of the first acts of the ,northern ,lights ,board in #aghf1 was to substitute reflectors in the room of the coal-light then in use at the ,isle of ,may in the ,frith of ,forth1 which1 along with the light on the ,cumbrae ,isle in the ,frith of ,clyde1 had1 till that period1 been the only beacons on the ,scotch coast4 ,the first reflectors employed in ,scotland were formed of facets of mirror glass1 placed in hollow parabolodal moulds of plaster1 according to the designs of the late ,mr ,,thomas ,,smith1 the ,engineer of the ,board1 who 7as appears from the article ,reflector1 in the ,supplement to the third edition of the ,encyclopdia ,britannica7 was not aware of what had been done in ,france1 and had himself conceived the idea of this combination4 ,the same system was also adopted in ,ireland2 and in time1 variously modified1 it became general wherever lighthouses are known4 ,reflection4 ,to enable us to enter on the subject of the proper forms of reflectors1 we must glance very briefly at the laws of reflection4 ,those laws are two in number4 #ast1 ,the ray which falls on a reflecting surface1 called the incident ray1 and the ray which leaves the reflector1 called the reflected ray1 are always in one plane1 which plane is perpendicular to the reflecting surface4 #b;d1 ,the angle which the reflected ray makes with the reflector is always equal to the angle which the incident ray makes with it1 or1 in other words1 the angle of incidence is equal to the angle of reflection4#da #da ,this will be more readily understood by referring to the accompanying figure 7,no4 #bb71 in which ,,cdef is the reflecting surface2 ,,ghoki the plane of reflection perpendicular to that surface2 ,,bo a line perpendicular or normal to the surface ,,cdef2 and ,,ao the incident ray4 ,then if in the plane ,,ghoki1 the angle ,,boi be made equal to ,,aob1 ,,oa is the reflected ray2 ,,bog is then the angle of incidence2 and ,,boi the angle of reflection4 ,,goh and ,,iok1 which are the complements of those angles1 are1 indeed1 more strictly speaking1 the angles of incidence and reflection2 but in cases where the reflecting surface is curved1 it is more convenient to refer the angles to the normal ,,bo4 ,illustration3 ,fig4 #bb4 ,it would lead to prolixity altogether superfluous in this place1 to explain1 in a rigorous manner1 the effects produced by various reflecting surfaces on the direction of the rays incident on them2 as any one who comprehends the laws of reflection just enumerated1 may easily satisfy himself of the following truths3 #ast1 ,that a plane mirror makes no change on the divergence of the rays1 but merely causes them to emerge from its surface in the same direction as if they had come from a point as much behind the mirror as the luminous body lies in front of it4 #b;d1 ,a convex reflecting surface increases divergence1 and disperses the rays in the same manner as if they had come directly from a point behind it1 whose distance from the mirror increases with the distance of the luminous body from its surface1 and diminishes with the degree of convexity of the mirror4 #c;d1 ,a concave surface diminishes the divergence of the rays incident upon it from a point between the surface and its centre of curvature2 the distance of the point in which the reflected rays converge diminishing as the distance of the radiant point or the concavity of the mirror is increased4 ,it is obvious1 therefore1 that concave mirrors are those which are required to produce a correction of the path of the rays1 so as to apply them to most advantage in a lighthouse1 the object to be attained being that of throwing the greatest amount of light towards given points in the horizon1 and collecting the divergent rays1 which1 as we have already seen1 are scattered above and below it4 ,to simplify our view of this matter1 ,i shall1 in the first place1 suppose that the object to be attained is to throw the whole rays of a single lamp1 with an infinitely small flame1 to a given mathematical point at a moderate distance2 and1 as this is a case which can hardly occur in the practice of ,lighthouse illumination1 ,i content myself with observing that this object may be attained approximately by placing the lamp in front of a spherical mirror at any distance greater than half the radius of the curve surface1 or accurately by placing it in one focus of an elliptical mirror2 in all those cases the rays would meet in the opposite1 or1 as they are termed1 conjugate foci4 ,let us next suppose that our object is to illuminate1 by means of a mathematical point of light1 a small circular space on the horizon equal in diameter to the mirror employed2 this object will be rigorously attained only by placing the light in the focus of a parabolodal reflector4 ,the same object may be approximately attained by placing the light in a spherical mirror1 at a point half-way between the centre of curvature and the surface of the mirror1 provided the surface of the mirror shall subtend only a small angle at the centre of curvature4 ,the parabolodal mirror1 on the contrary1 has the property of converging to the focus parallel rays falling upon every point of its surface1 however extended it may be4 ,parabolodal ,mirrors4 ,any one practically acquainted with this subject1 must at once perceive that the parabolodal mirror completely fulfils one great object required in a lighthouse2 and to render this more obvious to the general reader1 ,i shall1 for the present1 confine my remarks to the case of those lighthouses which exhibit to the mariner in every part of the horizon1 pencils of light at certain intervals of time1 separated by periods of darkness1 reserving the consideration of ,lights which are continually in sight all round the horizon or over a given portion of it1 for a subsequent part of these ,notes4 ,in doing this1 ,i am aware that ,i may appear to be departing from the strict order of investigation1 by suddenly introducing the idea of motion2 but a little consideration will1 ,i think1 satisfy the reader that this is1 in reality1 the more convenient mode of treating the subject4 ,let us suppose1 then1 that our object is to give occasional flashes of light1 separated by intervals of darkness1 to seamen in various azimuths and at various distances from a lighthouse4 ,it is obvious that this may be most efficiently done by causing concave mirrors1 which collect the rays from lamps placed in them and thereby increase the light in front of the mirror1 to revolve round a vertical axis with a velocity suited to produce the required number of flashes in a given time4 ,the parabolodal mirror is best adapted for producing this effect1 for the following reasons3 #ast1 ,because it alone produces a rigorous parallelism of all rays proceeding from its focus1 and falling upon any point of its surface1 however distant the point of reflection from that focus1 or however far in front of it4 #b;d1 ,because it therefore embraces in its action the greatest number of the whole rays coming from the focus1 and1 cteris paribus1 will produce the strongest light4 #c;d1 ,because the theoretical object to be attained is to make those flashes equally powerful at any distance1 an effect which would be rigorously fulfilled by placing an infinitely small flame in a perfect parabolodal mirror4 ,and1 #dth1 ,because1 although absolute equality of luminousness at any distance is not attainable1 and1 in practice1 is inconsistent with other conditions required in a useful light1 we still1 by using the parabolic mirror1 make the nearest approach to parallelism of the reflected rays1 and consequently obtain the strongest light which is consistent with a due regard to a certain duration of the flash on the eye of a distant observer1 which is measured by the angle of the luminous cone projected to the horizon4 ,having thus so far anticipated what some might think would more naturally have occurred in a subsequent part of these ,notes1 ,i return to a more detailed consideration of the parabola itself1 and its product1 the parabolodal mirror4 ,i content myself1 however1 with describing the parabola1 by that property which peculiarly adapts it to the purposes of a lighthouse4 ,the parabola1 then1 is a curve of the second order1 obtained by cutting a cone in a plane parallel to one side1 which possesses this remarkable property1 that a line drawn from the focus to any point in the curve1 makes1 with a tangent at that point1 an angle equal to that which a line parallel to the axis of the curve makes with that tangent4#db #db ,see third corollary to ,proposition ,,iii4 of ,wallace's ,conic ,sections1 which shews that a tangent to the parabola makes equal angles with the diameter which passes through the point of contact and a straight line drawn from that point to the focus4 ,the curve may be traced in two different ways1 both dependent on the property1 that the distance of any point in the parabola from the focus is equal to its distance from the directrix4 ,to draw the curve mechanically 7fig4 #bc71 let ,f be the focus1 ,,mf the focal distance 7chosen at pleasure according to rules which ,i shall afterwards notice71 ,,kmx is the axis1 and ,,ab the directrix 7the dotted line f ,f e1 bounded by the curve at either end1 would then be the parameter or latus rectum74 ,place the edge of the straight ruler ,,akhb along the directrix2 and let ,,lhb be a square ruler which may slide along the fixed ruler ,,akhb1 so that the edge ,,hl may be constantly perpendicular to ,,ab1 or parallel to ,,mx1 the axis2 let ,,ldf be a string equal in length to ,,hl1 and having one end fixed in ,f1 and the other at ,l1 a point in the sliding square4 ,then if the string be stretched by a pencil ,d1 so as to keep the part ,,dl close to the edge of the square1 and if at the same time the square be gently pushed along the line ,,ab1 the point ,d will be forced to move along the edge ,,lh of the square1 and will trace out a curve which will be the required parabola4 ,this is obvious from the consideration1 that the string ,,ldf being equal in length to ,,lh1 and ,,ld being common to both1 the remainder ,,df must be equal to the remainder ,,dh1 so that the point which traces the curve being equidistant from the directrix and the focus must1 in terms of the above definition1 describe a parabola4 ,illustration3 ,fig4 #bc4 ,in the second place1 the same property1 as already stated1 furnishes us with the means of tracing the curve by finding successive points therein4 ,draw a line a b perpendicular to the axis ,,ox1 and the position in this line1 of a point p through which the curve passes1 is easily found thus3 ,describe from ,f the focus as a centre with a radius equal to the perpendicular distance ,o d of the line a b from the directrix ,,ab1 a circle cutting the line a b in two points p and p2 then both these points are in the curve4 ,by repeating the same process1 any number of points in the curve may be obtained4 ,illustration3 ,fig4 #bd4 ,lastly1 from the equation to the curve1 the length y of any ordinate may be computed1 in terms of m its principal focal distance1 and x its abscissa1 by the simple expression1-- y 7#d m x74 ,it is easy to see1 that if this curve revolve about its axis1 it will generate a parabolic conoid1 which we may conceive to be concave or convex1 as we please4 ,if the surface be concave1 we obtain the mirror of which we are in search2 for every principal section1 or that passing through the axis of such a mirror1 will necessarily possess the same properties as that of the plane curve1 and will each have a focus meeting in one and the same point2 the union of all these sections will therefore form a mirror capable of reflecting1 in a direction parallel to the axis and to each other1 all the rays of light which fall on its surface4 ,divergence of ,parabolodal ,mirrors4 ,we have already seen that a perfect parabolodal mirror1 with a point of light infinitely small placed in the focus1 would project a beam equally intense at any distance1 every transverse section of which would be of the same superficial extent4 ,in practice1 these conditions can never be rigorously fulfilled4 ,no perfect instrument can come from the hands of man1 and every mirror must of necessity possess many defects4 ,to obtain a true mathematical point of light is also impossible2 and for the purposes of a lighthouse1 it would be completely useless1 as will appear from the following simple considerations4 ,let us suppose that a true parabolodal mirror1 having a double ordinate or space of two feet1 and illuminated by a point of light1 projects a truly cylindric beam of light to the horizon1 and that it revolves horizontally round a vertical axis1 with such a velocity as to cause the beam to pass over the eye of an observer stationed at the distance of #ajj feet in one second of time1 and we shall find that another observer1 at a distance of #ae miles from the mirror1 would not see the light at all1 although of equal size1 because its velocity at that distance would be so great as only to be present to his eye for d of a second1 a space of time far too short to make a perceptible impression on the eye of a distant observer4 ,this is no mere hypothesis unsupported by facts2 for ,i shall have occasion1 in another part of these ,notes1 to describe certain experiments1 by which it was ascertained that a beam of light emerging from a lens1 and passing over the eye of an observer at #ad miles distance1 in a space of time equal to th of a second1 became altogether invisible at that distance4 ,for this evil1 happily a very simple and efficient remedy may be found in what may be said to constitute a theoretical defect in the combination of the ,argand burner with the reflector4 ,the burner1 instead of being a mathematical point1 has generally a diameter of about one inch1 and a ray proceeding from the edge of the flame to any point on the surface of the mirror1 makes with the line joining that point and the principal focus an angle which1 being repeated by reflection1 gives the effective divergence of each side of the mirror at that point4#dc #dc ,this is easily understood by reference to the accompanying figure 7,no4 #be471 in which ,,aob is a central section of a parabolodal mirror4 ,illustration3 ,fig4 #be4 ,,pf distance from the focus ,f to a point in the curve ,p1 and ,,pg a tangent drawn from ,p to the surface of the flame at ,g2 ,,fg radius of the wick or flame2 and ,,gpf ,g,,pf divergence of one side of mirror1 and consequently #b ,,gpf the whole effective divergence of the mirror at that cross section4 ,,gf ,now sin ,,gpf -- ,,pf or the sine of the divergence from each point ,radius of flame4 ---------------------------------------- --- ,distance from focus to point of reflection4 ,illustration3 ,fig4 #bf4 ,it is obvious that this quantity which varies inversely with the distance of the reflecting surface from the focus1 is greatest at the vertex of the curve1 and least at the sides or edges of the parabolod4 ,the most useful part of the light1 or that which conduces to the strongest part of the flash in a revolving light1 is that which is derived from the cone of rays which is bounded by the limits of this minimum divergence2 for the faint light which first reaches the eye of a distant observer1 in the revolution of a reflector1 is not that which is reflected by the sides or edges1 as might at first be supposed1 but proceeds from the centre4 ,the light1 in fact1 gradually increases in power in proportion as additional rays of reflected light are brought to bear on the observer's eye1 until1 last of all1 the extreme edge of the mirror adds its effect4 ,the light continues in its best state until the opposite limit of minimum divergence has been reached1 when it begins gradually to decline1 receding from the margin of the mirror towards the centre1 and1 having at length reached the limit of its maximum divergence1 it finally disappears at the centre4 ,the increase and decline of the power of a mirror in the course of its movement round the circle of the lantern1 as seen by a distant observer1 will1 therefore1 in all its different states1 be measured by the areas of a series of circles described from its focus1 with radii equal to the distance of the focus from the point of the mirror which reflects to the observer's eye the extreme ray which can reach him in any given position of the mirror4 ,this will be more easily understood by referring to the accompanying diagram1 ,fig4 #bf1 in which e a e is the principal section of a parabolodal mirror1 ,f its focus1 ,,fa its axis1 and ,,fk the radius of the flame4 ,if the reflector revolve round a vertical axis at ,o1 an observer placed in front of it 7at a distance so great that the subtense of the mirror's width would be small enough to allow us safely to consider the lines drawn from e and e to his eye as parallel71 would receive the first ray of light in the direction a ,d1 as reflected at a1 from a single point on the edge of the flame 7where a tangent to the flame would pass through a72 and conversely he would lose the last ray at ,d1 as reflected at a1 from a single point on the opposite margin of the flame2 and hence1 as above1 the greatest divergence is measured by the angle which the flame subtends at the vertex a of the mirror1 being the sum of the angles and 4 ,we shall next suppose the mirror to move a little1 so that the observer may receive at ,g a ray of light from some other point in the flame which is reflected at b2 while another ray from an opposite point reflected at b would be seen in the parallel direction b ,g1 thus indicating the boundary of a circular portion of the mirror b a b1 the whole of which would reflect light to the distant observer's eye4 ,again1 let us suppose a ray to come from another part of the flame1 and be reflected at the mirror's edge e into the direction e ,h1 and another from the opposite side of the flame to be reflected at its opposite edge e1 into the direction e ,g1 and we obtain the full effect of the whole reflecting surface1 which will continue unabated until the mirror in the course of its revolution shall reflect at e to the observer's eye1 a ray from a point in the margin of the flame 7through which a tangent drawn from e to the flame would pass7 in such a direction1 that the angle which it makes with the axis of the mirror is equal to that subtended by the radius of the flame at the distance ,f e or ,f e4 ,after this the light would recede from the edges of the mirror in the same gradual manner1 until it should vanish in the direction a ,d1 which is the opposite limit of the extreme divergence of the instrument4 ,in the above explanation1 ,i have confined myself simply to the effects of the outer ring of the flame1 which is the source of divergence2 but ,i need not remind the reader that every portion of the flame radiates light1 which1 being reflected1 conduces to the effect4 ,some rays also are passing from the opposite sides of the flame through the true focus1 so as to be normally reflected in lines parallel to its axis4 ,the solid lines in the diagram shew the theoretical reflection of rays proceeding from ,f to b1 b1 e1 e1 where they are diverted into the directions b ,b1 b ,b1 e ,e1 and e ,e2 and by contrast with the dotted lines1 serve to render more perceptible the path of the divergent rays which come from the edge of the flame4 ,the ,greek letters indicate the angles of divergence1 and point out their relations to each other on either side of the mirror4 ,the arcs of greatest and least divergence are marked in the diagram4 ,this subject will be found treated less directly1 but1 certainly1 more concisely and neatly1 by ,mr ,w4 ,h4 ,,barlow1 in a paper on the ,illumination of ,lighthouses in the ,london ,transactions for #ahcg1 p4 #bah4 ,it is still more obvious that a perfect parabolodal figure1 and a luminous point mathematically true1 would render the illumination of the whole horizon by means of a fixed light impossible2 and it is only from the divergence caused by the size of the flame which is substituted for the point1 that we are enabled to render even revolving lights practically useful4 ,but for this aberration1 the slowest revolution in a revolving light would be inconsistent with a continued observable series1 such as the practical seamen could follow1 and would1 as we have seen1 render the flashes of a revolving light too transient for any useful purpose2 whilst fixed lights1 being visible in the azimuths only in which the mirrors are placed1 would1 over the greater part of the distant horizon1 be altogether invisible4 ,the size of the flame1 therefore1 which is placed in the focus of a parabolodal mirror1 when taken in connexion with the form of the mirror itself1 leads to those important modifications in the paths of the rays and the form of the resultant beam of light1 which have rendered the catoptric system of lights so great a benefit to the benighted seamen4 ,in order to obtain a mirror capable of producing a given divergence of the reflected beam1 therefore1 we must proportion its focal distance to the diameter of the flame in such a manner1 that the sine of one-half of the whole effective divergence of the mirror1 may be equal to the quotient of the radius of the flame1 divided by the distance of a given point on the surface of the mirror from the focus4 ,the best proportions for parabolodal mirrors depend on the objects which they are meant to attain4 ,those which are intended to give great divergence to the resultant beams1 as in fixed lights1 capable of illuminating the whole horizon at one time1 should have a short focal distance2 while those mirrors which are designed to produce a nearer approach to parallelism 7as in the case of revolving lights which illuminate but a few degrees of the horizon at any one instant of time71 will have the opposite form4 ,those two objects may1 no doubt1 be attained with the same mirror1 by increasing or diminishing the size of the burner2 but that is by no means desirable1 as any change on the size of a burner1 which is found to be the best in other respects1 must be considered as to some extent disadvantageous4 ,what ,i have stated above as to the use of mirrors with a short focal distance for lights of great divergence1 proceeds on the assumption1 that the penumbral portion of the light on each side of the strongest beam 7which is confined within the limits of the least divergence1 due to that portion of the mirror where the focal distance is the greatest7 is to be pressed into service in the illumination of the horizon2 and it is the chief inconvenience which attends the application of parabolodal mirrors to fixed lights1 that because it is impracticable to apply a number of mirrors sufficient to light the whole horizon with an equally strong light1 spaces occur on either side of each reflector in which the mariner has a light sensibly inferior to that which illuminates the sector near the axis of each mirror4 ,this will be best explained by stating the numerical results of the computations of the divergence of the mirrors used in the ,northern ,lights for this purpose1 both at the vertex and the sides4 ,in a mirror whose focal distance is #d inches1 and its greatest double ordinate #ba inches1 illuminated by a flame #a inch in diameter1 we find by computation1 that the greatest divergence is #ad #bb1 and that the strongest arc of light is only #e #af2 a difference so great1 that while the one may admit of the horizon being imperfectly illuminated by means of #bf reflectors1 the superior light which would result from confining the duty of each instrument within the range of its best effect1 could only be obtained by the use of #fh reflectors1 and the expenditure of a proportionately great quantity of oil1 not to speak of the great practical difficulty which would attend the arrangement of so many lamps in a lantern of moderate size4 ,in revolving lights1 the mirrors are not1 as in fixed lights1 inconveniently taxed for horizontal divergence1 because each portion of the divergent beam visits successively each point of the horizon4 ,in this view of the merits of fixed and revolving lights1 ,i should be disposed to recommend1 in any new organisation of lights with parabolic reflectors1 the adoption1 in fixed lights1 of reflectors with a short focal distance and small span1 so as to admit of many being ranged around the frame2 while in revolving lights1 it would be my aim to approach the largest size of reflector that could be made1 so as if possible to illuminate each face of the revolving frame by means of a large lamp in a single mirror1 with a great focal distance1 thereby diminishing the difference between the divergence of the powerful cone of rays reflected from the more distant parts of the mirror and that of the feebler and more diffuse light from its apex4 ,effect of ,parabolodal mirrors4 ,the maximum luminous effect of the reflectors ordinarily employed in fixed lights1 as determined by observation1 is generally equal to about #cej times the effect of the unassisted flame which is placed in the focus2 while for those employed in revolving lights1 which are of larger size1 it is valued at #dej4 ,this estimate1 however1 is strictly applicable only at the distances at which the observations have been made1 as the proportional value of the reflected beam must necessarily vary with the distance of the observer1 agreeably to some law dependent upon the unequal distribution of the light in the illuminous cone which proceeds from it4 ,the effect also varies very much in particular instruments4 ,the ordinary burners used in lighthouses are one inch in diameter1 and the focal distance generally adopted is #d inches1 so that the extreme divergence of the mirror in the horizontal plane may be estimated at about #ad #bb2 while the divergence of the most luminous cone is #e #af for the small reflectors1 and #d #be for the larger size4 ,in arranging reflectors on the frame of a fixed light1 however1 it is advisable to calculate upon a less amount of effective divergence1 for beyond #aa the light is very feeble2 but the difficulty of placing many mirrors on one frame1 and the great expense of oil required for so many lamps1 have generally led to the adoption of the first valuation of the effective divergence4 ,power of ,parabolodal ,mirrors4 ,the measure of the illuminating power of a parabolodal mirror may be estimated as the quotient of the ,,surface of the circle which cuts it in the plane of its greatest double ordinate1 divided by the surface of the largest vertical section of the flame1 and diminished by the loss of light in the process of reflection4 ,this estimate will be found near enough for all practical purposes2 but it is obviously inaccurate1 inasmuch as it overlooks the circumstance of the focal distance of each portion of the mirror being different1 and the consequent increase in the length of the various trajectories at each point of the surface as you recede from the axis2 and the only correct rule1 therefore1 is1 to find an imaginary focal distance which must be the radius of a spherical segment which shall answer the double condition of having its surface equal to that of the greatest cross section of the mirror1 and of including1 at the same time1 a number of degrees equal to those which are brought under the influence of the reflecting action of the parabolod4 ,this subject1 however1 as ,i have already hinted1 is not of great practical importance2 and ,i shall not therefore dilate on it farther1 but content myself with saying1 that such a line will be found to be a mean proportional between the greatest and least focal distances of the mirror4#dd ,the large mirrors used in the ,northern ,lights have about ths of the whole light of the lamp incident on their surface2 the rest escapes in the comparatively useless state of naturally radiating light4 #dd ,this subject is treated in detail in ,m4 ,,barlow',s ,paper already noticed4 7,london ,transactions for #ahcg1 p4 #bab47 ,manufacture of ,reflectors4 ,the reflectors used in the best lighthouses1 are made of sheet-copper plated in the proportion of six ounces of silver to sixteen ounces of copper4 ,they are moulded to the parabolodal form1 by a delicate and laborious process of beating with mallets and hammers of various forms and materials1 and are frequently tested during the operation by the application of a mould carefully formed4 ,after being brought to the curve1 they are stiffened round the edge by means of a strong bizzle1 and a strap of brass which is attached to it for the purpose of preventing any accidental alteration of the figure of the reflector4 ,polishing powders are then applied1 and the instrument receives its last finish4 ,the details of this manufacture are given in the ,appendix4 ,testing of ,mirrors4 ,two gauges of brass are employed to test the form of the reflector4 ,one is for the back1 and is used by the workmen during the process of hammering1 and the other is applied to the concave face as a test1 while the mirror is receiving its final polish4 ,it is then tested1 by trying a burner in the focus1 and measuring the intensity of the light at various points of the reflected conical beam4 ,another test may also be applied successively to various points in the surface1 by masking the rest of the mirror2 but as it proceeds upon the assumption that the surface of the reflector is perfect1 and that we can measure accurately the distance from a radiant coincident with the focus to the point of the mirror to be tried1 it is in practice almost useless4 ,for such a trial we must place a screen in the line of the axis of the mirror at some given distance from it1 and ascertain whether the image of a very small object placed in the conjugate focus1 which is due to the distance of the screen in front of the focus1 be reflected to any point considerably distant from the centre of the screen through which the prolongation of the axis of the mirror should pass4 ,we thus obtain a measure of the error of the instrument4 ,for this purpose1 we must find the position of the conjugate focus1 which corresponds to the distance of the screen4 ,if b be the distance to which the object should be removed outwards from the principal focus of the mirror1 d the distance from the focus to the screen1 and r the distance from the focus to that point of the mirror which is to be tested1 we shall have r b ---- d as the distance to which the object must be removed outwards from the true focus on the line of the axis4#de #de ,the truth of this equation may be easily ascertained as follows 7,see fig4 #bg73--,let ,,ap be the mirror1 ,f its principal focus1 and ,,ph the line of reflection of the ray ,,fp2 then an object at ,i will be reflected at ,p to the conjugate focus ,o1 where the screen is supposed to be placed4 ,but by construction1 ,,fpi ,,hpo ,,pof1 and the angle at ,f being common1 the triangle ,,fpi is similar to ,,fpo1 and hence ,,fo ,,pf ,,pf ,,fi1 and ,,pf ,,fi ---2 ,,fo and substituting the letters in the text1 we get d r r b1 and r b ----4 d ,illustration3 ,fig4 #bg4 ,illustration3 ,fig4 #bh4 ,illustration3 ,fig4 #bi4 ,illustration3 ,fig4 #cj4 ,illustration3 ,fig4 #ca4 ,argand ,lamps used in ,reflectors4 ,the flame generally used in reflectors1 is from an ,argand fountain-lamp1 whose wick is an inch in diameter4 ,much care is bestowed upon the manufacture of the lamps for the ,northern ,lighthouses1 which sometimes have their burners tipped with silver to prevent wasting by the great heat which is evolved4 ,the burners are also fitted with a sliding apparatus1 accurately formed1 by which they may be removed from the interior of the mirror at the time of cleaning them1 and returned exactly to the same place1 and locked by means of a key4 ,this arrangement1 which is shewn in figs4 #bh1 #bi1 and #cj1 is very important1 as it insures the burner always being in the focus1 and does not require that the reflector be lifted out of its place every time it is cleaned2 so that1 when once carefully set and screwed down to the frame1 it is never altered4 ,in these figs4 a a a represents one of the reflectors1 b is the burner1 and c a cylindric fountain1 which contains #bd ounces of oil4 ,the oil-pipe1 the fountain c for supplying oil1 and the burner b1 are connected with the rectangular frame d1 which is moveable in a vertical direction upon the guide-rods e and f1 by which it can be let down1 so that the burner may be lowered out of the reflector1 by simply turning the handle g 7as will be more fully understood by examining figs4 #bh and #bi71 which has the effect of forcing a thread 7like that of a screw7 on the outside of the guide into a groove in the frame1 or withdrawing it1 and thus allows it to slide down or locks it at pleasure4 ,an aperture of an elliptical form1 measuring about two inches by three1 is cut in the upper and lower part of the reflector1 the lower serving for the free egress and ingress of the burner1 and the upper1 to which the copper tube h is attached1 serving for ventilation2 i shews a cross section and a back view of the main bar of the chandelier or frame on which the reflectors are ranged1 each being made to rest on knobs of brass1 one of which1 as seen at k k1 is soldered to the brass band l1 that clasps the exterior of the reflector4 ,fig4 #bh is a section of the reflector a a1 shewing the position of the burner b1 with the glass chimney b1 and oil-cup l1 which receives any oil that may drop from the lamp4 ,fig4 #cj shews the apparatus for moving the lamp up and down1 so as to remove it from the reflector at the time of cleaning it4 ,in the diagram 7fig4 #cj7 the fountain c is moved partly down2 d d shews the rectangular frame on which the burner is mounted1 e e the elongated socket-guides through which the guide-rods slide1 and f the guide-rod1 connected with the perforated sockets on which the checking-handle g slides4 ,the oil-cup l 7covered with a lid and wick-holder1 as shewn in fig4 #ca7 also serves as a frost-lamp during the long nights of winter1 when the oil is apt to turn thick4 ,it is attached to the lower part of the oil-tube by the arm h2 and is lighted about an hour before sunset1 so as to prepare the reflector lamp for lighting at the proper time4 ,the communication between the burner and the fountain is easily opened or shut in the burners used in the ,scotch ,lighthouses1 by simply giving the fountain a turn of one quadrant of the horizon round its own vertical axis by means of the round knob at its top1 and thereby moving a simple slide-valve1 which shuts off the communication between the fountain-tube and lamp-tube4 ,by this mode1 the oil is cut off about fifteen minutes before extinguishing the lights1 so that when that is done1 the burner is quite free of oil4 ,illustration3 ,fig4 #cb4 ,arrangements for ,raising or lowering the ,argand ,wick4 ,it would needlessly occupy much time and space to describe the various means 7many of them sufficiently clumsy7 which have been employed1 and in many places are still in use1 for raising and depressing the wick2 it will be enough to say1 that they all involve some application of the rack and pinion4 ,i shall1 therefore1 only describe the method 7invented1 it is believed1 by ,m4 ,,verzy7 which is adopted in all the ,lighthouses in the district of the ,commissioners of ,northern ,lights4 ,the arrangement is as follows 7see figs4 #cb1 #cc1 #cd1 #ce1 #cf73--,the inner tube t of the burner is enclosed by a strong tube s1 which fits to it tightly1 so as not to be easily moved4 ,this strong tube has a spiral groove cut on its outer or convex surface4 ,the wick-holder has two small pegs projecting from it1 the one on the inside 7not seen71 and the other on the outside at a 7fig4 #cc74 ,that on the inside works in the spiral groove of the tube ,s 7figs4 #cb and #cc71 already described as embracing the inner tube t2 and all that is required for raising the wick is to make the wick-holder turn round on its vertical axis4 ,this is effected by means of the small external peg a of the wick-holder 7fig4 #cc71 which moves in a vertical slit a 7figs4 #cb and #cd71 cut in a tube standing in the burner1 and concentric with it1 and which also moves freely round its axis4 ,small knobs n n 7figs4 #cb1 #cd1 and #cf71 at the top of this tube1 fit into a notch in the upper ring of the gallery1 which supports the glass chimney4 ,by turning this gallery g 7see figs4 #cc and #cf71 therefore1 motion is given to the tube1 with its knobs n n1 whose vertical slit a 7while it holds the external peg of the wick-holder1 and also turns it round along with it7 permits that peg a to slide upwards or downwards1 and thus the wick-holder rises or falls1 according as its own internal peg moves up or down the spiral groove in the tube ,s4 ,in fig4 #cb1 ,c shews the glass chimney resting on the gallery g g4 ,illustration3 ,fig4 #cc4 ,illustration3 ,fig4 #cd4 ,illustration3 ,fig4 #ce4 ,illustration3 ,fig4 #cf4 ,flowing of the ,lamp4 ,an important point in the economy of the ,argand lamp1 is the level at which the outlet for the oil1 in its passage from the fountain to the burner1 should be cut4 ,the cutting of this hole 7generally called the flow-hole7 in the pipe is termed the flowing of the lamp1 and is commonly done by successive trials1 until the oil stands at the proper level of the burner1 before the wick is put in4 ,a more ready and accurate method of accomplishing this object and at once determining the level at which the flow-hole should be cut1 was introduced by ,mr ,,james ,,murdoch1 the ,foreman of ,lightroom ,repairs to the ,scotch ,board1 and is generally employed in the ,northern ,lighthouses4 ,its nature will be readily understood by a reference to the accompanying diagram1 ,no4 #cg3 ,illustration3 ,fig4 #cg4 ,the hatched surface represents a metallic ruler1 with a spirit-level at ,l2 ,c is the cup in which the bottom of the fountain f 7shewn in dotted lines7 rests4 ,when the fountain is removed1 and the ruler rests on the edge of the cup ,c1 the screw at ,a is used to adjust the level at ,l2 and a gauge ,,gg is allowed to fall until a notch in it at x rests on the outer tube of the burner ,f2 the pinching-screw ,b retains this ruler in its place1 and the point x indicates the level at which the oil should stand in the burner4 ,the level line x x indicates the level on which the top of the flow-hole ,h should be cut in the fountain-tube1 which is shewn in dotted lines within the outer tube1 or body of the lamp4 ,in other words1 y x measures the level at which the oil should stand in the burner below the lower edge of the metallic ruler1 while the corresponding line y x1 at the opposite end1 shews the level of the top of the flow-hole ,h1 below the edge of the cup ,c4 ,the gauge ,,gg applied to that point of the fountain which coincides with the edge of the cup 7so that y coincides with y7 measures the length yx y x2 and a set-square applied at x gives the position of ,h on the fountain-tube4 ,the round dot at a shews the position of the air-hole in the body of the lamp1 which establishes a connection between the external air and the surface of the oil4 ,the rods ,,ss shew the sliding gear 7described as d and f1 page #bba71 and are only introduced to identify this diagram with those of the fountain and burner which have preceded it4 ,the most advantageous level of the flow-hole depends on many circumstances too obscure and complicated to admit of any systematic elucidation2 and it is enough for all practical purposes1 to know that the capillary powers of the wick1 and the greater or less viscidity of the oil1 are the chief circumstances which determine that level4 ,actual experience is the only sure guide to the best practice in this respect2 and ,i therefore content myself with stating1 that it is generally found that the sperm oil should stand in the empty burner at about inch below its top4 ,for colza oil inch is sufficient4 ,in summer1 owing to the oil being more fluid1 there is sometimes a tendency to overflow the burner2 but any inconvenience arising from it is avoided by the plan adopted in the ,northern ,lights1 of shutting off the oil 7by means of the apparatus already alluded to on p4 #bbb7 about fifteen minutes before extinguishing the lights in the morning4 ,illustration3 ,fig4 #ch4 ,the arrangement for cutting off the oil is very simple1 as will be seen from the annexed diagram 7fig4 #ch71 in which ,f is the fountain1 ,t the oil-tube leading to the burner1 and ,v the flow-hole1 with its sliding valve4 ,by turning the handle ,h one quadrant of the circle1 the whole fountain ,f and tube ,t turn round their vertical axis1 while the valve ,v1 which rests in a notch in the cup of the lamp1 remains still1 and sliding over ,t1 opens the flow-hole4 ,s is the screw-plug which retains the oil in the fountain1 and which is unscrewed and removed when the fountain is to be filled4 ,placing the ,lamp in the ,focus4 ,illustration3 ,fig4 #ci4 ,illustration3 ,fig4 #dj4 ,in the reflecting apparatus of the ,northern ,lighthouses1 the focal position of the lamp is not1 as we have already seen1 liable to derangement1 by the removal of the burner for the purpose of cleaning1 as the sliding gear described at p4 #bba insures the return of the lamp to its true place4 ,the burner is originally set by means of a gauge1 which touches four points of the mirror's surface 7one of them being its vertex1 and the other three in the vertical plane of its greatest double ordinate74 ,this gauge being provided with a short tube or collar properly placed for the purpose of receiving the burner1 at once verifies its true position1 both vertical and horizontal4 ,the diagrams #ci and #dj shew the nature of the apparatus for adjusting the burners1 the one being a plan and the other a section4 ,the four points which touch the curve are one g at the vertex1 two in the same horizontal plane with the focus1 and near the edge of the mirror at ,,pp1 and the fourth1 also near the edge1 and in the same vertical plane with the focus4 ,f is the focus4 ,the horizontal arms are graduated1 and fitted with sliding pieces and clamping screws at ,r1 so as to admit of being varied with the width of the mirror2 but each gauge applies only to curves of the same focal distance2 the distance ,f g being fixed4 ,the gauge1 when applied to the mirror1 is properly secured by the screws at ,r1 ,r1 and ,r2 and the burner which is attached to the oil-tube in a temporary manner at ,a1 is raised into the interior of the mirror4 ,if the tube of the burner ascends into the circular tube at ,f until 7when fixed by the checking handle already noticed at p4 #bba7 its upper edge just touches a narrow projection inside the tube ,f 7so placed that the rim of the burner should just touch it when it is on the level required for putting the brightest part of the flame in the focus71 then the burner is in the proper position2 but if1 on the one hand1 the axis of the burner stands beyond ,f1 at some point between it and ,n 7which lies in the plane of the mirror's edge71 the bent tube ,o from the fountain must be shortened at ,a2 and if it rise too high1 that tube must be bent down 7and vice versa71 until1 by successive trials1 it shall exactly fit into the tube ,f1 and stand at the proper level4 ,a skilful workman soon comes to guess those quantities very accurately2 and1 almost at the first trial1 curtails the tube to the proper length1 and bends it to the suitable level4 ,all that is needful is to proceed cautiously1 so as not to cut the tube too short1 for this leads to some trouble4 ,distinctions of ,catoptric ,lights4 ,the great advantage derived by seamen from the establishment of lights on a coast1 soon makes the calls for additional lights so frequent1 that their very number itself produces a new evil1 in the difficulty of distinguishing the lights from each other4 ,as the object of a light is to make known to the benighted mariner the land he has made1 with as much certainty as the sight of a hill or tower would shew him his position during the day1 it becomes an object of the first importance to impress upon each light a distinctive character1 which shall effectually prevent the possibility of its being mistaken for any other4 ,catoptric lights are susceptible of nine separate distinctions1 which are called fixed1 revolving white1 revolving red and white1 revolving red with two whites1 revolving white with two reds1 flashing1 intermittent1 double fixed lights1 and double revolving white lights4 ,the first exhibits a steady and uniform appearance1 which is not subject to any change2 and the reflectors used for it 7as already noticed7 are of smaller dimensions than those employed in revolving lights4 ,this is necessary1 in order to permit them to be ranged round the circular frame1 with their axes inclined at such an angle1 as shall enable them to illuminate every point of the horizon4 ,the revolving light is produced by the revolution of a frame with three or four sides1 having reflectors of a larger size grouped on each side1 with their axes parallel2 and as the revolution exhibits once in two minutes1 or once in a minute1 as may be required1 a light gradually increasing to full strength1 and in the same gradual manner decreasing to total darkness1 its appearance is extremely well marked4 ,the succession of red and white lights is caused by the revolution of a frame whose different sides present red and white lights2 and these1 as already mentioned1 afford three separate distinctions1 namely1 alternate red and white2 the succession of two white lights after one red1 and the succession of two red lights after one white light4 ,the flashing light is produced in the same manner as the revolving light2 but owing to a different construction of the frame1 the reflectors on each of eight sides are arranged with their rims or faces in one vertical plane1 and their axes in a line inclined to the perpendicular1 a disposition of the mirrors which1 together with the greater quickness of the revolution1 which shews a flash once in five seconds of time1 produces a very striking effect1 totally different from that of a revolving light1 and presenting the appearance of the flash alternately rising and sinking4 ,the brightest and darkest periods being but momentary1 this light is farther characterised by a rapid succession of bright flashes1 from which it gets its name4 ,the intermittent light is distinguished by bursting suddenly into view and continuing steady for a short time1 after which it is suddenly eclipsed for half a minute4 ,its striking appearance is produced by the perpendicular motion of circular shades in front of the reflectors1 by which the light is alternately hid and displayed4 ,this distinction1 as well as that called the flashing light1 is peculiar to the ,scotch coast1 having been first introduced by the late ,engineer of the ,northern ,lights ,board4 ,the double lights 7which are seldom used except where there is a necessity for a leading line1 as a guide for taking some channel or avoiding some danger7 are generally exhibited from two ,towers1 one of which is higher than the other4 ,at the ,calf of ,man1 a striking variety has been introduced into the character of leading lights1 by substituting1 for two fixed lights1 two lights which revolve in the same periods1 and exhibit their flashes at the same instant2 and these lights are1 of course1 susceptible of the other variety enumerated above1 that of two revolving red and white lights1 or flashing lights1 coming into view at equal intervals of time4 ,the utility of all these distinctions is to be valued with reference to their property of at once striking the eye of an observer and being instantaneously obvious to strangers4 ,the introduction of colour1 as a source of distinction1 is necessary1 in order to obtain a sufficient number of distinctions2 but it is in itself an evil of no small magnitude2 as the effect is produced by interposing coloured media between the burner and the observer's eye1 and much light is thus lost by the absorption of those rays1 which are held back in order to cause the appearance which is desired4 ,trial has been made of various colours2 but red1 blue1 and green alone have been found useful1 and the two latter only at distances so short as to render them altogether unfit for sea-lights4 ,owing to the depth of tint which is required to produce a marked effect1 the red shades generally used absorb from ths to ths of the whole light1 an enormous loss1 and sufficient to discourage the adoption of that mode of distinction in every situation where it can possibly be avoided4 ,the red glass used in ,france absorbs only ths of the light2 but its colour produces1 as might be expected1 a much less marked distinction to the seaman's eye4 ,in the ,lighthouses of ,scotland1 a simple and convenient arrangement exists for colouring the lights1 which consists in using chimneys of red glass1 instead of placing large discs in front of the reflectors4 ,arrangement of ,reflectors on the ,frame4 ,illustration3 ,fig4 #da4 ,after what has been already said on the subject of divergence1 it will at once be seen1 that in revolving lights the reflectors are placed with their axes parallel to each other1 so as to concentrate their power in one direction2 whilst in fixed lights it is necessary1 in order to approach as near as possible to an equal distribution of the light over the horizon1 to place the reflectors1 with their axes inclined to each other1 at an angle somewhat less than that of the divergence of the reflected cone4 ,for this purpose1 a brass gauge 7see fig4 #da71 composed of two long arms1 ,,am1 ,,am1 somewhat in the form of a pair of common dividers1 connected by a means of a graduated limb ,a1 is employed4 ,the arms having been first placed at the angle1 which is supplemental to that of the inclination of the axes of the two adjacent mirrors at ,o1 are made to span the faces of the reflectors1 one of which is moved about till its edges are in close contact with the flat surface of one of the arms of the gauge4 ,illustration3 ,fig4 #db4 ,illustration3 ,fig4 #dc4 ,figs4 #db and #dc shew an elevation and plan of a revolving apparatus on the catoptric principle4 ,in these figures1 n n shews the reflector frame or chandelier2 o o1 the reflectors with their oil-fountains p p4 ,the whole is attached to the revolving axis or shaft q4 ,the copper tubes r r convey the smoke from the lamps2 s s are cross bars which support the shaft at t t2 u u is a copper pan for receiving any moisture which may accidentally enter at the central ventilator in the roof of the light-room2 l is a cast-iron bracket1 supporting the cup in which the pivot of the shaft turns2 m m are bevelled wheels1 which convey motion from the machine to the shaft4 ,the machinery does not require any particular notice1 being that of common clock-work1 moved by the descent of a weight4 ,illustration3 ,fig4 #dd4 ,fig4 #dd shews a plan of one tier of reflectors arranged in the manner employed in a fixed catoptric light2 n n shews the chandelier1 q the fixed shaft in the centre1 which supports the whole1 o o the reflectors1 and p p the fountains of their lamps4 ,in this figure 7in order to prevent confusion7 only one tier of reflectors is shewn2 the other tiers are so arranged1 that their axes divide into equal angles the arcs intercepted between the axes of the adjoining reflectors on the first tier1 thereby producing the nearest approach to an equal distribution of the light1 which is attainable by this arrangement4 ,in lighthouses of moderate height1 the proper position for the reflector itself is perfect horizontality of its axis1 which may be ascertained with sufficient accuracy1 by trying with a plummet1 whether the lips of the instrument1 which we may conclude to be at right angles to the plane of its axis1 be truly vertical4 ,in lightrooms very much elevated above the sea1 however1 the dip of the horizon becomes notable2 and a slight inclination forwards should be given to the face of the reflectors1 so that their axes produced may be tangents to the earth at the visible horizon of the light-room4 ,this1 however1 must not be permitted to interfere with the perfect horizontality of the top of the burner1 which is indispensable to its proper burning4 ,bordier ,marcet's ,reflectors4 ,fanal ,sidral4 ,various forms of the parabolic mirror were invented by ,m4 ,,bordier ,,marcet1 the pupil and successor of ,,argand1 who has laboured with much enthusiasm in perfecting catoptric instruments1 more especially with a view to their application in the illumination of lighthouses and the streets of towns4 ,amongst many other ingenious combinations1 he has invented and constructed an apparatus which is much used in harbour-lights on the ,french coast1 where it is known by the fanciful name of ,fanal#df sidral4 ,the object is to fulfil1 as economically as possible1 the conditions required in a fixed light1 by illuminating1 with perfect equality1 every part of the horizon1 by means of a single burner2 and ,m4 ,,bordier ,,marcet has in his work-shop an instrument of this kind1 eight feet in diameter1 which he constructed on speculation4 ,the apparatus used in harbour-lights1 on the ,french coast1 is of much smaller dimensions1 and does not exceed fifteen inches in diameter4 ,a perfect idea of the construction and effect of this instrument may be formed1 by conceiving a parabola to revolve about its parameter as a vertical axis1 so that its upper and lower limbs would become the generating lines of two surfaces possessing the property of reflecting1 in lines parallel to the axis of the parabola1 all the rays incident upon them1 from a light placed in the point where the parameter and axis of the generating parabola intersect each other4 ,this point being the focus of each parabolic section of this apparatus1 light is equally dispersed in every point of the horizon1 when the axis of the parabolic section is in a plane perpendicular to a vertical line4 ,but however perfectly this apparatus may attain its important object1 it necessarily produces a feeble effect2 because as its action is entirely confined to the vertical direction1 the light distributed by it decreases directly as the distance of the observer4 ,this beautiful little instrument is shewn at fig4 #de1 in which b shews the burner1 p p the upper reflecting surface1 and p p the lower reflecting surface1 both generated in the manner above described by the revolution of a parabola about its parameter x b2 ,f is the focus of the generating parabola2 and l l are small pillars1 which connect the two reflecting plates1 and give strength to the apparatus4 #df ,fanal1 from 1 a lantern4 ,illustration3 ,fig4 #de4 ,fanal double effet4 ,m4 ,,bordier ,,marcet has also prepared an ingenious modification of the parabolodal mirror1 which he has described under the name of fanal double effet2 and the object of which is to obtain a convenient degree of divergence from parabolic mirrors1 by the use of two flames and two reflecting surfaces1 each of which is acted upon by its own flame1 and also by that of the other4 ,this modification consists in the union of two portions of hollow parabolodal mirrors1 generated by the revolution of two parabolas about a common horizontal axis1 and illuminated by two lamps placed in the focus of each4 ,the first surface is generated by the revolution on its axis of a segment of a paraboloid intercepted between the parameter and some double ordinate greater than it1 and may1 from its form1 be called the ribbon-shaped mirror4 ,the second surface is that of a parabolic conoid1 which is cut off by a vertical plane passing through a double ordinate1 which is equal to the parameter of the parabolic ribbon1 which is placed in front of it4 ,the elements of the curve which forms the conodal mirror1 must be so chosen as to have its focus at a convenient distance in front of that of the ribbon-shaped mirror1 so as to admit of placing the two lamps separate from each other1 as well as to produce the necessary degree of divergence1 which is to be obtained by the action of these mirrors respectively on the flame placed in the focus of the other4 ,these two mirrors are joined together in the line of the parametric section of the ribbon1 which coincides with the lips of the conoid at some double ordinate behind its parameter4 ,each mirror produces1 by means of the lamp placed in its focus1 an approach to parallelism of the reflected rays1 which ,m4 ,,bordier ,,marcet has not inaptly termed the principal effect2 whilst the action of each surface on the lamp which is placed in the focus of the other1 causes what the inventor calls the secondary or lateral effect4 ,their secondary action may be described thus3 ,the lamp1 which is in the focus of the ribbon1 is much nearer the vertex of the conoid than its own focus2 so that its rays making1 with normals to the surface of the conoid1 angles greater than those which are formed by the rays proceeding from its focus1 are of necessity reflected in lines diverging from the axis of the mirror4 ,those1 on the contrary1 which proceed from the focus of the conoid1 meet the ribbon-shaped surface1 so as to make angles with its normals more acute than those which the rays from its own focus could do1 and which are1 therefore1 reflected in lines converging to the axis of the mirror4 ,those reflected rays must therefore cut the axis1 and diverge from it on the other side4 ,this apparatus has been used at ,la ,hve and some other lights on the ,french coast2 but it is impossible not to perceive the great loss of light which results from the use of two flames in one mirror2 and it must not be forgotten1 that the divergence which is obtained by means of it is not confined to the horizontal direction in which only it is wanted2 but that the light is at the same time scattered in every direction round the edge of the mirror4 ,arrangements of a similar kind were proposed and executed for the same purpose of uniting greater divergence with considerable power in the central parts of the resultant beam1 by ,,argand himself1 in #ahjf1 and also in #ahjh1 by ,m4 ,,haudry1 ,ingnieur des ,ponts et ,chausses4 ,,argand proposed the union of a paraboloid1 and an ellipsoid having their foci coincident in one point1 which being the posterior focus of the latter curve1 was illuminated by the rays reflected to it by means of the ellipsodal surface from the lamp placed in the anterior focus4 ,from the optical focus thus obtained1 some rays would fall on the parabolodal surface and produce1 by reflection1 a cylinder of parallel rays1 while the rest would diverge from the axis1 and form a zone of spreading rays4 ,m4 ,,haudry',s plan consisted of a combination of a conical with a parabolodal mirror1 so placed1 that the rays from the front part of the hollow cone might be nearly parallel to those sent out by the paraboloid2 while the rays from its base diverging from the axis might produce a ring of divergent rays1 similar to that obtained from the ellipsoid of ,,argand',s apparatus4 ,it would occupy much time to exhibit all the disadvantages of the arrangements in the fanal double effet of ,m4 ,,bordier ,,marcet1 and also in those of ,,argand and ,,haudry2 and ,i shall therefore dismiss the subject by observing1 that the loss of light due to the position of the flame in the apparatus of ,,argand1 is so great as to induce one to wonder that such combinations should ever have been attempted4 ,there can be no doubt1 that the most efficient mode of obtaining due divergence from mirrors1 is to adopt the paraboloid1 with a short focal distance1 which has the double advantage of increasing the divergence which is due inversely to the focal distance1 and1 at the same time1 subjecting to the action of the mirror a larger portion of the luminous sphere proceeding from the flame4 ,illustration3 ,fig4 #df4 ,fanal double face4 ,lastly1 ,i shall notice ,m4 ,,bordier ,,marcet',s fanal double face1 which consists of two parabolodal mirrors1 truncated in the vertical plane of the parameter1 and united together back to back1 so as to be illuminated by the same lamp placed in their common focus4 ,to save the light which would otherwise escape the catoptric action1 he adds a parabolic conoid of greater focal distance1 and so placed1 that while its focus may coincide with the common focus of the other mirrors1 its size may be so restricted1 that it shall not interfere with the effect of the truncated mirror opposite which it is placed4 ,the obvious consequence of such an arrangement is1 that the rays 7see fig4 #df7 produced from a lamp in the common focus of the three mirrors1 will produce in opposite directions a luminous ring from each of the truncated mirrors ,,ac1 ,,bc1 and ,a,c1 ,b,c1 while the central or conodal mirror ,,mn will fill the interior of one of those luminous rings with a cone of rays1 whose intensity will be in the inverse ratio of ,,mn to a b 7or ,,fm to ,f a71 which latter surface represents the whole amount of naturally divergent rays1 which strike on a b1 and which are spread over ,,mn4 ,two sets of reflectors of this form facing in opposite directions 7each set arranged in one plane1 and fixed on a frame which could be made to revolve round a vertical axis71 would thus present their brightest effect after considerable intervals of darkness2 but1 by arranging them with their axes slightly inclined1 they were made to prolong the light periods and curtail the dark ones4 ,m4 ,,bordier ,,marcet speaks of this apparatus with all the satisfaction generally felt by inventors2 but it is no difficult matter to identify its effect with that of the common parabolodal mirrors4 ,it is obvious1 that all the rays which fall from a true focal point on the three reflectors ,,ac1 ,,bc1 ,a,c1 ,b,c1 and ,,mn1 are merely those which would fall on a single reflector1 whose double ordinate and the portion of the abscissa between that ordinate and the focus1 are equal to those of the first reflector of the compound system1 so that the quantity of light reflected by the three reflectors is neither more nor less than that which would be projected by one4 ,all the difference that can exist is1 that in the case of a flame which has a notable size1 the surface ,,mn being farther distant than a b1 would produce less aberration and1 consequently1 a very slight increase of intensity in the small portion of the reflected beam of parallel rays due to that part of the compound mirror4 ,we cannot1 therefore1 sensibly err in rejecting any advantage to be derived from this arrangement as insignificant4#dg #dg ,see ,peclets ,trait de l,eclairage1 p4 #cjb1 from which fig4 #df is copied4 ,mr ,barlows ,spherical ,mirrors4 ,spherical mirrors have been employed in ,lighthouses chiefly when they can be introduced to aid the effect of refracting apparatus3 and it will not be necessary to say much of them in this place4 ,i must1 however1 notice an ingenious proposal of ,mr ,w4 ,h4 ,,barlow1#dh who suggests placing in front of the flame a small spherical reflector1 whose centre is coincident with the focus of a parabolod1 and whose subtense is the parameter of the generating curve4 ,the small mirror1 being somewhat less than a hemisphere1 would cause the light falling upon it to be returned through the focus so as to reach the parabolodal surface and to be finally reflected from that portion of it which is embraced between the limits of its extreme divergence4 ,if there were no loss of light at the surface of the small mirror1 its effect would be to increase the power of the beam of parallel rays by an amount equal to the sum of the rays incident on the spherical surface1 but at the same time to diminish it by intercepting a portion of the light reflected from the parabolod4 ,i am not aware that such a combination has been tried1 as it applies most advantageously to reflectors whose span does not exceed the parameter of the generating curve1 a form rarely adopted in lighthouses2 but it might also be adapted to reflectors which intercept a larger portion of light1 by making the spherical reflector some segment less than the hemisphere4 #dh ,in an excellent paper above noticed1 on the ,illumination of ,lighthouses1 in the ,london ,transactions1 for #ahcg4 ,captain ,smith's ,mirrors in the form of a parabolic spindle4 ,,captain ,,smith of the ,madras ,engineers1 has described in the 8,professional papers of the #8,corps of ,royal ,engineers1'#di a new system of fixed lights10 which consists in placing a flat wick in the focus of one-half of a hollow parabolic spindle generated by the rotation of a parabola about its parameter as a vertical axis4 ,the action of the instrument is obvious1 for each vertical section being parabolic1 effects a change only in the vertical divergence of the rays incident on it from the focus1 and suffers their horizontal direction to remain unaltered2 thus each vertical plate of reflected rays passes through the parameter of the curve and illuminates the opposite point of the horizon by means of a narrow strip or line of light4 ,two hollow spindles of that form1 each lighting #ahj and facing opposite azimuths1 would1 therefore1 be sufficient to illuminate the whole horizon4 ,the author of the paper1 however1 appears to contemplate the employment of a series of those mirrors ranged one above another and breaking joint vertically1 somewhat in the manner already described in speaking of the arrangement of the parabolodal mirrors used in fixed lights4 ,the advantages of this mode of illumination are much overrated by ,,captain ,,smith1 who seems to magnify beyond its real importance the risk attending the use1 in the dioptric apparatus1 of a single lamp1 whose sudden extinction would deprive at once the whole horizon of the benefit of the light2 while1 on the contrary1 he reckons the security obtained by his arrangement as an advantage of the highest value4 ,in certain situations1 where no regular establishment of trained light-keepers is maintained1 that security may be an object of more importance and may warrant a greater sacrifice1 than is necessary in ,great ,britain2 but ,i have no hesitation in saying1 that ,i know of no situation in which the plan proposed by ,,captain ,,smith could bear comparison with the mode of illumination for fixed lights by means of the catadioptric instruments of ,,fresnel4 #di ,vol4 v41 p4 #ef4 ,,dioptric#ej ,,system ,,of ,,lights4 #ej ,most probably directly derived from the ,greek 1 an optical instrument with holes for looking through1 whose name is a compound of 1 through1 and 1 ,i see4 ,one of the earliest notices of the application of lenses to lighthouses is that recorded by ,,smeaton in his ,narrative of the ,eddystone ,lighthouse1 where he mentions a ,london optician1 who1 in #agei1 proposed grinding the glass of the lantern to a radius of seven feet six inches2 but the description is too vague to admit of even a conjecture regarding the proposed arrangement of the apparatus4 ,about the middle of the last century1 however1 lenses were actually tried in several lighthouses in the south of ,england1 and in particular at the ,south ,foreland in the year #ageb2 but their imperfect figure and the quantity of light absorbed by the glass1 which was of impure quality and of considerable thickness1 rendered their effect so much inferior to that of the parabolic reflectors then in use1 that after trying some strange combinations of lenses and reflectors1 the former were finally abandoned4 ,lenses were also tried at the lights of ,portland1 ,hill of ,howth1 and ,waterford1 by ,mr ,thomas ,rogers1 a glass manufacturer in ,london2 who possessed1 it is said1 the art of blowing mirrors of glass1 8and by a new method silvered over the convex side without quicksilver40#ea #ea ,hutchinson's ,practical ,seamanship1 p4 #bjj4 ,see also the notice of the spherical mirrors made by ,messrs ,franois and ,letourneau of ,paris in a subsequent part of this volume4 ,the object to be attained by the use of lenses in a ,lighthouse is1 of course1 identical with that which is answered by employing reflectors2 and both instruments effect the same end by different means1 collecting the rays which diverge from a point called the focus1 and projecting them forward in a beam1 whose axis coincides with the produced axis of the instrument4 ,we have already seen that1 in the case of reflection1 this result is produced by the light being thrown back from a surface so formed as to make all the rays to proceed in one and the same required direction4 ,in the case of refraction1 on the other hand1 the rays pass through the refracting medium1 and are bent or refracted from their natural course into that which is desired4 ,the celebrated ,,buffon1 to prevent the great absorption of light by the thickness of the material1 which would necessarily result from giving to a lens of great dimensions a figure continuously spherical1 proposed to grind out of a solid piece of glass1 a lens in steps or concentric zones4 ,this suggestion of ,,buffon regarding the construction of large burning glasses1 was first executed1 with tolerable success1 about the year #aghj1 by the ,abb ,,rochon2 but such are the difficulties attending the process of working a solid piece of glass into the necessary form1 that it is believed the only other instrument ever constructed in this manner1 is that which was made by ,messrs ,,cookson of ,newcastle-upon-,tyne1 for the ,commissioners of ,northern ,lighthouses4 ,the merit of having first suggested the building of lenses in separate pieces1 seems to be due to ,,condorcet1 who1 in his ,eloge de ,buffon1 published so far back as #aggc1 enumerates the advantages to be derived from this method4 ,sir ,,david ,,brewster also described this mode of building lenses in #ahaa1 in the ,edinburgh ,encyclopdia2 and in #ahbb1 the late eminent ,,fresnel1 unacquainted with the suggestions of ,,condorcet or the description by ,sir ,,david ,,brewster1 explained1 with many ingenious and interesting details1 the same mode of constructing those instruments4 ,to ,,fresnel belongs the additional merit of having first followed up his invention1 by the construction of a lens and1 in conjunction with ,,mm4 ,,arago and ,,mathieu1 of placing a powerful lamp in its focus1 and indeed of finally applying it to the practical purposes of a ,lighthouse4 ,the great advantages which attend the mode of construction proposed by ,,condorcet are1--the ease of execution1 by which a more perfect figure may be given to each zone and spherical aberration in a great measure corrected1 and the power of forming a lens of larger dimensions than could easily be made from a solid piece4 ,both ,,buffon and ,,condorcet1 however1 chiefly speak of reducing the thickness of the material1 and do not seem to have thought of determining the radius and centre of the curvature of the generating arcs of each zone1 having contented themselves with simply depressing the spherical surface in separate portions4 ,,fresnel1 on the other hand1 determined those centres1 which constantly recede from the vertex of the lens in proportion as the zones to which they refer are removed from its centre2 and the surfaces of the zones of the annular lens1 consequently1 are not parts of concentric spheres1 as in ,,buffon',s lens4 ,it deserves notice1 that the first lenses constructed for ,,fresnel by ,m4 ,,soleil had their zones polygonal1 so that the surfaces were not annular1 a form which ,,fresnel considered less accommodated to the ordinary resources of the optician4 ,he also1 with his habitual penetration1 preferred the plano-convex to the double-convex form1 as more easily executed4#eb ,after mature consideration1 he finally adopted crown glass1 which1 notwithstanding its greenish colour1 he preferred to flint glass1 as being more free from stri4 ,all his calculations were made in reference to an index of refraction of #aea1 which he had verified by repeated experiments1 conducted with that patience and accuracy for which1 amidst his higher qualities1 he was so remarkably distinguished4#ec ,the instruments have received the name of annular lenses1 from the figure of the surface of the zones4 #eb ,the plano-convex lens1 with its curved side towards the parallel rays1 is also a form producing small spherical aberration1 a circumstance which may also have influenced his choice4 #ec ,my friend1 ,mr ,,william ,,swan1 carefully examined1 by his new and ingenious method1 described in the ,edinburgh ,new ,philosophical ,journal1 ,january #ahdd1 several specimens of the ,st ,gobain glass 7which is now used in the manufacture of the lenses71 and found its refractive index to be #aeagic1 the difference between the greatest and least values being only #jjjaji4 ,refraction4 ,a ray of light1 in passing obliquely from one transparent body into another of different density1 experiences at the point of the intersection of the common surface of the two planes1 a sudden change of direction1 to which the name of refraction has naturally been given1 in connection with the most familiar instance of the phenomenon1 which is exhibited by a straight ruler with one half plunged into a basin of water while the other remains in the air4 ,the ruler no longer appears straight1 but seems to be bent or broken at the point where it enters the water4 ,it may not be out of place to call attention to the laws which regulate the change of direction in the incident light1 which are three in number4 #a4 ,incidence and refraction1 in uncrystallized media of homogeneous structure such as glass1 always occur in a plane perpendicular to that of the refracting surface4 #b4 ,in the same substances1 the angle formed with the perpendicular by the ray at its entering the surface of the second medium1 has to the angle which it makes with the normal after it has entered the surface1 such a relation1 that their sines have a fixed ratio1 which is called the refractive index4 ,when a ray falls normally on the surface of any substance1 it suffers no refraction4 #c4 ,the effect of passing from a rare to a dense medium1 as from air into water or glass1 is to make the angle of refraction less than the angle of incidence2 and those angles are measured with reference to a normal to the plane which separates the media at the point of incidence4 ,the converse phenomenon1 of course1 takes place in the passage from a dense to a rare medium1 in which case the angle of incidence is less than the angle of refraction4 ,to this rule there are a few exceptions2 for there are certain combustible bodies1 such as diamond1 whose refractive powers are much greater than other substances of equal density4 ,illustration3 ,fig4 #dg4 ,the diagram 7fig4 #dg7 will serve to render those laws more intelligible4 ,let a ray of light a ,o meet a surface of water n m at ,o1 it will be immediately bent into the direction ,o a2 and if1 from the centre ,o1 we describe any circle1 and draw a line b ,o b1 perpendicular to nm2 then ab and a b1 perpendiculars drawn to the normal bb1 from the points a and a where the circle cuts the incident and refracted rays1 will be the sines of the angle of incidence b ,o a1 and of the angle of refraction b ,o a1 and the ratio of those sines to each other1 or b a ------- b a will be the relative index of refraction for the two media4 #d4 ,it may perhaps be added1 for convenience1 as a fourth law1 deducible from the others1 that since rays passing from a dense into a rare medium1 have their angle of refraction greater than the angle of incidence1 there must be some angle of incidence whose corresponding angle of refraction is a right angle2 beyond which no refraction can take place1 because there is no angle whose sine can be greater than the radius4 ,in such circumstances1 total reflection ensues4 ,for common glass1 whose index of refraction is #ae1 we have 7in the case of emergent rays7 sine of sine of refraction incidence ------------------2 #ae but1 as no sine can exceed radius or unity1 the angle of incidence must be limited to #da #di2 beyond which total reflection will take place1 and the light will return inwards into the glass1 being reflected at its surface4 ,thus1 if a ray proceed from a point ,o 7fig4 #dh71 within a piece of glass1 to a point ,c1 at its surface ,a ,b2 and if ,o ,c b1 its incidence1 be less than #da #di1 it will be refracted in some direction ,c f2 but if this angle be greater than #da #di1 as ,o ,c b1 the ray will be reflected back into the glass in the direction ,c ,o4 ,illustration3 ,fig4 #dh4 ,the material hitherto employed in the construction of lighthouse apparatus is crown glass1 which1 although it possesses a lower refractive power than flint glass and has1 besides1 a slightly greenish tinge1 offers the great practical advantages of being more easily obtained of homogeneous quality2 and1 being less subject to deterioration from atmospheric influences1 it is peculiarly suitable for use in the exposed situations generally occupied by ,lighthouses4 ,the refractive index of crown glass1 as already noticed1 is about #ae4 ,any one may easily satisfy himself by a careful protraction of the angles of incidence and refraction1 in the manner above described1 as to the truth of the following general propositions resulting from those laws3-- #a4 ,a ray of light passing through a plate of some diaphanous substance such as glass1 with parallel surfaces1 suffers no change of direction1 but emerges in a line parallel to its original path1 merely suffering a displacement1 depending on the obliquity of the incident ray1 and the refractive power and thickness of the plate4 ,the effect of this displacement is merely to give the ray an apparent point of origin different from the true one4 ,this will be easily understood by the diagram 7fig4 #di71 in which a b is a normal to the plate1 whose surfaces x x and x x are parallel1 r r r r shews the path of the ray1 r r the displacement1 and r the apparent point of origin resulting from its altered direction4 ,illustration3 ,fig4 #di4 #b4 ,when a ray passes through a triangular prism a b c1 the inclination of the faces a c and c b causes the emergent ray r to be bent towards a b1 the base of the prism1 in a measure depending on the inclination of the sides of the prism and the obliquity of the incident ray to the first surface4 ,illustration3 ,fig4 #ej4 #c4 ,when parallel rays fall on a concave lens1 they will1 at their emergence1 be divergent4 ,the section of the diaphanous body a b c d may be regarded as composed of innumerable frusta of prisms1 having their apices directed towards the centre line x r2 and the rays which pass through the centre1 being normal to the surface1 will be unchanged in their direction1 while all the others will 7as shewn in the figure7 suffer a change of direction1 increasing with their distance from the centre1 owing to the increasing inclination of the surfaces of the lens as they recede from its axis4 ,illustration3 ,fig4 #ea4 #d4 ,lastly1 when divergent rays fall on a convex lens a b1 from a point f1 called the principal focus1 they are made parallel at their emergence2 while1 conversely1 parallel rays which fall on the lens are united in that point4#ed ,this effect1 which is the opposite of that caused by the concave lens1 may be explained in a similar manner1 by conceiving the section a b of the convex lens to be composed of innumerable frusta of prisms1 arranged with their bases towards the centre of the lens4 #ed ,it is1 of course1 to be understood that only rays incident near the axis of the lens are refracted accurately to a focus4 ,illustration3 ,fig4 #eb4 ,now1 it is obvious1 that we can derive no assistance1 in economising the rays of a lamp for ,lighthouse purposes1 from concave lenses1 whose property is to increase the dispersion of the rays incident on them4 ,with concave lenses1 therefore1 we have no concern2 and we shall confine ourselves to the consideration of the convex or converging lenses4 ,the lens always used in ,lighthouses is 7for reasons already noticed7 plano-convex1 and differs from the last only by having a plane and a curve surface1 instead of two curve surfaces1 whose radii are on opposite sides of the lens4 ,the plano-convex is generally regarded1 by writers on optics1 as a case of the double convex having one side of an infinite radius4 ,both forms cause parallel rays to converge to a focus4 ,we commence with a general view of the relations which exist between the position of the radiant and the focus4 ,illustration3 ,fig4 #ec4 ,let ,q q be a section of a lens1 and f ,a r its optical axis1 or the line in which a ray of light passes unchanged in its direction through the lens1 from its being normal to both surfaces1 whether the lens be double-convex as above1 or plano-convex 7see fig4 #ec71 then the principal focus f is that point where the rays from r r r1 which fall parallel to the optic axis on the outer face of the lens1 meet after refraction at the two faces1--or1 to speak more in the language of the art which is under consideration1 the principal focus f is the point whence the rays of light1 proceeding in their naturally divergent course1 fall on the inner surface ,q ,a q of the lens1 and are so changed by refraction there and at the outer face1 that they finally emerge parallel to the optic axis in the directions ,q r1 q r4 ,the position of this point depends partly on the refractive power of the substance of which the lens is composed and partly on the curvature of the surface or surfaces which bound it4 ,it would be quite beyond the scope of these ,notes to attempt to present the subject of refraction at spherical surfaces before the reader's view in a rigorous or systematic manner1 and thus to advance1 step by step1 to the practical application of refracting instruments1 as a means of directing and economising the light in a ,pharos4 ,this would involve the repetition1 in a less elegant form1 of what is to be found in all the works on optics2 and instead of this1 ,i am content to refer1 where needful1 to those works1 and shall confine myself simply to what concerns ,lighthouse lenses and their use4 ,it would also be superfluous to determine the position of the principal focus of a plano-convex lens1 in terms of the refractive index and radius of curvature1#ee as it can be very accurately found in practice by exposing the instrument to the sun1 in such a manner that his rays may fall upon it in a direction parallel to its axis4 ,the point of union between the converging and diverging cones of rays 7where the spectrum is smallest and brightest71 which is the principal focus1 is easily found by moving a screen behind the lens1 farther from or nearer to it as may be required4 ,the path of the ,lighthouse optician1 moreover1 generally lies in the opposite direction2 and his duty is not so much to find the focal distance of a ready-made lens1 as to find the best form of a lens for the various circumstances of a particular ,pharos1 whose diameter1 in some measure1 determines the focal distance of the instruments to be employed4 ,all1 however1 that ,i shall really have to do is to give an account of what has been done by the late illustrious ,,fresnel1 who seems to have devoted such minute attention to every detail of the ,dioptric apparatus1 that he has foreseen and provided for every case that occurs in the practice of ,lighthouse illumination4 ,his brother1 ,mons4 ,,leonor ,,fresnel1 who succeeded him in the charge of the ,lighthouses of ,france1 has1 with the greatest liberality1 put me in possession of the various formul used by his lamented predecessor1 in determining the elements of those instruments which have so greatly improved the lighthouses of modern days4 #ee r ,f ------- m - #a in which r is the radius of curvature1 and m is the refractive index4--,coddington's ,optics1 ,chap4 ,,viii4 ,if the radiant be brought near the lens1 so as to cast divergent rays on its surface1 then the conjugate focus will recede behind the principal focus2 and when the luminous body reaches the principal focus in front of the lens1 the rays will emerge from its posterior surface in a direction parallel to its axis4 ,if it be brought still nearer the lens1 the rays would emerge as a divergent cone4 ,hence converging lenses can only collect rays into a focus1 when they proceed from some point more distant than the principal focus4 ,spherical lenses1 like spherical mirrors1 collect truly into the focus those rays only which are incident near the axis2 and it is1 therefore1 of the greatest importance to employ only a small segment of any sphere as a lens4 ,the experience of this fact1 among other considerations1 led ,,condorcet1 as already noticed1 to suggest the building of lenses in separate pieces4 ,,fresnel1 however1 was the first who actually constructed a lens on that principle2 and he has subdivided1 with such judgment1 the surface of the lens into a centre lens and concentric annular bands and has so carefully determined the elements of curvature for each1 that no farther improvement is likely to be made in their construction4 ,for the drawings of the great lens1 ,i have to refer to ,plate ,,xii41 which also contains a tabular view of the elements of its various parts4 ,the central disc of the lens1 which is employed in lights of the first order1 and whose focal distance is #ibj millimtres1 or #cfbb inches1 is about #aa inches in diameter2 and the annular rings which surround it vary slightly in breadth from #b to #a inches4 ,the breadth of any zone or ring is1 within certain limits1 a matter of choice1 it being desirable1 however1 that no part of the lens should be much thicker than the rest1 as well for the purpose of avoiding inconvenient projections on its surface1 as to permit the rays to pass through the whole of the lens with nearly equal loss by absorption4 ,the objects to be attained in the polyzonal or compound lens1 are chiefly1 as above noticed1 to correct the excessive aberration produced by refraction through a hemisphere or great segment1 whose edge would make the parallel rays falling on its curve surface converge to a point much nearer the lens than the principal focus1 as determined for rays near the optical axis1 and to avoid the increase of material1 which would not only add to the weight of the instrument and the expense of its construction1 but would greatly diminish by absorption the amount of transmitted light4 ,various modes of removing similar inconveniences in telescopic lenses have been devised2 and the suggestions of ,,descartes1 as to combinations of hyperbolic and elliptic surfaces with plane and spherical ones1 more especially fulfil the whole conditions of the case2 but the excessive difficulty which must attend grinding and polishing those surfaces1 has hitherto deprived us of the advantages which would result from the use of telescopic lenses entirely free from spherical aberration4 ,in ,lighthouse lenses1 where so near an approach to accurate convergence to a single focus is unnecessary1 every purpose is answered by the partial correction of aberration which may be obtained1 by determining an average radius of curvature for the central disc1 and for each successive belt or ring1 as you recede from the vertex of the lens4 ,in the lenses originally constructed for ,,fresnel by ,,soleil1 the zones were united by means of small dowels or joggles of copper1 passing from the one zone into the other2 but the greater exactness of the workmanship now attained1 has rendered it safe to dispense with those fixtures2 and the compound lens is now held together solely by a metallic frame and the close union between the concentric faces of the rings1 which1 however1 are in contact with each other at surfaces of only inch in depth1 as shewn in ,plate ,,xii4 ,it is remarkable1 that an instrument1 having about #acjj square inches of surface1 and weighing #aji lb41 and which is composed of so many parts1 should be held together by so slender a bond as two narrow strips of polished glass1 united by a thin film of cement4 ,i now proceed to the formul employed by ,,fresnel1 to determine the elements of the compound lens1#ef in the calculation of which two cases occur1 viz41 the central disc and a concentric ring4 ,the focal distance of the lens and the refractive index of the glass are the principal data from which we start4 #ef ,it may be proper to mention that1 while the formul given in the text are those of ,m4 ,,fresnel1 ,i am responsible for the investigations in the ,notes2 ,i have1 at the same time1 much pleasure in acknowledging my obligations1 at various times 7about ten years ago71 to ,mr ,,edward ,,sang1 and 7more recently7 to ,mr ,,william ,,swan1 for their kind advice on this part of the subject4 ,illustration3 ,fig4 #ed4 ,i begin with the case of the central disc or lens round which the annular rings are arranged4 ,its principal section is a mixtilinear figure 7fig4 #ed7 composed of a segment b a c1 resting on a parallelogram b c d e1 whose depth b d or c e is determined by the strength which is required for the joints which unite the various portions of the lens4 ,those particulars have1 as ,i already stated1 been determined with so much judgment by ,,fresnel and the dimensions of the lenses so varied to suit the case of various lights1 that nothing in this respect remains to be done by others4 ,illustration3 ,fig4 #ee4 ,referring to fig4 #ee1 we have1 for obtaining the radius of the central disc1 the following formul1 in which r ,,ab1 half the aperture of the lens r ,,ab ,,af1 the focal distance t ,a a1 the thickness of the lens at the vertex t ,b b1 the thickness of the joint the index of refraction the radius of curvature4 ,then for the radius of curvature near the axis we have3 7 t7 7 - #a77 ----7 7 7 and for that near the margin we have3 r tan i - sin i sin e -------- r r - t 4 tan e r tan i ---- sin i sin ------- r ---------7 - #b cos e #a7 sin e and1 finally #eg ------- #b #eg ,the following steps lead to the formul given in the text4 ,let ,,apqb 7fig4 #ef7 represent a section of the central lens by a plane passing through its axis ,,af2 ,f the focus for incident rays2 and ,,fqph the path of a ray refracted finally in the direction ,,ph1 parallel to the axis4 ,let ,c be the centre of curvature1 then ,,pc is a normal to the curve at ,p2 and1 producing ,,pq to meet the axis in ,g1 we have ,g the focus of the rays1 after refraction at the surface ,,bq4 ,illustration3 ,fig4 #ef4 ,then sin ,,pcg ,,pg ------- --2 sin ,,gpc ,,cg and also sin ,,qfg ,,qg ------- -- sin ,,qgf ,,qf ,now1 as ,p approaches ,a1 we have ultimately ,,pg ,,ag1 ,,qg ,,bg1 and ,,qf ,,bf2 ,therefore1 putting ,,ag and ,,ac ,,ag ,,bg - t -- ------2 -- --------1 ,,cg - ,,bf from which - 2 and - t and eliminating 1 we have t1 whence1 as above1 7 t7 7 - #a77 ----7 7 7 ,but as this value of the radius of curvature1 as already stated1 is calculated for rays near the axis1 it would produce a notable aberration for rays incident on the margin of the lens4 ,in order1 therefore1 to avoid the effects of aberration as much as possible1 a second radius of curvature must be calculated1 so that rays incident on the margin of the lens may be refracted in a direction parallel to the axis4 ,this second value of the radius is called in the text1 and is found as follows 7referring to fig4 #eg73 ,let ,,fb b x be the course of a ray refracted in the direction b x parallel to the axis ,a x4 ,this ray meets the surface ,,ab in the point ,b1 whose position may be found approximately by tracing the path of the ray ,,fb1 on the supposition that the surface of the refracting medium is produced in the directions ,,ab1 a b4 ,illustration3 ,fig4 #eg4 ,let ,c be the centre of curvature 7see fig4 #eg7 ,,ac b the angle of emergence ,bb ,c the second angle of refraction ,b b ,b the first angle of refraction i ,b,,fa the first angle of incidence i ,,bfa e b ,b b ,,ab r ,,ab r ,b b t the thickness of the lens at the edge ,,af the focal distance4 ,then r sin i tan i ---2 sin e -------- whence b b t tan e becomes known4 ,now1 since ,,bb b b nearly1 ,,ab ,,ab - b b or r r - t tan e4 ,from this is obtained the angle of incidence i1 and the first angle of refraction 2 for r sin i tan i ---- and sin -------4 ,next ,b b ,c ,b b ,c - ,b b ,b or - and sin sin sin 7 - 7 sin from which1 sin cos - cos sin ----- 7 #a7 whence sin 7cos - -7 cos sin 2 and 7 7 7 #b cos #a7 sin 7cos - ------- --7 cos sin 7 7 7#a - sin 7 sin sin - sin sin ,then transposing we have #b cos #a sin 7cos sin 7 - ------- -- sin and because 7cos sin 7 #a we have1 by dividing1 sin sin sin ------------------ ------------------ #b cos #a - #b cos #a #a - ------- -- and sin sin --------------------- 7#a - #b cos 7 ,next1 since a b r b ,c ---------- -----1 sin ,,ac b sin putting ,c b 1 and substituting we have r ------- 7 - #b cos #a7 sin and1 taking for the radius of curvature1 the mean of and the values calculated for the central and marginal rays1 we have finally ------- #b ,illustration3 ,fig4 #eh4 ,i come next to the second case1 which concerns the calculation of the elements of a concentric ring4 ,the section a b c d e 7fig4 #eh7 of one of those rings includes a mixtilinear triangle a b e1 and a rectangle b c e d1 the thickness b c being the same as that of the edge of the central disc2 and the elements to be determined are the radius of the curve surface1 and the position of the centre of curvature1 with reference to the vertex of the lens4 ,illustration3 ,fig4 #ei4 ,the radius of curvature of the zone may be calculated by the following formul1 in which 7see fig4 #ei7 r ,,ab the distance of the outer margin of the zone from the axis of the lens r ,,ae the distance of the inner margin from the axis l ,,be the breadth of the zone r - r the radius of curvature b ,c m ,c focal distance ,,af t thickness of the joint ,b b t ,b b refractive index of the glass i ,,bfa i ,,efa r r ,then tan i ----2 tan i ---- sin i sin i sin e ---------2 sin e --------- r r - t sin e2 r r - t sin e r r tan i -----2 tan i ----- sin i sin i sin --------2 sin -------- sin sin ---------------------2 7 - #b cos #a7 sin sin ---------------------2 - 7 - #b cos #a7 #b cos and lastly -------------------------------------- #b cos 7 - 7 sin 7 - 7 which is ,,fresnel',s value of the radius of curvature4#eh #eh ,the following steps will conduct us to this expression3 ,illustration3 ,fig4 #fj4 ,let ,b b f ,e 7fig4 #fj7 represent the section of a zone by a plane passing through the axis of the lens ,,af1 ,c the centre of curvature1 ,f the radiant point1 and ,,fb b x1 ,,fe m x the course of the extreme rays which are transmitted through the zone 7and the latter of which passes from ,e to e through a portion of the zone or lens in contact with that under consideration74 ,then putting ,,ab r2 ,,ab r2 ,c b ,,ae r2 ,,ae r2 ,b b t2 ,,be r - r l the first angle of refraction b ,b k the second angle of refraction ,b b ,c the first angle of refraction e ,e k the second angle of refraction e m ,c the angle of emergence b ,c q the angle of emergence m ,c q i ,,bfa2 i ,,efa2 i ,b,,fa2 i ,e,,fa e ,b b ,b2 e ,e e ,e4 ,proceeding exactly as in the case of the central lens we shall have ,,ba r ,,ea r tan i -- ----2 tan i -- ---- ,,af ,,af sin i sin i sin e ---------2 sin e --------- r r - t sin e2 r r - t sin e r r tan i -----2 tan i ----- sin i sin i sin --------2 sin --------- sin sin sin ---------------------2 and sin ---------------------- 7 - #b cos - #a7 7 - #b cos #a7 ,now1 the angle b ,c m - from which 7since the triangle b m ,c is isosceles7 b m ,c #ij - 7 - 72 also1 in the triangle b m e1 the angle b m e b m ,c - e m ,c #ij - 7 - 7 - and b e m k e ,e #ij - ,we have therefore in the triangle b m e b e sin b e m l cos b m ----------------------- --------------------- sin b m e cos 7 - 7 and in b m ,c b m sin b m ,c l cos cos 7 - 7 b ,c --------------------- ---------------------------------- sin b ,c m cos 7 7 - 77 sin 7 - 7 l cos cos 7 - 7 ---------------------------------------- ---------------- cos 7 - 7 #b sin 7 - 7 cos 7 - 7 from which1 putting b ,c l cos --------------------------------------- #b cos 7 - 7 sin 7 - 7 ,lastly1 the position of ,c the centre of curvature for a ring is easily determined by two co-ordinates in reference to their origin1 ,a1 which is the vertex of the lens 7see fig4 #fj below71 by the equations3 ,,cg 4 sin - a b 4 sin - r ,,cq 4 cos - q ,q 4 cos - t ,the elements of each successive zone are determined in the same manner4 ,the annular lens of the first order of lights in ,,fresnel',s system consists1 as already stated1 of a central disc #aa inches in diameter1 and #aj concentric rings1 all of which have a common principal focus1 where the rays of the sun meet after passing through the lens4 ,with such accuracy are those rings and the disc ground and placed relatively to each other1 that the position of the actual conjugate focus of the entire surface of the compound lens1 differs in a very small degree from that obtained by calculation in the manner described below4#ei #ei ,testing ,lenses4 ,the tests generally applied for examining the lenses used in ,lighthouses1 is to find the position of the conjugate focus behind the lens1 due to a given position of a lamp in front of it4 ,this test depends on the following considerations3--,draw a line from an object ,o in front of a lens1 to any point ,q in the lens2 and from ,a1 the centre of the lens1 draw ,,ar parallel to ,,oq1 and cutting a line ,,rf r which passes through the principal focus ,f1 at right angles to the axis of the lens2 then join the points ,q and ,r1 and produce the line joining them3 ,i1 the image of ,o must be in that line4 ,in the same way1 draw a line from ,o to q1 another point in the lens on the other side of its axis1 and parallel to it draw ,a r from the centre of the lens1 cutting the plane of the principal focus in r4 ,join q r1 in which line the image will lie2 and hence the intersection of ,,or and q r1 in ,i1 will be the point in which the image of ,o is formed1 or will be the conjugate focus of the lens due to the distance ,,oa4 ,this mode will serve to give the distance of the conjugate focus of a lens 7neglecting its thickness7 for rays falling on its surface at any angle4 ,illustration3 ,fig4 #fa4 ,we shall suppose ,,qa 7fig4 #fa7 to represent the half of a lens1 and remembering the conditions described in reference to the last figure1 we shall at once perceive the truth of the following analogy 7fig4 #fb73-- ,illustration3 ,fig4 #fb4 ,,oa ,,af ,,aq ,,fr ,,ai ,,fi1 and putting ,,oa 1 ,,ai 1 and ,,af 1 we have - 1 and1 consequently1 - 2 and hence the following equations1 which express the relations subsisting between the principal focus of the lens and the distance of any object and its corresponding image3 #ast1 ,to find the principal focal distance of a lens from the measured position of its object and its image refracted through it1 we have1 ------4 #b;d1 ,for the distance of the object1 when that of the image is known1 we have1 ------4 - #c;d1 ,for the position of the image1 when that of the object is known1 we have1 -----4 - ,illustration3 ,fig4 #fc4 ,in testing lenses1 of course1 it is this last equation which we use1 because the value of or the principal focus is always known1 and is that whose accuracy we wish to try1 while may be chosen within certain limits at will4 ,i have found that the best mode of proceeding is the following3--,in front of the lens ,q q 7see fig4 #fc7 firmly fixed on a frame1 place a lamp at ,o at the distance of about #ej yards4 ,calculate the value of due to #ej yards1 which in this case is equal to ,,af1 ,,oa being equal to 2 and move a screen of white paper backwards and forwards until you receive on it the smallest image that can be formed1 which is at the point where the cones of converging and diverging rays meet4 ,the image will always increase in size whether you approach nearer to the lens or recede farther from it1 according as you pass from the converging into the diverging cone of rays1 or vice versa2 and hence the intermediate point is easily found by a very little practice4 ,the distance from the centre of the lens to the face of the screen1 which must be adjusted so as to be at right angles to a line joining the centre of the lens and the lamp1 is then measured2 and its agreement with the calculated length of 1 is an indication of the accuracy of the workmanship of the lens4 ,when the measured distance is greater than the calculated 1 we know that the lens is too flat2 and it is on this side the error generally falls4 ,on the other hand1 when is greater than the measured distance1 we know that the lens has too great convexity4 ,i have only to add1 that an error of on the value of may be safely admitted in ,lighthouse lenses2 but ,i have had many instruments made by ,m4 ,,fran,,ois ,,soleil1 whose error fell below of 4 ,owing probably to the mode of grinding1 the surfaces of all the lenses ,i have yet examined are somewhat too flat4 ,divergence of ,annular ,lenses4 ,in the combination of lenses with the flame of a lamp1 similar considerations must influence us in making the necessary arrangements1 as in the case of reflectors4 ,we have already seen that the size of the flame and its distance from the surface of reflecting instruments have an important practical bearing on the utility of the instrument1 and that the divergence of the resultant beam materially affects its fitness for the purpose of a ,lighthouse4 ,so also1 in the case of the lens1 unless the diameter of the flame of the lamp has to the focal distance of the instrument a relation such as may cause an appreciable divergence of the rays refracted through it1 it could not be usefully applied to a ,lighthouse2 for1 without this1 the light would be in sight during so short a time1 that the seaman would have much difficulty in observing it4 ,to determine the amount of this divergence of the refracted beam1 therefore1 is a matter of great practical importance1 and ,i shall briefly point out the conditions which regulate its amount1 as they are nearly identical with those which determine the divergence of a parabolodal mirror illuminated by a lamp in its focus4 ,the divergence1 in the case of lenses1 may be described as the angle which the flame subtends at the principal focus of the lens1 the maximum of which1 produced at the vertex of ,,fresnel',s great lens by the lamp of four concentric wicks1 is about #e #i4fj #fj ,this will be easily seen by examining the annexed figure 7#fd71 in which ,q q represents the lens4 ,a its centre1 ,f the principal focus1 b ,f and b ,f the radius of the flame2 then is the angle b ,a b equal to the maximum divergence of the lens4 b ,f ,rad4 of flame ,sin b ,,af ----- sin b ,,af --------------2 ,,af ,focal distance and twice b ,,af the whole divergence at ,a4 ,then for the divergence at the margin of the lens1 or at any other point1 we have1 ,,fq 7,,aq ,,af7 and ,q x 7,,qf ,f x72 and for any angle at ,q1 we have ,f x sin ,,fq x -----4 ,,fq ,illustration3 ,fig4 #fd4 ,illuminating ,power of ,lenses4 ,on the subject of the illuminating power of the lenses1 it seems enough to say1 that the same general principle regulates the estimate as in reflectors4 ,owing to the square form of the lens1 however1 there is a greater difficulty in finding a mean focal distance whereby to correct our estimate of the angle subtended by the light1 so as to equate the varying distance of the several parts of the surface2 but1 practically1 we shall not greatly err if we consider the quotient of the surface of the lens divided by the surface of the flame as the increased power of illumination by the use of the lens4 ,the illuminating effect of the great lens1 as measured at moderate distances1 has generally been taken at #cjjj ,argand flames1 the value of the great flame in its focus being about #af1 thus giving its increasing power as nearly equal to #ahj4 ,the more perfect lenses have produced a considerably greater effect4 ,arrangement of the ,lenses in a ,lighthouse4 ,the application of lenses to ,lighthouses is so obvious as scarcely to admit of farther explanation than simply to state1 that those instruments are arranged round a lamp placed in their centre1 and on the level of the focal plane in the manner shewn in ,plates ,,xiii4 and ,,xiv41#fa so as to form by their union a right octagonal hollow prism1 circulating round the flame which is fixed in the centre1 and shewing to a distant observer successive flashes or blazes of light1 whenever they cross a line joining his eye and the lamp1 in a manner similar to that already noticed in describing the action of the mirrors4 ,the chief difference in the effect consists in the greater intensity and shorter duration of the blaze produced by the lens2 which latter quantity is1 of course1 proportional to the divergence of the resultant beam4 ,each lens subtends a central horizontal pyramid of light of about #df of inclination1 beyond which limits the lenticular action could not be advantageously pushed1 owing to the extreme obliquity of the incidence of light2 but ,,fresnel at once conceived the idea of pressing into the service of the mariner1 by means of two very simple expedients1 the light which would otherwise have uselessly escaped above and below the lenses4 #fa ,the ,plates shew the nature of the mechanical power which gives movement to the lenses4 ,it consists of a clockwork movement driven by a weight which sets in motion a plate bearing brackets that carry the lenses4 ,all this1 however1 can be seen from the ,plates2 and ,i am unwilling to expend time in a detailed explanation of what is obvious by inspection4 ,pyramidal ,lenses and ,mirrors4 ,for intercepting the upper portion of the light1 ,,fresnel employed eight smaller lenses of #ejj mm4 focal distance 7#aifh inches7 inclined inwards towards the lamp1 which is also their common focus and thus forming1 by their union1 a frustum of a hollow octagonal pyramid of #ej of inclination4 ,the light falling on those lenses is formed into eight beams parallel to the axis of the smaller lenses1 and rising upwards at an angle of #ej inclination4 ,above them are ranged eight plane mirrors1 so inclined 7see ,plates ,,xiii4 and ,,xiv47 as to project the beams transmitted by the small lenses in the horizontal direction1 so as finally to increase the effect of the light4 ,in placing those upper lenses1 it is generally thought advisable to give their axis an horizontal deviation of #g or #h from that of the great lenses and in the direction contrary to that of the revolution of the frame which carries the lenticular apparatus4 ,by this arrangement1 the flashes of the smaller lenses precede that of the large ones1 and thus tend to correct the chief practical defect of revolving lenticular lights by prolonging the bright periods4 ,the elements of the subsidiary lenses depend upon the very same principles1 and are calculated by the same formul as those given for the great lenses4 ,in fixing the focal distance and inclination of those subsidiary lenses1 ,,fresnel was guided by a consideration of the necessity for keeping them sufficiently high to prevent interference with the free access to the lamp4 ,he also restricted their dimensions within very moderate limits1 so as to avoid too great weight4 ,the focal distance is the same as that for lenses of the third order of lights4 ,curved ,mirrors4 ,illustration3 ,fig4 #fe4 ,owing to the necessary arrangements of a lantern1 only a very small portion of those rays1 which escape from below the lenses1 can be rendered available for the purposes of a ,lighthouse2 and any attempt to subject it to lenticular action1 so as to add it to the periodic flashes1 would have led to a most inconvenient complication of the apparatus4 ,,fresnel adopted the more natural and simple course of transmitting it to the horizon in the form of flat rings of light1 or rather of divergent pencils1 directed to various points of the horizon4 ,this he effected by means of small curved mirrors1 disposed in tiers1 one above another1 like the leaves of a ,venetian blind--an arrangement which he also adopted 7shewn in ,plates ,,xv4 and ,,xvi47 for intercepting the light which escapes above as well as below the dioptric belt in fixed lights4 ,those curved mirrors are1 strictly speaking1 generated 7see fig4 #fe7 by portions1 such as a b1 of parabolas1 having their foci coincident with ,f1 the common flame of the system4 ,in practice1 however1 they are formed as portions of a curved surface1 ground by the radius of the circle1 which osculates the given parabolic segment4#fb ,the mirrors are plates of glass1 silvered on the back and set in flat cases of sheet-brass4 ,they are suspended on a circular frame by screws1 which are attached to the backs of the brass cases1 and which afford the means of adjusting them to their true inclination1 so that they may reflect objects on the horizon of the ,lighthouse to an observer's eye1 placed in the common focus of the system4#fc #fb ,to find the radius and centre of a circle1 which shall osculate a given parabola1 whose focus is in ,f1 draw the normals to the curve from p and ,p1 meeting in ,o1 and draw ,n e parallel to a tangent of the curve1 or to p ,p1 then ,p ,o or p ,o is the radius required4 ,now1 we have similar triangles ,p p d and ,n e n1 and ,p ,h and p h are 7proximate7 ordinates2 hence we have the following analogies3-- ,p d ,p p ,,ph ,,pn ,n e ,n n ,,ph ,,pn ,illustration3 ,fig4 #ff4 ,hence compounding those ratios 7in which ,p d ,n n nearly7 ,n e ,p p ,,ph ,,pn also ,n e ,p p ,,no ,,po1 7for ,o ,p p and ,n o e are similar triangles7 ,,ph ,,pn ,,no ,,op1 then ,,pn- ,,ph ,,hn and ,,po - ,,no ,,np1 therefore ,,hn ,,pn ,,np ,,po1 and finally1 ,,pn ,,po ---4 ,,hn ,then put ,,fp ,,hc ,,fn 2 ,,hn - z2 then as ,,fp - ,,fh ,,ph - z ,,pn ,,ph ,,hn 7 - z7 7 - #b z z7 #b - #b z ,,pn 7#b 7 - z77 ,therefore #b 7 - z7 ,,po ---------------- 7 - z7 7#b 7 - z77 ------------------ 7 - z7 7 7 and finally1 ,,po #b #b 7-------7 7 - z7 ,illustration3 ,fig4 #fg4 ,to find the versed sine of the curvature 7which may be useful in the examination of the mirrors by a mould7 we may proceed 7see fig4 #fg7 to put ,,ag f2 ,,be ,c2 ,,ac ,r then ,,bg ,,ag 4 ,,gd #d ,,bg ,,be #d ,,ag 4 ,,gd ,c #d f 4 7#b ,r - f7 ,c #h f ,r - #d f ,from which equation1 ,c ,c #b f - #b ,r 7#d ,r - ,c7 --- - ----- c4 #d ,r #fd ,r ,c ,c #b f --- - ----- #d ,r #fd ,r ,c ,c f --- - -------4 #h ,r #abh ,r ,illustration3 ,fig4 #fh4 ,in order to test the accuracy of the workmanship of the mirrors1 recourse must again be had1 as in the case of the lenses and parabolic mirrors1 to the formula of conjugate foci1 in which we shall call ,r the radius of curvature of the mirror ,m m 7fig4 #fh72 a the distance of a light1 f1 which is arbitrarily placed in front of the mirror2 and b the distance of a moveable screen ,s1 on which the rays reflected from the mirror may converge in a focus4 ,we must find the distance b1 at which1 with any given distance a1 such convergence should take place4 f ,m a ,,sm b ,,om ,r ,then 7because f ,,ms is bisected by ,,om1 and for points near the vertex of the mirror at ,m7 ,,sm f ,m ,,so ,o f or b a ,r - b a - ,r a b - ,r a ,r b - a b4 ,r a ,from which b ---------1 #b a - ,r the distance required1 in which an error of 7of its whole length7 may be safely admitted4 #fc ,at such times when the horizon cannot be seen1 the mirror may be placed1 by means of a clinometer1 with a spirit-level1 set to the proper angle1 which may be easily mechanically determined as follows3 ,draw a line from the focus ,f through the point ,o1 where the centre of the mirror is to be1 producing it beyond that point to a convenient distance at ,i2 through ,o draw ,,hoh1 parallel to the horizon ,,fh2 bisect ,,ioh by ,,mom1 which coincides with a tangent to the mirror at its centre ,o2 and ,,moh is the angle required to be laid off1 or its complement4 ,illustration3 ,fig4 #fi4 ,cylindric ,refractors for ,fixed ,lights4 ,having once contemplated the possibility of illuminating ,lighthouses by dioptric means1 ,,fresnel quickly perceived the advantage of employing for fixed lights a lamp placed in the centre of a polygonal hoop1 consisting of a series of refractors1 infinitely small in their length and having their axes in planes parallel to the horizon4 ,such a continuation of vertical sections1 by refracting the rays proceeding from the focus1 only in the vertical direction1 must distribute a zone of light equally brilliant in every point of the horizon4 ,this effect will be easily understood1 by considering the middle vertical section of one of the great annular lenses1 already described1 abstractly from its relation to the rest of the instrument4 ,it will readily be perceived that this section possesses the property of simply refracting the rays in one plane coincident with the line of the section and in a direction parallel to the horizon1 and cannot collect the rays from either side of the vertical line2 and if this section1 by its revolution about a vertical axis1 becomes the generating line of the enveloping hoop1 above noticed1 such a hoop will of course possess the property of refracting an equally diffused zone of light round the horizon4 ,the difficulty1 however1 of forming this apparatus appeared so great1 that ,,fresnel determined to substitute for it a vertical polygon1 composed of what have been improperly called cylindric lenses1 but which in reality are mixtilinear and horizontal prisms1 distributing the light which they receive from the focus nearly equally over the horizontal sector which they subtend4 ,this polygon has a sufficient number of sides to enable it to give1 at the angle formed by the junction of two of them1 a light not very much inferior to what is produced by one of the sides2 and the upper and lower courses of curved mirrors are always so placed as partly to make up for the deficiency of the light at the angles4 ,the effect sought for in a fixed light is thus obtained in a much more perfect manner1 than by any combination of the parabolic mirrors used in the ,british ,lighthouses4 ,application of crossed prisms to cause occasional flashes4 ,an ingenious modification of the fixed apparatus is also due to the inventive mind of ,,fresnel1 who conceived the idea of placing one apparatus of this kind in front of another1 with the axis of the cylindric pieces crossing each other at right angles4 ,as those cylindric pieces have the property of refracting all the rays which they receive from the focus1 in a direction perpendicular to the mixtilinear section which generates them1 it is obvious that if two refracting media of this sort be arranged as above described1 their joint action will unite the rays which come from their common focus into a beam1 whose sectional area is equal to the overlapped surface of the two instruments1 and that they will thus produce1 although in a disadvantageous manner1 the effect of an annular lens4 ,it was by availing himself of this property of crossed prisms1 that ,,fresnel invented the distinction for lights1 which he calls a fixed light varied by flashes2 in which the flashes are caused by the revolution of cylindric refractors with vertical axes1 ranged round the outside of the fixed light apparatus already described4 ,true ,cylindric form given to the ,refractors and other improvements in their ,construction4 ,having been directed by the ,commissioners of the ,northern ,lighthouses to convert the fixed catoptric light of the ,isle of ,may1 into a dioptric light of the first order1 ,i proposed1 that an attempt should be made to form a true cylindric1 instead of a polygonal belt for the refracting part of the apparatus2 and this task was successfully completed by ,messrs ,,cookson of ,newcastle in the year #ahcf4 ,the disadvantage of the polygon lies in the excess of the radius of the circumscribing circle over that of the inscribed circle1 which occasions an unequal distribution of light between its angles and the centre of each of its sides2 and this fault can only be fully remedied by constructing a cylindric belt1 whose generating line is the middle mixtilinear section of an annular lens1 revolving about a vertical axis passing through its principal focus4 ,this is1 in fact1 the only form which can possibly produce an equal diffusion of the incident light over every part of the horizon4 ,i at first imagined that the whole hoop of refractors might be built between two metallic rings1 connecting them to each other solely by the means employed in cementing the pieces of the annular lenses2 but a little consideration convinced me that this construction would make it necessary to build the zone at the lighthouse itself1 and would thus greatly increase the risk of fracture4 ,i was therefore reluctantly induced to divide the whole cylinder into ten arcs1 each of which being set in a metallic frame1 might be capable of being moved separately4 ,the chance of any error in the figure of the instrument has thus a probability of being confined within narrower limits2 whilst the rectification of any defective part becomes at the same time more easy4 ,one other variation from the mode of construction at first contemplated for the ,isle of ,may refractors1 was forced upon me by the repeated failures which occurred in attempting to form the middle zone in one piece2 and it was at length found necessary to divide this belt by a line passing through the horizontal plane of the focus4 ,such a division of the central zone1 however1 was not attended with any appreciable loss of light1 as the entire coincidence of the junction of the two pieces with the horizontal plane of the focus1 confines the interception of the light to the fine joint at which they are cemented4 ,with the exception of those trifling changes1 the idea at first entertained of the construction of the instrument was fully realised at the manufactory of ,messrs ,,cookson4 ,i also1 at a subsequent period1 greatly improved the arrangement of this apparatus1 by giving to the metallic frames which contain the prisms1 a rhomboidal1#fd instead of a rectangular form4 ,the junction of the frames being thus inclined from the perpendicular1 do not in any azimuth intercept the light throughout the whole height of the refracting belt1 but the interception is confined to a small rhomboidal space1 whose area is inversely proportional to the sine of the angle of inclination2 and if the helical joints be formed between the opposite angles of the old rectangular frames1 the amount of intercepted light becomes absolutely equal in every azimuth4#fe #fd ,the form would not be exactly rhomboidal1 but would be a portion of a flat helix intercepted between two planes1 cutting the enveloped cylinder at right angles to its axis4 #fe ,see my ,report on the ,refractors of the ,isle of ,may ,light1 #hth ,october #ahcf4 ,illustration3 ,fig4 #gj4 ,such an apparatus is shewn in ,plate ,,xvii42 and the accompanying diagram 7fig4 #gj7 shews an elevation ,,abcd1 a section ,,bd1 and a plan ,,abd1 of a single pannel of this improved compound belt4 ,,ac and ,,bd are the diagonal joints above described4 ,time and perseverance1 and the patience and skill of ,monsieur ,,fran,,ois ,,soleil1 whom ,i urged to undertake the task1 were at length crowned with success2 and ,i had the satisfaction at last of seeing a fixed light apparatus1 having its form truly cylindric1 and its central belt in one piece1 while the joints were inclined to the horizon at such an angle as to render the light perfectly equal in every azimuth4 ,catadioptric ,zones4 ,the loss of light by reflection at the surface of the most perfect mirrors1 and the perishable nature of the material composing their polish1 induced me1 so far back as #ahce1 in a ,report on the ,light of ,inchkeith1 which had just been altered to the dioptric system1 to propose the substitution of totally reflecting prisms1 even in lights of the first order or largest dimensions4 ,in this attempt ,i was much encouraged by the singular liberality of ,mr ,,leonor ,,fresnel1 to whose friendship 7as ,i have often1 with much pleasure1 acknowledged7 ,i owe all that ,i know of dioptric ,lighthouses4 ,he not only freely communicated to me the method pursued by his distinguished brother ,,augustin ,,fresnel1 in determining the forms of the zones of the small apparatus1 introduced by him into the ,harbour ,lights of ,france1 and his own mode of rigorously solving some of the preliminary questions involved in the computations2 but put me in possession of various important suggestions1 which substantially embrace the whole subject4 ,another friend also helped me1 by pointing out certain less direct methods of determining some of the elements1 which greatly abridged the labours of computation4 ,mr ,,fresnel agreed with me in anticipating a considerable increase of the light derived from the accessory part of the apparatus2 but he expressed his opinion1 that in order to prevent great absorption1 the rings should not greatly exceed those of the small apparatus in their sectional area4 ,this would have required about forty rings to intercept the same quantity of light acted upon by the curved mirrors2 and1 although the difficulties of grinding were somewhat similar to those which had already been encountered in forming the cylindric belt for the ,isle of ,may apparatus1 there were also some special difficulties attending the formation of the catadioptric zones1 which appeared so formidable as to deter me by the expense of grinding so many zones1 and led me to think of adopting flint glass4 ,considerable masses1 of a very pure and homogeneous appearance1 had been shewn to me by the late ,dr ,,ritchie of the ,london ,university1 who calculated upon the uniform and permanent success of his process2 but1 whatever foundation there might have been for this hope1 it was removed by his death1 which occurred soon afterwards1 and ,i was forced to return to the idea of using crown glass4 ,in order1 therefore1 to enable me to estimate more correctly the advantage of the zones1 ,i procured from ,messrs ,,cookson of ,newcastle1 an average specimen of crown glass1 of the thickness of #dj mm4 7about #a inch71 which is the distance traversed by the ray between its immergence into and its emergence out of the zones of the small apparatus2 and having had it carefully polished1 with both faces parallel1 ,i found1 as the result of numerous trials1 conducted with every precaution ,i could think of1 that the loss of light due to the transmission through it1 was somewhat less than ths of the incident light4 ,according to the experiments of ,,bougeur1 the loss by the two refractions may be assumed at th2 so that we could not sensibly err in concluding that the whole loss due to the transmission of the light through the zones would not much exceed ths of the incident light4 ,in the lights of the first order1 the loss by reflection from the surface of the mirrors1 and by the escape of light through the interstices which separate them1 is not less than ds of the light incident on that part of the apparatus4 ,on the most moderate expectation1 therefore1 which this proportion seemed to warrant1 it appeared that1 without any allowance for imperfections in the figure of the zones1 at least twice as much light would be transmitted through the zones as can be reflected by the mirrors4 ,the prospect even of a part of this increase being obtained without the expenditure of more oil1 seemed too important to be readily renounced1 more especially when it was considered that the fixed lights1 to which it chiefly applies1 are necessarily much feebler than the revolving lights1 as well as more numerous and more expensive4 ,so many motives pressed me to the work1 that ,i commenced my labours 7during my leisure hours while engaged at the ,skerryvore71 and computed ,tables of the ,elements of #de zones1 whose lesser sides were #dj millimtres in length1 which were printed in #ahdj4 ,in #ahda1 in consequence of having seen at ,paris specimens of purer crown glass1 ,i printed other ,tables from computations of larger zones1 which ,i had made in #ahch1 but had discarded as unsuited to the inferior quality of ,english glass1 whose absorption rendered the use of smaller dimensions of the zone imperative4 ,in the first ,table1 ,i had adopted the form of isosceles triangles1 to avoid the difficulty of grinding annular surfaces with radii of great length 7which ,i found required to be nearly #cj feet71 but in the second ,table1 ,i adopted a suggestion1 conveyed to me in a letter from ,m4 ,,leonor ,,fresnel1 by giving each zone the form of an oblique triangle whose base is the chord of the circle which osculates the surface of the reflecting side of the zone4 ,some attempts were made by ,messrs ,,cookson at ,newcastle to execute the largest of the zones2 but the forms differed so widely from the dimensions assigned in the ,table1 that ,i had begun to despair of success4 ,about this time1 ,i received a communication from ,m4 ,,fresnel1 pointing out several inaccuracies in my ,tables1 and more especially directing my attention to the disadvantage of choosing1 for the focus of the upper series of zones1 a high part of the flame1 as ,i had done with the view of throwing all the light below the horizon1 so that none might be lost4 ,he1 at the same time1 informed me of the success of ,m4 ,,fran,,ois ,,soleil1 in executing zones for the smaller apparatus1 known by the name of the ,third ,order2 and put me in possession of the results of his computations of large zones of the ,first ,order1 suited to the greatly improved quality of the crown glass of ,st ,gobain1 with an invitation1 before ,i should adopt his dimensions1 to verify his calculations4 ,this ,i willingly undertook1 and computed the elements of the zones in ,m4 ,,fresnel',s ,table afresh1 with results differing from his only in one or two instances1 to an amount whose angular value does not exceed more than #b4 ,the ,table in the ,appendix contains the result of my calculations1 which are verifications of those of ,m4 ,,fresnel4 ,the subject of the zones has thus been very fully weighed2 and it is most satisfactory to think that complete success has attended the perseverance and ardour of ,m4 ,,fran,,ois ,,soleil1 who at once boldly undertook to furnish for the ,skerryvore ,lighthouse the first catadioptric apparatus ever constructed on so magnificent a scale4 ,on the #bc;d ,december #ahdc1 ,m4 ,,fresnel announced1 in a letter to me1 the complete success which had attended a trial of the apparatus at the ,royal ,observatory at ,paris1 whereby it appeared that the illuminating effect of the cupola of zones1 was to that of the seven upper tiers of mirrors of the first order1 as #adj to #hg4 ,nothing can be more beautiful than an entire apparatus for a fixed light of the first order1 such as that shewn in ,plates ,,xvii4 and ,,xviii4 ,it consists of a central belt of refractors1 forming a hollow cylinder #f feet in diameter1 and #cj inches high2 below it are six triangular rings of glass1 ranged in a cylindrical form1 and above a crown of thirteen rings of glass1 forming by their union a hollow cage1 composed of polished glass1 #aj feet high and #f feet in diameter6 ,i know no work of art more beautiful or creditable to the boldness1 ardour1 intelligence1 and zeal of the artist4 ,i must now endeavour to trace the various steps by which the elements of the zones given in the appended ,table have been determined2 and this1 ,i fear1 ,i cannot do without considerable prolixity of detail4 ,referring to ,plates ,,xv41 ,,xvi41 ,,xvii41 and ,,xviii41 in which ,f shews the flame1 ,,rr1 the refractors1 and ,,mrm and ,,mrm1 the spaces through which the light would escape uselessly above and below the lens1 but for the corrective action of the mirrors ,,mm1 which project the rays falling on them to the horizon1 ,i have to observe that a similar effect is obtained1 but in a more perfect manner1 by means of the zones ,,abc and ,a,b,c 7fig4 #ga1 on page #bga71 whose action on the divergent rays of the lamp causes the rays ,,fc1 ,,fb and ,,fc1 ,,fb to emerge horizontally1 by refracting them at the inner surfaces ,,bc1 ,b,c1 reflecting them at ,,ab1 ,a,b1 and a second time refracting them at ,,ac1 ,a,c4 ,illustration3 ,fig4 #ga4 ,the problem proposed is1 therefore1 the determination of the elements and position of a triangle ,,abc1 which1 by its revolution about a vertical axis1 passing through the focus of a system of annular lenses or refractors in ,f1 would generate a ring or zone capable of transmitting in an horizontal direction by means of total reflection1 the light incident upon its inner side ,,bc from a lamp placed in the point ,f4 ,the conditions of the question are based upon the well-known laws of total reflection1 and require that all the rays coming from the focus ,f shall be so refracted at entering the surface ,,bc1 as to meet the side ,,ba at such an angle1 that instead of passing out they shall be totally reflected from it1 and passing onwards to the side ,,ca shall1 after a second refraction at that surface1 finally emerge from the zone in an horizontal direction4 ,for the solution of this problem1 we have given the positions of ,f the focus1 of the apex ,c of the generating triangle of the zone1 the length of the side ,,bc or ,,ca1 and the refractive index of the glass4 ,the form of the zone must then be such as to fulfil the following conditions3-- #a4 ,the extreme ray ,,fb must suffer refraction and reflection at ,b1 and pass to ,c1 where being a second time refracted1 it must follow the horizontal direction ,,ch4 #b4 ,the other extreme ray ,,fc must be refracted in ,c and passing to ,a1 must at the point be reflected1 and a second time reflected1 so as to follow the horizontal course ,,ag 7see fig4 #gb1 on opposite page74 ,these two propositions involve other two in the form of corollaries4 #a4 ,that every intermediate ray proceeding from ,f1 and falling upon ,,bc in any point ,e1 between ,b and ,c1 must1 after refraction at the surface ,,bc in ,e into the direction ,,ew1 be so reflected at ,w from ,,ab into the direction ,,wi1 that being parallel to ,,bc1 it shall1 after a second refraction in ,i1 at the surface ,,ac1 emerge horizontally in the line ,,ik4 ,and1 #b4 ,that the paths of the two extreme rays must therefore trace the position of the generating triangle of the zone4 ,to these considerations it may be added1 that as the angles ,,bch and ,,fca are each of them solely due to the refraction at ,c1 as their common cause1 they must be equal to each other1 and ,,bca being common to both1 the remaining angle ,,ach the remaining angle ,,bcf4 ,we naturally begin by the consideration of the lowest ray ,,fc1 whose path being traced gives the direction of the two refracting sides ,,bc and ,,ac1 leaving only the direction of the reflecting side ,,ba to be determined4 ,i shall not now explain the reason for neglecting entirely the consideration of the reflecting side at present1 as ,i could not do so without anticipating what must be more fully discussed in the sequel2 but ,i may content myself with stating1 that as the positions of ,,bc and ,,ac depend upon the direction of the incident ray ,,fc1 and on the refractive index of the glass1 this part of the investigation may be carried on apart from any interference with the reflecting side4 ,as we know the relation existing between the angles of incidence and refraction1 we might determine the relative positions of the sides ,,ac and ,,bc1 by means of successive corrections obtained by protraction1 tracing the paths of the rays from the horizontal directions backwards through the zones to the focus4 ,this method1 however1 depends entirely upon accurate protraction1 and is therefore unsatisfactory as a final determination1 or if employed for any other purpose than that of affording a rough approximation to the value of the angle1 a knowledge of which may occasionally save trouble in the employment of more exact means of determination4 ,i have not1 however1 on any occasion employed this process1 as ,i found that a little practice enabled me to make my first estimation very near the truth4 ,i shall therefore at once proceed to give a view of the reasoning employed in the investigation4 ,illustration3 ,fig4 #gb4 ,referring to fig4 #gb1 which shews the first and second zone of the upper series1 we have ,,fl ,tan ,,lcf --2 ,,cl and if we make the known angle1 ,,scf ,,ocf the complement of ,,bcf the angle of incidence for ,,fc4 ,,dc angle of refraction4 ,,lcf 7,,hcf - #ij7 7#b - #ij7 ,,scd 7 - 7 ,and m the index of refraction for crown glass1 we obtain the means of determining the angles and in two equations1 which are based upon the relation between the angles of incidence and refraction1 and on the interdependence of the various angles about ,c4 ,these primary equations are3 sin m 4 sin and #ff #b - 7making #b - #ij 7 #ff ,the truth of the first of these equations 7sin m 4 sin 7 which merely expresses the ratio of the sines of the angles of incidence and refraction is obvious2 but owing to the great number of small angles about ,c1 a little consideration may be required to enable one to perceive the truth of the second4 ,i therefore subjoin the steps by which ,i reached it4 ,it is obvious 7see fig4 #gb71 that as ,,ach and ,,bcf are equal1 the line ,,sc bisecting ,,hcf must bisect ,,acb4 ,but the production of ,,ac clearly gives ,,scd opposite and equal to ,,acw and ,,scd is by construction 7 - 7 7 - 71 and1 therefore1 ,,acb1 which is twice ,,acw or ,,scd 7#b #b - #b 74 ,now1 by construction ,,oc is a normal to the refracting surface ,,cb and its production ,c g gives ,,ac g 4 ,but ,,acb - g ,,cb 7#b #b - #b 7 - g ,,cb 7#b #b - #b 7 - #ij1 hence #b #b - #b - #ij1 and - #b - -#b 7#b - #ij7 by transposition1 and finally changing signs1 we have as above3 #b - 7#b - #ij7 #b - 4 ,eliminating between these two equations we obtain3 sin m 4 sin 7#b - 7 an expression1 which1 after various transformations of circular functions1 assumes the form #a 7 #a 7 sin - --- sin 4 sin 7------ - #a7 4 sin m 7#d m 7 #a ------ sin 4 sin sin #jfg #b m #fg ,this expression is equivalent to that of ,m4 ,fresnel1 but owing to a simplification in the fractional coefficients1 it is not literally the same4 ,i was led to it by the following steps1 starting from the original equation sin m sin 7#b - 7 sin m sin 7#b - 7 m sin #b 4 cos - cos #b sin m cos 4 sin #b - m sin 4 cos #b m cos 4 #b sin 4 cos - m sin 4 #a - #b sin #b m cos 4 sin 4 cos - m sin #b m sin 4 sin 4 ,therefore1 m sin sin - #b m sin sin #b m cos 4 sin 4 cos 4 ,then3 m sin #b m sin 4 sin - #d m sin sin sin - #d m sin 4 sin #d m sin 4 sin #d m cos sin 7#a - sin 7 #d m 4 cos 4 sin - #d m cos sin 4 ,hence we have3 m sin #b m sin 4 sin 7#a - #d m7 4 sin - #d m sin 4 sin #d m sin #j ,then dividing by #d m and arranging according to powers of 1 we have as above3 #a 7 #a 7 #a sin - --- sin 4 sin 7------ - #a7 4 sin ----- 4 sin 4 m 7#d m 7 #b m sin sin #j ,the solution of this equation1 which is of the fourth degree1 is somewhat tedious2 but as the root1 which will satisfy the optical conditions of the question1 must be the sine of an angle1 and necessarily lies between zero and unity2 and as the protraction1 if conducted with due care in the manner already described1 affords the means of at once assuming a probable value of not very distant from the truth1 the labour of the calculation1 in this particular case1 is not quite so great as might be expected4 ,but notwithstanding all the abridgments of which the particular case admits1 a considerable amount of labour is required1 and a corresponding risk of error incurred1 in merely introducing the numerical values into the equation preparatory to its solution2 and any other method requiring less arithmetical operation1 is1 of course1 greatly to be preferred4 ,i therefore willingly adopted the suggestion of a friend1 the benefit of whose advice ,i have on many occasions experienced1 and made use of the following ordinary method of approximating to the root of the equation4 ,if the equation sin - m sin 7#b - 7 #j 7see page #bgd7 be regarded as an expression for the error1 when the true value of which would satisfy the equation has been introduced into its first member1 we may consider any error in the value of as expressed by the equation3 sin - m 4 sin 7#b - 7 and differentiating this expression we have3 d cos 4 d - #b m cos 7#b - 7 4 d cos - #b m cos 7#b - 7 4 d ,then dividing by the differential coefficient we obtain d d --------------------------- cos - #b m cos 7#b - 7 ,but when becomes d 1 will also become d 2 but d #j therefore d - hence by substitution we have - d --------------------------- cos - #b m cos 7#b - 7 -sin - m sin 7#b - 7 ---------------------------- cos - #b m cos 7#b - 7 -sin m sin 7#b - 7 d --------------------------- cos - #b m cos 7#b - 7 ,by substituting1 therefore1 in this last equation the known values of m and 1 and the assumed value of 1 a correction is obtained1 which being applied to and the same process repeated1 new corrections may be found until the value of d falls within the limits of error1 which may be considered safe in the particular case4 ,i need hardly say1 that where so great a body of flame is employed as in the lights of the first order1 these limits are soon passed1 more especially as one soon acquires by a little experience the means of guessing a value of not very far from the truth4 ,it is this method ,i have employed in calculating the appended tables of the zones1 in which ,i have on all occasions1 though1 perhaps1 with needless exactness1 pushed my angular determinations to seconds4 ,having in this manner determined the angles of ,,bcf1 the obtuse angle ,,bca of the generating triangle of the zone is easily and directly deduced by the following expression1 which results from the obvious relations existing among the known angles about ,c2 and we have 7see fig4 #gc71 ,,bca #ij #ij #b - 4 ,we next proceed to consider the form of ,,ba1 the reflecting side of the zone1 which is a point of the greatest consequence1 as an error in the inclination of any part of its surface is doubled in the resulting direction of the reflected rays4 ,the conditions of the question require1 that every ray ,,ew1 after reflection at the surface ,,ab1 shall1 like ,,wi1 be parallel to the first ray1 which is reflected in the direction ,,bc1 and after a second refraction at ,c1 emerges horizontally in ,,ch4 ,but1 let us trace backwards the rays as they emerge in their horizontal directions ,,ik1 and it is obvious that if ,,ba be made a straight line1 then will every ray ,,ew meet the first refracting side ,,bc at the same angle1 and there suffering the same refraction1 they will go on parallel to each other1 and never meet in the focus ,f4 ,this convergence to ,f1 which is a necessary condition of the problem1 may1 however1 be produced by a curvature of ,,ab1 such that all the rays shall have a degree of convergence before falling on ,,bc1 sufficient to cause them to be finally refracted1 so as to meet in ,f4 ,on this account1 they will occupy less space in passing through ,,bc1 than they did in passing through ,,ac2 and thus ,,bc will be shorter than ,,ac by some quantity which shall give to that part of ,,ab which is at ,b the amount of downward inclination required for causing the ray ,,bf finally to converge to ,f2 and the line joining ,b and ,a must be a curve1 every point of which has its tangent inclined so as to serve the same purpose4 ,illustration3 ,fig4 #gc4 ,to trace tangents to this curve1 is therefore the next step in the process4 ,the direction of the first tangent ,,az depends upon very simple considerations2 and all that is necessary to be done is to draw a line ,,au 7fig4 #gc71 parallel to ,,bc 7which is the parallel to the direction of the reflected rays71 and forming an angle ,,cau1 which is1 of course1 equal to the inclination of the extreme rays refracted by ,,cb at ,c1 with rays reflected from the arc which we have yet to trace4 ,the line ,,ax bisecting this angle1 must therefore be a normal to the reflecting surface at ,a1 and ,,ab drawn perpendicular to ,,ax1 is consequently a tangent to the reflecting arc4 ,we must next find the direction of the second tangent ,z b1 which must be so inclined that the ray ,f b will1 after refraction at b1 be reflected into the direction1 b ,c2 but as the rigorous determination of this is difficult1 ,i shall describe two approximations suggested to me by ,m4 ,,leonor ,,fresnel4 ,the first method is based upon assuming the inclination of the ray refracted at b to the ray refracted at ,c as equal to3 b ,,fc ------ m 7in which expression1 m is the refractive index of the glass72 a supposition which obviously differs very little from the truth1 as small arcs may be assumed as nearly equal to their sines4 ,now1 it will be recollected1 that the rays refracted at ,c and b1 must be reflected at ,a and b1 in a direction parallel to ,c b1 and therefore the inclination of the reflecting surfaces1 or that which should be formed by the tangents ,,za and ,z b1 being half that of the incident rays1 is1 according to the assumption1 equal to b ,,fc ------1 #b m which may be expressed by b ,,fc1 m being equal to #aea4 ,but as the inclination of the two radii ,,ax and ,,bx is equal to the inclination of the tangents of the reflecting surfaces to which they are normals1 we obtain for the excess ,b of the secant of the reflecting arc over its radius the following expression3 ,b ,,ab 4 tan ,,bfc4#fh ,the value of ,b b gives1 of course1 the direction of the second tangent ,z b 7which must be equal in length to ,,az71 whence we easily deduce the chord of the reflecting side ,a b4 #fh ,the following steps will shew the mode of obtaining this expression3 ,suppose 7fig4 #gd1 on opposite page7 ,f n to be a ray incident on the surface ,,bc very near b or ,b 7which1 although exaggerated in the figure for more easy reference1 are close together71 and let this ray ,f n be refracted in the direction n ,o1 and draw n n parallel to ,,ca1 the ray which is refracted at ,c1 then will n n ,o m 4 b ,,fc b ,,fc4 ,but the tangent ,,az should make with the tangent b ,z an angle equal b ,,fc1 or one-half the inclination of the rays refracted at b and ,c1 which are afterwards by the agency of those tangents1 to be reflected in the directions parallel to b ,c and to each other4 ,hence we have ,,ax b 7which is the inclination of the normals to those tangents71 b ,,fc b ,,fc or ,,ax b ,,bz b ------ ------ nearly4 #b m #c ,illustration3 ,fig4 #gd4 ,but putting ,,axb 7fig4 #gc1 p4 #bgg7 for ,,ax b1 and ,,bfc for b ,,fc1 a supposition which may be safely made when the differences are so small1 and founding upon the analogy ,,ax ,,ab ,r tan ,,axb1 we have ,,ba ,,ax 4 tan ,,axb ,,ax 4 tan ,,bfc4 ,then ,,ab ,b 7,b #b ,,ax7 ,b #b ,b 4 ,,ax and neglecting ,b 1 which is very small1 we have3 ,,ba ,b 4 #b ,,ax nearly1 ,,ba hence ,b ---- #b ,,ax ,,ba ,but as above ,,ax ------------- tan 7 ,,bfc7 and substituting this value of ,,ax we obtain3 ,,ba ,b ----------------- 7 ,,ba 7 7#b -------------7 7 tan 7 ,,bfc77 hence we have1 as in the text1 ,b ,,ba 4 tan7 ,,bfc7 ,the second mode proposed by ,m4 ,,fresnel1 and that which ,i found most convenient in practice1 consists in forming successive hypotheses as to the length of the side ,,bc1 and tracing the path of the incident ray ,,fb1 which being refracted at ,b1 so as to make with the normal ,,bk an angle ,,bky y1 and finally reflected in the direction ,,bc1 must make the angle ,,ybz ,,mbc4 ,i shall describe it as follows3 ,in the annexed figure 7fig4 #ge7 ,,mbz is a tangent to the reflecting surface at ,b1 and ,,kbf is the angle of incidence of the ray ,,bf before its refraction at ,b4 ,if ,,kbf x1 and the angle of incidence of ,,fc ,,ecf x1 we have ,,bfc 7which is the inclination of those rays to each other1 and must be equal to the difference of their angles of incidence to the same surface7 x - x1 whence knowing x1 we easily find a value of x corresponding to the length of ,,bc4 ,then for finding the angle of refraction ,,kby y we have3 sin x sin y -------- m ,illustration3 ,fig4 #ge4 ,now1 if ,,fb be refracted1 so as to make with the reflecting side an angle equal to ,,zby1 it must 7if the position of ,b be rightly chosen71 be reflected so as to follow ,,bc1 thus making ,,mbc ,,ybz1 and calling each of these angles 1 we have the right angle ,,nbz made up of y ,,nbk4 ,but ,,nbk clearly equals 1 because it is the inclination of the normals to ,,bc and ,,bz1 and hence y #b #ij4 ,this1 therefore1 forms a crucial test for the length of ,,bc4 ,i may only remark1 that we already know the numerical value of y2 and that of is easily found1 for ,,cba ,,abm ,,cba ,,bam ,,cba 7,,mac - ,,bac7 ,,cba 7#ahj - 7 - ,,bac4 ,thus knowing and y1 we have only to see whether 7y - #b 7 - #ij #j ,we have now only to find the length of the radius ,,ax or b ,x 7see fig4 #gc1 p4 #bgg71 which will describe the reflecting surface or arc ,,az b1 and to determine the position of its centre ,x4 ,we already know the values of y and y1 the angles of refraction of ,c and b1 and their difference y - y gives us the inclination of the rays which are to be reflected 7into directions parallel to ,c b7 at b and at ,a4 ,this quantity is1 of course1 double the inclination of tangents to the reflecting surface ,,az and b ,z1 and of their normals ,,ax and b ,x4 ,again1 we have the chord line sin 7,,ac b7 ,a b ,,ac 4 ------------2 sin 7b ,,ca7 and1 as above1 ,,ax b 7y - y7 sin 7 7#ahj - 77 ,and ,,ax b ,x ,a b 4 ------------------- sin ,a b 4 cosec7 74 ,and1 lastly1 for the co-ordinates to ,x1 the centre of curvature for the reflecting arc1 we have ,,ox 4 sin ,,oax and ,,oa 4 cos ,,oax4#fi #fi ,the angle ,,oax is easily found1 as will be seen by referring to fig4 #gc1 p4 #bgg2 for1 ,,ah being horizontal by construction and ,,ao vertical1 ,,hao #ij2 and ,,hac and ,,cau being both known1 we have ,,oax #ij - 7,,hau ,,uax7 #ij - 7,,hau ,,cau74 ,illustration3 ,fig4 #gf4 ,the positions of the apices ,a and ,b of the angles of the zones are also easily found in reference to the focus1 and are given in the ,table in the ,appendix4 ,in fig4 #gf we may1 in reference to the known position of ,c1 find that of ,a or ,b1 by simply adding the quantities ,,ah1 ,,hc1 and ,,bk1 to ,c y or ,c x1 and by deducting ,,ck from ,c y2 while it is obvious that those quantities are respectively proportional to the length of the known sides ,,ac and ,,bc1 modified by the inclination of those sides with the horizon4 ,hence we have ,,ah ,,ac 4 sin ,,ach2 ,,hc ,,ac 4 cos ,,ach2 ,,bk ,,bc 4 sin ,,bck2 and ,,ck ,,bc 4 cos ,,bck4 ,in the process of grinding the zones1 it is found convenient for the workman to give a curved form to the refracting sides ,,bc and ,,ac1 the one being made convex and the other concave1 so that both being ground to the same radius1 the convergence of the rays produced by the first shall be neutralized by the divergence caused by the second4 ,by this arrangement we have three points given in space from which1 with given radii1 to describe a curvilinear triangle whose revolution round the vertical axis of the system generates the zone required4 ,co-ordinates to those two centres of curvature for the surfaces ,,ac and ,,bc were determined in reference to arris ,a of each zone1 and will be found in the ,appendix4 ,the mode of finding those co-ordinates is1 of course1 similar to that already given2 and1 the radii being assumed at #djjj millimtres1 the co-ordinates are respectively proportional to the sine and cosine of the inclination of the radius at ,a to the vertical line1 which inclination depends upon the relations of known angles around ,a and ,c4 ,the section ,,abc 7fig4 #ga1 p4 #bga7 of the first zone being thus determined1 we proceed by fixing the point ,c of the second zone1 which is at the intersection of the horizon ,,gag with the ray ,,fbc passing through ,b4 ,this arrangement prevents any loss of light between the adjacent zones4 ,the calculation of the elements of the second and of every following zone1 is precisely similar to that of the first4 ,testing of ,zones4 ,the mode of grinding the zones ,i shall not notice here2 but shall refer the more curious reader to the ,appendix1 in which ,i have given the details of the process followed by ,m4 ,,theodore ,,letourneau1 who now manufactures the apparatus for the ,northern ,lights ,board1 in the room of ,m4 ,,fran,,ois ,,soleil1 who is engaged at ,st ,petersburg in the same work4 ,i accordingly proceed to consider what mode should be followed in testing the accuracy of the zones4 ,for this purpose1 various expedients suggested themselves1 such as the application of gauges in the form of a radius1 having at one end a plate with a triangular space cut through it1 equal and similar to the cross section of the zone4 ,the horizontal motion of this arm would1 of course1 detect the inaccuracies of the successive sections of the inclosed zone4 ,the application of such a gauge1 however1 seemed difficult1 and in order to test the form of the zones1 ,i satisfied myself with using callipers 7similar to the sliding rules used by shoemakers7 for measuring the length of the sides of the zone1 and a goniometer for the angles1 which is represented in the figure 7fig4 #gg71 in which ,,abc represents the prism1 with one angle inclosed between the arms ,,ac and ,,ab1 moveable round a centre ,o1 and ,,rr the graduated limb4 ,this instrument is inconvenient and defective1 as the convexity of the sides ,,ab and ,,bc of the zone requires some skill in getting the arms to be tangents to them4 ,illustration3 ,fig4 #gg4 ,illustration3 ,fig4 #gh4 ,a practical test1 however1 yet remained to be made of the zones when fixed in the brass frames 7shewn at ,plate ,,xviii471 and assembled around the common focus of the system1 by measuring the final inaccuracy in the path of the rays emergent from them4 ,i have successfully used the following mode4 ,having mounted the frames containing the zones on a carriage revolving round a small flame placed truly in the common focus1 ,i carefully marked with a piece of soap the centre of the emergent surface of each zone2 and having attached to a vertical rod of metal a telescope1 provided with a spirit-level and cross-hairs 7for cutting the centre of the image of the flame reflected through the zone7 in such a manner as to be capable of sliding on the rod1 ,i observed the cutting of the centre of the flame by the cross-hairs4 ,in the case of any aberration from a normal emergence of the central ray1 ,i had thus the means of at once determining its amount and direction4 ,the telescope was moved up or down1 and its vertical inclination was varied until the axis of the instrument coincided with the direction of the ray emergent from the centre of each zone1 which was made to circulate round the flame1 the observer noting any change in the position of the reflected image of the flame1 and causing an attendant to mark the zones in which the change occurred1 that they might again be subjected to separate examination of the same kind1 by adjusting the telescope to the error of each4 ,the vertical inclination of the telescope and the consequent aberration of the ray1 was then measured by a graduated arc1 with an adjusting spirit-level1 moved by a rack and pinion4 ,the accompanying figure 7fig4 #gh7 shews the arrangement just described4 ,e is the small flame in the focus2 ,,abc is the zone2 ,,tt is the telescope2 and ,r a graduated limb1 on which is read the angular deviation of the axis of the telescope from the horizon4 ,in the figure1 the ray emergent from the centre of ,,ac is shewn dipping below the true level1 to which the line ,,tc is supposed to be parallel4 ,i have succeeded by this method in detecting the inaccurate position of some of the zones in the frame2 and the error has been reduced by carefully resetting them1 so as to diminish considerably the error of a great proportion of the emergent rays4 ,another mode1 and that which1 owing to its convenience1 was chiefly employed in preference to that just described1 was to measure the vertical inclination 7given in the ,table in the ,appendix71 of each surface of the zone1 and more especially the reflecting surface1 by means of the instrument1 shewn in figures #gi and #hj1 after the zones were fixed in their place4 ,the figure 7,no4 #gi7 shews the mode of gauging the reflecting side ,,ab of a zone of the upper series2 and the second 7,no4 #hj7 shews the position of the instrument in gauging the reflecting side ,,ab of a zone of the under series4 ,in those figures1 ,l is a spirit-level2 ,r1 a graduated limb for reading the angular deviation from the true inclination of the tangents to each surface2 and ,,ss are studs which rest on the convex surfaces ,,ab and ,,bc of the zones1 so as to make the ruler parallel to the tangents of those sides4 ,i have only to add1 that ,i have restricted the error1 in the position of the reflecting side of the zones1 to #ej as an extreme limit2 and ,i have invariably endeavoured1 in altering the position of the zone in the frame1 to throw any error on the side of safety1 by causing the rays to dip below the horizon1 rather than to rise above it4#gj ,illustration3 ,fig4 #gi4 ,illustration3 ,fig4 #hj4 #gj ,in connection with the use of the clinometer1 ,i determined the inclinations of the tangents or chords of the three curve surfaces ,,ab1 ,,bc1 and ,,ac of each zone with ,,np1 the axis of the system1 by means of the obvious relations of the known angles about ,c1 ,a1 and ,b4 ,those inclinations 7fig4 #ha7 are shewn by the angles ,,bno1 ,,bon1 and ,,cpf2 and are given in the ,table of the ,zones in the ,appendix4 ,illustration3 ,fig4 #ha4 ,framing of ,zones4 ,the mode of framing the greater zones is shewn in ,plate ,,xviii4 and is nearly the same as that used for the ,small ,harbour ,light apparatus of the fourth order 7,plate ,,xix474 ,the chief difference consists in the diagonal framing1 which ,i adopted for supporting the cupola of #ac zones1 which1 from its great weight1 could not be safely made to rest on the dioptric belt below4 ,that frame is seen in ,plates ,,xvii4 and ,,xviii4 and is in accordance with the mode of jointing the refractors already described4 ,this system has now been rendered still more complete by the adoption of lanterns composed of diagonal framework1 afterwards described and shewn at ,plate ,,xxvi4 ,mechanical ,lamp4 ,we have next to consider the great ,lamp1 to the proper distribution of whose light1 the whole of the apparatus1 above described1 is applied4 ,,fresnel immediately perceived the necessity of combining with the dioptric instruments which he had invented1 a burner capable of producing a large volume of flame2 and the rapidity with which he matured his notions on this subject and at once produced an instrument admirably adapted for the end he had in view1 affords one of the many proofs of that happy union of practical with theoretical talent1 for which he was so distinguished4 ,,fresnel himself has modestly attributed much of the merit of the invention of this ,lamp to ,m4 ,,arago2 but that gentleman1 with great candour1 gives the whole credit to his deceased friend1 in a notice regarding lighthouses1 which appeared in the ,annuaire du ,bureau des ,longitudes of #ahca4 ,the lamp has four concentric burners1 which are defended from the action of the excessive heat1 produced by their united flames1 by means of a superabundant supply of oil1 which is thrown up from a cistern below by a clockwork movement and constantly overflows the wicks1 as in the mechanical lamp of ,carcel4 ,a very tall chimney is found to be necessary1 in order to supply fresh currents of air to each wick with sufficient rapidity to support the combustion4 ,the carbonisation of the wicks1 however1 is by no means so rapid as might be expected1 and it is even found that after they have suffered a good deal1 the flame is not sensibly diminished1 as the great heat evolved from the mass of flame1 promotes the rising of the oil in the cotton4 ,i have seen the large lamp at the ,tour de ,corduan burn for seven hours without being snuffed or even having the wicks raised2 and1 in the ,scotch ,lighthouses1 it has often1 with ,colza oil1 maintained1 untouched1 a full flame for no less a period than seventeen hours4 ,illustration3 ,fig4 #hb4 ,illustration3 ,fig4 #hc4 ,illustration3 ,fig4 #hd4 ,the annexed diagrams will give a perfect idea of the nature of the concentric burner4 ,the first 7fig4 #hb7 shews a plan of a burner of four concentric wicks4 ,the intervals which separate the wicks from each other and allow the currents of air to pass1 diminish a little in width as they recede from the centre4 ,the next 7fig4 #hc7 shews a section of this burner4 ,c1 ,c1 ,c1 ,c are the rack-handles for raising or depressing each wick2 ,,ab is the horizontal duct which leads the oil to the four wicks2 ,l1 ,l1 ,l1 are small plates of tin by which the burners are soldered to each other1 and which are so placed as not to hinder the free passage of the air2 ,p is a clamping screw1 which keeps at its proper level the gallery ,r1 ,r1 which carries the chimney4 ,the last figure 7,no4 #hd7 shews the burner with its glass chimney and damper4 ,e is the glass chimney2 ,f is a sheet-iron cylinder1 which serves to give it a greater length1 and has a small damper ,d1 capable of being turned by a handle1 for regulating the currents of air2 and ,b is the pipe which supplies the oil to the wicks4 ,the only risk in using this lamp arises from the liability to occasional derangement of its leathern valves that force the oil by means of clockwork2 and several of the lights on the ,french coast1 and more especially the ,corduan1 have been extinguished by the failure of the lamp for a few minutes1 an accident which has never happened1 and scarcely can occur with the fountain lamps which illuminate the reflectors4 ,to prevent the occurrence of such accidents1 and to render their consequences less serious1 various precautions have been resorted to4 ,amongst others1 an alarum is attached to the lamp1 consisting of a small cup pierced in the bottom1 which receives part of the overflowing oil from the wicks1 and is capable1 when full1 of balancing a weight placed at the opposite end of a lever4 ,the moment the machinery stops1 the cup ceases to receive the supply of oil1 and1 the remainder running out at the bottom1 the equilibrium of the lever is destroyed1 so that it falls and disengages a spring which rings a bell sufficiently loud to waken the keeper should he chance to be asleep4 ,it may justly be questioned whether this alarum would not prove a temptation to the keepers to relax in their watchfulness and fall asleep2 and ,i have1 in all the lamps of the dioptric lights on the ,scotch coast1 adopted the converse mode of causing the bell to cease when the clockwork stops4 ,there is another precaution of more importance1 which consists of having always at hand in the light-room a spare lamp1 trimmed and adjusted to the height for the focus1 which may be substituted for the other in case of accident4 ,it ought to be noticed1 however1 that it takes about twenty minutes from the time of applying the light to the wicks to bring the flame to its full strength1 which1 in order to produce its best effect1 should stand at the height of nearly four inches 7#aj;cm474 ,the inconveniences attending this lamp have led to several attempts to improve it2 and1 amongst others1 ,m4 ,,delaveleye has proposed to substitute a pump having a metallic piston1 in place of the leathern valves1 which require constant care1 and must be frequently renewed4 ,a lamp was constructed in this manner by ,m4 ,,lepaute1 and tried at ,corduan2 but was afterwards discontinued until some further improvements could be made upon it4 ,it has lately been much improved by ,m4 ,,wagner1 an ingenious artist whom ,m4 ,,fresnel employed to carry some of his improvements into effect4 ,in the dioptric lights on the ,scotch coast1 a common lamp1 with a large wick1 is kept constantly ready for lighting2 and1 in the event of the sudden extinction of the mechanical lamp by the failure of the valves1 it is only necessary to unscrew and remove its burner1 and put the reserve-lamp in its place4 ,the height of this lamp is so arranged1 that its flame is in the focus of the lenses1 when the lamp is placed on the ring which supports the burner of the mechanical lamp2 and as its flame1 though not very brilliant1 has a considerable volume1 it will answer the purpose of maintaining the light in a tolerably efficient state for a short time1 until the light-keepers have time to repair the valves of the mechanical lamp4 ,only three occasions for the use of this reserve-lamp have yet occurred4 ,height of the flame of the ,mechanical ,lamp4 ,the most advantageous heights for the flames in dioptric lights are as follows3-- ,inches4 #ast ,order1 #aj to #aa centimtres #cid to #dcc #b;d ,order1 #h to #i 444444 #cae to #ced #c;d ,order1 #g to #h 444444 #bgf to #cae ,those heights of flame can be obtained only by a careful adjustment of the heights of the wicks and the relative levels of the shoulder of the glass-chimney and the burner1 together with a due proportion for the area of the opening of the iron-damper which surmounts it4 ,the wicks must be gradually raised during the first hours of burning to the level of #g millimtres 7#jbg inch7 above the burner1 a height which they may only very rarely and but slightly exceed4 ,by raising the shoulder of the glass-chimney the volume of the flame is increased2 but1 after a certain height is exceeded1 the flame1 on the other hand1 becomes reddish1 and its brilliancy is diminished4 ,the height of the flame is decreased1 and it becomes whiter by lowering the chimney4 ,the chimney is lowered or raised by simply turning to the right or to the left the cylindric glass-holder in which it rests 7see ,plate ,,xxv474 ,in regulating the flame1 however1 recourse is most frequently had to the use of the damper1 by enlarging the opening of which the flame falls and becomes whiter and purer2 while by diminishing its aperture1 the contrary effect is produced4 ,the area of the opening depends on the inclination of a circular disc capable of turning1 vertically through a quadrant1 on a slender axle of wire1 which is commanded by the light-keeper by means of a fine cord which hangs from it to the table below4 ,when the disc 7see fig4 #hd1 p4 #bhg7 is in a horizontal plane the chimney is shut1 when in a vertical plane it is open2 and each intermediate inclination increases or decreases the aperture4 ,position of flame in reference to focus of apparatus4 ,i need scarcely add1 that in order to produce the proper effect of a system of lenses or refractors1 the vertical axis of the flame should coincide with their common axis2 and it is further necessary1 in order to bring the best portion of the flame into a suitable position with reference to the apparatus1 that the top of the burner should be quite level1 and should stand below the plane of the focus in the following proportions1 viz43-- ,for #ast order1 #bh millimtres #aaj inches4 444 #b;d order1 #bf 444 #ajb 444 444 #c;d order1 #bd 444 #jie 444 ,illustration3 ,fig4 #he4 ,for the purpose of placing the lamp in the centre of the apparatus1 a plumbet with a sharp point suspended in the axis of the apparatus1 is used to indicate1 by its apex1 the place for the centre of the burner4 ,the lamp is then raised or lowered as required by means of four adjusting screws ,q at the bottom of its pedestal 7,plate ,,xx472 and the top of the burner is made horizontal by a spirit-level1 the most convenient form of which is that of the spherical segment1 which acts in every azimuth4 ,its application to this purpose is due1 ,i believe1 to ,m4 ,,letourneau1 the successor of ,m4 ,,fran,,ois in the construction of dioptric apparatus at ,paris4 ,this level is shewn in the annexed figure 7fig4 #he71 in which a b is the brass frame containing the level1 and ,o the air-bubble2 and e shews circles of equal altitudes engraved on the glass4 ,after the first application of this level1 the adjustment of the burner as to its central position is carefully repeated by means of a centre gauge 7shewn at fig4 #ij1 p4 #bie71 with reference to the vertex of each lens1 or to many points on the internal surface of the refractors2 and being found correct1 the level is again applied to the top of the burner1 to detect any deviation from horizontality that may have occurred during the process of adjusting it to the axis4 ,the lamp is subject to derangement1 chiefly from the stiffness of the clack-valves for want of regular cleaning1 bursting of the leathern valves of the oil-box1 stiffness of the regulator1 and the wearing of the bevelled gearing which gives motion to the connecting-rod that works the valves of the oil-pumps4 ,working of the ,pumps of the ,lamp4 ,the pumps of the lamp should raise1 in a given time1 four times the quantity of oil actually consumed by burning during that time4 ,their hourly produce should be1 lb4 avoirdupois4 ,for the lamp with four wicks1 #ffae 444444 three wicks1 #ddaj 444444 two wicks1 #afge ,this surplus of three times what is burned is necessary to prevent the wick from being carbonised too quickly2 and it has been found quite sufficient for that purpose4 ,the discharge from the pumps is1 of course1 regulated by changes in the angle of the fans of the regulator1 or in the amount of the moving weight4 ,care must be taken1 in preparing the leathern valves of the pump-box or chamber1 shewn in ,plate ,,xxii41 that they be neither too flaccid from largeness nor too tense from smallness2 and also that1 after being fitted1 they draw no air4 ,to remove the old valves and replace them by fresh ones1 is a very simple process1 more especially when a proper die or mould is used1 which at once cuts the kid-leather1 of which the valves are formed1 to the required size and squeezes them into the proper shape4 ,in ,plates ,,xx41 ,,xxi41 ,,xxii41 ,,xxiii41 ,,xxiv41 and ,,xxv41 the most minute details are given as to the clockwork1 pumps1 burners1 and flame of the great lamp4#ga #ga ,see also ,m4 ,,leonor ,,fresnel',s ,instructions sur l'organisation et la surveillance du service des ,phares et ,fanaux de ,france4 ,paris1 #ahdb1 pp4 #ab1 #ac1 #ad1 and #ae4 ,choice of ,focal ,point for various parts of the apparatus4 ,the focal point for the lenses and refractors is in the centre of the flame and on the level of its brightest film1 as shewn in ,plate ,,xxv4 ,the choice of a focus for the zones naturally formed a most important practical consideration in their arrangement2 and the judicious remarks of ,m4 ,,leonor ,,fresnel on that subject1 already noticed1 would alone have induced me to discard my former calculations in favour of his4 ,for the upper zones1 ,m4 ,,fresnel had adopted a point in the centre of the flame #aj millimtres above the focus of the lenses1 so that all the light below that point necessarily falls between the horizon and the ,lighthouse2 but for the lower zones1 it was necessary1 owing to their arrangement for convenience in a cylindric form1 to adopt a separate focus for each zone in the direction of the centre of gravity of that part of the flame which would light each zone4 ,in this manner 7fig4 #hf7 the foci of the zones recede upwards from a to f in proportion to the depression of the zones a1 b1 c1 d1 e1 f1 so that the line joining each zone and its focus1 must revolve as a radius vector round some point ,o between them4 ,the details of this arrangement are shewn in ,plate ,,xviii42 and are also given in the ,table of the ,catadioptric ,zones in the ,appendix4 ,illustration3 ,fig4 #hf4 ,application of ,spherical ,mirrors to fixed ,dioptric ,lights4 ,illustration3 ,fig4 #hg4 ,in the arc next the land1 in fixed lights1 a great loss of light ensues from the escape of the rays uselessly in that direction4 ,so far back as #ahcd1 ,i suggested the placing a segment of a spherical mirror1 with its centre of curvature coincident with ,f the focus of the system1 so that the luminous pyramid ,,mfm1 of which the mirror ,,mm forms the base1 might be thrown back through the focal point and finally refracted into such a direction as to contribute to the effect of the lens ,,qa q in seaward and opposite arc4 ,in the diagram 7fig4 #hg71 r r indicate rays proceeding directly from ,f2 r r rays reflected from ,,mm through ,f1 and finally refracted at ,,qa q2 and r r is the beam compounded of both4 ,in the best glass-silvered mirrors1 this accession of light would amount to nearly half of the light incident on them4 ,in such an arrangement1 a considerable radius is desirable to decrease the amount of aberration produced by a large flame4 ,in the case of revolving lights of the first order1 the radius would1 of course1 be limited to somewhat less than three feet1 which is the focal distance of the lenses1 between which and the focus1 the reflecting segment must be placed2 but in fixed lights1 the lantern is the limit of radius1 so that a focal length of five feet ten inches may be obtained4 ,m4 ,,fran,,ois ground some beautiful mirrors of three feet radius1 which were afterwards tinned by his successor1 ,m4 ,,letourneau1 by a new process discovered by himself2#gb and that gentleman is at present engaged in the construction of reflecting spherical segments #abjjmm4 square 7about #af superficial feet71 to a radius of #aggjmm4 7#e feet #aj inches71 which subtend a vertical arc of about #dj4 #gb ,see notice of a similar process practised about the year #agej by ,mr ,,rogers of ,london1 ante1 p4 #bdj4 ,arrangement of ,dioptric ,apparatus4 ,the arrangements of the dioptric apparatus in the lightroom will be more fully understood by referring to the ,plates4 ,plate ,,xiii4 shews an elevation of a revolving dioptric apparatus of the first order2 ,f is the focal point1 in which the flame is placed2 ,l1 ,l great annular lenses1 forming by their union an octagonal prism1 with the lamp in its axis1 and projecting1 in horizontal beams1 the light which they receive from the focus2 ,l,l1 the upper lenses1 forming by their union a frustum of an octagonal pyramid of #ej of inclination1 and having their foci coinciding in the point ,f4 ,they parallelise the rays of light which pass over the lenses4 ,m1 ,m are plane mirrors1 placed above the pyramidal lenses ,l,l1 and so inclined as to project the beams reflected from them in planes parallel to the horizon2 ,z1 ,z are the lower zones1 first used at ,skerryvore1 in the room of the curved mirrors which were used at ,corduan4 ,the lower part of ,plate ,,xiii4 shews the moveable framework which carries the lenses and mirrors1 and the rollers on which it circulates1 with the clockwork which gives motion to the whole4 ,plate ,,xiv4 is the plan of the apparatus shewn in ,plate ,,xiii4 ,plate ,,xv4 shews a section of a fixed dioptric light of the first order4 ,f is the focal point in which the flame is placed2 ,r1 ,r cylindric refractors1 forming by their union a prism of thirty-two sides1 or a true cylinder1 with the lamp in its axis1 and producing a zone of light of equal intensity in every point of the horizon2 ,m1 ,m1 curved mirrors1 ranged in tiers above and below the cylindric refractors1 and having their foci coinciding in the point ,f2 the effect of the mirrors increases the power of the light1 by collecting and transmitting the rays which would otherwise pass above and below them1 without increasing the effect of the light4 ,plate ,,xvi4 gives the elements of the curved mirrors ,,mm of ,plate ,,xv4 ,after the details given of the nature of the catadioptric zones1 all that is needful is briefly to refer to ,plate ,,xvii41 in which ,,abc and ,a,b,c shew the upper and lower zones which supply the place of the mirrors shewn at ,m1 ,m1 in ,plate ,,xv42 while ,,def shews the cylindric belt as lately improved1 with the diagonal joints ,m1 ,n1 ,c2 and ,x1 ,x1 represent the diagonal supports for the cupola ,,abc4 ,this plate1 in connection with the enlarged view of the same apparatus at ,plate ,,xviii41 affords a complete explanation of the arrangement of all the parts4 ,arrangement of the ,dioptric ,apparatus in the ,lightroom4 ,for the purpose of arranging the various parts of the dioptric apparatus in their proper positions1 three gauges are employed4 ,the first 7fig4 #hh7 is for ascertaining that the lenses l1 l1 meet at the proper horizontal angle1 so that their axes shall meet with the proper inclination in ,f the focus4 ,this is done by means of two arms1 whose projecting points r1 r1 r1 r touch the backs of the lenses1 while the graduated arc c indicates the inclination of l1 l1 to l1 l1 or the complement of that inclination at ,f4 ,illustration3 ,fig4 #hh4 ,illustration3 ,fig4 #hi4 ,again1 for ascertaining the verticality of the main lenses1 or for setting the subsidiary lenses or mirrors shewn in ,plates ,,xiii4 and ,,xiv41 at the required angle of inclination1 recourse is had to a clinometer 7fig4 #hi7 touching the back of the lens ,,ll by means of studs at ,a1 ,a1 while the spirit-level ,s indicates1 on the graduated limb1 the amount of deviation from the vertical position of the instrument1 whether accidental or intentional4 ,illustration3 ,fig4 #ij4 ,lastly1 to test the true position of the lamp itself1 with reference to the lenses thus properly arranged1 we apply a radius or trainer 7fig4 #ij7 which fits into the centre burner at ,f1 while its point ,a touches the centre of the lens l1 l2 at ,b is a graduated slide1 which admits of the trainer being lengthened or shortened to suit various focal distances2 and the spirit-level at c at once corrects any error in the length of the trainer arising from depression or elevation1 and also serves to indicate the proper level for the burner which is noticed at page #bij1 in speaking of the lamp4 ,the dotted line ,f c,b,a shews the position of the trainer in reference to an adjacent lens4 ,the elegant apparatus invented by ,,augustin ,,fresnel for ,harbour ,lights1 on the same principle as that just described for ,sea ,lights1 is shewn beneath 7fig4 #ia74 ,it consists of thirteen rings of glass of various diameters arranged one above another1 in an oval form4 ,the five middle rings have an interior diameter of #aaha inches 7#cj;cm471 and like those of the larger apparatus1 refract equally over the horizontal plane of the focus the light which they receive from it4 ,the other rings or prisms1 five of which are upper and three lower1 are ground and set in such a manner1 that they project all the light derived from the focus in a direction parallel to the other rays by total reflection4 ,illustration3 ,fig4 #ia4 ,the arrangements of this apparatus1 which is distinguished by the addition of external refractors arranged vertically1 will be more fully understood by a reference to fig4 #ia1 which shews its section and plan4 ,f is the focal point in which the flame is placed2 r1 r cylindric refractors1 forming by their union a cylinder with a lamp in its axis1 and producing a zone of light of equal intensity all round the horizon2 x1 x are catadioptric prismatic rings acting by total reflection1 and giving out zones of light of equal intensity at every point of the horizon4 ,the dotted lines shew the course traversed by the rays of light which proceed from the lamp1 and are acted upon by the rings of glass4 ,the letters r r shew the external prisms1 having their axes at right angles to those of the principal bent prisms1 composing the refractors at r1 r1 and revolving around them4 ,this ingenious application of the property of crossed prism is already described at page #bfd4 ,when this apparatus is employed to light only a part of the horizon1 the rings are discontinued on the side next the land1 and room is thus obtained for using a common fountain lamp2 but when the whole horizon is illuminated1 the apparatus must inclose the flame on every side2 and it has in that case been found most convenient to employ the hydrostatic lamp of ,,thilorier1 which has a balance of sulphate of zinc in solution4 ,an instrument differing from this small apparatus only in size1 has lately been introduced into the ,lighthouses in ,france1 and has also been adopted in ,scotland for lights in narrow seas4 ,it has the same number of rings of glass as the small apparatus1 and of the same proportional dimensions4 ,its internal diameter1 however1 is #ejj millimtres 7about #ai inches74 ,drawings of the smaller apparatus are given at ,plate ,,xix41 which also contains the radii and the centre of curvature for the rings of the central dioptric belt2 while the following ,table gives the elements of the eight prismatic zones 7above and below the belt71 with the co-ordinates to their centres of curvature1 measured from the arris ,a of the outer or emergent surfaces1 in whatever position the zone may lie on the lathe4 ,the dimensions are in millimtres2 but may be easily converted into imperial inches1 in the manner described in the ,table of the ,great ,zones1 which will be found in the ,appendix3-- ---------------------------------------- ------------------ ,hori- ,hori- zontal zontal distance,vertical distance,vertical ,radii from thedistance ,radii from thedistance ,number of axis offrom the,number of axis offrom the of curva- the outer of curva- the outer ,zone4 ture4 system4 arris4 ,zone4 ture4 system4 arris4 ---------------------------------------- ------------------ ,,reflecting ,,surfaces 7,,convex74 ,i4 #ajide #gbce #hccgh ,v4#abbbi #ebcf #aafia ,,ii4 #ajdeg #febh #hiaja ,,vi4#abdid #eddj #aaiba ,,iii4 #ajdde #eihd #iccfg ,,vii4#aaejd #eice #ajfbi ,,iv4 #ajhgc #eeai #ajajbj ,,viii4#aaacf #feje #ihei ---------------------------------------- ------------------ ,,outer ,,refracting ,,surfaces 7,,concave74 ,i4 #abejj #abijg #cjcai ,v4#abejjj #aajjbb #hbieb ,,ii4 #abejj #abgdb #ddehi ,,vi4#abejjj #aaabgd #hbaaf ,,iii4 #abejj #abcdj #ehgje ,,vii4#abejjj #aaijej #fihjj ,,iv4 #abejj #aagcj #gagga ,,viii4#abejjj #abeaij #eegbb ---------------------------------------- ------------------ ,,inner ,,refracting ,,surfaces 7,,convex74 ,i4 #abejj #aejfg #abaaij ,v4#abejjj #debbc #aahdbj ,,ii4 #abejj #bbhai #abjhhj ,,vi4#abejjj #decjg #aahebj ,,iii4 #abejj #cjeaj #abjcce ,,vii4#abejjj #cgdfj #aaifjj ,,iv4 #abejj #chajj #aaiecj ,,viii4#abejjj #bidce #abjchj ---------------------------------------- ------------------ ,power of ,dioptric ,instruments4 ,the effect of an annular lens1 in combination with the great lamp1 may be estimated at moderate distances to be nearly equal to that of #cjjj ,argand flames of about an inch diameter2 that of a cylindric refractor at about #bej2 and that of a curved mirror may perhaps on an average be assumed at about #aj ,argand flames4 ,orders of the ,french ,lights4 ,the dioptric lights used in ,france are divided into four orders1 in relation to their power and range2 but in regard to their characteristic appearances1 this division does not apply1 as1 in each of the orders1 lights of identically the same character may be found1 differing only in the distance at which they can be seen1 and in the expense of their maintenance4 ,the four orders may be briefly described as follows3-- #ast1 ,lights of the first order having an interior radius or focal distance of #cfbb inches 7#ib;cm471 and lighted by a lamp of four concentric wicks1 consuming #egj gallons of oil per annum4 #b;d1 ,lights of the second order having an interior radius of #bgee inches 7#gj;cm471 lighted by a lamp of three concentric wicks1 consuming #chd gallons of oil per annum4 #c;d1 ,lights of the third order1 lighted by a lamp of two concentric wicks1 consuming #ahc gallons of oil per annum4 ,the instruments used in those lights are of two kinds1 one having a focal distance of #aifh inches 7#ej;cm471 and the other of #ihd inches 7#be;cm474 #dth1 ,lights of the fourth order1 or harbour-lights1 having an internal radius of #ei inches 7#ae;cm471 and lighted by a lamp of one wick1 or ,argand burner1 consuming #dh gallons of oil per annum4 ,this apparatus is1 as already noticed1 now more generally used of a larger scale1 having a focal distance of #ihd inches 7#be;cm471 and a lamp of two concentric wicks1 consuming about #acj gallons of oil per annum4#gc #gc ,an apparatus of #jm4#ahe;cm4 was recently added to the list of ,french lights under the name of the ,fifth order2 while that of #be;cm4 radius has been called the ,fourth1 and that of #ae;cm4 radius is styled the ,sixth order4 ,those minute subdivisions ,i consider to be unnecessary4 ,distinctions of the ,dioptric ,lights4 ,those four orders are not intended as distinctions2 but are characteristic of the power and range of lights1 which render them suitable for different localities on the coast1 according to the distance at which they can be seen4 ,this division1 therefore1 is analogous to that which separates our lights into sea-lights1 secondary lights1 and harbour-lights1 terms which are used to designate the power and position1 and not the appearance of the lights to which they are applied4 ,each of the above orders is susceptible of certain combinations1 which produce various appearances1 and constitute the distinctions used for dioptric lights2 but the following are those which have been actually employed as the most useful in practice3-- ,the first order contains1 #ast1 ,lights producing1 once in every minute1 a great flash1 preceded by a smaller one1 by the revolution of eight great lenses and eight smaller ones combined with eight mirrors2 #b;d1 ,lights flashing once in every half minute1 and composed of sixteen half lenses4 ,those lights may have the subsidiary parts simply catoptric1 or diacatoptric2 and1 #c;d1 ,fixed lights1 composed of a combination of cylindric pieces1 with curved mirrors or catadioptric zones ranged in tiers above and below them4 ,the second order comprises revolving lights with sixteen or twelve lenses1 which make flashes every half minute2 and fixed lights varied by flashes once in every four minutes1 an effect which1 as already noticed1 is produced by the revolution of exterior cylindrical pieces4 ,the third order 7larger diameter7 contains common fixed lights1 and fixed lights varied by flashes once in every four minutes4 ,the third order 7smaller diameter7 contains fixed lights1 varied by flashes once in three minutes4 ,the fourth order has fixed lights varied by flashes once in every three minutes1 and fixed lights of the common kind4 ,it has been thought necessary to change the term 8fixed lights varied by flashes10 for 8fixed light with short eclipses10 because it has been found that1 at certain distances1 a momentary eclipse precedes the flash4 ,these distinctions depend upon the periods of revolution1 rather than upon the characteristic appearance of the light2 and therefore seems less calculated to strike the eye of a seaman1 than those employed on the coasts of ,great ,britain and ,ireland4 ,in conformity with this system1 and in consideration of the great loss of light which results from the application of coloured media1 all distinctions based upon colour have been discarded in the ,french lights4 ,the distinctions are1 in fact1 only four in number1 viz43 ,fixed2 ,fixed1 varied by flashes2#gd ,revolving1 with flashes once a minute2 and ,revolving1 with flashes every half minute4 ,to those might be added1 ,revolving1 with bright periods once in two minutes1 and perhaps ,flashing once in five seconds 7as introduced by me at the ,little ,ross1 but ,i cannot say with such complete success as would induce me to recommend its general adoption74 ,my own experience would also lead me to reject the distinction called 8,fixed1 varied by flashes10 which ,i do not consider as possessing a marked or efficient character4 #gd ,the 8,feu fixe1 vari par des clats10 or 8,feu fixe1 courtes clipses10 of ,fresnel4 ,comparison of ,dioptric and ,catoptric ,apparatus for ,revolving ,lights4 ,having thus fully described the nature of the catoptric and dioptric modes of illuminating lighthouses1 ,i shall next compare the merits of both systems1 with a view to determine their eligibility in revolving or in fixed lights4 ,repeated experiments were made at ,gullan-hill1 which is distant from ,edinburgh about fifteen miles1 during the winters of #ahcb and #ahcc1 under the inspection of the ,commissioners of ,northern ,lights1 the result of which was1 that the light of one of the great annular lenses used in the revolving lights of the first order1 was equal to the united effect of about eight of the large reflectors employed in the revolving lights on the ,scotch coast4 ,it may be said1 however1 that the dia-catoptric#ge combination of pyramidal lenses and plane mirrors of ,corduan1 adds the power of more than two reflectors to the effect of the great lens2 but it ought to be remembered that in the ,french lights1 this additional power is used only to compensate for one of the defects of the system by lengthening the duration of the flash1 and therefore contributes1 if at all1 only in a very indirect manner1 to render the light visible to the mariner at a greater distance4 ,m4 ,,fresnel found1 from the smaller divergence of the lens1 that the eclipses were too long and the bright periods of the revolution too short2 and he therefore determined to adopt the horizontal deviation of #g for the upper lenses1 with a view to remedy this defect4 ,assuming1 therefore1 that it were required to increase the number of reflectors in a revolving light of three sides1 so as to render it equal in power to a dioptric revolving light of the first order1 it would be necessary to place eight reflectors on each face1 so that the greatest number of reflectors required for this purpose may be taken at twenty-four4 ,m4 ,,fresnel has stated the expenditure of oil in the lamp of four concentric wicks at #gej grammes of colza oil per hour2 and it is found by experience at the ,isle of ,may and ,inchkeith1 that the quantity of spermaceti oil consumed by the great lamp1 is equal to that burned by from fourteen to sixteen of the ,argand lamps used in the ,scotch lights4 ,it therefore follows that1 by dioptric means1 the consumption of oil necessary for between fourteen and sixteen reflectors1 will produce a light as powerful as that which would require the oil of twenty-four reflectors in the catoptric system of ,scotland2 and1 consequently1 that there is an excess of oil equal to that consumed by ten reflectors1 or #djj gallons in the year1 against the ,scotch system4 ,but in order fully to compare the economy of producing two revolving lights of equal power by those two methods1 it will be necessary to take into the calculation the interest of the first outlay in establishing them4 #ge ,i use this word to designate the arrangement of pyramidal lenses and plane mirrors1 by which the light is first refracted1 and then reflected4 ,the expense of fitting up a revolving light with twenty-four reflectors1 ranged on three faces1 may be estimated at ,l4#abih1 and the annual maintenance1 including the interest of the first cost of the apparatus1 may be calculated at ,l4#dah1 #hs4 #d;d4 ,the fitting up a revolving light with eight lenses and the dia-catoptric accessory apparatus1 may be estimated at ,l4#adei1 and the annual maintenance at ,l4#ced1 #ajs4 #d;d4 ,it therefore follows1 that to establish and afterwards maintain a catoptric light of the kind called revolving white1 with a frame of three faces1 each equal in power to a face of the dioptric light of ,corduan1 an annual outlay of ,l4#fc1 #ahs4 more would be required for the reflecting light than for the lens light2 while for a light of the kind called revolving red and white1 whose frame has four faces1 at least thirty-six reflectors would be required in order to make the light even approach an equality to that of ,corduan2 and the catoptric light would in that case cost ,l4#bbe more than the dioptric light4 ,the effect produced by burning an equal quantity of oil1 in revolving lights on either system1 may be estimated as follows3--,in a revolving light1 like that of ,skerryvore1 having eight sides1 each lighting with its greatest power a horizontal sector of #d1 we have #cb 7or units7 of the horizon illuminated with the full power of #cbjj ,argand flames1 and consequently an aggregate effect of #ajb1djj flames1 produced by burning the oil required for sixteen reflectors2 while in a catoptric apparatus1 like that of the old light at ,inchkeith1 having seven sides of one reflector1 each lighting with its greatest power a sector of #dbe1 we have nearly #ca 7or units7 of the horizon illuminated with the full power of #djj ,argand flames1 and consequently an aggregate effect of #ab1djj flames as the result of burning the oil required for seven reflectors4 ,hence1 the effect of burning the same quantity of oil in revolving lights on either system1 will be represented respectively by 77 #ab1djj #bh1cdc for the catoptric1 contrasted with #ajb1djj for the dioptric light2 or1 in other words1 revolving lights on the dioptric principle use the oil more economically than those on the catoptric plan1 nearly in the ratio of #cf to #a4 ,comparison of ,catoptric and ,dioptric ,apparatus for ,fixed ,lights4 ,i shall now speak of fixed lights1 to which the dioptric method is peculiarly well adapted4 ,the effect produced by the consumption of a gallon of oil in a fixed light1 with twenty-six reflectors1 which is the smallest number that can be properly employed1 may be estimated as follows3--,the mean effect of the light spread over the horizontal sector1 subtended by one reflector1 as deduced from measurements made at each horizontal degree1 by the method of shadows1 is equal to #agd unassisted ,argand burners4 ,if1 then1 this quantity be multiplied by #cfj degrees1 we shall obtain an aggregate effect of #fb1fdj1 which1 divided by #ajdj 7the number of gallons burned during a year in twenty-six reflectors71 would give #fj ,argand flames for the effect of the light maintained throughout the year by the combustion of a gallon of oil4 ,on the other hand1 the power of a catadioptric light of the first order1 like that lately established at ,girdleness1 may be estimated thus3--,the mean effect of the light produced by the joint effect of both the dioptric and catadioptric parts of a fixed light apparatus1 may be valued at #dej ,argand flames1 which1 multiplied by #cfj degrees1 gives an aggregate of #afb1jjj2 and if this quantity be divided by #egj 7the number of gallons burned by the great lamp in a year71 we shall have about #bhd ,argand flames for the effect of the light produced by the combustion of a gallon of oil4 ,it would thus appear that in fixed lights1 the ,french apparatus1 as lately improved1 produces1 as the average effect of the combustion of the same quantity of oil over the whole horizon1 upwards of four times the amount of light that is obtained by the catoptric mode2 although1 in certain directions1 opposite the axis of each reflector1 the catoptric light be fully #ej per centum more powerful than the dioptric light4 ,but the great superiority of the dioptric method chiefly rests upon its perfect fulfilment of an important condition required in a fixed light1 by distributing the rays equally in every point of the horizon4 ,in the event of the whole horizon not requiring to be illuminated1 the dioptric light would lose a part of its superiority in economy1 and when half the horizon only is lighted1 it would be more expensive than the reflected light2 but the greater power and more equal distribution of the light1 may be considered of so great importance1 as far to outweigh the difference of expense4 ,in the latter case1 too1 an additional power 7as noticed p4 #bic7 can be given to the dioptric light1 by placing at the landward side of the lightroom1 spherical mirrors with their centres in the focus of the refracting apparatus4#gf ,the luminous cones1 or pyramids of which such reflectors would form the bases1 instead of passing off uselessly to the land1 would thus be thrown back through the focal point1 and finally refracted1 so as to increase the effect of the light seaward1 by nearly one-third of the light which would otherwise be lost4 #gf ,a similar arrangement can also be made in revolving lights by making the radius of the mirrors somewhat less than that of the inscribed circle of the octagon bounded by the lenses1 so that they may circulate freely round the backs of the mirrors4 ,the shortness of the radius of the reflecting surface would1 of course1 increase the divergence of the beam of light refracted through the lenses1 as the flame would1 in this case1 subtend a greater angle at the face of the mirrors4 ,the expense of establishing a fixed light composed of twenty-six reflectors1 may be estimated at ,l4#iej1 and its annual maintenance1 including interest on the first cost of the apparatus1 may be reckoned at ,l4#dbe1 #ajs43 and the expense of fitting up a fixed light on the dioptric principle with catadioptric zones is ,l4#aeaa1 while its annual maintenance may be taken at ,l4#bhe1 #fs4 #d;d4 ,it thus appears that the annual expenditure of the dioptric fixed light is ,l4#adj1 #cs4 #h;d4 less than that of a fixed light composed of twenty-six reflectors2 while the average effect1 equally diffused over the horizon1 is four times greater4 ,the comparative views already given of the catoptric and dioptric modes of illuminating lighthouses1 demonstrate that the latter produces more powerful lights by the combustion of the same quantity of oil2 while it is obvious that the catoptric system insures a more certain exhibition of the light1 from the fountain-lamps being less liable to derangement than the mechanical lamps used in dioptric lights4 ,the balance1 therefore1 of real advantages or disadvantages1 and1 consequently1 the propriety of adopting the one or the other system1 involves a mixed question1 not susceptible of a very precise solution1 and leaving room for different decisions1 according to the value which may be set upon obtaining a cheaper and better light1 on the one hand1 as contrasted1 on the other1 with less certainty in its exhibition4 ,summary of considerations as to the fitness of the two systems for ,revolving ,lights4 ,a few general considerations1 serving briefly to recapitulate the arguments for and against the two systems1 may not be out of place4 ,and1 first1 regarding the fitness of dioptric instruments for revolving lights1 it appears from the details above given1-- #ast1 ,that by placing eight reflectors on each face of a revolving frame1 a light may be obtained as brilliant as that derived from the great annular lens2 and that1 in the case of a frame of three sides1 the excess of expense by the reflecting mode1 would be ,l4#fc1 #ahs42 and in the case of a frame of four sides1 the excess would amount to ,l4#bbe4 #b;d1 ,that for burning oil economically in revolving lighthouses1 which illuminate every point of the horizon successively1 the lens is more advantageous than the reflector in the ratio of #cf to #a4 #c;d1 ,that the divergence of the rays from the lens being less than from the reflector1 it becomes difficult to produce1 by lenses1 the appearance which characterises the catoptric revolving lights1 already so well known to ,british mariners2 and any change of existing lights which would1 of course1 affect their appearance1 must1 therefore1 involve many grave practical objections which would not at all apply to the case of new lights4 #dth1 ,that the uncertainty in the management of the lamp renders it more difficult to maintain the revolving dioptric lights without risk of extinction1 an accident which has several times occurred at ,corduan and other lighthouses both in ,france and elsewhere4 #eth1 ,that the extinction of one lamp in a revolving catoptric light is not only less probable1 but leads to much less serious consequences than the extinction of the single lamp in a dioptric light2 because1 in the first case1 the evil is limited to diminishing the power of one face by an eighth part2 whilst1 in the second1 the whole horizon is totally deprived of light4 ,the extinction of a lamp1 therefore1 in a dioptric light1 leads to evils which may be considered infinitely great in comparison with the consequences which attend the same accident in a catoptric light4 ,summary of considerations as to the fitness of the two systems for ,fixed ,lights4 ,in comparing the fixed dioptric1 and the fixed catoptric apparatus1 the results may be summed up under the following heads3-- #ast1 ,it is impossible1 by means of any practicable combination of parabolodal reflectors1 to distribute round the horizon a zone of light of exactly equal intensity2 while this may be easily effected1 by dioptric means1 in the manner already described4 ,in other words1 the qualities required in fixed lights cannot be so fully obtained by reflectors as by refractors4 #b;d1 ,the average light produced in every azimuth by burning one gallon of oil in ,argand lamps1 with reflectors1 is only about one-fourth of that produced by burning the same quantity in the dioptric apparatus2 and the annual expenditure is ,l4#adj1 #cs4 #h;d4 less for the entire dioptric light than for the catoptric light4 #c;d1 ,the characteristic appearance of the fixed reflecting light in any one azimuth would not be changed by the adoption of the dioptric method1 although its increased mean power would render it visible at a greater distance in almost every direction2 the only exception being in the azimuths opposite the axis of each reflector1 where the catoptric light has an excess of power equal to about #ej per centum4 #dth1 ,from the equal distribution of the rays1 the dioptric light would be observed at equal distances in every point of the horizon2 an effect which cannot be fully attained by any practicable combination of parabolodal reflectors4 #eth1 ,the inconveniences arising from the uncertainty which attends the use of the mechanical lamp1 are not perhaps so much felt in a fixed as in a revolving light1 because the greater simplicity of the apparatus admits of easier access to it1 in case of accident4 #fth1 ,but the extinction of a lamp in a catoptric light1 leaves only one twenty-sixth part of the horizon without the benefit of the light1 and the chance of accident arising to vessels from it1 may1 therefore1 be considered as incalculably less than the danger resulting from the extinction of the single lamp of the dioptric light1 which deprives the whole horizon of light4 #gth1 ,there may also1 in certain situations1 be some risk arising from irregularity in the distances at which the same fixed catoptric light can be seen in the different azimuths4 ,this defect1 of course1 does not exist in the dioptric light4 ,advantages and disadvantages of both systems under certain circumstances4 ,there can be little doubt1 that the more fully the system of ,,fresnel is understood1 the more certainly will it be preferred to the catoptric system of illuminating lighthouses1 at least in those countries where this important branch of administration is conducted with the care and solicitude which it deserves4 ,it must not1 however1 be imagined1 that there are no circumstances in which the catoptric system is not absolutely preferable to illumination by means of lenses4 ,we have hitherto attended only to horizontal divergence and its effects1 and this is unquestionably the more important view2 but the consideration of vertical divergence must not be altogether overlooked4 ,now1 while it is obvious that vertical divergence1 at least above the horizon1 involves a total loss of the light which escapes uselessly upwards into space1 it is no less true1 that if the sheet of light which reaches the most distant horizon of the lighthouse1 however brilliant1 were as thin as the absence of all vertical divergence would imply1 it would be practically useless2 and some measure of dispersion in the arc below the horizon is therefore absolutely indispensable to constitute a really useful light4 ,in the reflector1 the greatest vertical divergence below the horizontal plane of the focus is #af #h1 and that of the lens is about #d #cj4 ,let us consider for a moment the bearing of those facts upon the application of the two modes of illumination to special circumstances4 ,the powerful beam of light transmitted by the lens1 peculiarly fits that instrument for the great sea-lights which are intended to warn the mariner of his approach to a distant coast which he first makes on an over-sea voyage2 and the deficiency of its divergence1 whether horizontal or vertical1 is not practically felt as an inconvenience in lights of that character1 which seldom require to serve the double purpose of being visible at a great distance1 and at the same time of acting as guides for dangers near the shore4 ,for such purposes1 the lens applies the light much more economically than the reflector1 because1 while the duration of its least divergent beam is nearly equal to that of the reflector1 it is eight times more powerful4 ,a revolving system of eight lenses illuminates an horizontal arc of #cb with this bright beam4 ,the reflector1 on the other hand1 spreads the light over a larger arc of the horizon2 and1 while its least divergent beam is much less powerful than that of the lens1 the light which is shed over its extreme arc is so feeble as to be practically of little use in lights of extensive range1 even during clear weather4 ,when a lighthouse is placed on a very high headland1 however1 the deficiency of divergence in the vertical direction is often found to be productive of some practical inconvenience2 but this defect may be partially remedied by giving to the lenses a slight inclination outwards from the vertical plane of the focus1 so as to cause the most brilliant portion of the emergent beam to reach the visible horizon which is due to the height of the lantern4 ,it may be observed1 also1 that a lantern at the height of #aej feet1 which1 taking into account the common height of the observer's eye at sea1 commands a range of upwards of #bj ,english miles1 is sufficient for all the ordinary purposes of the navigator1 and that the intermediate space is practically easily illuminated1 even to within a mile of the lighthouse1 by means of a slight inclination of the subsidiary mirrors1 even where the light from the principal part of the apparatus passes over the seaman's head4 ,for the purpose of leading lights1 in narrow channels1 on the other hand1 and for the illumination of certain narrow seas1 there can be no doubt that reflectors are much more suitable and convenient4 ,in such cases1 the amount of vertical divergence below the horizon1 forms an important element in the question1 because it is absolutely necessary that the mariner should keep sight of the lights even when he is very near them2 while there is not the same call for a very powerful beam which exists in the case of sea-lights4 ,yet even in narrow seas1 where low towers1 corresponding to the extent of the range of the light1 are used1 but where it is1 at the same time1 needful to illuminate the whole or the greater part of the horizon1 the use of dioptric instruments will be found almost unavoidable1 especially in fixed lights1 as well from their equalizing the distribution of the light in every azimuth1 as from their much greater economy in situations where a large annual expenditure would often be disproportionate to the revenue at disposal4 ,in such places1 where certain peculiarities of the situation require the combination of a light equally diffused over the greater portion of the horizon1 along with a greater vertical divergence in certain azimuths1 than dioptric instruments afford1 ,i have found it convenient and economical to add to the fixed refracting apparatus a single parabolodal reflector1 in order to produce the desired effect1 instead of adapting the whole light to the more expensive plan for the sake of meeting the wants of a single narrow sector of its range4 ,in other cases1 where the whole horizon is to be illuminated1 and great vertical divergence is at the same time desirable1 a slight elevation of the burner1 at the expense1 no doubt1 of a small loss of light1 is sometimes resorted to1 and is found to produce1 with good effect1 the requisite depression of the emergent rays4 ,in certain situations1 where a great range and1 consequently1 a powerful light must be combined with tolerably powerful illumination in the immediate vicinity of the lighthouse1 we might1 perhaps1 advantageously adopt a variation of the form and dimensions of the mirrors employed1 so as to resemble those formerly employed at the ,tour de ,corduan1 which were of considerably larger surface and longer focal distance than those which are used in ,britain4 ,if such a form were adopted1 the power of the light for the purpose of the distant range would be increased2 and ,i would propose to compensate for the deficiency of divergence consequent on a long focal distance1 by placing a second burner in some position between the parameter and the vertex1 and slightly elevated above the axis of the instrument1 so as to throw the greater portion of the beam resulting from this second burner below the horizontal plane of the focus4 ,such an expedient is no doubt somewhat clumsy and would at the same time involve the consumption of twice the quantity of oil used in an ordinary catoptric light2 but ,i can still conceive it to be preferable1 in certain situations1 to the use of lenses alone4 ,thus it appears that we must not too absolutely conclude against one1 or in favour of the other mode of illumination for lighthouses2 but1 as in every other department of the arts1 we shall find the necessity of patiently weighing all the circumstances of each particular case that comes before us1 before selecting that instrument1 or combination of instruments1 which appears most suitable4 ,distinctions of the ,dioptric ,lights1 and the application of coloured media4 ,the mode of distinguishing lights in the system of ,,fresnel1 depends more upon their magnitude and the measured interval of the time of their revolution1 than upon their appearance2 and no other very marked distinctions1 except ,fixed and ,revolving1 have been successfully attempted in ,france4 ,as above stated1 ,i consider the distinction of the fixed light varied by flashes1 to possess an appearance too slightly differing from that of a revolving light1 to admit of its being safely adopted in situations where revolving lights are near4 ,the trial which ,i made at the ,little ,ross1 in the ,solway ,frith1 of producing1 by means of lenses1 a light flashing once in five seconds of time1 although successful so far as mere distinction is concerned1 has several practical defects1 arising from the shortness of the duration of the flashes1 compared with the powerful effect of the fixed part of the apparatus1 which ,i consider sufficient to prevent its adoption in future1 especially considering that a much more marked appearance can be produced1 by means of reflectors1 as has been done at the ,buchanness in ,aberdeenshire1 and the ,rhinns of ,islay in ,argyllshire4 ,coloured media have never1 so far as ,i know1 been applied to ,dioptric apparatus1 except in the case of the ,maplin ,light at the mouth of the ,thames1 and ,cromarty ,point ,light at the entrance to the ,cromarty ,frith1 and in both instances successfully4 ,the enormous loss of light1 however1 amounting to no less than #jhj of the whole incident rays1 forms a great bar to the adoption of colour as a distinction2 and any means which could tend to lessen that absorption1 and at the same time produce the characteristic appearance1 would be most valuable4 ,i have tried some glasses of a pink tinge1 prepared by ,m4 ,,letourneau of ,paris1 whose absorption does not exceed #jeg of the incident rays2 but the appearance of the light1 at a distance1 is much less marked than that produced by the glasses used in ,britain4#gg ,such deficiency of characteristic colour might lead to serious consequences1 as the transmission of white rays1 through a hazy atmosphere1 too often produces1 by absorption1 a reddish tinge of the light1 for which the less marked appearance given by the paler media might be easily mistaken4 ,this colouring power of absorption is so well known1 that red lights are seldom used except in direct contrast with white ones2 but1 on a coast so thickly studded with ,lighthouses as that of ,britain1 the number of distinctions is insufficient to supply all our wants1 so that we are sometimes reluctantly compelled to adopt a single red light in some situation of lesser importance1 or which1 from some local circumstances and the appearance of the lights which must be seen by the mariner before passing it1 is not likely to be mistaken4 ,the great loss of light by coloured media causes the red beam1 in a revolving light1 to be seen at a shorter distance than the white2 and it is conceivable that1 in certain circumstances1 this might lead the mariner to mistake a red and white light for a white light revolving at half the velocity4 ,such a mistake might perhaps prove dangerous2 but the lights are generally so situated that there is ample time for the mariner1 after first discovering the red light1 and thus correcting any mistake1 to shape his course accordingly4 ,all other coloured media except red have been found useless as distinctions for any lights of extensive range1 and fail to be efficient1 owing to the necessity of absorbing almost all the light before a marked appearance can be obtained4 ,in a few pier or ferry lights1 green and blue media have been tried1 and found available at the distance of a few cables' lengths4 #gg ,see page #bbi1 ante4 ,captain ,,basil ,,hall's proposal for producing the appearance of ,fixed ,lights by rapid movement4 ,it seems to be a natural consequence of the physical distribution of light1 that fixed lights1 which illuminate the whole horizon1 should be less powerful than revolving lights which have their effect concentrated within narrow sectors of the horizon4 ,any attempt to increase the power of fixed lights is1 therefore1 worthy of attention2 and when the late ,captain ,,basil ,,hall proposed a plan for effecting this object1 it received1 as it deserved1 the full consideration of the ,lighthouse ,board1 who authorised me to repeat ,captain ,,hall',s experiments1 and verify his results by observations made at a considerable distance4 ,as some interesting phenomena of irradiation were evolved in the course of those trials1 ,i think it right to give some account of the results which were obtained1 as they bear upon various questions connected with the practical arrangements of ,lighthouses1 under certain circumstances4 ,in revolving lights on the dioptric principle1 the annular lens of ,fresnel1 as formerly stated1 is employed4 ,this instrument1 as the reader already knows1 possesses the property of projecting to the horizon1 in the form of one pencil or beam1 all the light which falls on its inner surface from a lamp placed in its principal focus4 ,the consequence of this action is1 that when several lenses are so arranged as to form a right prism which circulates round a lamp placed in the common focus1 a distant observer receives from each lens1 as its axis crosses his line of vision1 a bright flash1 which is succeeded by total darkness1 when one of the dark spaces intermediate between the lenses passes over his eye2 and this succession of bright flashes alternating with dark intervals1 produces the characteristic appearance of a revolving light4 ,the fixed light1 on the other hand1 presents to the eye a steady and unchanging appearance2 and the chief object to be obtained in its construction1 is to unite the greatest brilliancy with an equal distribution of the light in every direction4 ,the condition of perfect distribution1 as already said1 is most rigorously fulfilled by the use of refracting zones or belts1 which form1 by their union1 a cylinder enveloping the flame placed in its centre1 and possess the property of refracting the light in the vertical direction only1 without affecting its natural divergence horizontally4 ,the light from the focus which is incident on the inner surface of the belt is therefore projected forwards in the shape of a flat ring of equal brilliancy all round the horizon4 ,this repetition may seem needless1 but it is hoped it will be found useful in rendering intelligible the following outline of the plan proposed by ,captain ,,hall for the improvement of fixed lights1 and the account of the trials that were made with that object in view4 ,the familiar experiment of whirling a burning stick quickly round the head1 so as to produce a ribbon of light1 proves the possibility of causing a continuous impression on the retina by intermittent images succeeding each other with a certain rapidity4 ,from the moderate velocity at which this continuity of impression is obtained1 we should be warranted in concluding1 a priori1 that the time required to make an impression on the retina is considerably less than the duration of the impression itself2 for the continuity of effect must1 of course1 be caused by fresh impulses succeeding each other before the preceding ones have entirely faded4 ,if it were otherwise1 and the time required to make the impression were equal to the duration of the sensation1 it would obviously be impossible to obtain a series of impulses so close or continuous in their effects as to run into and overlap each other1 and thus throw out the intervals of darkness2 because the same velocity which would tend to shorten the dark intervals1 would also curtail the bright flashes1 and thus prevent their acting on the eye long enough to cause an impression4 ,accordingly1 we find that the duration of an impression is in reality much greater than the time required for producing the effect on the retina4 ,it is stated by ,professor ,,wheatstone1 in the ,london ,transactions for #ahcd1 that only about one millionth part of a second is required for making a distinct impression on the eye2 and it appears1 from a statement made by ,lam1 at p4 #dbe of his ,cours de ,physique1 that ,m4 ,,plateau found that an impression on the retina preserved its intensity unabated during one hundredth of a second1 so that1 however small those times may be in themselves1 the one is yet #aj1jjj greater than the other4 ,it has been ascertained by direct experiment1#gh that the eye can receive a fresh impression before the preceding one has faded2 and1 indeed1 if this were impossible1 absolute continuity of impression from any succession of impulses1 however rapid1 would seem to be unattainable2 and the approach to perfect continuity would be inversely as the time required to make an impression4 #gh ,lam1 ,cours de ,physique1 p4 #dbd4 8,l'impression peut subsister encore lorsque la suivante a lieu40 ,effects of rapid motion on the power of ,lights4 ,from this property which bright bodies passing rapidly before the eye possess of communicating a continuous impression to the sense of sight1 ,captain ,,hall conceived the idea1 not merely of obtaining all the effects of a fixed light1 by causing a system of lenses to revolve with such a velocity as to produce a continuous impression1 but1 at the same time1 of obtaining a much more brilliant appearance1 by the compensating influence of the bright flashes1 which he expected would produce impulses sufficiently powerful and durable to make the deficiency of light in the dark spaces almost imperceptible4 ,the mean effect of the whole series of changes would1 he imagined1 be thus greatly superior to that which can be obtained from the same quantity of light equally distributed1 as in fixed lights1 over the whole horizon4 ,now this expectation1 if it be considered solely in reference to the physical distribution of the light1 involves various difficulties4 ,the quantity of light subjected to instrumental action is the same whether we employ the refracting zones at present used in fixed dioptric lights1 or attempt to obtain continuity of effect by the rapid revolution of lenses2 and the only difference in the action of those two arrangements is this1 that while the zones distribute the light equally over the whole horizon1 or rather do not interfere with its natural horizontal distribution1 the effect of the proposed method is to collect the light into pencils1 which are made to revolve with such rapidity1 that the impression from each pencil succeeds the preceding one in time to prevent a sensible occurrence of darkness4 ,to expect that the mean effect of the light1 so applied1 should be greater than when it is left to its natural horizontal divergence1 certainly appears at first to involve something approaching to a contradiction of physical laws4 ,in both cases1 the same quantity of light is acted upon by the instrument2 and in either case1 any one observer will receive an impression similar and equal to that received by any other stationed at a different part of the horizon2 so that1 unless we imagine that there is some loss of light peculiar to one of the methods1 we are1 in the physical view of the question1 shut up to the conclusion1 that the impressions received by each class of observers must be of equal intensity4 ,in other words1 the same quantity of light is by both methods employed to convey a continuous impression to the senses of spectators in every direction1 and in both methods equality of distribution is effected1 since it does not at all consist with our hypothesis1 that any one observer in the same class should receive more or less than his equal share of the light4 ,then1 as to the probability of the loss of light1 it seems natural to expect that this should occur in connection with the revolving system1 because the velocity is an extraneous circumstance1 by no means necessary to an equal distribution of the light1 which can1 as we already know1 be more naturally and at the same time perfectly1 attained by the use of the zones4 ,on the other hand1 it must not be forgotten1 that although the effect of both methods is to give each part of the horizon an equal share of light1 there is yet this difference between them1 that while the light from the zones is equally intense at every instant of time1 that evolved by the rapidly circulating lenses is constantly passing through every phase between total darkness and the brightest flash of the lens2 and this difference1 taken in connection with some curious physiological observations regarding the sensibility of the retina1 gives considerable countenance to the expectation on which ,captain ,,hall',s ingenious expedient is based4 ,the fact which has already been noticed1 and which the beautiful experiments of ,m4 ,,plateau and ,professor ,,wheatstone have of late rendered more precise1 that the duration of an impression on the retina is not only appreciable1 but is much greater than the time required to cause it1 seems to encourage us in expecting1 that while the velocity required to produce continuity of effect would not be found so great as to interfere with the formation of a full impression1 the duration of the impulse from each flash would remain unaltered1 and the dark intervals which do not excite the retina would1 at the same time1 be shortened1 and that1 therefore1 we might in this manner obtain an effect on the senses exceeding the brilliancy of a steady light distributed equally in every direction by the ordinary method4 ,some persons1 indeed1 who have speculated on this subject1 seem even to be of opinion1 that1 so far from the whole effect of the series of continuous impressions being weakened by a blending of the dark with the bright intervals1 the eye would in reality be stimulated by the contrast of light and darkness1 so as thereby to receive a more complete and durable impulse from the light4 ,it is obvious1 however1 that this question regarding the probable effect to be anticipated from a revolution so rapid as to cause a continuous impression1 could only have been satisfactorily answered by an appeal to experiment4 ,in experimenting on this subject1 ,i used the apparatus formerly employed by ,captain ,,hall4 ,it consisted of an octagonal frame1 which carried eight of the discs that compose the central part of ,fresnel's compound lens1 and was susceptible of being revolved slowly or quickly at pleasure1 by means of a crank-handle and some intermediate gearing4 ,the experiments were nearly identical with those made by ,captain ,,hall1 who contrasted the effect of a single lens at rest1 or moving very slowly1 with that produced by the eight lenses1 revolving with such velocity as to cause an apparently continuous impression on the eye4 ,to this experiment ,i added that of comparing the beam thrown out by the central portion of a cylindric refractor1 such as is used at the fixed light of the ,isle of ,may1 with the continuous impression obtained by the rapid revolution of the lenses4 ,captain ,,hall made all his comparisons at the short distance of #ajj yards2 and in order to obtain some measure of the intensity1 he viewed the lights through plates of coloured glass until the luminous discs became invisible to the eye4 ,i repeated those experiments at ,gullan1 under similar circumstances1 but with very different results4 ,i shall not1 however1 enter upon the discussion of those differences here1 although they are susceptible of explanation1 and are corroborative of the conclusions at which ,i arrived1 by comparing the lights from a distance of #ad miles2 but shall briefly notice the more important results which were obtained by the distant view4 ,they are as follows3-- #a4 ,the flash of the lens revolving slowly was very much larger than that of the rapidly revolving series2 and this decrease of size in the luminous object presented to the eye1 became more marked as the rate of revolution was accelerated1 so that1 at the velocity of eight or ten flashes in a second1 the naked eye could hardly detect it1 and only a few of the observers saw it2 while the steady light from the fixed refractor was distinctly visible4 #b4 ,there was also a marked falling off in the brilliancy of the rapid flashes as compared with that of the slow ones2 but this effect was by no means so striking as the decrease of volume4 #c4 ,continuity of impression was not attained at the rate of five flashes in a second1 but each flash appeared to be distinctly separated by an interval of darkness2 and even when the nearest approach to continuity was made1 by the recurrence of eight or ten flashes in a second1 the light still presented a twinkling appearance1 which was well contrasted with the steady and unchanging effect of the cylindric refractor4 #d4 ,the light of the cylindric refractor was1 as already stated1 steady and unchanging1 and of much larger volume than the rapidly revolving flashes4 ,it did not1 however1 appear so brilliant as the flashes of the quickly revolving lenses1 more especially at the lower rate of five flashes in a second4 #e4 ,when viewed through a telescope1 the difference of volume between the light of the cylindric refractor and that produced by the lenses at their greatest velocity was very striking4 ,the former presented a large diffuse object of inferior brilliancy1 while the latter exhibited a sharp pin-point of brilliant light4 ,upon a careful consideration of these facts it appears warrantable to draw the following general conclusions3-- #a4 ,that our expectations as to the effects of light1 when distributed according to the law of its natural horizontal divergence1 are supported by observed facts as to the visibility of such lights1 contrasted with those whose continuity of effect is produced by collecting the whole light into bright pencils1 and causing them to revolve with great velocity4 #b4 ,it appears that this deficiency of visibility seems to be chiefly due to a want of volume in the luminous object1 and also1 although in a less degree1 to a loss of intensity1 both of which defects appear to increase in proportion as the motion of the luminous object is accelerated4 #c4 ,that this deficiency of volume is the most remarkable optical phenomenon connected with the rapid motion of luminous bodies1 and that it appears to be directly proportional to the velocity of their passage over the eye4 #d4 ,that there is reason to suspect that the visibility of distant lights depends on the volume of the impression in a greater degree than has perhaps been generally imagined4 #e4 ,that1 as the size and intensity of the radiants causing these various impressions to a distant observer were the same1 the volume of the light and1 consequently1 cteris paribus1 its visibility1 are1 within certain limits1 proportionate to the time during which the object is present to the eye4 ,such appear to be the general conclusions which those experiments warrant us in drawing2 and the practical result1 in so far as lighthouses are concerned1 is sufficient to discourage us from attempting to improve the visibility of fixed lights in the manner proposed by ,captain ,,hall1 even supposing the practical difficulties connected with the great centrifugal force generated by the rapid revolution of the lenses to be less than they really are4 ,connection of the experiments with ,irradiation4 ,this decrease in the volume of the luminous object caused by the rapid motion of the lights is interesting1 from its apparent connection with the curious phenomenon of irradiation4 ,when luminous bodies1 such as the lights of distant lamps1 are seen by night1 they appear much larger than they would do by day2 and this effect is said to be produced by irradiation4 ,m4 ,,plateau1 in his elaborate essay on this subject1 after a careful examination of all the theories of irradiation1 states it to be his opinion1 that the most probable mode of accounting for the various observed phenomena of irradiation is to suppose1 that1 in the case of a night-view1 the excitement caused by light is propagated over the retina beyond the limits of the day-image of the object1 owing to the increased stimulus produced by the contrast of light and darkness2 and he also lays it down as a law confirmed by numerous experiments1 that irradiation increases with the duration of the observation4 ,it appears1 therefore1 not unreasonable to conjecture1 that the deficiency of volume observed during the rapid revolution of the lenses may have been caused by the light being present to the eye so short a time1 that the retina was not stimulated in a degree sufficient to produce the amount of irradiation required for causing a large visual object4 ,when1 indeed1 the statement of ,m4 ,,plateau1 that irradiation is proportional to the duration of the observation1 is taken in connection with the observed fact1 that the volume of the light decreased as the motion of the lenses was accelerated1 it seems almost impossible to avoid connecting together the two phenomena as cause and effect4 ,,various ,,general ,,considerations ,,connected ,,with ,,lighthouses4 ,masking ,lights4 ,in the course of supplying the numerous wants of navigation1 it will often be found necessary to cut off1 on a given bearing1 the beam proceeding from a ,lighthouse1 as a guide to the seaman to avoid some shoal1 or as a hint to put about and seek the opposite side of a channel4 ,this is attended with some little practical difficulty1 especially in lights from reflectors arranged externally on a circle1 because a certain portion of light1 chiefly due to the divergence caused by the size of the flames1 and partly from the effects of the diffraction or inflexion of the light1 spreads faintly over a narrow sector between the light arc and the dark one4 ,it becomes necessary1 of course1 to make allowance for this penumbral arc by increasing the masked portion of the lantern2 and1 where a very sharp line of demarcation is required1 a board is sometimes placed on the outside of the ,lightroom1 in such a position1 and of such length1 that while it does not enter the boundaries of the luminous sector1 it prevents the more powerful part of the penumbral beam from reaching the observer's eye4 ,this effect is1 of course1 more conveniently produced1 where the circumstances admit of its adoption1 by distributing the reflectors round the concave side of the lantern1 towards the land2 but such an arrangement is inapplicable when the illuminated sector exceeds the dark one4 ,i have found1 by observation1 that the sector intercepted between the azimuth on which the lantern is masked and that on which total darkness is produced to an observer1 at moderate distances1 may be estimated at not less than #c for dioptric1 and #g for catoptric lights of the highest class4#gi #gi ,the method which ,i adopted for determining those quantities1 was to mask a certain portion of the lantern of a lighthouse subtending an horizontal sector of about #cj or #dj1 and at night to fix1 by actual observation1 at the distance of #e or #f miles1 two points on the coast between which the light so masked was obscured4 ,the angle included between the lines joining those points and the centre of the lantern was then determined by triangulation next day1 and half the difference between the observed angle 7which is always the lesser of the two7 and the computed subtense of the masked sector of the lantern1 is1 in each case1 the amount of the allowance stated in the text4 ,those quantities may therefore serve to guide the ,lighthouse engineer to approximate more rapidly to his object1 as he will generally be safe in increasing the dark sector1 by one or other of the above constants1 according to the kind of apparatus employed4 ,i need not add1 that in a matter of this kind1 a final appeal to actual observation is1 in all cases1 indispensable4 ,double ,lights4 ,a few words on the subject of double lights1 naturally spring out of what has been said about the masking of lights4 ,the term double lights is properly and distinctly confined to lights on different levels1 but not necessarily 7as leading-lights are7 in separate towers4 ,the sole object of using double lights is for distinction from neighbouring lights2 and they are unquestionably most effective in this respect1 when they are placed in the same tower4 ,in this point of view1 therefore1 ,i shall speak of them2 and it is obvious that all that peculiarly belongs to them is1 that the difference of level between them shall be sufficiently great to present the lights as separate objects to the eye of the seaman1 when placed at the greatest distance at which it may be desirable that he should be able to recognise their characteristic appearance4 ,in many cases it is not necessary 7but it is certainly always desirable7 that the lights should1 from the first moment of their being seen1 be known as double lights2 but in others1 it may well consist with safety1 that two lights1 which appear as a single light when first seen at the distance of #bj miles1 shall at #ae or #aj miles distance be discovered to be double4 ,now we should at first be apt hastily to imagine1 that all that is required to produce that effect1 is to raise the one light above the other to such an extent1 that the distance between them shall be somewhat more than a minimum visibile at the most distant point of observation1 or1 in other words1 that the difference of the height of the lights should be such as to subtend to the eye at the point of observation1 an angle greater than #acjb1 which is the subtense of a minimum visibile during the day4#hj ,but the effect of irradiation1 to which ,i have already alluded1 tends to blend together the images of the lights long before their distance apart has become so low a fraction of the observer's distance from the ,lighthouse1 as to subtend so small an angle2 and ,i have accordingly found by experiments1 conducted under various circumstances1 and at various distances1 that repeated observations gave me #c #ah as the mean of the subtenses calculated in reference to the distances at which the lights began to be blended into one4 #hj ,this quantity is deduced from observations made by my friend ,mr ,,james ,,gardner1 while engaged on the ,ordnance ,survey1 and may be regarded as the extreme limit of visibility1 under the most favourable circumstances as to the state of the atmosphere and also the contrast of colours4 ,the observed object1 also1 was a pole1 not a round disc2 and it is familiar to every one accustomed to view distant objects1 that vertical length is an important constituent in their visibility4 ,adopting this as the smallest angle which the two lights should subtend at the observer's eye1 we may find the least vertical distance between them which will cause them to appear as separate objects by the following formula3 ,h #b 4 tan in which is the observer's distance in feet2 1 half the subtense1 #a #ci2 and ,h the required height of the tower between the two lights in feet4 ,the following ,table gives the height in feet corresponding to the distance in nautic miles1 from #a to #bj inclusive3 the heights1 which are the bases of similar isosceles triangles1 increase1 of course1 in an arithmetical series3 ---------------------------------------- ------------------------ ,distance of the,vertical distance,distance of the,vertical distance observer in in feet between observer in in feet between ,nautic ,miles4 the ,lights4 ,nautic ,miles4 the ,lights4 ---------------------------------------- ------------------------ #a #fjb #aa #ffbb #b #abjd #ab #gbbd #c #ahjf #ac #ghbf #d #bdjh #ad #hdbh #e #cjaj #ae #ijcj #f #cfab #af #ifcb #g #dbad #ag #ajbcd #h #dhaf #ah #ajhcf #i #edah #ai #aadch #aj #fjbj #bj #abjdj ---------------------------------------- ------------------------ ,leading ,lights4 ,akin to the subject of ,double ,lights1 is that of ,leading ,lights1 the object of which is to indicate to the mariner a given line of direction by their being seen in one line4 ,in most instances1 this line of direction is used to point out the central part of a narrow channel2 and the alternate opening of the lights1 on either side of their conjunction1 serves to indicate to the mariner 7who ought to conjoin with his watching of the lights the observation of the elapsed time and also frequent soundings7 the proper moment for changing his tack4 ,in some places1 the line of conjunction of the lights is placed nearer to one side of a channel than the other1 according as the set of the tides1 or the position of shoals1 may seem to require4 ,in other situations1 this line only serves as a cross-bearing to shew the mariner his approach to some danger1 or to indicate his having passed it1 and thus to assure him of his entry on wider sea-room4 ,similar considerations to those which determine the difference of elevation for double lights regulate the choice of the distance between two leading lights2 but the question is less narrow1 and may be generally solved graphically by simply drawing the lines on an accurate chart of the locality4 ,in some few situations1 the configuration of the coast does not admit of a separation between the lights1 sufficient to cause what is called a sharp intersection2 but1 in most cases1 there is room enough to place them so far apart1 that but a few yards of deviation in the vessel's course1 from the exact line of the conjunction of the lights in one1 produces a distinct opening between them on the opposite side of that line4 ,in order to insure the requisite sharpness of intersection1 the distance between the lights1 wherever attainable1 should be not less than one-sixth of the distance between the more seaward of the two ,towers and that point at which the seaman begins to use the line of conjunction as his guide4 ,i have only to add1 that in situations where the land prevents a considerable separation between leading lights1 they should be placed as nearly on one level as is consistent with their being seen as vertically separated1 so as in some measure to compensate for their horizontal nearness1 by rendering their intersection more sharp and striking than it can be where the observer must draw from the upper light an imaginary perpendicular in his mind1 and then estimate the separation of the lights by the sine of an angle1 which decreases as the difference of their apparent elevations increases4 ,distribution of ,lights on a ,coast4 ,the considerations which enter into the choice of the position and character of the ,lights on a line of coast1 are either1 on the one hand1 so simple and self-evident as scarcely to admit of being stated in a general form1 without becoming mere truisms2 or are1 on the other hand1 so very numerous and often so complicated as scarcely to be susceptible of compression into any general laws4 ,i shall not1 therefore1 do more than very briefly allude to a few of the chief considerations which should guide us in the selection of the sites and characteristic appearance of the ,lighthouses to be placed on a line of coast4 ,perhaps those views may be most conveniently stated in the form of distinct propositions3-- #a4 ,the most prominent points of a line of coast1 or those first made on over-sea voyages1 should be first lighted2 and the most powerful lights should be adapted to them1 so that they may be discovered by the mariner as long as possible before his reaching land4 #b4 ,so far as is consistent with a due attention to distinction1 revolving lights of some description1 which are necessarily more powerful than fixed lights1 should be employed at the outposts on a line of coast4 #c4 ,lights of precisely identical character and appearance should not1 if possible1 occur within a less distance than #ajj miles of each other on the same line of coast1 which is made by over-sea vessels4 #d4 ,in all cases1 the distinction of colour should never be adopted except from absolute necessity4 #e4 ,fixed lights and others of less power1 may be more readily adopted in narrow seas1 because the range of the lights in such situations is generally less than that of open sea-lights4 #f4 ,in narrow seas also1 the distance between lights of the same appearance may often be safely reduced within much lower limits than is desirable for the greater sea-lights2 and there are many instances in which the distance separating lights of the same character need not exceed #ej miles1 and there are peculiar cases in which even a much less separation between similar lights may be sufficient4 #g4 ,lights intended to guard vessels from reefs1 shoals1 or other dangers1 should in every case be placed1 where practicable1 to the seaward of the danger itself1 as it is desirable that seamen be enabled to make the lights with confidence4 #h4 ,views of economy in the first cost of a ,lighthouse should never be permitted to interfere with placing it in the best possible position2 and1 when funds are deficient1 it will generally be found that the wisest course is to delay the work until a sum shall have been obtained sufficient for the erection of the lighthouse on the best site4 #i4 ,the elevation of the lantern above the sea should not1 if possible1 for sea-lights1 exceed #bjj feet2 and about #aej feet is sufficient1 under almost any circumstances1 to give the range which is required4 ,lights placed on high headlands are subject to be frequently wrapped in fog1 and are often thereby rendered useless1 at times when lights on a lower level might be perfectly efficient4 ,but this rule must not1 and indeed cannot1 be strictly followed1 especially on the ,british coast1 where there are so many projecting cliffs1 which1 while they subject the lights placed on them to occasional obscuration by fog1 would also entirely and permanently hide from view lights placed on the lower land adjoining them4 ,in such cases1 all that can be done is carefully to weigh all the circumstances of the locality1 and choose that site for the lighthouse which seems to afford the greatest balance of advantage to navigation4 ,as might be expected1 in questions of this kind1 the opinions of the most experienced persons are often very conflicting1 according to the value which is set on the various elements which enter into the inquiry4 #aj4 ,the best position for a sea-light ought rarely to be neglected for the sake of some neighbouring port1 however important or influential2 and the interests of navigation1 as well as the true welfare of the port itself1 will generally be much better served by placing the sea-light where it ought to be1 and adding1 on a smaller scale1 such subsidiary lights as the channel leading to the entrance of the port may require4 #aa4 ,it may be held as a general maxim1 that the fewer lights that can be employed in the illumination of a coast the better1 not only on the score of economy1 but also of real efficiency4 ,every light needlessly erected may1 in certain circumstances1 become a source of confusion to the mariner1 and1 in the event of another light being required in the neighbourhood1 it becomes a deduction from the means of distinguishing it from the lights which existed previous to its establishment4 ,by the needless erection of a new ,lighthouse1 therefore1 we not only expend public treasure1 but waste the means of distinction among the neighbouring lights4 #ab4 ,distinctions of lights1 founded upon the minute estimation of intervals of time between flashes1 and especially on the measurement of the duration of light and dark periods1 are less satisfactory to the great majority of coasting seamen1 and are more liable to derangement by atmospheric changes1 than those distinctions which are founded on what may more properly be called the characteristic appearance of the lights1 in which the times for the recurrence of certain appearances differ so widely from each other as not to require for their detection any very minute observation in a stormy night4 ,thus1 for example1 flashing lights of five seconds interval1 and revolving lights of half a minute1 one minute1 and two minutes1 are much more characteristic than those which are distinguished from each other by intervals varying according to a slower series of #e1 #aj1 #bj1 #dj1 c4 #ac4 ,harbour and local lights1 which have a circumscribed range1 should generally be fixed instead of revolving2 and may often1 for the same reason1 be safely distinguished by coloured media4 ,in many cases also1 where the purpose of guiding into a narrow channel is to be gained1 the leading lights which are used1 should1 at the same time1 be so arranged as to serve for a distinction from any neighbouring lights4 #ad4 ,floating lights1 which are very expensive and more or less uncertain from their liability to drift from their moorings1 as well as defective in power1 should never be employed to indicate a turning point in a navigation in any situation where the conjunction of lights on the shore can be applied at any reasonable expense4 ,height of ,lighthouse ,tower1 and its relation to range of ,light4 ,the spherodal form of the ,earth requires that the height of a ,lighthouse ,tower should increase proportionally to the difference between the ,earth's radius and the secant of the angle intercepted between the normal to the spherod at the ,lighthouse and the normal at the point of the light's occultation from the view of a distant observer4 ,the effect of atmospheric refraction1 however1 is too considerable to be neglected in estimating the range of a light1 or in computing the height of a ,tower which is required to give to any light a given range2 and we must1 therefore1 in accordance with the influence of this element1 on the one hand increase the range due to any given height1 and vice versa reduce the height required for any given range1 which a simple consideration of the form of the globe would assign4 ,in considering this height1 we may proceed as follows3-- ,illustration3 ,fig4 #ib4 ,referring to the accompanying figure 7,no4 #ib71 in which ,s d ,l is a segment of the ocean's surface1 ,o the centre of the earth1 ,l,l a ,lighthouse1 and ,s the position of the mariner's eye1 we obtain the value of ,,ll ,h1 the height of the tower in feet by the formula1 #b l ,h ------ 7#a47 #c in which l the distance in ,english miles ,l d at which the light would strike the ocean's surface4 ,we then reduce this value of ,h by the correction for mean refraction1 which permits the light to be seen at a greater distance1 and which #b l ------1 7#b47 #ba #b l #b l #d l ,so as to get1 ,h ------ - ------ ------ 7#c47 #c #ba #g an expression which at once gives the height of the tower required1 if the eye of the mariner were just on the surface of the water at d1 where the tangent between his eye at ,s and the light at ,l would touch the sea4 ,we must1 therefore1 in the first instance1 find the distance d ,s l1 which is the radius of the visible horizon due to the height ,,ss h of his eye above the water1 and is1 of course1 at once obtained conversely by the expression3-- 7#g h7 l -------- 7#d47 #b ,deducting this distance from ,,sl1 the whole effective range of the light1 we have ,l d l1 and operating with this value in the former equation1 #dl ,h ----- #g we find the height of the tower which answers the conditions of the case4#ha ,from the above data the following ,table has been computed4 #ha ,in the above expressions l and l are given in ,english miles1 which in ,scotland may be considered as bearing to nautical miles the ratio of #ebhj to #fjhh4 ,in order to convert a distance given in nautical miles to ,english miles1 all that is needful is to add the log of the number of nautical miles to log #ebhj1 and subtract log #fjhh4 ---------------------------------------- ------ ,h ,lengths,lengths ,h ,lengths,lengths ,heights in in ,heights in in in ,english ,nautical in ,english ,nautical ,feet4 ,miles4 ,miles4 ,feet4 ,miles4 ,miles4 ---------------------------------------- ------ #e #bieh #befe #aaj #achgd #abjc #aj #dahd #cfbh #abj #addij #abef #ae #eabc #dddc #acj #aejhc #acjh #bj #eiaf #eacj #adj #aefeb #aceg #be #ffad #egcf #aej #agbja #adia #cj #gbde #fbhc #bjj #ahgjh #afbb #ce #ghbf #fghg #bej #bjiaf #ahad #dj #hcff #gbee #cjj #bbiab #aihg #de #hhgd #gfif #cej #bdgdh #badf #ej #iced #haab #djj #bfdeg #bbid #ee #ihaa #heji #dej #bhjfb #bdcc #fj #ajbdf #hhhf #ejj #biehj #befe #fe #ajffe #ibdi #eej #cajbd #bfij #gj #aajfg #ieih #fjj #cbdjc #bhaj #ge #aadef #iice #fej #ccgbf #bibe #hj #aahcb #ajbf #gjj #cejjj #cjbh #he #abaif #ajeg #hjj #cgdaf #cbde #ij #abedi #ajhh #ijj #cihcf #cded #ie #abhic #aaah #ajjj #dahcc #cfbh #ajj #acbbh #aadg ---------------------------------------- ------ ,if the distance at which a light of given height can be seen by a person on a given level be required1 it is only needful to add together the two numbers in the column of lengths or 7according as ,nautical or ,english miles may be sought7 corresponding to those in the column of heights ,h1 which represent respectively the height of the observer's eye and the height of the lantern above the sea4 ,when the height required to render a light visible at a given distance is required1 we must seek first for the number in or corresponding to the height of the observer's eye1 and deduct this from the whole proposed range of the light1 and opposite the remainder in or seek for the corresponding number in ,h4 ,diagonal ,lantern4 ,a considerable practical defect in all the lighthouse lanterns which ,i have ever seen1 with the exception of those recently constructed for the ,scotch ,lighthouses1 consists in the vertical direction of the astragals1 which1 of course1 tend to intercept the whole or a great part of the light in the azimuth which they subtend4#hb ,the consideration of the improvement which ,i had effected in giving a diagonal direction to the joints of the fixed refractors1 first led me 7as stated at p4 #bff1 ante71 to adopt a diagonal arrangement of the framework which carries the cupola of zones and afterwards for the astragals of the lantern4 ,not only is this direction of the astragals more advantageous for equalising the effect of the light2 but the greater stiffness and strength which this arrangement gives to the frame-work of the lantern make it safe to use more slender bars and thus also absolutely less light is intercepted4 ,the panes of glass at the same time become triangular1 and are necessarily stronger than rectangular panes of equal surface4 ,this form of lantern is extremely light and elegant1 and is shewn1 with detailed drawings of some of its principal parts1 in ,plate ,,xxvi4 ,to avoid the necessity of painting1 which1 in situations so exposed as those which lighthouses generally occupy1 is attended with many inconveniences and no small risk1 the framework of the lantern is now formed of gun-metal and the dome is of copper2 so that a first order lantern of #ab feet diameter and #aj feet height of glass costs1 when glazed1 about ,l4#abfj4 ,in order to give the lightkeepers free access to cleanse and wash the upper panes of the lantern 7an operation which in snowy weather must sometimes be frequently repeated during the night71 a narrow gangway1 on which they may safely stand1 is placed on the level of the top of the lower panes1 and at the top of the second panes1 rings are provided of which the lightkeepers may lay hold for security in stormy weather4 ,a light trap-ladder is also attached to the outside of the lantern by means of which there is an easy access to the ventilator on the dome4 #hb ,i must also except the small pier light at ,kirkcaldy1 erected 7,i believe in #ahcf7 by my friend ,mr ,,edward ,,sang4 ,glazing of the ,lantern4 ,great care is bestowed on the glazing of the lantern1 in order that it may be quite impervious to water1 even during the heaviest gales4 ,when iron is used for the frames1 they are carefully and frequently painted2 but gun-metal1 as just noticed1 is now generally used in the ,scotch ,lighthouses4 ,there is great risk of the glass plates being broken by the shaking of the lantern during high winds2 and as much as possible to prevent this1 various precautions are adopted4 ,the arris of each plate is always carefully rounded by grinding2 and grooves about inch wide1 capable of holding a good thickness of putty1 are provided in the astragals for receiving the glass1 which is inch thick4 ,small pieces of lead or wood are inserted between the frames and the plates of glass against which they may press1 and by which they are completely separated from the more unyielding material of which the lantern-frames are composed4 ,panes glazed in frames padded with cushions1 and capable of being temporarily fixed in a few minutes1 in the room of a broken plate1 are kept ready for use in the ,store-room4 ,those framed plates are called storm-panes1 and have been found very useful on several occasions1 when the glass has been shattered by large sea-birds coming against it in a stormy night1 or by small stones violently driven against the lantern by the force of the wind4 ,ventilation of the ,lanterns4 ,the ventilation of the lanterns forms a most important element in the preservation of a good and efficient light4 ,an ill-ventilated lantern has its sides continually covered with the water of condensation1 which is produced by the contact of the ascending current of heated air2 and the glass thus obscured obstructs the passage of the rays1 and diminishes the power of the light4 ,in the ,northern ,lighthouses1 ventilators1 capable of being opened and shut at pleasure1 so as to admit from without a supply of air when required1 are provided in the parapet-wall on which the lantern stands2 the lantern roof also is surmounted by a cover which1 while it closes the top of an open cylindric tube against the entrance of rain1 and descends over it only so far as is needful for that purpose1 still leaves an open air-space between it and the dome4 ,this arrangement permits the current of heated air1 which is continually flowing from the lantern through the cylindric tube1 to pass between it and the outer cover1 from which it finally escapes to the open air through the space between the cover and the dome4 ,the door which communicates from the lightroom through the parapet to the balcony outside1 is also made the means of ventilating the lightroom2 and1 for that purpose1 it is provided with a sliding bolt at the bottom1 which1 being dropped into one or other of the holes cut in the balcony for its reception1 serves to keep the door open at any angle that may be found necessary4 ,a useful precaution was introduced by my predecessor1 as ,engineer to the ,northern ,lights ,board1 in order to prevent the too rapid condensation of heated air on the large internal surface of the lantern roof1 which consists in having two domes with an air-space between them1 as shewn in the enlarged diagrams in ,plate ,,xxvi4 ,an important improvement in the ventilation of ,lighthouses was some years ago introduced by ,dr ,,faraday into several of the ,lighthouses belonging to the ,trinity ,house1 and has since been adopted in all the dioptric lights belonging to the ,commissioners of ,northern ,lighthouses4 ,after mentioning several proofs of extremely bad ventilation in ,lighthouses1 ,dr ,,faraday thus describes his apparatus3#hc #hc ,minutes of ,institution of ,civil ,engineers1 vol4 i41 p4 #bjg4 8,the ventilating pipe or chimney is a copper tube1 #d inches in diameter1 not1 however1 in one length1 but divided into three or four pieces2 the lower end of each of these pieces for about #a inch is opened out into a conical form1 about #e inches in diameter at the lowest part4 ,when the chimney is put together1 the upper end of the bottom piece is inserted about inch into the cone of the next piece above1 and fixed there by three ties or pins1 so that the two pieces are firmly held together2 but there is still plenty of air-way or entrance into the chimney between them4 ,the same arrangement holds good with each succeeding piece4 ,when the ventilating chimney is fixed in its place1 it is adjusted so that the lamp-chimney enters about inch into the lower cone1 and the top of the ventilating chimney enters into the cowl or head of the lantern4 8,with this arrangement1 it is found that the action of the ventilating flue is to carry up every portion of the products of combustion into the cowl2 none passes by the cone apertures out of the flue into the air of the lantern1 but a portion of the air passes from the lantern by these apertures into the flue1 and so the lantern itself is in some degree ventilated4 8,the important use of these cone apertures is that when a sudden gust or eddy of wind strikes into the cowl of the lantern1 it should not have any effect in disturbing or altering the flame4 ,it is found that the wind may blow suddenly in at the cowl1 and the effect never reaches the lamp4 ,the upper1 or the second1 or the third1 or even the fourth portion of the ventilating flue might be entirely closed1 yet without altering the flame4 ,the cone junctions in no way interfere with the tube in carrying up all the products of combustion2 but if any downward current occurs1 they dispose of the whole of it into the room without ever affecting the lamp4 ,the ventilating flue is in fact a tube1 which1 as regards the lamp1 can carry everything up but conveys nothing down40 ,the advantages of this arrangement1 as applied to the ,northern ,lighthouses1 were much less palpable than those which are described in the beginning of ,dr ,,faraday',s paper1 because their ventilation was very good before its introduction2 and the flame in particular was perfectly steady1 being by no means subject to derangement from sudden gusts of wind from the roof in the manner noticed above4 ,arrangements and internal management of a ,lighthouse4 ,all the ,lighthouses in the district of the ,commissioners are under the charge of at least two ,lightkeepers1 whose duties are to cleanse and prepare the apparatus for the night illumination1 to mount guard singly after the light is exhibited1 and to relieve each other at stated hours1 fixed by the printed regulations and instructions1 under which they act4 ,the rule is1 that no keeper on watch shall1 under any circumstances1 leave the ,lightroom until relieved by his comrade2 and1 for the purpose of cutting off all pretext for the neglect of this universal law1 the dwelling-houses are built close to the ,light ,tower1 and means are provided for making signals directly from the ,lightroom to the sleeping apartments below4 ,these signals are communicated by air-tubes1 through which1 by means of a small piston1 or a puff of wind from the mouth1 calls can be exchanged between the keepers1 enabling the man on guard in the ,lightroom1 at the end of the watch1 or on any sudden emergence1 to summon his comrade from below1 who1 on being thus called1 answers by a counter-blast1 to shew that the summons has been heard and will be obeyed4 ,for the purpose of greater security1 in such situations as the ,bell ,rock and the ,skerryvore1 four keepers are provided for one lightroom2 one being always ashore on leave with his family1 and the other three being at the ,lighthouse1 so that1 in case of the illness of one lightkeeper1 an efficient establishment of two keepers for watching the light may remain4 ,at all the land-lighthouses also1 an agreement is made with some steady person residing in the neighbourhood1 who is instructed in the management of the light and cleansing of the apparatus1 and comes under an obligation to be ready to do duty in the light-room when called upon1 in the event of the sickness or absence of one of the lightkeepers4 ,this person is called the occasional keeper1 and receives pay only while actually employed at the ,lighthouse2 but in order to keep him in the practice of the duty1 he is required to serve in the lightroom for a fortnight annually in the month of ,january4 ,the details of the lightkeeper's duty may be seen by referring to the instructions already alluded to1 which will be found in the ,appendix4 ,each of the two lightkeepers has a house for himself and family1 both being under a common roof1 but entering by separate doors1 as shewn in ,plates ,,xxvii4 and ,,xxviii41 which exhibit the buildings for the new ,lighthouse at ,ardnamurchan ,point1 on the coast of ,argyllshire4 ,the principal keeper's house consists of six rooms1 two of which are at the disposal of the visiting officers of the ,board1 whose duty in inspecting the ,lighthouse1 or superintending repairs1 may call them to the station2 and the assistant has four rooms1 one of which is used as a barrack-room for the workmen1 who1 under the direction of the ,foreman of the lightroom works1 execute the annual repairs of the apparatus4 ,the early ,lighthouses contained accommodation for the lightkeepers in the ,tower itself2 but the dust caused by the cleaning of those rooms in the ,tower was found to be very injurious to the delicate apparatus and machinery in the lightroom4 ,unless1 therefore1 in situations such as ,skerryvore1 where it is unavoidable1 the dwellings of the lightkeepers ought not to be placed in the ,light ,tower1 but in an adjoining building4 ,great care should be bestowed to produce the utmost cleanliness in everything connected with a ,lighthouse1 the optical apparatus of which is of such a nature as to suffer materially from the effect of dust in injuring its polish4 ,for this purpose covered ash-pits are provided at all the dwelling-houses1 in order that the dust of the fire-places may not be carried by the wind to the lightroom2 and for similar reasons1 iron floors are used for the lightrooms instead of stone1 which is often liable to abrasion1 and all the stonework near the lantern is regularly painted in oil4 ,cleansing of ,apparatus4 ,if1 in all that belongs to a lighthouse1 the greatest cleanliness be desirable1 it is in a still higher degree necessary in every part of the lightroom apparatus1 without which the optical instruments and the machinery will neither last long nor work well4 ,every part of the apparatus1 whether lenses or reflectors1 should be carefully freed from dust before being either washed or burnished2 and without such a precaution1 the cleansing process would only serve to scratch them4 ,for burnishing the reflectors1 prepared rouge 7tritoxide of iron7 of the finest description1 which should be in the state of an impalpable powder of a deep orange-red colour1 is applied1 by means of soft chamois skins1 as occasion may require2 but the great art of keeping reflectors clean consists in the daily1 patient1 and skilful application of manual labour in rubbing the surface of the instrument with a perfectly dry1 soft1 and clean skin1 without rouge4 ,the form of the hollow paraboloid is such1 that some practice is necessary in order to acquire a free movement of the hand in rubbing reflectors2 and its attainment forms one of the principal lessons in the course of the preliminary instruction1 to which candidates for the situation of a light-keeper are subjected at the ,bell ,rock ,lighthouse4 ,for cleansing the lenses and glass mirrors1 spirit of wine is used4 ,having washed the surface of the instrument with a linen cloth steeped in spirit of wine1 it is carefully dried with a soft and dry linen rubber1 and finally rubbed with a fine chamois skin1 free from any dust which would injure the polish of the glass1 as well as from grease4 ,it is sometimes necessary to use a little fine rouge with a chamois skin1 for restoring any deficiency of polish which may occur from time to time2 but in a well-managed lighthouse this application will seldom1 if ever1 be required4 ,the machinery of all kinds1 whether that of the mechanical lamp or the revolving apparatus1 should also be kept scrupulously clean1 and all the journals should be carefully oiled4 ,mode of measuring the relative intensity and power of ,lights4 ,as ,i have had frequent occasion to speak of the comparative power of lights1 it will not be out of place to present the reader with a few practical observations1 chiefly drawn from the excellent work of ,m4 ,,peclet to which ,i have so often referred1 on the measurement of the intensity of lights by the method of shadows4 ,illustration3 ,fig4 #ic4 ,the intensity of light decreases as the observer recedes from the luminous body1 in proportion to the square of his distance4 ,suppose a beam of light to proceed from a radiant at ,f1 and we shall have the rays which1 of course1 move in straight lines1 gradually receding from each other1 as b1 b1 b1 b1 and c1 c1 c1 c1 so that the section of the beam will increase with the distances ,f b1 and ,f c2 and the same number of rays1 being thus spread over spaces continually increasing1 will illuminate the surfaces with a less intensity4 ,this decrease of intensity will1 therefore1 be in the inverse ratio of the extent of the transverse parallel sections of the luminous cones at b and c1 which1 we know1 increase as the square of their distances from the apex of the cone at ,f4 ,hence we conclude1 that the intensity of any section of a divergent beam of light decreases as the square of its distance from the radiant4 ,this law furnishes us with a simple measure of the comparative intensity of lights4 ,if we suppose two lights so placed that they may separately illuminate adjacent portions of a vertical screen of paper1 we may1 by repeatedly comparing the luminousness of those surfaces1 and moving one of the lights farther from1 or nearer to the screen1 at length cause the separate portions of the paper to become equally luminous4 ,this arrangement1 however1 has many practical difficulties1 which ,i shall not wait to specify2 but shall at once indicate a more simple and equally correct mode of obtaining the same result1 by means of the shadows cast by the lights from an opaque rod1 in a vertical position at ,o 7fig4 #id71 placed between them1 and a screen covered with white paper on which the shadows fall4 ,it is obvious that the light at ,f would cause the object ,o to cast a shadow at ,,ss1 while the light at ,f would cast a shadow at ,s,s4 ,but while the shadow at ,s would still receive light from ,f1 ,s would receive light from ,f1 so that those two shadows are1 in fact1 the only portions of the screen which are each illuminated only by one of the lights1 while every other portion of its surface receives light from both the radiants at ,f and ,f4 ,if we suppose ,f to be the weaker light1 we can bring it nearer the screen1 until the shadow ,s,s1 shall become similar in appearance to the shadow ,,ss2 and we shall have the ratio of the intensity of the light at ,f to that of the light at ,f1 as 7,,fs7 is to 7,f,s71 which distances must be measured with the greatest exactness4 ,such is the mode commonly used in estimating the comparative intensities of two lights2 but there are various precautions which are needful in order to prevent errors in comparing the deepness of the shadows1 and to insure the greatest attainable accuracy in the estimate of the power of the lights1 which ,i shall endeavour briefly to describe4 ,illustration3 ,fig4 #id4 ,more accurate comparison of the intensity of ,lights4 ,the difficulties of estimating the deepness or sharpness of the shadow is very great1 and many persons seem quite incapable of arriving at any right judgment in this matter4 ,the same person also will discover such unaccountable variations in his decision after observations made at short intervals of time1 as1 one would think1 can only arise from a sudden change of the intensity of one or both lights4 ,m4 ,peclet1 in his ,trait de l'clairage1 gives1 as the result of his experience 7and ,i can fully confirm his result by my own71 that those differences depend less frequently on any real difficulty of estimating the deepness of the shadows1 than on variations in the position of the observer1 or rather in the angle at which he views the shadows1 and that1 consequently1 in proportion to the distance between the two shadows1 this source of error is increased4 ,any thing like a glossy texture of the surface of the screen1 which then1 of course1 becomes a reflector1 also tends to aggravate this evil4 ,thus1 if the two lights which are to be compared be placed on a table1 in such situations as to spread pretty far apart on the screen the shadows of a vertical rod placed between them2 and if the shadow nearer to the observer seem to be a little deeper or sharper than the other1 let the observer look at them from the other side of the table1 and their difference will be reversed1 and that which seemed the paler1 will become the deeper4 ,again1 if the difference between the two shadows be very great when seen from the right side of the screen1 it may happen that1 on viewing them from the left hand1 the difference may still be in favour of the same shadow1 but in a much less degree4 8,when ,i observed this effect10 says ,m4 ,peclet1#hd 8,i tried to view the shadows through a transparent screen1 but ,i remarked the same variations4 ,they were indeed even more sensible2 for a variation in the distance of the eye of a few centimtres1 made a prodigious change in the deepness of the shadows4 ,i observed also that the shadow was much deeper when seen in the line of the light1 and that in every other direction1 it became paler in proportion as the eye receded from that direction4 #hd ,trait de l'clairage1 p4 #bad4 8,in all the cases which ,i have just described1 the differences of the tints when the position is changed1 increase in proportion as the shadows are farther separate2 and they grow very minute when the shadows are almost touching each other4 ,illustration3 ,fig4 #ie4 8,let ,,ab 7fig4 #ie7 be a white opaque surface1 a1 a luminous body1 and m1 a black opaque body1 then the shadow b cast on ,,ab1 will appear deeper when observed from ,p1 than as seen from ,q4 ,this is a fact which may be easily verified1 and the cause of which is easily conceived4 ,in fact1 the surface ,,ab1 although it disperses the light1 must still reflect more of it1 in the directions in which the regular reflection takes place2 and hence the rays which are reflected round about the shadow1 must have a greater intensity in the direction of ,p than in that of ,q1 and1 consequently1 the shadow b must appear deeper from the point ,p than from ,q4 ,illustration3 ,fig4 #if4 8,if we now place 7fig4 #if7 two lights in front of the screen ,,ab1 at such distances that the two shadows a and b should have equal intensities1 it is evident that if the eye be placed at ,p1 the shadow b must appear more intense than the shadow a1 and that the reverse will take place if the eye be at ,q4 ,but the difference which is then observed1 arises not only from the difference in the brightness of the parts surrounding the shadows1 but also from a difference in the intensity of the shadows themselves2 for the shadow b is illuminated by b1 and radiates much more towards ,q than towards ,p2 and1 on the contrary1 the shadow a1 which is illuminated by a1 radiates much more towards ,p than towards ,q4 ,we perceive also why the differences of the tints increase with the separation of the two shadows1 and why they become very small when the shadows touch each other2 it is because1 in proportion as the shadows are farther apart1 each of them is illuminated more obliquely1 and a greater quantity of light is radiated 7by reflection7 in the regular direction4 ,when they touch each other1 on the contrary1 they are illuminated almost perpendicularly1 and consequently the shadows radiate light almost equally on either side4 8,those anomalies of a like kind which are observed when the shadows are viewed through a translucent body1 such as paper or linen1 may be referred to a similar cause4 ,we know1 in fact1 that1 in looking through a translucent medium1 we always1 more or less1 distinctly perceive the luminous body behind it1 and1 also1 that there is a very large proportion of the rays which traverse the body1 which stray but a little from the direction which they would follow if the substance were absolutely transparent4 ,consequently1 the space which surrounds the shadow is more luminous in proportion as we come nearer to the direction of the shadow2 and as the absolute intensity of the shadows diminishes as we come nearer to the direction of the rays which light them1 those two effects concur to increase the intensity of that shadow to which the eye is nearer4 8,as the dispersion by reflection is much more complete than by refraction1 the variations of which we have just spoken are much greater with a transparent screen1 through which the shadows are viewed1 than with an opaque screen 7from which they are reflected74 8,this1 then1 is the mode of observing which has appeared to me the best1 and by means of which we may obtain very great precision in measuring the intensity of two lights4 ,i view1 first1 the two shadows in such a manner that both of them may be seen in succession from either side of the body which produces them1 and at equal distances4 ,for this purpose ,i use a good opera-glass4 ,i alter the distance of the flames until in those two positions ,i perceive the differences 7of the intensity in the shadows7 to be in opposite directions4 ,the distances of the lamps may then be considered as very nearly in the proper proportion for producing equal shadows1 and to make them exactly so1 the differences1 which are observed on either side 7of the centre line between them71 should be equal2 and1 of course1 the two shadows themselves1 seen at one moment from either side of the opaque body1 should be perfectly equal also4#he ,these three observations1 which mutually serve to verify or correct each other1 will lead1 with a little practice1 to very great precision in the result4 ,we may1 also1 by using a narrow screen1 bring the shadows sufficiently near to touch each other2 the variations of the tints then become very small by any change of our position1 and we may1 in this case1 rest content with observing them from one point4 ,to get rid of large penumbrae which are always an obstacle in forming a right estimate of the tints of the shadows1 ,i place the opaque body very near the screen4 #he ,i prefer to view the exterior portions of both shadows from the central line itself1 in which case the opaque rod stands between them1 because1 in this manner1 ,i obtain a more correct comparison by the direct contrast of the surfaces than by successive views of them1 however quickly taken4 ,illustration3 ,fig4 #ig4 8,when we wish to make a great many observations1 it is very convenient to mark divisions on the table 7which carries the lights71 in order to read off1 by means of them1 the distance of the lamps from the shadows which they illuminate4 ,by this means1 each observation need not occupy more than two minutes4 ,i generally use a table ,,cc ,,dd 7fig4 #ig71 about two mtres long 7#f feet #f inches71 by #hj centimtres wide 7#b feet #h inches74 ,at one end ,i place the screen ,,ab1 covered with white paper1 dull 7or not glazed71 and kept in a vertical plane by two small pieces ,p and ,q4 ,through the point ,m1 the centre of the opaque body1 ,i draw two lines ,m f and ,m g1 equally inclined to the central line x y1 whose extremities b1 a are the axes of the two shadows4 ,these lines must be inclined in such a manner that the distance of the shadows may be a little less than the diameter of the opaque body1 or so that they may actually touch each other1 according to the mode of observing which you wish to follow4 ,these lines ,m f1 ,m g ,i divide into decimtres and centimtres1 starting from the points a1 b and over these lines ,i place the centres of the flames2 the distance between the shadows remains always the same1 whatever may be the distance of the lamps3 to determine the distance of each lamp from the shadow which it illuminates1 we ought1 strictly speaking1 to take the distance of the centre of the flame b from the point a2 but as the distance from the point b to the point a differs little from the distance between the points b and b1 we assume the latter for the former1 without causing any sensible error4 ,that distance may be obtained very conveniently by taking the half of the sum of the distances of the two extremities z and z of the diameter of the pedestal of the lamp4 ,when the burner is not placed over the centre of the pedestal1 we may suspend from it a small plummet1 whose point will touch some division and indicate the distance between the centre of the burner and the shadow4 8,when the lights are coloured1 the shadows are coloured also1 and it is then far more difficult to judge accurately of their intensity4 ,they may in that case be much better seen from the point x1 as the black opaque body which is interposed between them renders the difference of colour less sensible to the eye4 8,the opaque body ,m is a cylindric rod of iron1 whose upper part is blackened in the flame of a lamp1 in order to prevent the reflection which might interfere with the sharpness 7nettet7 of the shadows1 and to make them more distinct when they are viewed from the point x40#hf #hf ,those who feel a curiosity to look farther into this subject may consult ,count ,rumford's elaborate paper in the ,phil4 ,trans4 for #agid1 p4 #fg4 ,i shall make a few trifling additions to ,m4 ,peclet's clear description of his excellent mode of measuring the intensity of lights4 ,it is1 of course1 presumed throughout1 that the centres of the flames should be on one level2 and ,i have found it most convenient to place the lamps on small carriages with rollers1 which are guided by means of fine strips of wood nailed along the table in the directions g ,m and f ,m1 and carrying the divided scales of centimtres4 ,this affords the means of making any slight change in the position of the lamps so easily1 as entirely to avoid the disturbance of the flame which ensues from lifting the lamp and readjusting it in another position2 and will1 in practice1 be found very convenient when many observations are to be made4 ,i have already said that my own experience has satisfied me that1 with the aid of a good opera-glass1 the central observation of the two shadows1 with the opaque rod between them1 is by far the best1 and conducts1 at once1 to a result which is confirmed by the observations of two assistants who watch the shadows at the same time on opposite sides of the table1 and at equal distances from them4 ,i have found it convenient in comparing lights1 to cover the table with dull black linen cloth1 and to surround it with curtains of the same material1 hung from slender brackets1 in such a manner as to leave space for the observer to move freely round the table within them4 ,the curtains prevent reflection from the walls of the chamber in which the experiments may be conducted1 and also lessen the disturbing effects of currents of air4 ,when a comparison of the intensity1 and not of the aggregate power of two flames1 is to be made1 it is necessary to adopt the precaution of inclosing the lights in opaque boxes1 with slits of equal area in each1 placed on the same level1 and so arranged1 in reference to the flames1 as to be directly opposite the brightest portion of each4 ,after what has been said1 it will be almost needless to add that the quotient of the square of the greater observed distance divided by the lesser1 is the ratio of the illuminating power of the two flames4 ,the most convenient mode of registering observations1 and that which is generally practised1 is in the form of a ,table like the following3-- ---------------------------------------- ------------ ,illuminating ,power1 ,squares of or ,quotient ,distance4 ,distances4 of ,squares4 ---------------------------------------- -- ,trials4,lamp ,a4,lamp ,b4,lamp ,a4,lamp ,b4,lamp ,a4,lamp ,b4 ---------------------------------------- --------- #a #adc #adj #bj1ddi #ai1gjj #ajj #jieh #b #aag #aad #ac1fhi #ab1iif #ajj #jidi ---------------------------------------- --------- ,as a standard lamp by which to test others1 ,i believe few will be found superior to the best ,carcel lamp1 which has a clockwork movement1 and whose flame continues to increase in power for about four hours after it is lighted2 after which it maintains its state permanently1 until the supply of oil fails4 ,this fact was verified by ,m4 ,peclet with the greatest care4 8,i took10 says he1 8two similar lamps4 ,they were lighted at the same time1 and their relative intensities were measured4 ,one was then extinguished1 without touching the wick1 and its clockwork movement was stopped4 ,one hour afterwards1 ,i set the clockwork in motion and relighted the lamp1 but without touching the wick4 ,it was found in the same state as at the first comparison1 and ,i measured its intensity in reference to the first4 ,those experiments ,i repeated every hour1 and these are the results which ,i obtained4 ,the lamp which ,i call ,no4 #a1 is that which remained continually burning2 ,no4 #b1 is that which was only lighted during the continuance of the 7successive7 observations40 ------------------------------------- ,intensities4 ,times of ------------------------ ,observation4,lamp1 ,no4 #a4,lamp1 ,no4 #b4 ----------------------------------- ,h4 ,m4 #e #cj #ajj #ajj #f #cj #ajc #ajj #g #cj #ajf #ajj #h #cj #aaj #ajj #i #cj #aag #ajj #aj #cj #aag #ajj #aa #cj #aag #ajj #ab #cj #aag #ajj ----------------------------------- ,this curious scale of increase in power1 seems to be solely due to a peculiarity of the manner in which the lamp1 that derives its supply of oil by clockwork1 becomes heated2 and the effect may be described as follows3 ,the heating of the wicks1 the chimney1 and the oil in this burner1 as in that of all other lamps1 tends to increase the light2 but1 in an ordinary lamp1 acting by a constant pressure1 this maximum of heat is soon attained2 whereas in the clockwork-lamp1 into the burner of which the oil is thrown up by a pump1 the whole of the oil in the cistern must reach its maximum temperature before the best effect of that lamp is produced4 ,after this state has been reached1 there is no disturbing influence at work1 and the lamp burns steadily as long as the oil lasts4 ,i have myself tried what may naturally appear to be the most simple mode of obtaining an unvarying standard-light1 by employing a gas-burner1 supplied from a gasometer under a constant pressure2 but ,i found it very difficult to obtain satisfactory proof of the constancy of the pressure2 and in a large town1 where there are many burners around one1 their lighting or extinction is found to exercise a material influence in changing the condition of the flame4 ,i must confess that ,i have always been disappointed in attempting to use a gas-flame as a standard of comparison4 ,floating ,lights4 ,there are various dangers on the shores of ,britain1 more especially at the entrance of the great estuaries of ,england and also in ,ireland1 whose position is such as to put them beyond the reach of regular lighthouses4 ,sand-banks which are too soft to sustain a solid structure1 and have too deep water on them to admit of the erection of screw-pile lighthouses1 are often the sites for mooring light-vessels1 to guide the mariner into the entrance of some estuary1 or enable him to thread his way through the mazes of gats and channels1 which1 even during the daytime1 baffle the mariner1 who sees no natural object on the low sandy shores of the neighbouring coast to help him to guess at his true position4 ,the first ,light-vessel moored on the coast of ,great ,britain1 was that at the ,nore in #agcd4 ,there are now no fewer than #bf floating lights on the coast of ,england4 ,by the kindness of the ,elder ,brethren of the ,corporation of ,trinity ,house of ,deptford ,strond1 ,i am enabled to give the following brief sketch of the nature and peculiarities of ,floating ,lights which was communicated to me by ,mr ,herbert1 the secretary of the ,corporation3-- 8,the annual expense of maintaining a ,floating ,light1 including the wages and victualling of the crew1 who are eleven in number1 is1 on an average1 ,l4#ajjj2 and the first cost of such a vessel1 fitted complete with lantern and lighting apparatus1 anchors1 cables1 c41 is nearly ,l4#ejjj4 ,the lanterns are octagonal in form1 #e feet #f inches in diameter2 and1 where fixed lights are exhibited1 they are fitted with eight ,argand lamps1 each in the focus of a parabolic reflector of twelve inches diameter2 but1 in the revolving lights1 four lamps and reflectors only are fitted4 ,the greatest depth of water in which any light-vessel belonging to the ,corporation of ,trinity ,house of ,deptford ,strond at present rides1 is about #dj fathoms 7which is at the station of the ,seven ,stones between the ,scilly ,islands and the coast of ,cornwall74 8,the ,corporation's light-vessels are moored with chain-cables of #a inch diameter1 and a single mushroom anchor of #cb cwt41 in which cases the chain-cables are #bjj fathoms in length2 some of the said vessels are moored to span-ground moorings1 consisting of #ajj fathoms of chain to each arm1 and a mushroom anchor of similar weight at the end of each2 a riding cable of #aej fathoms being in such cases attached to the centre ring of the ground chain4 ,the tonnage and general dimensions of the light-vessel are given on the drawing of the lines40 7,see ,plate ,,xxix47 ,beacons and ,buoys4 ,still lower in the scale of 8signs and marks of the sea10 are ,beacons and ,buoys1 which are used to point out those dangers which1 either owing to the difficulty and expense that would attend the placing of more efficient marks to serve by night as well as by day1 are necessarily left without lights1 or which1 from the peculiarity of their position1 in passages too intricate for navigation by night1 are1 in practice1 considered to be sufficiently indicated by day-marks alone4 ,beacons1 as being more permanent1 are preferred to ,buoys2 but they are generally placed only on rocks or banks which are dry at some period of the tide4 ,on rocks1 in exposed situations1 the kind of ,beacon used is generally that of squared masonry1 secured by numerous joggles 7as shewn at ,plate ,,xxxii472 and in situations difficult of access1 and in which works of uncompleted masonry could not be safely left during the winter season1 an open framework of cast-iron pipes1 firmly trussed and braced1 and secured to the rock with strong louis-bats1 is preferred4 ,the details of this framework are shewn at ,plates ,,xxx4 and ,,xxxi4 ,a stone ,beacon of the form and dimensions shewn in ,plate ,,xxxii41 may be erected for about ,l4#gjj1 and the iron ,beacon shewn at ,plate ,,xxx41 for about ,l4#fdj4 ,in less exposed places1 where the bottom is gravel or hard sand1 a conical form of ,beacon1 composed of cast-iron plates1 united with flanges and screws1 with rust-joints between them1 is sometimes used4 ,a ,beacon of this kind is shewn at ,plate ,,xxxii41 which can be erected for about ,l4#djj4 ,lastly1 ,buoys1 which may be regarded as the least efficient kind of mark1 and as bearing the same relation to a ,beacon that a ,floating-light does to a ,lighthouse1 are used to mark by day dangers which are always covered even at low water1 and also to line out the fair-ways of channels4 ,they are1 for the most part1 of one of the three forms shewn in ,plate ,,xxxiii41 viz41 the ,nun-buoy1 in the form of a parabolic spindle1 generally truncated at one end1 so as to carry a mast or frame of cage-work1 and loaded at the other end1 so as to float in a vertical position2 the ,can-buoy1 which is a conoid floating on its side2 and1 lastly1 the ,cask-buoy1 which is a short frustum of a spindle truncated at both ends1 but almost exclusively used for carrying the warps of vessels riding at moorings4 ,those buoys are of various sizes and differ in cost4 ,mast-buoys1 from #aj to #ae feet in length1 cost from ,l4#bc1 #aes4 to ,l4#dh2 and those of the ,ribble and the ,tay1 which are #ba and #bd feet long1 cost respectively ,l4#aje and ,l4#gi2 the ,can-buoys are from #e to #h feet long1 and cost from ,l4#ac1 #acs4 to ,l4#bj1 #es4 ,large buoys are often built on kneed frames resembling the timbers of vessels4 ,the ,cask-buoy is generally #f feet long1 and costs ,l4#bb1 #aes4 ,all these buoys are formed of strong oaken barrel-staves1 well hooped with iron rings1 and shielded with soft timber2 and the nozzle-pieces at the small end of the ,nun and ,can buoys are generally solid quoins of oak1 formed with a raglet or groove to receive the ends of the staves4 ,much skill1 on the part of the cooper1 is required in heating and moulding the staves to the required form2 and great care must be taken that they be of well-seasoned timber4 ,buoys are not caulked with oakum1 but with dry flags closely compressed between the edges of the staves1 which swell on being wet2 and they are carefully proved by steaming them like barrels1 to see if they be quite tight4 ,buoys are also formed of sheet-iron1 in which case they are sometimes protected with fenders of timber2 but they have been found more troublesome for transport1 and1 for most situations1 are considered less convenient than those of timber4 ,in the beginning of #ahde1 ,i suggested the idea of rendering ,beacons and ,buoys useful during night1 by coating them with some phosphorescent substance1 or surmounting them with a globe of strong glass filled with such a preparation1 whose combustion is very slow1 and emits a dull whitish light and little heat4 ,some experiments were accordingly made by my suggestion2 but ,i cannot add that any practically useful result has been obtained4 ,in laying down ,beacons or ,buoys1 their position is fixed1 as may be seen in the ,table in the ,appendix1 either by the intersection of two lines drawn through two leading objects on the shore 7the magnetic bearings of which are given for the sake of easy reference on the spot1 in finding out the marks71 or by means of the angles contained between lines drawn to various objects on the shore1 which meet at the ,beacon or ,buoy from which they are measured by means of a sextant4 ,in the latter case1 the angles are always measured around the whole horizon1 thus affording a check by the difference of their sum from #cfj4 ,the magnetic bearing of one of those lines is afterwards carefully ascertained1 by means of the prismatic compass 7if possible from one of the objects on shore1 and if not1 conversely from the ,beacon or ,buoy71 so as to afford the means of translating the whole into magnetic bearings for the use of seamen4 ,the buoys are moored1 as shewn in ,plate ,,xxxiii41 by means of chains and iron sinkers1 with a sufficient allowance in the length of the chain to permit them to ride easily4 ,,appendix4 ,,appendix1 ,no4 ,i4 ,,table ,,of ,,co-,,ordinates ,,of ,,an ,,hyperbolic ,,column ,,whose ,,diameter ,,at ,,the ,,top #af ,,feet1 ,,at ,,the ,,base #db ,,feet1 ,,and ,,height #abjbe ,,feet4 ,the column is generated by the revolution of a rectangular hyperbola about one of its asymptotes4 ,in the annexed figure 7,no4 #ih71 a f is the height of the column1 a c and f h the radii of its base and top2 and we have to determine the particular hyperbola which will pass through the points c1 h4 ,putting b e x2 e g y1 the equation to the curve1 referred to its asymptotes1 is a x y ----1 #b in which the value of the constant a ---- #b is to be found4 ,for this purpose we have the conditions a c #ba2 f h #h2 and a f #abjbe4 ,let the co-ordinates of the point c be x1 y1 and of h1 x1 y1 then y #ba2 y #h2 x x #abjbe4 ,illustration3 ,fig4 #ih4 a ,and since x y ---- x y #b we have #ba x #h 7x #abjbe7 from which x #gd a and ---- x y #gd #ba #aeed4 #b ,therefore x y #aeed4 ,transferring the origin to a1 x becomes x - x x - #gd1 and y 7x - #gd7 #aeed1 and the required equation by which the following ,table was computed is1 #aeed y --------4 x - #gd ,,table of the ,radii of the ,hyperbolic ,column at each foot of its ,height4 ---------------------------------------- ---------------- ,height4,radius4,height4,radius4,height4 ,radius4,height4,radius4 ---------------------------------------- ---------------- #j #bajjj #ca #adhjj #fb #aadbf #ic #icje #a #bjgbj #cb #adffj #fc #aacdc #id #ibej #b #bjddg #cc #adebc #fd #aabfa #ie #iaie #c #bjahb #cd #adchi #fe #aaahj #if #iada #d #aiibc #ce #adbeg #ff #aaajj #ig #ijhh #e #aifga #cf #adabg #fg #aajba #ih #ijce #f #aidbe #cg #adjjj #fh #ajidd #ii #hihc #g #aiahe #ch #achge #fi #ajhfg #ajj #hica #h #ahiea #ci #acgeb #gj #ajgib #aja #hhhj #i #ahgbc #dj #acfcb #ga #ajgag #ajb #hhcj #aj #ahejj #da #aceac #gb #ajfdd #ajc #hghj #aa #ahbhb #db #accig #gc #ajega #ajd #hgcj #ab #ahjgj #dc #acbhb #gd #ajejj #aje #hfha #ac #aghfb #dd #acagj #ge #ajdcj #ajf #hfcc #ad #agfei #de #acjei #gf #ajcfj #ajg #hehf #ae #agdfa #df #abiej #gg #ajbia #ajh #heci #af #agbfg #dg #abhdc #gh #ajbbd #aji #hdib #ag #agjgg #dh #abgch #gi #ajaeg #aaj #hddf #ah #afhia #di #abfcd #hj #ajjia #aaa #hdjj #ai #afgaj #ej #abecb #ha #ajjbf #aab #hcee #bj #afecb #ea #abdcb #hb #iifb #aac #hcaj #ba #afceh #eb #abccc #hc #ihih #aad #hbff #bb #afahh #ec #abbcf #hd #ihce #aae #hbbb #bc #afjba #ed #abada #he #iggd #aaf #hagi #bd #aeheg #ee #abjdf #hf #igab #aag #hacf #be #aefig #ef #aaied #hg #ifeb #aah #hjid #bf #aeedj #eg #aahfb #hh #ieic #aai #hjeb #bg #aechf #eh #aaggc #hi #iecd #abj #hjaj #bh #aebce #ei #aafhd #ij #idgf #abjbe #hjjj #bi #aejhg #fj #aaeig #ia #idah 444 444 #cj #adidb #fa #aaeaa #ib #icfa 444 444 ---------------------------------------- ---------------- ,,appendix1 ,no4 ,,ii4 ,,notes ,,on ,,the ,,manufacture ,,of ,,parabolo,,dal ,,reflectors1 from ,information furnished by ,mr ,,james ,,murdoch1 ,,of ,,the ,,northern ,,lights ,,service4 ,illustration3 ,fig4 #ii4 ,the reflector-plate consists of virgin-silver and the purest copper 7from the ingot71 in the proportion of #f oz4 of silver to #af oz4 of copper4 ,the two metals are in pieces1 forming a flat parallelopepid of about nine inches of surface4 ,being first thoroughly scraped and cleared from rust with a file1 they are tied together with wire and placed in the furnace1 where they are united by means of a flux composed of burnt borax and nitre1 mixed to the consistence of cream4 ,their thickness is sufficient to admit of their being repeatedly passed through the rolling-mill1 so as at last to come out a plate twenty-eight inches square4 ,every time it is passed through the rollers1 the plate is annealed in the furnace before being again pressed4 ,it is then cut into a circular disc ready for working2 and great care should be taken to keep the metal perfectly clean during the whole of the hammering and polishing processes4 ,the first step towards forming the plate to the curve1 is to raise the back or copper side to a slight convexity by beating1 with the boxwood mallet 7fig4 #ii71 rounded at each end1 c and d1 its inner or silver side upon a large block of beechwood1 of a form slightly concave4 ,this beating is begun at the edge of the plate1 and gradually reaches the centre4 ,after the disc has been raised to the proper height on the wooden block1 the next step is to take it to the horse 7fig4 #ajc1 opposite page71 where it is beaten with the wooden mallet 7fig4 #ajj71 its concave face being in contact with the bright steel-head a 7fig4 #ajc71 until it has nearly reached the proper height for the reflector1 for which the workman has a gauge or mould to guide him2 in this course of raising1 as it is called1 the peened face b a b 7fig4 #ajj7 is first used1 and then recourse is had to the opposite or flat face for smoothing it after being raised4 ,in this last course of raising1 as well as in the process of smoothing the reflector all over1 the workman bestrides the horse4 ,illustration3 ,fig4 #ajj4 ,illustration3 ,fig4 #aja4 ,during the process of raising with the peened side of the mallet1 an external mould ,,fghf 7fig4 #aja71 with a needle-point ,p1 at its vertex1 is applied1 to indicate its proper position with reference to the mould2 and allowance is made on the height and diameter of the reflector to meet the expansion of the metal during the hard-hammering which is to follow4 ,after each course of the raising with the wooden mallets1 the reflector must be annealed in the following manner3--,the reflector is first damped with clean water1 and its surface dusted over with a powder1 composed of one pint of powdered charcoal to one ounce of saltpetre1 which is applied by means of a thin flannel bag4 ,the reflector is then put on a clear charcoal fire1 where it is turned round as the powder flies off1 which is an indication that the metal is duly heated4 ,over-heating is very injurious4 ,when removed from the fire1 the reflector is plunged into a large tub1 containing what is called the pickle1 which is a solution of one quart of vitriol in five or six gallons of water4 ,after this it is washed with clean water1 and scoured with ,calais sand4 ,the next step is to put the reflector1 thus raised nearly to its true form1 into an iron stool1 where a small hole being drilled in its vertex1 a circle is described from this point with a beam-compass1 so as to cut the parabolod to the proposed size4 ,illustration3 ,fig4 #ajb4 ,illustration3 ,fig4 #ajc4 ,illustration3 ,fig4 #ajd4 ,illustration3 ,fig4 #aje4 ,the reflector is next hard-hammered all over 7or planished1 as it is technically termed7 on the bright steel-head a 7fig4 #ajc71 with the planishing hammer 7fig4 #ajb72 and to facilitate working1 the reflector is slung in a flexible frame ,,ss1 and counterbalanced by a weight w1 hanging by a cord over the pulleys p p4 ,when the reflector is all planished over1 the next process is the smoothing1 which is done on the steel-head a1 with a lighter hammer 7fig4 #ajd71 muffled with fine parchment at each end4 ,after it is smoothed comes the finishing1 or what is called the filling up to the mould4 ,this is a tedious process1 and the workman requires continually to have recourse to the marble table at ,m1 on which he lays the reflector1 as shewn in fig4 #aje1 and applies to successive portions of its surface the mould g n1 which has a needle-point centred at n1 in the small hole drilled in the vertex4 ,during this examination1 he marks with a fine slate-pencil those portions of the reflector which do not meet the mould g n4 ,the parts1 so marked1 are gently gone over with the muffled hammer1 until every point touches the mould4 ,this last process requires great caution2 for1 if any part of the surface be raised above the gauge1 it is hardly possible to remedy it4 ,such a mistake1 indeed1 can only be corrected by annealing the reflector afresh1 and bringing it back to the true form with the mallet2 but reflectors so cobbled are never good4 ,the table ,m 7fig4 #aje7 rests on a square box ,c1 in which the tools and moulds are kept4 ,illustration3 ,fig4 #ajf4 ,when thus finished from the hammer1 the reflector is put into the apparatus shewn in fig4 #ajf1 which is placed at the end of a long dark corridor4 ,,rr is a wooden frame fixed to the wall with projecting brackets at ,k1 which carry the reflector1 fixed at ,e1 ,e1 by means of screws1 so as always to have a definite position with reference to the bracket ,b1 which carries the lamp and its fountain f1 so arranged that its flame may admit of perfect adjustment to the point which ought to be the focus of the reflector4 ,for the purpose of this adjustment1 ,s shews screws for raising and depressing the level of the burner2 and the lines or marks ,m1 ,m shewn at the sockets ,j being brought into line1 regulate the position of the burner in the plane of the focus1 after it has been raised to the level of that plane by means of the screws at ,s4 ,the lamp being lighted and thus properly placed1 its effect on the reflector's surface is observed by some one stationed at a convenient distance2 and if the whole surface appear luminous1 the instrument is considered fit for polishing2 but if any dark spaces be found in it1 the whole reflector must be again carefully tested by means of the mould1 and the defective parts remedied in the manner above described4 ,the next step is to turn over the edge of the reflector1 so as to stiffen it4 ,for this purpose it is placed in the matrix ,p,p 7fig4 #ajg71 and the needle-point at ,v is adjusted by the screw at ,d1 so as just to enter the small hole formerly drilled in the vertex of the reflector4 ,the die-plate ,,pp 7which is worked by means of the arms ,,aa1 which turn the screw ,s7 then descends and presses the edge over1 which is finished with a finely polished tool ,c1 revolving round the axis of the instrument1 which coincides with the centre of the matrix and die4 ,in order to ensure a steady vertical movement of the die-plate ,,pp1 cross-arms ,,ff1 which are provided with sockets ,,hh1 which slide over the rods ,,gg1 ,,gg1 are added to prevent any lateral shake or derangement4 ,the whole frame is stiffened by the cross-head in which the screw ,s works4 ,illustration3 ,fig4 #ajg4 ,illustration3 ,fig4 #ajh4 ,illustration3 ,fig4 #aji4 ,the reflector is then placed on the circular cast-iron table 7figs4 #ajh1 #aji71 to which it is attached by the clamp-screws ,s1 ,s4 ,in this position1 the bizzle ,w 7fig4 #ajh7 and back-belt ,,nan 7fig4 #aji71 are soldered on4 ,after this the reflector is ready for being finally polished2 for which purpose1 it is placed in a chaise perce1 padded round the edges1 and is first scoured all over with a piece of pure charcoal of hard wood1 and next with a mixture of ,florence oil and finely washed rottenstone1 applied by means of a large ball of superfine cloth4 ,it is then carefully cleansed with a piece of fine flannel dipped in ,florence oil1 and afterwards dusted over with the powder of well washed whiting1 and wiped out with a soft cotton cloth4 ,lastly1 it is carefully rubbed by the naked hand1 with finely washed rouge and clean water1 and wiped with a smooth chamois skin4 ,in all the polishing and cleansing processes1 some skill in manipulation is required1 as the hand is generally moved in such a manner as to describe successive circles with their planes parallel to the lips of the reflector1 and their centres in the axis of the generating curve4 ,the prices paid to the workmen for the various departments of the reflector-making are generally as follows3-- ,raising the plate to the curve1 with the wooden mallet1 ,l4#j #aj #j ,hammering and smoothing to the mould1 #a #e #j ,finishing in the die1 and putting on bizzle and back-belt1 #j #f #j ,polishing1 #j #ab #j ------- ,l4#b #ac #j ,the prices paid to the manufacturer were for the large reflectors of #bd inches aperture1 ,l4#dc2 for the small ones of #ba inches1 ,l4#ca1 #abs4 ,the lamp with the sliding-carriage1 required for each1 costs ,l4#f4 ,,appendix1 ,no4 ,,iii4 ,,notes ,,on ,,the ,,grinding ,,of ,,the ,,various ,,pieces ,,composing ,,the ,,instruments ,,used ,,in ,,dioptric ,,lighthouses1 ,,chiefly ,,from ,,notes ,,furnished ,,by ,m4 ,,theodore ,,letourneau ,,of ,,paris4 ,the glass used in all the parts of the optical apparatus of the dioptric ,lighthouses is that of ,st ,gobain1 whose index of refraction is #aea4 ,as well on account of the difficulty experienced in producing at all times regular castings of glass from the moulds1 as in order to compensate for the frequent accidents1 which occur in the first application of the rubbers to the inequalities of the surface of the glass1 the castings1 whether for rings of lenses or prisms1 are made from moulds1 exceeding the intended size of the finished pieces by one-eighth part4 ,we shall take as an example1 which is well calculated to illustrate the difficulties of the grinding process1 one of the prismatic rings of a ,catadioptric ,light of the first order4 ,the first operation will be to take off the rough arris at the angles of the pieces as they come from the moulds1 and to reduce to equality the length of each of the four quadrantal prisms or segments by removing from each the quantity that may be necessary to make those four pieces1 when placed on a circle1 exactly equal to that of the finished zones4 ,each of them must have an excess of material at the various surfaces just sufficient to insure the rubber having scope enough to remove all the flaws or defects of the two surfaces to be first ground1 which are the 7concave and convex7 refracting faces of the zone 7the sides ,,ac and ,,bc in the ,table in the ,appendix1 ,no4 ,,iv47 ,illustration3 ,fig4 #aaj4 ,the pieces must be placed end to end on the horizontal plane or table of the lathe at ,,aa 7fig4 #aaj71 and must rest on the exterior arris ,a of the reflecting side1 on which arris there is ground a narrow plane whose width is proportionate to the projection of the outer edge beyond the inner edge of the zone1 foreshortened by the bevel or inclination of the reflecting side1 when resting 7as in fig4 #aaj7 on the circular iron belt1 which is screwed to the table of the lathe provided for its reception4 ,this narrow plane at the arris ,a should be sufficient to give the prism a solid and regular bearing on the circular iron belt4 ,in this figure 7fig4 #aaj7 a b is the vertical axis of the lathe1 n the point from which the co-ordinates for ,o1 the grinding centre for the exterior concave refracting surface ,,ac1 are measured1 and e ,,ac the arc swept by the grinding surface4 ,conversely1 n is the origin of the co-ordinates for the grinding centre ,o of the interior convex refracting surface ,,bc1 and e ,,cb the arc swept by its grinding surface4 ,some skill is required in fixing the prism on the belt1 for1 on the one hand1 there is an obstacle to correct workmanship from the dragging motion of the platform1 and1 on the other1 by the unequal subdivision of the weight of the glass1 which should be nearly balanced4 ,this narrow plane being perfectly adjusted for all the segments so as to bed them quite level1 the circular iron belt on which the ring should be ground1 is placed on its platform1 in the manner represented in the figure4 ,it should be as truly levelled as possible1 otherwise all the subsequent operations will be deranged by it4 ,this iron belt is heated by means of heating pans2 and the degree of heat may be practically judged of by the ebullition of drops of water let fall on it4 ,the segments of glass are also at the same time placed in a stove heated with steam1 and are generally raised to about #abj centigrade4 ,the difference between the time required for the two operations of heating the iron belt and the glass segments is employed in laying or bedding a quantity of cement on the reflecting side of the segment1 so as to fill up the angular space between the glass and the iron belt1 and also to serve as a seat for the segment in the manner shewn in fig4 #aaj4 ,this operation is performed on a plane surface1 in order that the lower part of the mastic may be precisely on a level with the narrow plane already ground on the outer arris of the reflecting side4 ,after being sure that the heat is equally spread over every part of the circular iron belt1 the segment is arranged on it2 and the workman must1 at this juncture1 exert all his skill in placing the parts of the segment in a position nearly concentric with the belt1 or in a truly circular form1 making due allowance1 however1 for the inequalities existing at various parts of the rough material1 and at the same time taking care that there should be an interval of at least two millimtres 7or about th inch7 between the ends of each of the two adjacent segments4 ,without this interval the heat evolved during the polishing would either dilate the glass so much as to cause the ends of the segments to fly into splinters1 or make it needful to remove the zone before this should take place1 the inevitable consequence of which would be the fracture of the pieces4 ,those intervals between the segments are filled with statuary's plaster1 which must be carefully washed and brushed at each change of the emery employed in grinding4 ,the exterior diameter of the circular iron belt must be precisely equal to that of the ring1 because1 if larger1 the free movement of the rubbers to and fro on the concave refracting surface ,,ac 7fig4 #aaj7 could not take place4 ,by what is already said1 it will be obvious that the grinding process is begun at the refracting sides ,,ac and ,,bc1 and a few words will shew that this could hardly be otherwise4 ,if a commencement be made on the reflecting side1 which appears at first sight more natural1 the consequence is obvious4 ,having provided for an excess of material in every direction1 the segment must consequently be larger than it will be when finished2 and the surfaces therefore cannot be true and perfect1 except they be ground throughout their entire segmental section1 from their centres of curvature1 in reference to some given apex of the generating triangle4 ,now1 if the reflecting side were finished first1 it might continue to possess this excess of size after being finished1 and would1 therefore1 afford no accurate starting point for the grinding of the other surfaces2 it would also present no surface or narrow plane for resting firmly on the iron belt1 but would then depend merely on its own finished plane1 which1 being curved and considerably inclined1 would not give a solid bearing for the glass4 ,the other mode of commencing with the two refracting sides1 on the contrary1 gives a solid bearing on the narrow plane already ground on the reflecting side at ,a2 and after these surfaces have been ground1 and the segments inverted 7as shewn in fig4 #aaa71 the outer edge of this narrow plane at the arris ,a1 which has been fully defined by the intersection of the finished surface ,,ac just ground1 and also the apex at ,c1 which has been determined by the intersection of ,,ac and ,,bc1 combine to fix an accurate starting point for the rubber1 in grinding the reflecting surface ,,ab4 ,illustration3 ,fig4 #aaa4 ,dressing off the rough part of the ,ring4 ,the ring is generally reduced from the rough state by means of fixed rubbers1 the adjustment of which is more easily regulated than that of the moveable beam or radius of the arc1 which is used to give the exact curvature of the surface4 ,those fixed rubbers are #aej millimtres 7nearly #f inches7 wide1 by #bjj millimtres 7nearly #h inches7 long1 and are of cast-iron4 ,three such rubbers are placed at equidistant points of the circle4 ,two cutters of sheet-iron attached to arms placed vertically 7as are also those which carry the rubbers71 and moving in grooves radiating towards the centre of the lathe1 so as to admit of adjustment to suit the varying radii of the zones1 serve gradually to abrade the outer and inner arrises of the segments1 so as to prevent the splintering to which1 from becoming too sharp1 those arrises1 without this precaution1 would be liable4 ,those rubbers are1 besides1 fixed by stems to frames1 in the form of quadrants of the circle1 which allow of a change in the direction of the planes1 as occasion may require4 ,instead of the siliceous sand formerly used1 the powder of pounded freestone is employed1 as it is found to wear the tools less1 and to form a better preparation for the subsequent grinding operations4 ,it is easy to conceive that the action of the fixed rubbers necessarily produces ruts or inequalities in the circular direction4 ,the operation of rough dressing1 therefore1 is not finished until1 when those first rubbers are removed1 the surfaces of the segments have been subject1 for the required time1 to the action of moveable rubbers1 attached to arms working as radii of curvature1 in a plane at right angles to the horizontal movement of the lathe1 which carries the zones4 ,the ,emery ,grinding4 ,the form of the segment should be nearly perfect1 after the rough grinding is finished4 ,the lathe and the zone are then subjected to an extremely careful washing4 ,every place where the stone-powder might adhere is dusted4 ,the radius of curvature is verified afresh1 agreeably to the co-ordinates 7,appendix1 ,no4 ,,iv472 and emery is used instead of powdered stone2 beginning with that called ,no4 #a1 which is drawn after suspension in water for one minute4 ,brushes are used for spreading the emery on the surface of the glass4 ,the quantity ought always to be sufficient to prevent the direct contact of the cast-iron rubber with the glass4 ,splintering or scratching1 which cannot be easily effaced1 may result from the neglect of this precaution4 ,practice alone1 and an eye duly trained by continual experience1 can determine the point of time at which each kind of emery must be discontinued4 ,the celerity of the work depends on circumstances very difficult to appreciate1 such as the amount of the pressure of the rubbers1 or the degree of accuracy with which the radius of curvature has been adjusted1 during the rough grinding4 ,each kind of emery in succession thus corrects the form of the zone and refines the grain of the surface of the glass2 and each change to a fresh material requires the same attention to cleanliness1 so as to remove every trace of the substance last used in grinding1 and thus to give each successive process its full and legitimate effect4 ,the douci is the fifth and last kind of emery which precedes the polish4 ,it is drawn off after ten minutes' suspension in water1 and is extremely fine4 ,before applying it1 the greatest care is necessary to insure cleanliness1 as a single grain of any of the preceding kinds of emery might cause scratches1 which the polish cannot remove4 ,the ,polish4 ,the same considerations which induce the workman most carefully to cleanse the lathe and everything connected with it1 before employing the last emery called the douci1 are still more urgent in the case of the final polish4 ,the only change which is made at this last stage of the work is to replace the first rubber by a new one1 both longer and wider by about #ej millimtres 7nearly #b inches74 ,on its lower face is attached with cement a piece of soft carpet1 whose edges are fixed to the rubber by means of flat bands of iron1 attached with screws4 ,this security1 added to that given by the cement1 is necessary to fit it to resist the great pressure it must sustain4 ,a practical question1 which experience alone can resolve1 occurs at this stage1 as the operation of polishing may1 in the hands of unskilful persons1 be so inopportunely commenced1 as to make that work almost endless4 ,thus1 the mere circumstance of spreading at the beginning too thick layers of rouge1 or using unsuitable kinds of carpet1 would cut scratches in the glass1 and thus perhaps make it necessary to return to the use of the emery called douci4 ,sometimes1 also1 if the carpets be not washed at the very time of using them1 scratches are formed by the dust which they may contain4 ,this shews1 that the use of rouge should be rather sparing than otherwise1 at the commencement of the polish2 and that the carpet-cloths should be brushed and washed twice rather than once4 ,in all cases1 the quality of the carpet forms an important element in the success of the working4 ,when the polish is finished1 the ring is detached from the circular belt1 simply by the tap of a hammer1 on the inner edge of the circle4 ,the division of the zones 7which are quarters of the circle7 into eighths1 is done by means of a sawing machine consisting of a flat copper-wheel1 one-half millimtre 7th inch7 in thickness1 attached to an arm with a counterpoise4 ,this wheel descends and cuts the zone by means of emery1 which is continually applied to it2 the direction of the cut is radial4 ,the two halves of the zone are detached from each other1 as soon as their weight exceeds the resistance of the part which remains to be sawn4 ,adjustment of the ,prisms4 ,the adjustment of the prisms in the frames1 involves an operation which is not without risk4 ,much care is required in handling the sharp arrises of the glass1 which are very acute and delicate and at the same time lie in a curved direction1 which makes them liable to be splintered in the hands of unskilful persons4 ,with the exception of the plane vertical surfaces of the annular lenses1 and the central band and rings of the dioptric belts of fixed lights1 which are ground by means of vertical rubbers with a reciprocating movement1 every other plane surface is executed by hand on a flat table4 ,composition of the ,cement for fixing the glass on the lathe4 #h parts ,swedish pitch4 #a do4 of wood ashes4 ,the whole is heated in an iron pot until fully liquified and thoroughly mixed4 ,this cement is used almost in a state of ebullition1 so that it cannot be handled without the precaution of continually dipping the hands in cold water4 ,composition of cement used for the adjustment of the pieces of glass which touch each other4 #ab parts white lead4 #a do4 minium or red lead4 #e do4 boiled lintseed oil4 ,the whole is pounded on an iron table by means of a flat mullet1 like that used by painters 7fig4 #aab71 whose grinding surface is a b1 and c the knob for the hand4 ,this cement is applied liquid so as to offer no resistance to the close union of the pieces1 which it is intended to unite4 ,illustration3 ,fig4 #aab4 ,cement for filling up voids1 and fixing the rings in the frames4 #ab parts white lead4 #c do4 whiting4 #a do4 minium4 #d do4 boiled lintseed oil4 ,this last composition differs from the former only in the introduction of whiting1 which1 while like minium it has a desiccative property1 gives more body to the cement and prevents the formation of cracks4 ,the oil is also decreased in quantity1 as the cement must be used in a more compact state4 ,the trituration of this cement is performed by means of a cylindric iron roller a b1 with a centre-spoke c d for the hand 7fig4 #aac74 ,illustration3 ,fig4 #aac4 ,it is essential for the production of good cement1 that the mixture of the ingredients be complete4 ,prices of the various parts of the ,dioptric ,apparatus4 ,the expense of the various parts of the ,dioptric apparatus is as follows3 ,great lens of first order1 ,l4#eh 7#h of which are required72 pyramidal lens and mirror1 ,l4#ad1 #abs4 7#h of which are required72 catadioptric cupola1 ,l4#dhj2 catadioptric rings below lenses1 ,l4#cfj2 pannel of dioptric belt for fixed light of first order1 ,l4#ef 7of which #h are required for the whole circle72 apparatus of fourth order1 for a fixed light1 for whole horizon1 ,l4#abh2 apparatus of sixth order1 for whole horizon1 ,l4#dd4 ,the expense of the mechanical lamp of the first order with four wicks1 as made for the ,scotch ,lighthouses by ,mr ,,john ,,milne of ,edinburgh1 is ,l4#cj4 ,diagrams illustrative of the ,table1 ,appendix1 ,no4 ,,iv4 ,illustration3 ,fig4 #aad4 ,illustration3 ,fig4 #aae4 ,illustration3 ,fig4 #aaf4 ,illustration3 ,fig4 #aag4 ,,appendix1 ,no4 ,,iv4 ,,table ,,of ,,the ,,elements ,,of ,,catadioptric ,,zones ,,suited ,,for ,,lights ,,of ,,the ,,first ,,order ,,in ,,the ,,system ,,of ,,augustin ,,fresnel4 ,,note4--,the ,six co-ordinates of the ,generating ,triangle of each ,zone in these ,tables have the ,focus of the ,principal ,lenses of the ,system for their origin2 it being considered more convenient1 in executing the necessary protractions1 preparatory to the construction of the grinding apparatus1 at once to refer the whole of the grinding machinery to the axis of the apparatus4 ,to prevent the appearance of any inconsistency1 however1 it is proper to mention1 that the radiant points of the series of ,zones1 do not exactly coincide with the ,focus of the ,lenses nor with each other2 and that to avoid the parallax which the distance of the radiant points from the origin of the co-ordinates would occasion1 it is necessary to make some corrections upon the linear dimensions1 so as to find the line corresponding to the angles 1 1 and the distance 4 ,in the ,hyperpyral series1 which stands above the flame1 the ,zones have the radiant point #aj millimetres above the ,focus of the ,lenses1 and each y of this series1 therefore1 requires a reduction of that quantity2 while the x remains unchanged4 ,in the ,hypopyral series1 which stands below the flame1 the ,focus or radiant points of each ,zone1 varies its place in the flame1 moving upwards as the ,zone is lower1 so that the line joining the ,zones and the ,foci1 revolves as a radius vector round a point between them4 ,in this way1 the x's remain unaltered2 but the y's will be lengthened successively by the addition of #aj1 #ad1 #ai1 #be1 #cb1 and #dj millimetres4 ,as these ,tables contain the dimensions of ,zones which are intended as an addition to the apparatus of ,,fresnel1 ,i have adopted the metric scale1 so as to render them at once applicable to the existing protractions of that system4 ,it is only necessary to add1 that the conversion of millimetres into imperial inches1 is easily effected by adding the log4 millimetres to the log4 #beieaf1 the sum being the log4 of the equivalent of the first term in imperial inches4 ---------------------------------------- ------------- ,,bca1 ,,abc1 ,,bac1 ,incli- nation ,obtuse of ,inci- ,angle ,ray ,,fc dence of the to the of ,ray ,gener- ,angle of,angle of ,vertical ,,fc on ating ,gener- ,gener- ,axis ,side ,triangle ating ating of the ,,bc of of the ,triangle,triangle ,system4 ,zone4 ,zone4 of ,zone4of ,zone4 ,no4 of 7,fig4 7,fig4 7,fig4 7,fig4 7,fig4 ,,zone4 #aad47 #aad47 #aad47 #aad47 #aad47 ---------------------------------------- ------ #a #fj #de #chdd #jf #jiaag #bf #djca #dh #ajcj #de #aj #b #ef #ee #chda #bh #ajaaf #jj #dbcb #cb #jaca #bg #ag #c #ec #je #chch #dh #biaad #ca #bjcc #ag #cjcb #aa #aj #d #di #ae #chcf #jg #jiaab #eh #djcd #jd #cfcb #ef #dd ,,hyper- #e #de #be #chcc #bd #aiaaa #bc #jjcd #ec #jgcc #dc #ec ,,pyral #f #da #ce #chcj #dj #jeaji #dd #cbce #db #egcd #cb #ca ,,series #g #cg #de #chbg #ed #cdajh #jc #cjcf #cd #jace #bb #bi ,,of #h #cc #ee #chbe #jg #ebajf #bj #jfcg #bf #aacf #ac #dc ,,zones4 #i #cj #je #chbb #bj #jgajd #cd #cfch #ai #bccg #jf #ja #aj #bf #ae #chai #ca #beajb #dg #abci #ac #bgcg #ei #ba #aa #bb #be #chaf #da #edajj #eh #ajdj #jg #adch #ed #cf #ab #ah #db #jbac #ef #bf #ii #aj #ejdj #ei #ecci #di #ag #ac #ae #jf #jcaa #af #jd #ig #bf #jgda #ea #jcdj #db #di #a #ei #di #afdc #bg #cfaag #je #efca #eh #cgcj #ee #bg ,,hypo- #b #ee #dh #eedj #db #jaaae #ce #jgcb #dd #dcca #dj #ji ,,pyral #c #ea #dh #cccg #ed #cbaad #jj #cacc #bh #afcb #bg #ac ,,series4 #d #dg #ea #aace #jg #cbaab #bc #eccd #bj #bccc #ae #dd #e #dc #ei #djcb #bc #jfaaj #df #cbce #jh #bccd #je #je #f #dj #af #cdbi #dc #aiaji #aj #jdce #ee #cgcd #ed #ah ---------------------------------------- ------------- --------------------------------- ,,ba1 ,,bc1 ,,ac1 ,re- flect- ing ,side of ,zone in ,inner ,outer ,milli- ,re- ,re- metres fract- fract- being ing ing ,chord ,side of,side of of ,zone in,zone in the ,arc ,milli- ,milli- b ,a4 metres4metres4 ,no4 of 7,fig4 7,fig4 7,fig4 ,,zone4 #aae47 #aae47 #aae47 -------------------------- #a #afjcca #ibcgi #iebji #b #aeedcj #ijbdi #icjaa #c #aeaeea #hhgbi #iadcd #d #adhehj #hggfh #ijdbd ,,hyper- #e #adfddd #hgccb #hiidg ,,pyral #f #adejhg #hgdjc #hiihf ,,series #g #adddha #hgigg #ijecf ,,of #h #addfji #hijfj #iafjd ,,zones4 #i #adedgf #ijfga #icbji #aj #adgjhi #ibhdc #iechd #aa #adecfa #icjjj #iedac #ab #adccfb #icjjj #iebga #ac #adacgi #icjjj #ieabg #a #aeicfi #ibjjj #idhjf ,,hypo- #b #aehjea #ibjjj #idghc ,,pyral #c #aefeib #ibjjj #idgai ,,series4 #d #aeejhc #ibjjj #idfai #e #aecdhi #ibjjj #iddhh #f #aeahfc #ibjjj #idccd --------------------------------- ---------------------------------------- ---------------------- ,co-ordinates of the ,apices of the ,generating ,triangle1 in ,millimetres1 having the ,axis of the ,system cut by the horizontal plane of the focus of the ,annular ,lenses1 for its origin4 7,fig4 #aaf47 ---------------------------------------- ----- ,no4 of ,,zone4 ,ay,ax ,by,bx ,cy,cx ---------------------------------------- ---------- #a #eiccfiihfbfj #eeadhahcadig #ebejjjibjjjj #b #ffcjfciegdaj #fagdbchjhhcb #eiccfihiehaf #c #gcdcacibfijh #fhdiehghcfai #ffcjfchfifje #d #hjgceghidbbb #gedbfggeedea #gcdcachdjibj ,,hyper- #e #hhbddehehheh #hbeedggbciba #hjgceghjiccg ,,pyral #f #ieihdghbjcbe #hiijaafhhfjh #hhbddeggddbf ,,series #g #ajcihebgghajh #igdhiifdijea #ieihdggcegcj ,,of #h #aabbghdgcafdeajecdgafjdgcjajcihebfibgdb ,,zones4 #i #abjijjjfhjcbbaacejbeeeejeiaabbghdfddijj #aj #abihijjfbcdccabaihibdiicedabjijjjeiaeef #aa #acijbijeeicghacjhahcdcidbhabhhijjecaifc #ab #adhbgeedijafiacihjjgcgdechacijbijdfgbag #ac #aegfjdhdaeiiaadhhigbcjdfaaadhbgeecigdjc #a #eichaeihebab #eejiaehcagbe #ebejjjibjjjj ,,hypo- #b #fhbgcaihahaj #fcdhfbhcaahc #fajhgbibjjjj ,,pyral #c #ggidfdighiag #gbfhcahcjfid #gjdgcjibjjjj ,,series4 #d #hhejdfigddda #hbgibfhcjbfa #hjgfegibjjjj #e #ajjjffcigjfjh #icichehbihhb #ibjhgaibjjjj #f #aabgffeiffggaajfbeiahbieegajdegdjibjjjj ---------------------------------------- ----------------- -------------------------------------- ,inclination of the ,sides of the ,generating ,triangle to the ,vertical ,axis of the ,system4 7,fig4 #aag47 ------------------------ ,incli- ,incli- ,incli- ,no4 nation nation nation of of of of ,,zone4 ,,ab4 ,,bc4 ,,ac4 ----------------------------- #a #gd #ea #aigc #bj #cadd #jf #ji #b #gb #ee #bggd #cb #cbda #bh #aj #c #gj #ei #cige #db #each #dh #bi #d #fi #jc #ecgf #ea #cacf #jg #ji ,,hyper- #e #fg #jh #abgg #eh #dacc #bd #ai ,,pyral #f #fe #ab #cfgi #jd #bgcj #dj #je ,,series #g #fc #ag #jchj #jh #efbg #ed #cd ,,of #h #fa #ba #ceha #ab #adbe #jg #eb ,,zones4 #i #ei #bf #jhhb #ad #bibb #bj #jg #aj #eg #cj #dfhc #ae #dgai #ca #be #aa #ee #cf #cjhd #af #afaf #da #ed #ab #ec #de #dche #ad #bdac #ef #bf #ac #ea #eh #echf #aj #jbaa #af #jd #a #gd #bc #jcgc #ch #bjdc #bg #cf ,,hypo- #b #gb #bb #ajgd #ec #jfdj #db #ja ,,pyral #c #gj #ba #degf #je #eicg #ed #cb ,,series4 #d #fh #bc #afgg #af #bace #jg #cb #e #ff #bh #aagh #bc #bfcb #bc #jf #f #fd #cg #cggi #bf #debi #dc #ai ------------------------------------ ---------------------------------------- ------------ ,,ab1 ,reflecting ,surfaces 7convex74 7,fig4 #aae47 ------------------------------------ ,verti- ,hori- cal zontal dis- dis- tance tance of of centre centre of of curva- curva- ture ,x ture below ,x from the ,radius the outer ,inclina- of axis arris ,in- tion ,curva- of the of the clina- of the ture in ,system ,zonetion of ,outer ,milli- in at ,a inthe ,two ,radius ,no4 metres1 ,milli- ,milli- ,radii in ,a of ,,xa or metres metres in ,a to the ,,zone4 ,x b4 ,,ox4 ,,oa4 and ,b4 ,vertex4 ---------------------------------------- - #a #hgejaicaidgfhdffhha #jb #eiad #ch #aa #b #hbecijccjfhjgijiida #jd #deaf #cb #aa #c #ghejcjcdaagegddffga #jf #bbah #bg #aa #d #gebgjhceadbbgjefcia #jg #eabj #bb #aa ,,hyper- #e #gbgebccfageffgcjffa #ji #abbb #ag #aa ,,pyral #f #gjhbagcgbchafdeifca #aj #bebd #ab #aa ,,series #g #fiddjichcebcfbcdica #aa #cabf #jg #aa ,,of #h #fhegjcciedfgfjebcfa #ab #cjbh #jb #aa ,,zones4 #i #fhaghgdjhagjeijbeca #ac #bjbi #eg #aa #aj #fhbddfdbbffgegiefha #ad #jeca #eb #aa #aa #fhhjebdchefcegaheba #ab #cgcc #dg #aa #ab #fihjhideehhcefgbfda #aj #cfce #ch #ei #ac #gabcjedgdgbdefediba #jh #aecg #bf #ei #a #hfgdgdcbdcdhhcgefda #jc #jiae #je #bb ,,hypo- #b #hdaifjcdefddhjdggba #jd #caag #je #cb ,,pyral #c #hbghhbcfhedaghbcfha #je #jaai #je #ac ,,series4 #d #hbebiecidahiggjajja #jd #cfba #jd #bd #e #hccehfdbbhjfgfgcjea #jc #ahbc #jj #aj #f #hebbfddediigggcbhja #ja #aebd #ea #dc ---------------------------------------- -------- ---------------------------------------- ------------ ,,ac1 ,outer ,refracting ,surfaces 7concave74 ------------------------------------ ,verti- cal ,hori- dis- zontal tance dis- of tance centre of of centre curva- of ture curva-above ture the ,in- from outer clina- the arris ,in- tion ,radius axis of the clina- of the of of the ,zone tion ,outer ,curva- ,system at of the ,radius ,no4 ture in in ,a in ,radii at ,a of ,milli- ,milli- ,milli- in ,a to the ,,zone4metres4metres4metres4 and ,c4 ,vertex4 ---------------------------------------- - #a #djjjjjchbecabhaggga #ba #ejde #ab #ef #b 444 #cibcfebfhceea #ai #efdg #ea #eb #c 444 #djaejfbedbcaa #ah #cdej #cb #ad #d 444 #djihedbcidbca #ag #dbec #ad #jj ,,hyper- #e 444 #dagcjhbbcifda #ag #ahee #eg #jb ,,pyral #f 444 #dbcggjbjghhba #ag #bjeh #da #ae ,,series #g 444 #dbiadeaiabaha #ag #dhfa #bf #cb ,,of #h 444 #dccccjagdjaba #ah #ddfd #ab #df ,,zones4 #i 444 #dcfbbfaefcaja #bj #jfff #ei #ej #aj 444 #dcggbdachafca #ba #ehfi #dg #cf #aa 444 #dcgfgbaaidida #bb #jjgb #cg #jf #ab 444 #dcfjgjajjidaa #ba #abge #bb #eh #ac 444 #dcbica #hbhaia #ba #dfgh #jc #jb #a #djjjjjcheehcbghefja #ba #bhde #ea #dj ,,hypo- #b 444 #cihcbabfddafa #ba #bhdh #cg #ae ,,pyral #c 444 #dajdhdbdidhba #ba #bdea #bd #df ,,series4 #d 444 #dbahefbcdjjba #ba #bjed #aa #dh #e 444 #dcbbiebahbaga #ba #abef #ef #ah #f 444 #ddafiabjbciia #ba #jdei #cf #ji ---------------------------------------- -------- ---------------------------------------- ------------------- 1 ,,bc1 ,inner ,refracting ,surfaces 7convex74 ------------------------------------ ,verti- ,hori- cal zontal dis- dis- tance ,dis- tance of tance of centre of centre of ,c from of curva- the curva- ture ,focus ture below ,in- for the from the clina- ,zones1 the outer ,in- tion of in ,radius axis arris clina- of the ,milli- of of the of the tion ,outer metres ,curva- ,system ,zone of the ,radius ,,fc4 ,no4 ture in in at ,a in ,radii in ,c of ,milli- ,milli- ,milli- in ,c to the 7,fig4 ,,zone4metres4metres4metres4 and ,b4 ,vertex4 #aad47 ---------------------------------------- -------- #a #djjjjjbjbaaicgggjga #ai #bdae #eh #dgajedcd #b 444 #aiahcgcgigdja #ag #cdad #dh #daajfijb #c 444 #ahacfjchaegga #af #afac #ci #jaajhgeb #d 444 #agjgeechcaiea #ae #bfab #cj #dfaajihe ,,hyper- #e 444 #aeiigbchdfjda #ae #jdaa #bc #dgaacfad ,,pyral #f 444 #adhifbchehada #ae #jhaj #ag #eiaaffeg ,,series #g 444 #acgfgachfhcja #ae #cf #i #ac #afabjadf ,,of #h 444 #abfjchchgfeia #af #cb #h #ji #cjabdaaf ,,zones4 #i 444 #aaciidchhcjca #ag #ef #g #jf #ccabhfae #aj 444 #ajadfgchhgffa #ai #dh #f #jd #aiaccfii #aa 444 #hhdiechicjja #ai #ef #e #jc #dfacidcf #ab 444 #gebghchigcba #ai #ef #d #je #chadegbb #ac 444 #fahcgcijaaja #ai #ef #c #aj #jjaebedc #a #djjjjjbjjbebcghaiaa #ai #jdae #db #jh -- ,,hypo- #b 444 #aiaheechjaeaa #ai #jdad #bg #bb -- ,,pyral #c 444 #ahcfbbchahica #ai #jdac #ad #bi -- ,,series4 #d 444 #agefccchcdbja #ai #jdab #jd #jg -- #e 444 #afgihechdgcha #ai #jdaj #eg #jb -- #f 444 #afjgcichehefa #ai #jd #i #ec #dc -- ---------------------------------------- --------------- ,,appendix1 ,no4 ,v4 ,,notice ,,to ,,mariners4--,,skerryvore ,,lighthouse4 ,the ,commissioners of the ,northern ,lighthouses hereby give notice1 that a ,lighthouse has been erected upon the ,skerryvore ,rock1 which lies off the ,island of ,tyree1 in the county of ,argyll1 the ,light of which will be exhibited on the ,night of the #ast ,february #ahdd1 and every ,night thereafter1 from sunset to sunrise4 ,a specification of the bearings of the ,lighthouse and character of the ,light will be found on the next page4 ,and the ,commissioners hereby further give notice1 that by virtue of a ,warrant from the ,queen in ,council1 of date the #acth ,december #ahdc1 the following ,tolls will be levied for voyages in respect of which benefit will be derived from this ,light1 viz41 from every ,british ,vessel 7the same not belonging to ,her ,majesty1 or being navigated wholly in ballast71 and for every ,foreign ,vessel which1 by any ,act of ,parliament1 ,order in ,council1 ,convention1 or ,treaty1 shall be privileged to enter the ,ports of the ,united ,kingdom of ,great ,britain and ,ireland1 upon paying the same duties of tonnage as are paid by ,british ,vessels 7the same not being navigated wholly in ballast71 the ,toll of ,one ,penny per ,ton of the ,burden of every such ,vessel2 and for every ,foreign ,vessel not so privileged1 the ,toll of ,two ,pence per ,ton4 ,by ,order of the ,commissioners1 7,signed7 ,c4 ,,cuningham1 ,,alex4 ,,cuningham1 ,joint ,secs4 ,,edinburgh1 #bc;d ,december #ahdc4 ,the following is a ,specification of the ,position of the ,lighthouse1 and the ,appearance of the ,light1 by ,mr ,,alan ,,stevenson1 ,engineer to the ,commissioners4 ,the ,skerryvore ,rock lies off the ,island of ,tyree1 in ,lat4 #ef #ai #bb ,n42 ,long4 #g #f #cb ,w4 ,by ,compass1 the ,lighthouse bears from ,barrahead ,lighthouse ,s4 ,e41 distant #cc nautic miles2 from ,hynish ,point1 in ,tyree1 ,,wsw4 ,w41 distant #aj miles2 from ,iona ,island1 ,,wnw4 ,n41 distant #bj miles2 from ,rhinns of ,islay ,lighthouse1 ,n4 ,e41 distant #dd miles2 and from ,innistrahull ,lighthouse in ,ireland1 ,,ne4 by ,n41 distant #ec miles4 ,owing to the distance to which the foul ground extends on every side of the rock on which the ,lighthouse is placed1 and the weight of sea which breaks on the shallow ground all round it1 it is necessary to give the ,light a wide berth4 ,the better to enable seamen to judge of this1 their attention is called to the prefixed ,chart1#hg which exhibits the relative position of the ,skerryvore ,rock1 and the various dangers around it4 ,in particular1 it is necessary to notice the position of those rocks which lie seaward of the ,lighthouse1 viz4 ,mackenzie's ,rock1 about #c miles ,w4 by ,s4 ,s4 from the ,lighthouse2 ,stevenson's1 #b miles ,w4 ,n42 and ,fresnel's1 which lies between these two ,rocks4 ,to the left of the prefixed ,chart is a small diagram1 which exhibits the position of the ,skerryvore ,rock in reference to the principal landmarks above noticed4 #hg ,a copy of the ,chart referred to will be found at ,plate ,,ii4 at the end of this volume4 ,the ,skerryvore ,light will be known to mariners as a ,revolving ,light1 producing a ,bright ,flash once every minute4 ,the ,lantern1 which is open all round1 is elevated #aej feet above the level of the sea4 ,in clear weather the flashes of the ,light will be seen at the distance of six leagues1 and at lesser distances according to the state of the atmosphere2 and to a near observer1 in favourable circumstances1 the ,light will not wholly disappear between the flashes4 ,,appendix1 ,no4 ,,vi4 ,,account ,,of ,,the ,,expense ,,of ,,erecting ,,the ,,skerryvore ,,lighthouse ,,and ,,of ,,the ,,subsidiary ,,works4 ,,establishment ,,at ,,hynish4 ,wages of the different workmen quarrying and dressing the stones1 and building the dwelling-houses1 barracks1 storehouses1 inclosure and subdivision dykes1 draining and trenching the ground1 c41 at ,hynish1 and the wages of joiners preparing and fitting up the joiner work1 #biif #g #g ,timber1 pavement1 bricks1 ironmongery1 glass1 c41 c41 used in the erections1 #acgf #af #i ,slater1 plaster1 and plumber work of the houses1 #dcf #a #j ,paid the tenant of ,hynish for a barn which was used as a barrack to accommodate the workmen when they first landed at ,tyree1 #ac #j #j --------------- #dhbb #e #d ,,note4--,although these buildings had been erected for the purposes of the works1 yet the greater part of them were designed to serve as part of the permanent accommodation required at ,tyree in connection with the ,lighthouse ,establishment1 and have accordingly been so applied4 ,,rock ,,barrack1 ,no4 #a4 ,cost of the barrack on the ,rock1 which was destroyed1 including the contractor's account for extra work1 c41 #gdb #ag #g ,lead for running up the bats and for other purposes about the barrack1 #ad #aa #f ,a smith's forge1 bellows1 anvil1 and smith's tools used at ,rock in erecting the barrack1 #cb #ai #a --------------- #gij #h #b ,,rock ,,barrack1 ,no4 #b4 ,cost of the carpenter and joiner work on the second barrack1 the expense of fitting and erecting it at ,greenock1 the wages of four joiners and a smith1 furnished by the contractor to assist in its erection at ,skerryvore1 including sundry other minor charges1 #iaa #ad #d ,cost of the iron-work of the barrack1 #cfi #aa #h ,lead for running up the bats and protecting the timber of cooking apartment1 c41 #bi #aa #aj ,cooking apparatus for the cook-room of barrack1 sheet-iron smoke tube1 cooking utensils1 c41 #ed #af #f ,bedding for beds of barrack1 #ij #i #a ,expense of upholding and making sundry small repairs on the barrack since its erection1 #bb #ah #f --------------- #adgi #a #aa ,cost of the furniture1 bedding1 and other utensils required for the dwelling-houses1 barracks1 c41 connected with the different establishments of the works1 #hcj #ai #b ,,establishment ,,at ,,north ,,bay4 ,wages of the quarriers1 masons1 joiners1 c41 quarrying stones1 building the barracks1 storehouses1 c41 c41 and fitting up the joiner work1 #cgh #aa #i ,timber and other furnishings for the erections1 the expense of making the doors and windows1 including furnishings required for erecting the habitable part of ,skerryvore ,barrack at ,north ,bay as a temporary accommodation for the workmen1 and sundry other charges1 #cfa #d #g ,sundry furnishings--such as utensils for provision store1 smithy1 c41 #ac #b #e --------------- #geb #ah #i ,,quarries ,,at ,,north ,,bay4 ,cost of rails and timber for railway and timber1 c41 for shipping-pier at ,north ,bay1 #aca #e #a ,wages of workmen who were employed at quarries in ,north ,bay1 quarrying the lighthouse blocks1 constructing the pier1 railway1 c41 #ageb #e #c --------------- #ahhc #aj #d ,,temporary ,,wharf ,,and ,,railway ,,at ,,the ,,skerryvore ,,rock4 ,cost of timber used in the wharf and railway at the ,skerryvore ,rock1 #ajc #ah #f ,iron bats1 bolts1 c41 for fastening the timber1 rails for railway1 and sundry furnishings connected with an apparatus for blasting under water1 #aai #g #f ,wages of the workmen constructing the railway1 fastening the timber of wharf1 c41 #cd #aj #e --------------- #beg #af #e ,,excavation ,,at ,,rock ,,and ,,platform1 c4 ,wages of the workmen excavating the foundation for the ,lighthouse ,tower1 on the ,skerryvore ,rock1 #fji #b #c ,a portable forge1 and other smith's tools1 used at the rock for this work1 #ba #ae #aj ,wages of the workmen excavating the site of a platform at the workyard in ,hynish1 and quarrying and dressing stones for sill of platform1 #ajg #af #e ,cost of freestone from ,garscube ,quarry1 ,glasgow1 for part of the sill of platform1 #bd #ad #j --------------- #gfc #h #f ,,dressing ,,lighthouse ,,blocks4 ,wages of masons1 including the assistance of labourers1 carters1 c41 in dressing the blocks for the ,lighthouse ,tower at ,hynish1 #hehi #h #g ,timber for moulds of the various blocks1 and the joiners' wages making the moulds1 #chd #ah #aj ,timber1 c41 and wages of joiners in erecting sheds for the masons1 #iee #d #e --------------- #iibi #aa #aj ,expense of victualling the workmen and others who were employed at the rock during the operation of the whole works1 #aejc #ah #f ,,implements ,,and ,,tools ,,for ,,masons1 ,,smiths1 c4 ,amount paid to sundry persons for the implements and tools used by the workmen in all the departments of the works1 #aagf #i #f ,wages of the smiths and their hammermen keeping these tools in repair and making others1 #ijh #af #e --------------- #bjhe #e #aa ,,machinery ,,for ,,the ,,works ,,at ,,the ,,rock1 ,,hynish1 ,,and ,,north ,,bay4 ,cost of cranes1 crabs1 winches1 trucks1 iron blocks1 chains1 rope-guys1 c41 with sundry other furnishings connected with these articles1 #aeaf #i #e #a ,woolwich or sling-cart1 a janker for wood1 and four jack-screws1 #hi #f #d ,large balance crane used in building the ,lighthouse ,tower1 #ecc #aj #j ,hoisting beams or needles1 and a pair of strong sheer-poles1 used in building the ,lighthouse ,tower1 #db #aa #b --------------- #baha #af #aa ,,cartage ,,account4 ,cost of #c large draught horses and a pony1 for the use of the works1 #abg #i #aj ,carts and stable utensils1 #fe #ad #b ,harness and other furniture1 and keeping them in repair1 #eb #b #c ,provender for the horses for seven years1 #heh #ad #h --------------- #aajd #a #j ,,mortar ,,account4 ,cost of the lime which was used for all the departments of the works1 #cca #i #h ,pozzolano which was used for the building of the ,lighthouse ,tower1 excepting a small portion for the works of the harbour or dock1 #cgf #af #d ,mastic1 cements1 and stucco1 #ci #f #aj ,wages of labourers grinding and sifting ,pozzolano at ,hynish1 and burning and sifting a portion of the lime1 #aba #ah #h ,packages to contain ,pozzolano1 to prevent its admixture with other cargo when on board ship1 #bj #j #a --------------- #hhi #aa #g ,,signal ,,tower ,,at ,,hynish4 ,expense of quarrying1 dressing1 and building the stones1 and executing the joiner work of the ,signal ,tower at ,hynish1 #cgj #ac #b ,pavement and bricks for the interior1 #cb #ac #a ,cast-iron floor1 with lintels and sole plates for windows1 and cast-iron supports for do41 #aaj #ac #d ,timber for joisting of floors1 lining of walls and windows1 including the glazing of them1 a wooden trap1 flag-pole1 and other furnishings for interior1 #bhd #i #j ,plumber work of roof1 #ce #i #f ,a #e feet achromatic telescope1 with stand1 c41 for ,signal ,tower1 #ce #aj #j ,cost of a code of signals1 flags1 return books1 and other furnishings1 #aa #aj #f --------------- #hhj #ah #g ,,lights ,,account4 ,expense of the apparatus required for the lights at the ,pier and ,signal ,tower at ,hynish1 including fitting up1 c41 #ff #g #j ,cost of oil and other requisites for upholding these lights1 #acf #e #h ,salary of the ,lightkeepers1 c41 #aca #aa #g --------------- #ccd #d #c 8,,skerryvore0 ,,steamer4 ,first cost and complete outfit of the steamer ,skerryvore1 #eicj #j #aa ,alteration on the engines1 by raising the shafts1 c41 #dbc #e #j ,repairs on the hull and engines1 on various occasions1 during the progress of the works1 #ajeg #d #b ,sailing expenses 7exclusive of the cost of coals supplied when the steamer was at ,hynish71 and sundry other minor charges1 #eech #aj #aa --------------- #ab1idi #a #j 8,,queen0 ,,tender4 ,first cost and complete outfit of the 8,queen0 ,tender1 #ice #ac #c ,sailing expenses and other charges1 #ajaj #g #i ,repairs on the hull1 rigging1 sails1 c41 #gg #ab #h --------------- #bjbc #ac #h ,,stone ,,lighters ,first cost and outfit of four lighters for transporting the ,lighthouse blocks1 c41 from ,hynish to the ,skerryvore ,rock1 #afff #ae #f ,hawsers for towing1 mooring-ropes1 heaving-lines1 c41 used in the course of transporting the stones to the ,rock1 #bdi #a #f ,upholding the lighters in repair1 and sundry other charges1 #agh #i #i ,expense transporting the lighters on various occasions to different places1 #eh #ae #aj ,expense shifting and attending upon the lighters when lying at ,leith1 and advertising them for sale1 #ai #i #aj --------------- #bagb #ab #f ,,moorings4 ,cost of the buoys for mooring the vessels belonging to the works in ,hynish ,bay1 and at the ,rock1 when lying there1 #bdj #a #c ,cast-iron mushroom anchors for mooring the buoys1 #aah #g #d ,wrought-iron common anchors1 grapnels1 c41 for mooring the vessels1 warping1 kedging1 c41 #dh #af #a ,chains and shackles for do41 c41 #ced #b #g ,upholding and keeping in repair the buoys1 #d #ag #a --------------- #gff #d #d ,,boats ,,and ,,attendance4 ,cost of #h boats1 with oars1 sails1 tackling1 c41 #bjg #ai #aa ,upholding these boats in repair1 #bh #ac #i ,amount paid for the use of boats and their crews assisting to discharge cargoes from vessels previous to the pier being built1 #aai #f #j --------------- #cee #ai #h ,amount paid the owners of hired vessels1 as freights of the ,lighthouse blocks from the quarries at ,north ,bay1 in ,mull1 to the workyard at ,hynish1 #acjj #ad #h ,,freight ,,and ,,sailing ,,expenses4 ,freights and other charges paid the owners of hired vessels1 vessels1 for the materials which were imported for the use of various departments of the works1 exclusive of the ,lighthouse blocks from ,north ,bay1 #djde #i #g ,wages of labourers1 c41 discharging the cargoes from the vessels at the ,pier at ,hynish1 and the wages of workmen quarrying stones for ballast1 and putting it on board the vessels1 #icc #ab #aj ,amount paid for travelling expenses1 and other charges connected with the transport of the workmen1 including the expenses of the ,officers1 c41 travelling on the business of the works1 #agaa #aa #b ,cost of the coals supplied to the steamer 8,skerryvore10 when plying between the ,skerryvore ,rock1 ,hynish1 c41 for the household purposes of the different departments of the works1 and also for the smith's forge1 #adfc #j #g ,cost of the blasting powder used for the purpose of quarrying stones1 excavating rocks1 c4 #cge #ad #b ,,lighthouse ,,tower4 ,wages of the workmen who were engaged at ,skerryvore ,rock in building the ,tower1 and shipping the materials at ,hynish for ,rock1 including the wages of masons1 c41 assisting the other tradesmen in the respective departments of their work1 after the completion of the building operations1 #bcha #aa #g ,cost of the wainscot and other articles for the joinery of the interior of the ,lighthouse2 the wages of the joiners preparing the wood at ,hynish1 and fitting it up at the ,tower1 #adae #e #a ,green heart and oak for treenails1 for securing the lower courses of ,lighthouse ,tower1 #dj #aj #d ,plate-glass for windows and borrowed lights in partitions of ,tower1 #hd #g #d ,lewis bats1 hinges1 c41 for entrance-door and shutters of ,tower1 and the locks and other mounting for the interior1 #bah #ae #b #ad ,copper oil-cisterns1 a copper-pump1 gauging-rods for do41 #bgf #aj #g ,cast-iron water-tanks and coal-boxes1 for interior of ,tower1 #afj #ac #i ,a large cooking apparatus for kitchen of ,tower1 a stove to heat the lower apartments1 and cast-iron smoke-tubes for both fire-places1 #aag #ag #g ,a bell-metal railing for balcony1 #cda #ac #a ,a bell-metal ladder from rock to entrance-door of ,tower1 #aid #ac #d ,a cast-iron pillar to support floor of light-room1 #ag #h #g ,a bell-metal lightning-conductor for ,tower1 and fixtures1 #fe #ac #j ,cast-iron permanent railway on the ,skerryvore ,rock1 from the landing creek to the ,tower2 a cast-iron platform near the ,tower1 and stairs at landing creek1 #dic #aa #h ,a crane erected at the landing creek1 for landing materials on the rock1 #ih #ac #b ,a copper flagstaff and ball for the top of the ,lighthouse ,tower1 with bell-metal base1 fixtures1 pulleys1 c41 #ff #aj #h ,a brass force-pump1 for pumping water up from tanks to kitchen of ,lighthouse1 #ca #ag #e ,premiums paid the seamen who were employed in the shipping department1 in lieu of extra time1 #ded #b #f ,premiums paid #ag seamen who were employed in the building works at the ,rock during the season of #ahdb1 in lieu of extra time1 #aba #aa #j ,premiums of the landing master at ,rock1 foreman of masons1 c41 #if #ab #j ,cost of the furniture1 bedding1 utensils1 books1 c41 for the ,lighthouse ,tower1 #cjd #f #aj ,sundry furnishings connected with the building of the ,lighthouse ,tower1--the wages of workmen quarrying stones at ,hynish for ,lighthouse ,tower1 previous to opening quarries at ,north ,bay1 and the wages of workmen1 and furnishings for the general purposes of the works1 #achf #ah #e ,cost of three models1 in stucco1 of different forms of the ,lighthouse1 #bb #d #f ,cast-iron water-tanks1 which were built and secured into recesses of the rock1 for the supplying of the rock works1--new water-casks1 and their repairs1 for taking off water1 #ag #e #aa ,feu-duty1 rent of ground1 assessed taxes1 c41 for the establishment at ,hynish1 #adc #f #d --------------- #heea #ai #aj ,cost of the iron and steel which were used for all the departments of the works1 #abii #c #e ,,lightroom ,,and ,,apparatus4 ,cost of the lantern of cast-iron1 with facings of bell-metal1 including the cleaning and trimming paths1 and bell-metal ladder outside of lantern1 and the wages of the contractor's workmen fitting them up at ,skerryvore1 #hfc #ac #f ,plate-glass for the lantern1 #bfh #d #f ,copper dome of lantern1 including the internal frame of do41 drip-pan1 copper steps1 handles1 air-tubes1 rain-water pipes1 a platform outside of dome for cleaning the vents1 with the wages of the contractor's workmen fitting them up at ,skerryvore1 #cdh #af #i ,machinery of the revolving apparatus1 and brass case for do4 complete2 three machines for pumping the oil for supplying the burner2 the expense of the lamps1 fountains1 c42 and bell-metal frames for annular lenses1 zones1 pyramidal lenses1 c41 with the wages of the contractor's workmen fitting up the above apparatus at ,skerryvore1 #abdd #aj #f ,the charge of ,mr ,franois of ,paris furnishing eight annular lenses1 and two spare do41 with eight catadioptric frames of the first order for lower part1 and eight pyramidal lenses1 with mirrors1 for upper part1 #gfb #j #j ,expense of transporting the whole apparatus to ,leith1 #gi #g #aj ---------- #hda #g #aj ,cost of two bells1 and one spare do41 used during foggy weather1 #ajg #f #c ,shafting for do42 bevel wheels1 levers1 hammers1 c41 connecting with the machinery of apparatus1 #fc #ad #aa ------------- #aga #a #b ,eighteen screens for lantern1 cased with iron1 and brass mounted1 with rollers1 c41 and the time of workmen fitting them up at ,skerryvore1 #dh #g #f ,air watch-bells from lightroom to bedrooms and kitchen1 time of workmen fitting them up at ,skerryvore1 and furnishings for the complete working of do41 #cd #ac #j ,brass medallion heads and copper tubes for ventilation of lightroom1 #h #i #f ,wood and workmanship making models of the catadioptric zones to a full size1 and a brass model of frame for zones to a small scale1 #bb #a #b --------------- #chea #e #f ,,salaries1 ,,agencies1 ,,and ,,office ,,expenses4 ,salaries of the ,engineer1 ,surveyor1 ,clerk1 and ,store-keeper1 including expenses of the survey of the rocks and adjoining ,islands1 #cbfb #aj #e ,agency of the ,agent at ,aberdeen1 who made the monthly payments to the workmen's relatives1 and for some time superintending the making of tools2 and the agency of the ,lighthouse ,agent at ,greenock transacting business for the works1 #bid #ac #aa ,iron safe1 c41 books1 and other stationery for the various departments of the works1 #ii #aj #aj --------------- #cfef #ae #b ,petty disbursements and miscellaneous expenses1 made on account of the general purposes of the works1 #cjh #g #i ,,lightkeepers' ,,houses4 ,wages of workmen1 quarrying1 dressing1 and building the stones of houses at ,hynish for light-keepers1 building the brick partitions and lining of walls1 and the wages of joiners executing the joiner-work1 #ahic #f #b ,timber and other articles used in the joinery of the houses1 #dfb #ai #i ,plumber-work of roof1 including the expense of bringing the water into the houses1 c41 #ifc #ah #f ,bricks for partitions1 lining of external walls1 c41 #gc #aj #j ,pavement for floors1 water-cisterns1 c41 #ea #af #j ,workmanship1 executing the plaster-work 7the lime being charged in a special account for this article71 #ch #ab #aa ,glass for glazing the windows and fan-lights1 #bj #ab #c ,locks1 hinges1 and other mounting for the doors and windows1 #aja #aa #aa ,cans for the chimney heads1 #i #af #f ,furniture1 bedding1 utensils1 c41 supplied for these houses1 #bii #j #d --------------- #ciae #d #d ,,pier ,,at ,,hynish4 ,wages of masons1 quarriers1 carters1 labourers1 c41 quarrying1 dressing1 and building the stones of a pier at ,hynish for the landing and shipping of materials1 #bcjj #ag #a ,iron rails for the works of building the pier1 #ec #aj #a ,timbers for fenders of pier1 and other purposes connected with the building of it1 #acj #ai #d ,cost of a pont for building the pier1 #ajf #h #aa --------------- #beia #ae #e ,,dock ,,or ,,harbour ,,for ,,tender4 ,wages of workmen1 quarrying1 dressing1 and building stones to form a talus wall and parapet along the south side and round the point of the pier at ,hynish2 raising the pier one course2 excavating rock in the interior of the harbour or dock and along the point of pier2 quarrying1 dressing1 and building the stones of boom-heads and walls of dock2 excavating reservoir and forming embankment of do1 for scouring sand1 c41 from the dock2 forming the feeders to reservoir1 and the tail-race from reservoir to dock1 refreshments to workmen during night and tide works1 c41 #ffgf #aj #f ,timber for double set of boom-gates of dock1 copper for sheathing their ends1 and mounting for booms1 #aja #b #f ,timber used in constructing coffer-dams1 and for the general purposes of the harbour works1 #ace #ah #j ,cost of two sluices1 and of the machinery1 c41 complete for working them1 #ha #ad #j ,two cast-iron ladders for sides of pier and dock1 #ac #a #i ,cost of sea-boots1 c41 and keeping them in repair1 which were used by the workmen at tide works1 #bf #ab #j ,cost of silt-pumps1 and furnishings of leather1 c41 for making others1 and keeping them in repair1 #i #aj #j ,compensation paid the tenant of the farm of ,hynish1 for liberty to cut drains for a supply of water for a reservoir1 #e #j #j ,two signal lamps1 two torches1 turpentine1 c41 for signalizing when the tender enters the dock at night1 #e #ad #h --------------- #gjee #c #e ---------------- ,,total1 #hi1hag #f #aa ,,deductions-- ,price of steamer 8,skerryvore10 sold1 #afaf #j #f ,do4 of sloop 8,queen10 sold1 #bjj #j #j ,do4 of #d ,stone ,lighters1 sold1 #bbe #j #j ,do4 of ,horses and ,carts1 sold1 #fj #j #j ,implements sold or afterwards used at other works of the ,board1 #gch #h #aj --------------- #bhci #i #d ---------------- #hf1igg #ag #g ,,appendix1 ,no4 ,,vii4 ,,excerpts ,,from ,,an ,,account ,,of ,,experiments ,,upon ,,the ,,force ,,of ,,the ,,waves ,,of ,,the ,,atlantic ,,and ,,german ,,oceans4 ,by ,,thomas ,,stevenson1 ,f4,r4,s4,e41 ,,civil-,,engineer1 ,,edinburgh4 7,from the ,transactions of the ,royal ,society of ,edinburgh1 ,vol4 ,,xvi47 ,the letters 7see ,plate ,,iv47 ,d ,e ,f ,d represent a cast-iron cylinder1 which is firmly bolted at the projecting flanges ,g to the rock where the experiments are wanted4 ,this cylinder has a flange at ,d ,d4 ,l ,l is a door1 which is opened when the observation is to be read off4 ,a ,a is of iron1 and forms a circular plate or disc1 on which the sea impinges4 ,fastened to the disc are four guide-rods ,b ,b ,b ,b4 ,these rods pass through a circular plate ,c ,c 7which is screwed down to the flange ,d ,d71 and also through holes in the bottom ,e ,f4 ,within the cylinder there is attached to the plate ,c ,c a powerful steel spring1 to the other or free end of which is fastened the small circular plate ,k ,k1 which again is secured to the guide-rods ,b ,b ,b ,b4 ,there are also rings of leather ,t ,t1 that slide on the guide-rods1 and serve as indices for registering how far the rods are pushed through the holes in the bottom2 or1 in other words1 how much the spring has been drawn out or lengthened by the force of the sea acting upon the plate or disc ,a ,a4 ,the object of having four leathern rings1 where one might have answered the purpose1 was merely that they might serve as a check upon each other2 and so perfectly did they answer the purpose intended1 that in every instance they were found equidistant from the bottom of the cylinder2 proving thereby1 that after the recoil of the spring1 they had all kept their places4 ,the guide-rods are graduated1 so as to enable the observer to note exactly the quantity that the spring has yielded4 ,this instrument1 which may1 perhaps1 be not improperly termed a ,marine ,dynamometer1 is1 therefore1 a self-registering apparatus which indicates the maximum force of the waves4 ,in the graduation of the instrument1 the power of the spring is ascertained by carefully loading the disc with weights1 so that when the quantity that the spring has yielded by the action of the sea is known1 the pressure due to the area of the disc exposed is known also4 ,the discs employed were from #c to #i inches diameter1 but generally #f inches1 and the powers of the springs varied from #aj lb4 to about #ej lb4 for every inch of elongation4 ,their respective effects were afterwards reduced to a value per square foot4 ,the instrument was generally placed so as to be immersed at about three-fourths tide1 and in such situations as would afford a considerable depth of water4 ,it is not desirable to have the instrument placed at a much lower level1 as it has not unfrequently happened during a gale1 that for days together no one could approach it to read off the result and readjust the indices to zero4 ,it must1 however1 at the same time be remarked1 that it is in most situations almost impossible to receive the force unimpaired1 as the waves are more or less broken by hidden rocks or shoal ground before they reach the instrument4 ,in connection with the apparatus above described1 a graduated pole was erected on an outlying sunken rock1 for the purpose of ascertaining the height of the waves2 but the observations were not of so satisfactory a nature as could have been desired1 and the poles soon worked loose from their attachments1 and disappeared4 ,with the instrument which has been explained1 ,i entered upon the following train of observations3-- ,in #ahdb several observations were made on the waves of the ,irish ,sea at the island of ,little ,ross1 lying off the ,bay of ,kirkcudbright4 ,since ,april #ahdc till now1 continued observations have been made on the ,atlantic at the ,skerryvore and neighbouring rocks lying off the island of ,tyree1 ,argyllshire2 and in #ahdd a series of observations was begun on the ,german ,ocean at the ,bell ,rock4 ,it will be seen1 that in selecting these localities a varied exposure has been embraced1 comprising the comparatively sheltered ,irish ,sea1 the more exposed eastern shore of ,scotland1 and the wild ,rocks of ,skerryvore1 which are open to the full fury of the ,atlantic1 the far distant shores of ,north ,america being the nearest land on the west4 ,referring for more full information to the tables of experiments which are given at the end of this paper1 it will be sufficient in this place to state generally the following as the results obtained4 ,in the ,atlantic ,ocean1 according to the observations made at the ,skerryvore rocks1 the average of results for five of the summer months during the years #ahdc and #ahdd1 is #faa lb4 per square foot4 ,the average results for six of the winter months 7#ahdc and #ahdd71 is #bjhf lb4 per square foot1 or thrice as great as in the summer months4 ,the greatest result yet obtained at ,skerryvore was during the heavy westerly gale of #bith ,march #ahde1 when a pressure of #fjhc lb4 per square foot was registered4 ,the next highest is #ecbc lb4 ,in the ,german ,ocean1 according to the observations made at the ,bell ,rock1 the greatest result yet obtained is #cjac lb4 per square foot4 ,it thus appears1 that the greatest effect of the sea1 which has been observed1 is that of the ,atlantic at ,skerryvore1 which is nearly equal to three tons per square foot4 ,these experiments1 amounting to #bfg in number1 and on the ,atlantic alone1 extending over #bc months continuously1 are not intended to prove anything farther than the simple fact1 that the sea has been known to exert a force equivalent to a pressure of three tons per square foot1 however much more4 ,it is proper1 however1 to observe1 that there may be some objection to referring the action of the sea to a statical value4 ,although the instrument might perhaps be made capable of giving a dynamical result1 it was considered unnecessary1 in these preliminary experiments1 to do anything more than represent the maximum pressure registered by the spring1 because the effects of the waves may1 from supposing them to have continuity of action1 be perhaps regarded as similar to a statical pressure1 rather than to the impact of a hard body4 ,the near coincidence1 or indeed almost perfect agreement of the results of the experiments made with different instruments1 goes far to shew that the waves act in very much the same manner as a pressure1 although both pressure and impact must obviously enter into their effect4 ,in the experiments1 begun ,february #ahdd1 and given at the end of the paper1 the three instruments had not only different areas of discs1 but very different powers of springs1 and yet the results were almost identical4 ,now1 the same force1 supposing the waves to act like the impact of a hard body1 would1 in the ,marine ,dynamometer1 have assumed very different statical values1 according to the spaces in which that force was expended or developed2 so that with the same force of impact1 the indication of a weak spring would be less than that of a stronger4 ,in future experiments it may be interesting1 however1 to test the springs dynamically1 by means of the impact of a heavy body dropped from a given height upon the plate or disc of the instrument4 ,in some experiments lately made in this way1 by dropping a cannon-ball upon the disc1 it appeared1 that1 within the limits of the experiments1 there was for each individual spring a ratio between the value registered by the leathern index and the calculated momentum of the impinging body4 ,these ratios were1 of course1 found to vary in springs of different power1 and to be constant only for springs of the same power4 ,did the waves1 therefore1 act by a sudden finite impact1 like the cannon-ball employed in this instance1 we could scarcely have found such harmony between the results of instruments with different springs1 as the experiments alluded to afford4 ,at the same time1 the result cannot1 perhaps1 be in strictness considered correct2 but1 from the elongation of the spring being very small1 the results may be regarded as practically correct1--the more so when we find so remarkable a coincidence of results as that alluded to4 ,,experiments4--,with reference to the following experiments ,i have only to observe1 that those which were made at ,little ,ross1 upon the ,irish ,sea1 cannot1 from the unusual fineness of the weather at the time1 be regarded as affording a true value of the effects of a hard gale in these seas4 ,of the others it is to be noticed1 that where two or three instruments were for some time employed as a check upon each other1 and only one or two readings are given1 the want has occurred either from the instruments being under repair1 or being difficult of access in stormy weather1 or during neap tides4 ,it often happened also1 in consequence of the springs proving too weak1 when new ones had to be made1 or the area of the disc reduced4 ,registers of the state of the weather1 apparent height of spray1 c41 were generally kept2 but it was not considered necessary to complicate the ,tables by inserting these1 excepting in one or two instances4 ---------------------------------- lbs4 to a ,dates4 ,square ,foot4 ---------------------------------- ,observations at ,little ,ross4 #ahdb4 ,april #be #ae #bh #ea ,june #a #cf #d #hae #bj #hfe #bd #hdjj #be #dehj ,july #be #chjj ,aug4 #b #egjj #e #ffej #f #chjj #i #chjj ,the ,observations at the ,skerryvore ,rock1 and the neighbouring ,island of ,tyree1 distant #ac miles from the ,skerryvore1 are as follows3-- #ahdc4 ,april #bd #dee #be #gjg ,may #g #bdc #aa #ahb #ab #bdc #af #cfd #bj #die #dgf ,june #c #ahb #d #eai #g #dbh #h #hee #i #agc ,july #b #dgf #c #gbc #hff #cj #dcc ,aug4 #i #cdf #bb #gbc #cj #chi ,sept4 #e #hff #ba #ieb ,oct4 #e #aece #f #afjf ,nov4 #ah #agaa #ai #adig #bg #adig #bi #bcec ,dec4 #e #bfgd #h #cdba ,at least #ad #bdfj #bf #aidg ,in ,january1 two instruments were placed beside each other1 but not set parallel4 ,these instruments had springs of different power1 the one being about double that of the other1 and one had a disc of #c inches diameter1 the other #f inches4 #ahdd4 ,jan4 #f #ifb #ibh #g #bcec #ceg #i #aibe #ajjj #aj #hbf #ajjj ,both instruments set parallel4 #ahdd4 ,jan4 #af #dbd #af #dbg ,another instrument was placed beside them1 but the two marked thus99 were found to be too weak1 as the leathers were found flattened1 and one of the instruments was broken1 and was not repaired till the #aeth ,february4 #ahdd4 ,jan4 #bh #cdbb99 #bbhe99 #ccac ,feb4 #b #dbi #deg #c #dbi #deg #ac #bad #bbh #ae #cba #bhj #cba #af #dbh #djb #cdc #bd #abhd #acfd #fhe #bf #bjcb #bjfh #cii #bg #cba #cba #cdb ,march #d #ccaf #ccfi #cdbg #g #ajfi #ifc #iac #aj #aibe #aibe #agac #aa #ece #dha #def #ab #ccaf #djaa #bigj #ac #aadb #abhc #abhc ,april #aj #deg #dbh #dha #aa #hjj #ab #cdc #cba #ad #ega #ece #af #ega #fdb #dha #ag #hjj #hef #hfb #ah #ega #dha #ai #hjj #ece #dha #bb #iac #dhb #ifb #bd #aidb #afjd #acgj #be #abhc #cdc #cba #bg #deg #dha ,night #hjj tide #fdb #cj #bbi #bda ,may #ae #cdc #ad #dha ,june #f #ega #ae #ahbh ,july #aa #ajbh #ac #deg #ah #iad #bc #aecb #be #ega #bf #iga #bg #deg #bh #aadb #bi #bhf #cj #iad #ca #ajbh ,aug4 #a #ega #g #iad #ac #iad #ad #iad #ba #hjj #cj #agac ,sept4 #ab #ajbh #ad #iad #bj #deg #bc #aadb #be #fhe #cj #aeii ,oct4 #b #bcii #c #adhe #d #ahbh #aa #cdbghh #ad #aeii #ai #aeii #bj #beac ---------------------------------- #ahdd4 ,oct4 #bb #hjj #bd #ahbg #bh #adhe #bi #deg ,nov4 #b #aidb #aj #ajbh #ad #abeg #ae #bjef #af #bjef #bb #bfbg #bc #cdbg #bg #caii #bh #daab ,dec4 #g #acfi #i #bgch #aj #ahbe #ac #aibe #ad #ajbg #ae #agfd ---------------------------------- #hh ,on this occasion1 #ad stones were slightly moved1 and #ad scattered1 all of which had been built into the round-head or end of ,hynish ,pier1 which was still in an unfinished state1 and a ,dynamometer which was attached to the ,pier1 registered on this occasion #beeg lb4 ,these stones weighed from #a to #a tons1 and exposed1 when built into the wall1 about two square feet of surface4 ,the stone to which the instrument was fixed was turned upside down1 although it weighed about #a ton #bhjj lb4 ,a more exposed point of the ,skerryvore ,rock was at this time chosen for experiment2 and with the view of ascertaining the effect of the waves at different heights upon the rock1 two instruments were fixed1 the one 7,no4 ,i47 several feet lower1 and about #dj feet seaward of the other 7,no4 ,,ii474 ,it was observed1 that about half-flood the force of the waves was a good deal expended before they reached the place where ,no4 ,i4 was placed1 from there being so little water on the rocks outside2 whereas when the tide was higher1 the waves were1 from the greater depth of water1 not so much broken when they reached ,no4 ,,ii4 ,the results of the ,marine ,dynamometer shew generally about twice the force at ,no4 ,,ii4 as at ,no4 ,i42 a result which shews how important it would be to ascertain the relative forces of the waves at different levels upon our breakwaters and other seaworks4 ---------------------------------------- ---------------- ,pressure in ,no4 of lbs4 per ,date4 ,remarks4 ,instrument4,square ,foot4 ---------------------------------------- ---------------- #ahde4 ,jan4 #g;,heavy sea4 ,i4 #agad ,,ii4 #dahb #ab,very heavy swell4 ,i4 #bhef ,,ii4 #ejcb #af;,heavy ground swell4 ,i4 #bhef ,,ii4 #dgeb #bb;,a good deal of sea4 ,i4 #bhef ,,ii4 #ecbc #bh;,heavy ground swell4 ,i4 #bfbg ,,ii4 #defb ,feb4 #e;,fresh gales4 ,i4 #hef ,,ii4 #cjdb #ba ,i4 #ahbg ,,ii4 #cdbb #bd;,fresh breezes4 ,i4 #abef ,,ii4 #chjb ,march #i;,ground swell4 ,i4 #abef ,waves supposed about #aj ,,ii4 #cjda feet high4 #aa,short sea4 ,i4 #ajbh #bd;,heavy sea4 ,i4 #bbha ,waves supposed about #bj ,,ii4 #defb feet high4 #bf,swell4 ,i4 #abef ,waves about #f feet high4 ,,ii4 #cjda ,strong gale1 with heavy sea1 the highest waves ,i4 #bhef #bisupposed #bj feet high1 and the spray rose ,,ii4 #fjhc about #gj feet4 ---------------------------------------- ---------------- ,register of ,observations on the force of the ,sea1 made at the ,bell ,rock1 ,german ,ocean4 ---------------------------------- lbs4 to a ,dates4 ,square ,foot4 ---------------------------------- #ahdd4 ,sept4 #ae #hec #bj #bbfj ,oct4 #i #cjac #befb #bf #aadb #bg #ieh ,nov4 #ab #afhj #ac #aibj ,dec4 #ac #aefj #bf #adci #ahde4 ,jan4 #g #aeei #aj #adci #aa #adci #ae #aeei #be #iei #bf #gai ,jan4 #bg #aaii #cj #bhgi #ca #aeei ,feb4 #f #biii #bd #aaii #be #iei #bg #hci #bh #acai ,march #d #iei #g #ajgi #aa #aiai #bj #beai #ba #bgei #bd #acai #be #iei #bh #eii #cj #ajgi ---------------------------------- ,,appendix1 ,no4 ,,viii4 ,,list ,,of ,,northern ,,lighthouses1 ,,beacons ,,and ,,buoys4 ,,for #ahdh4 ---------------------------------------- --------------------------- ,name of ,light4 ,situation of ,light4 ---------------------------------------- --------------------------- ,,inchkeith ,highest ,land on the ,island of ,inchkeith1 in ,fifeshire ---------------------------------------- --------------------------- ,,isle ,,of ,,may,highest ,land on ,isle of ,may1 in ,fifeshire ---------------------------------------- --------------------------- ,,do4 ,,leading,placed about #acj feet below the ,high ,light1 and to the ,,light ,,ne4 by ,n4 of it ---------------------------------------- --------------------------- ,,bell ,,rock ,bell ,rock1 a sunk reef1 #aa miles ,s4 by ,e4 ,e4 off ,arbroath1 in ,forfarshire ---------------------------------------- --------------------------- ,,girdleness ,girdleness1 ,kincardineshire ---------------------------------------- --------------------------- ,,buchanness ,buchanness1 ,aberdeenshire ---------------------------------------- --------------------------- ,,kinnaird- ,kinnairdhead1 ,aberdeenshire ,,head ---------------------------------------- --------------------------- ,,covesea ,craighead1 ,morayshire ,,skerries ---------------------------------------- --------------------------- ,,chanonry ,chanonry ,point1 ,ross-shire ,,point ---------------------------------------- --------------------------- ,,cromarty ,cromartyshire ,,point ---------------------------------------- --------------------------- ,,tarbetness ,tarbetness1 ,cromartyshire ---------------------------------------- --------------------------- ,,nosshead ,nosshead1 ,caithness-shire 7building7 ---------------------------------------- --------------------------- ,,dunnethead ,dunnethead1 most northern point of the ,mainland of ,scotland1 ,caithness-shire ---------------------------------------- --------------------------- ,,pentland ,pentland ,skerries ,island1 ,orkney ,,skerries ---------------------------------------- --------------------------- ,,start ,,point,start ,point1 ,sanday ,island1 the most eastern point of ,orkney ---------------------------------------- --------------------------- ,,sumburgh- ,the most southern ,headland of ,zetland ,,head ---------------------------------------- --------------------------- ,,cape ,,wrath ,cape ,wrath1 north-western ,headland of ,sutherlandshire ---------------------------------------- --------------------------- ,,island ,island ,glass1 one of the ,harris ,isles1 ,inverness-shire ,,glass ---------------------------------------- --------------------------- ,,barrahead ,highest land on ,bernera ,island1 ,inverness-shire ---------------------------------------- --------------------------- ,,ardna- ,ardnamurchan ,point1 ,argyleshire 7building7 ,,murchan ---------------------------------------- --------------------------- ,,lismore ,mousedale1 small ,island off ,lismore1 ,argyleshire ---------------------------------------- --------------------------- ,,skerry- ,skerryvore ,reef1 #ab miles ,,wsw4 ,w4 from ,tyree ,island1 ,,vore#hi with foul ground all round it ---------------------------------------- --------------------------- ,,rhins ,,of ,oversay1 small ,island off ,islay1 ,argyleshire ,,islay ---------------------------------------- --------------------------- ,,mull ,,of ,south-western ,headland of ,argyleshire ,,kintyre ---------------------------------------- --------------------------- ,,pladda ,pladda ,isle1 off south-east point of ,arran1 county of ,bute ---------------------------------------- --------------------------- ,,corsewall ,western side of entrance to ,loch ,ryan1 in ,wigtonshire ---------------------------------------- --------------------------- ,,loch ,,ryan ,cairn ,ryan ,point1 within ,loch ,ryan1 ,wigtonshire ---------------------------------------- --------------------------- ,,mull ,,of ,southern extremity of the ,mainland of ,scotland1 ,,galloway ,wigtonshire ---------------------------------------- --------------------------- ,,little ,,ross,little ,ross ,island1 ,kirkcudbrightshire ---------------------------------------- --------------------------- ,,point ,,of ,northern extremity of ,isle of ,man ,,ayre ---------------------------------------- --------------------------- ,,calf ,,of ,,man,west side ,calf ,island1 at the southern extremity of ,isle of ,man ---------------------------------------- --------------------------- ---------------------------------------- -------------------------- ,number ,name of of ,light4 ,lights4 ,appearance of ,light4 ---------------------------------------- -------------------------- ,,inchkeith ,one ,revolving1 and appearing in its brightest state once every minute ---------------------------------------- -------------------------- ,,isle ,,of ,,may,one ,fixed ---------------------------------------- -------------------------- ,,do4 ,,leading,one ,fixed ,,light ---------------------------------------- -------------------------- ,,bell ,,rock ,one ,revolving1 and shewing alternately a red and white light every #b minutes ---------------------------------------- -------------------------- ,,girdleness ,two ,fixed ,lights1 one above the other ---------------------------------------- -------------------------- ,,buchanness ,one ,flashing once every #e seconds ---------------------------------------- -------------------------- ,,kinnaird- ,one ,fixed ,,head ---------------------------------------- -------------------------- ,,covesea ,one ,revolving1 and appearing in its brightest state ,,skerries once every minute4 ,from ,w4 by ,n4 ,n4 to ,,se4 by ,e4 ,e4 the light is of the natural appearance2 but from ,,se4 by ,e4 ,e4 to ,,se4 ,s4 it is coloured ,,red ---------------------------------------- -------------------------- ,,chanonry ,one ,fixed ,,point ---------------------------------------- -------------------------- ,,cromarty ,one ,fixed and red ,,point ---------------------------------------- -------------------------- ,,tarbetness ,one ,intermittent1 suddenly bursting into view1 and continuing in sight #b min41 then suddenly eclipsed for half a minute4 ,but within the ,moray ,frith1 in ,southerly and ,south-westerly directions from ,tarbetness1 the light does not intermit1 but is permanently visible ---------------------------------------- -------------------------- ,,nosshead ---------------------------------------- -------------------------- ,,dunnethead ,one ,fixed ---------------------------------------- -------------------------- ,,pentland ,two ,fixed1 and #ajj feet apart ,,skerries ---------------------------------------- -------------------------- ,,start ,,point,one ,revolving1 and appearing in its brightest state once every minute ---------------------------------------- -------------------------- ,,sumburgh- ,one ,fixed ,,head ---------------------------------------- -------------------------- ,,cape ,,wrath ,one ,revolving1 and shewing alternately a red and white light every #b minutes ---------------------------------------- -------------------------- ,,island ,one ,fixed ,,glass ---------------------------------------- -------------------------- ,,barrahead ,one ,intermittent1 suddenly bursting into view1 and continuing in sight #b min41 then suddenly eclipsed for half a minute ---------------------------------------- -------------------------- ,,ardna- ,,murchan ---------------------------------------- -------------------------- ,,lismore ,one ,fixed ---------------------------------------- -------------------------- ,,skerry- ,one ,revolving1 and appearing at its brightest once ,,vore#hi every minute ---------------------------------------- -------------------------- ,,rhins ,,of ,one ,flashing once every #e seconds ,,islay ---------------------------------------- -------------------------- ,,mull ,,of ,one ,fixed ,,kintyre ---------------------------------------- -------------------------- ,,pladda ,two ,fixed1 the one above the other ---------------------------------------- -------------------------- ,,corsewall ,one ,revolving1 and shewing alternately a red and white light every #b minutes ---------------------------------------- -------------------------- ,,loch ,,ryan ,one ,fixed ---------------------------------------- -------------------------- ,,mull ,,of ,one ,intermittent1 suddenly bursting into view1 and ,,galloway continuing in sight #b min41 then suddenly eclipsed for half a minute ---------------------------------------- -------------------------- ,,little ,,ross,one ,flashing once every #e seconds ---------------------------------------- -------------------------- ,,point ,,of ,one ,revolving1 and shewing alternately a red and ,,ayre white light every #b minutes ---------------------------------------- -------------------------- ,,calf ,,of ,,man,two ,revolving1 and shewing white lights every #b minutes ---------------------------------------- -------------------------- ---------------------------------------- -------------------------- ,dis- tance visi- ble in ,name ,nautic of ,light4 ,miles4 ,points of ,compass within which ,light is ,visible4 ---------------------------------------- -------------------------- ,,inchkeith #ah ,all round the ,compass ---------------------------------------- -------------------------- ,,isle ,,of ,,may #ba ,all round the ,compass ---------------------------------------- -------------------------- ,,do4 ,,leading #ae ,when seen in ,,one line with the ,high ,light1 ,,light these two ,lights bear ,,ne4 by ,n4 ,n41 and ,,sw4 by ,s4 ,s41 and in this line lead about half a mile to the ,eastward of the ,north ,carr ,rock4 ,the ,lights must on no account be opened to the ,westward ---------------------------------------- -------------------------- ,,bell ,,rock #ad ,all round the ,compass ---------------------------------------- -------------------------- ,,girdleness #ai ,from ,,nne4 to ,,wsw4 ,w4 ,easterly and ,southerly #af ---------------------------------------- -------------------------- ,,buchanness #af ,from ,n4 by ,e4 to ,,sw4 by ,w4 ,easterly ---------------------------------------- -------------------------- ,,kinnaird- #ae ,from ,,wnw4 to ,,se4 ,northerly ,,head ---------------------------------------- -------------------------- ,,covesea #ah ,from ,w4 by ,n4 ,n4 to ,,se4 ,s4 ,northerly ,,skerries ---------------------------------------- -------------------------- ,,chanonry #aa ,from ,w4 ,n4 to ,n4 by ,e4 ,southerly ,,point ---------------------------------------- -------------------------- ,,cromarty #i ,from ,,wnw4 to ,,se4 by ,e4 ,s4 ,northerly ,,point ---------------------------------------- -------------------------- ,,tarbetness #ah ,from ,,sw4 ,w4 to ,w4 ,n4 ,easterly ---------------------------------------- -------------------------- ,,nosshead ---------------------------------------- -------------------------- ,,dunnethead #bc ,from ,,se4 ,e4 to ,w4 ,northerly ---------------------------------------- -------------------------- ,,pentland #af ,all round the ,compass ,,skerries #ah ---------------------------------------- -------------------------- ,,start ,,point #ae ,all round the ,compass ---------------------------------------- -------------------------- ,,sumburgh- #bb ,from ,,ne4 by ,e4 ,e4 to ,,nw4 by ,n4 ,n4 ,,head ,southerly ---------------------------------------- -------------------------- ,,cape ,,wrath #be ,from ,,se4 ,e4 to ,,sw4 by ,w4 ,northerly ---------------------------------------- -------------------------- ,,island #af ,from ,w4 by ,s4 to ,,ene4 ,e4 ,southerly ,,glass ---------------------------------------- -------------------------- ,,barrahead #cb ,from ,n4 by ,e4 to ,,ene4 ,westerly and ,southerly ---------------------------------------- -------------------------- ,,ardna- ,,murchan ---------------------------------------- -------------------------- ,,lismore #ae ,from ,e4 to ,,ne4 by ,e4 ,e4 ,westerly ---------------------------------------- -------------------------- ,,skerry- #ah ,all round the ,compass ,,vore#hi ---------------------------------------- -------------------------- ,,rhins ,,of #ag ,from ,,nne4 to ,,se4 ,southerly ,,islay ---------------------------------------- -------------------------- ,,mull ,,of #bb ,from ,,nne4 ,e4 to ,s4 by ,w4 ,w4 ,southerly ,,kintyre ---------------------------------------- -------------------------- ,,pladda #ac ,from ,,nw4 by ,w4 to ,,ne4 by ,e4 ,southerly #af ---------------------------------------- -------------------------- ,,corsewall #ae ,from ,,ne4 by ,e4 to ,,sw4 ,northerly ---------------------------------------- -------------------------- ,,loch ,,ryan #aj ,from ,s4 by ,w4 ,w4 to ,n4 ,e4 ,westerly ---------------------------------------- -------------------------- ,,mull ,,of #bc ,from ,,ne4 to ,,nw4 ,w4 ,southerly ,,galloway ---------------------------------------- -------------------------- ,,little ,,ross #ah ,from ,n4 by ,e4 to ,,nw4 by ,w4 ,southerly ---------------------------------------- -------------------------- ,,point ,,of #ae ,from ,s4 by ,w4 to ,w4 by ,n4 ,northerly ,,ayre ---------------------------------------- -------------------------- ,,calf ,,of ,,man #bb ,from ,,ne4 to ,,sw4 ,w4 ,southerly #bd ---------------------------------------- -------------------------- --------------------------------------- ,height of ,lantern in feet above ,high- ,date of water ,north ,west first ,name ,spring ,lati- ,longi- ,exhi- of ,light4 ,tides4 tude4 tude4 bition4 --------------------------------------- ,,inchkeith #bbj #ef #b #c #h #ahjd --------------------------------------- ,,isle ,,of ,,may #bdj #ef #aa #b #cc #ahaf --------------------------------------- ,,do4 ,,leading #aaj #ahdd ,,light --------------------------------------- ,,bell ,,rock #ij #ef #bf #b #bc #ahaa --------------------------------------- ,,girdleness #ahe #eg #h #b #c #ahcc #aae --------------------------------------- ,,buchanness #acj #eg #bh #a #df #ahbg --------------------------------------- ,,kinnaird- #abj #eg #db #b #j #aghg ,,head --------------------------------------- ,,covesea #afj #eg #dc #c #bj #ahdf ,,skerries --------------------------------------- ,,chanonry #dj #eg #ce #d #e #ahdf ,,point --------------------------------------- ,,cromarty #ej #eg #da #d #b #ahdf ,,point --------------------------------------- ,,tarbetness #age #eg #ea #h #dh #ahcj --------------------------------------- ,,nosshead --------------------------------------- ,,dunnethead #cdf #eh #dj #c #ba #ahca --------------------------------------- ,,pentland #adj #eh #da #b #ee #agid ,,skerries #agj --------------------------------------- ,,start ,,point #ajj #ei #ag #b #bc #ahjf --------------------------------------- ,,sumburgh- #cjj #ei #ea #a #af #ahba ,,head --------------------------------------- ,,cape ,,wrath #djj #eh #cg #e #j #ahbh --------------------------------------- ,,island #acj #eg #eb #f #cc #aghi ,,glass --------------------------------------- ,,barrahead #fhj #ef #dh #g #ch #ahcc --------------------------------------- ,,ardna- ,,murchan --------------------------------------- ,,lismore #ajc #ef #cj #e #ch #ahcc --------------------------------------- ,,skerry- #aej #ef #ai #g #g #ahdd ,,vore#hi --------------------------------------- ,,rhins ,,of #aej #ee #da #f #bi #ahbe ,,islay --------------------------------------- ,,mull ,,of #big #ee #a #e #di #aghg ,,kintyre --------------------------------------- ,,pladda #gg #ee #bf #e #g #agij #acj --------------------------------------- ,,corsewall #aab #ee #a #e #i #ahag --------------------------------------- ,,loch ,,ryan #cj #ed #eh #e #b #ahdg --------------------------------------- ,,mull ,,of #cbe #ed #ch #d #ea #ahcj ,,galloway --------------------------------------- ,,little ,,ross #age #ed #df #d #e #ahdc --------------------------------------- ,,point ,,of #ajf #ed #be #d #bb #ahah ,,ayre --------------------------------------- ,,calf ,,of ,,man #bge #ed #c #d #di #ahah #cfh --------------------------------------- #hi ,at ,hynish ,point in ,tyree ,island1 two fixed ,lights are shewn from the ,pier1 but ,,only when the ,vessel which attends the ,lighthouse is expected to enter the ,dock at ,hynish4 ,in the ,trinity ,house ,chart1 ,skerryvore ,light is erroneously described as 8,intermittent40 ,,beacons ,,and ,,buoys4 ,,frith ,,of ,,forth ,,district4 ---------------------------------------- ------------------------- ,depth at ,low ,water of ,bearings of ,marks and of ,lines ,name of ,description ,spring of ,intersection ,meeting at ,station4 of ,mark4 ,tides4 the ,station4 ---------------------------------------- ------------------------- ,,middle ,,bank1#f ,feet ,buoy1#c ,,alloa ,,tower in line with the ,,west ,,end1 ,red4 ,feet4 ,centre of ,,clackmannan ,,pier-- ,,buoy4 ,bearing ,n4 by ,e4 ,,clackmannan ,,church ,,spire in line with ,,high ,,chimney-,,stack of ,,park-,,farm ,,house--,bearing ,,ne4 ,e4 ,,middle ,,bank ,,buoy1 ,east ,end-- ,bearing ,,se4 by ,s4 ---------------------------------------- ------------------------- ,,middle ,,bank1#f ,feet ,buoy1#d ,feet4 ,,tullyallan ,,house in line with ,,east ,,end1 ,red4 ,,tullyallan ,,old ,,church ,,spire1 in ,,buoy4 ruins--,bearing ,,ese4 ,s4 ,remarkable ,,clump of ,,trees on distant high land in line with ,,airth ,,church ,,spire--,bearing ,w4 by ,n4 ,n4 ,,buoy off ,,inch ,,brake ,,rock--,bearing ,s4 by ,e4 ---------------------------------------- ------------------------- ,,inch ,,brake #f ,feet ,buoy1#e ,feet4 ,,flagstaff on the ,,ferry ,,pier1 ,,buoy4 ,black4 ,,kincardine1 clear outside of ,,kincardine ,,stone ,,pier--,bearing ,n4 by ,e4 ,,alloa ,,church ,,spire in line with ,south ,corner of ,,kennet ,,pans ,,distillery ,,garden ,,wall--,bearing ,n4 by ,w4 ,,long ,,annat ,,buoy--,bearing ,,sse4 ,e4 ---------------------------------------- ------------------------- ,,long ,,annat #f ,feet ,buoy1#i ,feet4 ,,sands ,,house1 ,west ,wing1 in line ,,buoy4 ,black4 with ,,west ,,face of ,,annat ,,quarry-- ,bearing ,,nne4 ,e4 ,,binns ,,monument in line with the ,middle of ,,bo',,ness ,,pier--,bearing ,,se4 by ,s4 ,,hen and ,,chicken',s ,,buoy--,bearing ,,se4 by ,e4 ,s4 ---------------------------------------- ------------------------- ,,hen ,,and #f ,feet ,buoy1#ab ,feet4,the ,east ,wing of ,,culross ,,abbey in ,,chicken',s ,black4 line with ,eastmost ,house in ,,buoy4 ,,culross ,,village--,bearing ,,nne4 ,e4 ,,airth ,,castle1 in line with ,,high-,,water ,,mark on ,,long ,,annat ,,point--,bearing ,,nw4 ,w4 ,,buoy on ,east ,end of ,,dods' ,,bank-- ,bearing ,,sse4 ,e4 ---------------------------------------- ------------------------- ,,dods' ,,bank #g ,feet ,buoy1#ae ,feet4,,berry-,,law ,,trees in line with the ,,buoy4 ,red4 ,,chimney-,,stack of ,,bunyan',s ,,farm-- ,bearing ,e4 by ,n4 ,,chimney ,,stack of the ,,snub ,,coal ,,pit 7the first ,stack ,west of ,kinneil ,new ,iron ,works71 in line with the ,,west ,,pier ,,wall of ,,bo',,ness--,bearing ,,wsw4 ,w4 ,,comary ,,house1 ,east ,wing1 in line with the ,west ,wing of the ,,factor',s ,,house--,bearing ,n4 by ,e4 ,e4 ,,valleyfield ,,house1 a little ,east of the ,eastern ,house on ,,preston ,,island1 about half-way between the house and where the ,island dries at half-tide--,bearing ,n4 by ,e4 ,e4 ,the ,buoy of ,,hen and ,,chicken',s ,,rock--,bearing ,,nnw4 ,w4 ---------------------------------------- ------------------------- ,,beamer ,painted ,rock ,dry,,bo',,ness ,,pier--,bearing ,,nw4 by ,w4 ,,beacon4 ,black1 with at ,low ,spherical ,water4 ,,charleston ,,pier1 ,outer ,end-- ,ball at top4 ,bearing ,,nw4 by ,n4 ,south-,west ,extremity of the ,point at ,,north ,,queensferry--,bearing ,,ese4 ,e4 ,the ,,halls1 or principal ,,south ,,queensferry ,,pier--,bearing ,,sse4 ,e4 ---------------------------------------- ------------------------- ,,drum ,,sand #g ,feet ,buoy1#ab ,feet4,,newbigging ,,house in line with ,,east ,,buoy4 ,red4 ,east ,edge of ,,carcraig ,,rock-- ,bearing ,,ne4 ,e4 ,,oxscare ,,beacon--,bearing ,e4 ,n4 ,,inchkeith ,,lighthouse--,bearing ,,ese4 ,e4 ,highest ,point of ,,arthur',s ,,seat in line with ,,nelson',s ,,monument--,bearing ,s4 by ,e4 ,e4 ---------------------------------------- ------------------------- ,,drum ,,sand #h ,feet ,buoy1#c ,,south ,,point of ,,inchkeith in line ,,west ,,buoy4 ,red1 with ,fathoms4with ,,centre of ,,opening of ,,mickery ,fenders4 ,,stone--,bearing ,,ese4 ,e4 ,,inchkeith ,,lighthouse--,bearing ,,ese4 ,e4 ,,fordel ,,house in line with ,,centre of ,,donibristle ,,house--,bearing ,n4 ,e4 ,,chimney-,,stack of ,,castle ,,landhill ,,farm-,,house in line with ,,end of ,,lazarett ,,pier--,bearing ,,nw4 ,n4 ---------------------------------------- ------------------------- ,,oxscare ,painted ,red1,rock ,dry,south ,point of ,,carlin',s ,,nose-- ,,beacon4 with ,flat at ,low ,bearing ,w4 ,n4 ,cone at top4,water4 ,,burntisland ,,pier--,bearing ,,ene4 ,extremity of ,,kinghornness-- ,bearing ,e4 ,n4 ,,inchkeith ,,lighthouse--,bearing ,,ese4 ,e4 ,,martello ,,tower--,bearing ,,sse4 ,e4 ,,granton ,,pier--,bearing ,s4 by ,e4 ,e4 ---------------------------------------- ------------------------- ,,west ,,gunnet #h ,feet ,buoy1#c ,,nelson',s ,,monument just clear ,east ,,buoy4 ,white4 ,fathoms4of ,,north ,,leith ,,church ,,spire-- ,bearing ,,ssw4 ,,north ,,berwick ,,law in line with ,north ,end of ,,long ,,craig--,bearing ,,ese4 ,e4 ,,clump of ,,trees ,east of ,,grange ,,house in line with ,,burntisland ,,church ,,spire--,bearing ,n4 ,w4 ,,inchkeith ,,lighthouse--,bearing ,e4 ,s4 ---------------------------------------- ------------------------- ,,east ,,gunnet #h ,feet ,buoy1#c ,,notch at the foot of ,east ,brow of ,,buoy4 ,white4 ,fathoms4the ,,pentland ,,hills in line with ,,north ,,leith ,,church ,,spire--,bearing ,,ssw4 ,w4 ,,carlin',s ,,nose clear of the ,north ,side of ,,mickery ,,stone--,bearing ,,wnw4 ,w4 ,,kinghorn ,,new ,,free ,,church in line with ,,kinghornness--,bearing ,,ne4 by ,n4 ,,inchkeith ,,lighthouse--,bearing ,e4 ---------------------------------------- ------------------------- ,,pallas ,,buoy4#g ,feet ,buoy1#c ,,kinghorn ,,free ,,church in line with striped ,fathoms4,,swan',s ,,factory--,bearing ,n4 by ,e4 ,white and ,e4 ,black hori- zontally4 ,north ,brow of ,,inchkeith in line with the ,centre of ,,silly ,,carr ,,rock--,bearing ,,ene4 ,n4 ,,assembly ,,hall ,,spire1 ,,edinburgh1 in line with ,,martello ,,tower-- ,bearing ,,sw4 ,s4 ,,inchkeith ,,lighthouse--,bearing ,,ene4 ,e4 ---------------------------------------- ------------------------- ,,herwit ,,buoy4#h ,feet ,buoy1#d ,east ,brow of ,,pentland ,,hills1 ,black4 ,fathoms4touching ,west ,brow of ,,arthur',s ,,seat 7half way up7--,bearing ,,sw4 ,w4 ,east ,stables 7,red-tiled ,house7 of ,,pettycur in line with ,east ,brow of ,,inchkeith--,bearing ,n4 by ,w4 ,,inchkeith ,,lighthouse--,bearing ,n4 by ,w4 ,w4 ---------------------------------------- ------------------------- ,,craig ,,waugh #h ,feet ,buoy1#d ,,pettycur ,,pier in line with ,,buoy4 ,red4 ,fathoms4,eastern ,brow of ,,inchkeith-- ,bearing ,n4 by ,w4 ,w4 ,,assembly ,,hall ,,spire just clear1 ,west of ,,nelson',s ,,monument-- ,bearing ,w4 ,s4 ,,inchkeith ,,lighthouse--,bearing ,n4 by ,w4 ,w4 ---------------------------------------- ------------------------- ,,north ,,craig #ab ,feet ,mast#c ,,nelson',s ,,monument in line with ,,mast ,,buoy4 ,buoy1 ,fathoms4,west ,wing of ,,leith ,,baths--,bearing ,chequered ,,wsw4 ,w4 ,red and ,white4 ,summit of ,,east ,,lomond ,,hill in line with ,,big ,,house ,,trees-- ,bearing ,n4 ,e4 ,,carlin',s ,,nose in line with ,centre of ,,mickery ,,stone--,bearing ,,wnw4 ---------------------------------------- ------------------------- ,,west #f ,feet ,buoy1#c ,,dysart ,,coal-,,pit ,,chimney-,,stack in ,,rock-,,head1 ,red4 ,fathoms4line with ,,middle of ,,gable of ,,pan ,,off ,,dysart1 ,,hall ,,house--,bearing ,n4 ,e4 ,,buoy4 ,,north ,,end of ,,portbrae ,,church1 ,,kirkcaldy1 just clear of the ,,end of ,,kirkcaldy ,,pier--,bearing ,,wnw4 ,w4 ,,inchkeith ,,lighthouse--,bearing ,,sw4 by ,s4 ,n4,b4--,the highest part of the ,rock bearing ,n4 ,e4 distant about one-half cable's length from ,buoy4 ---------------------------------------- ------------------------- ,,east #f ,feet ,buoy1#c ,,wemyss ,,old ,,castle in line with ,,rock-,,head1 ,black4 ,fathoms4,,southern ,,houses of ,,east ,,wemyss-- ,,off ,,dysart1 ,bearing ,,ne4 by ,e4 ,e4 ,,buoy4 ,,east ,,wing of ,,dysart ,,church in line with ,,town-,,house ,,steeple-- ,bearing ,,nnw4 ,w4 ,,buoy on ,,west ,,rock-,,head--,bearing ,w4 by ,n4 ,n4 ,,inchkeith ,,lighthouse--,bearing ,,sw4 ,s4 ,n4,b4--,the highest part of ,rock1 bearing ,,nw4 ,w41 distant about two cables' lengths4 ---------------------------------------- ------------------------- ,,east ,,vows ,pyramid of ,rock ,dry,,ruins on ,,chapelness--,bearing ,n4 ,,rock1 ,iron ,pil- at ,low ,e4 ,,beacon1 ,,off lars1 with ,water4 ,,elie4 open ,cylin- ,,north ,,end of ,,elie ,,pier--,bearing dric ,cage on ,e4 ,n4 top1 painted ,,extremity of ,,elieness--,bearing ,e4 ,red4 by ,s4 ,s4 ,,isle of ,,may ,,lighthouse--,bearing ,,ese4 ,s4 ,,west ,,vows ,,rock--,bearing ,,wnw4 ,n4 distant mile4 ,,buoy on ,,thill ,,rock--,bearing ,,ese4 ,s4 distant two cables' lengths4 ---------------------------------------- ------------------------- ,,thill ,,rock #g ,feet ,buoy1#c ,,west ,,end of ,,millhouse ,,cottage in ,,buoy4 ,black4 ,fathoms4line with ,,north ,,end of ,,elie ,,pier --,bearing ,,ne4 ,,pettie ,,law in line with ,,west ,,chimney-,,stack of ,,david ,,ovenstone',s ,,house--,bearing ,n4 ,w4 ,,ruin on ,,chapelness--,bearing ,,nnw4 ,w4 ,,beacon on ,,east ,,vows ,,rock--,bearing ,,wnw4 ,n4 ,n4,b4--,the ,buoy lies about #ce fathoms to the ,,sse4 of the highest part of the ,rock4 ---------------------------------------- ------------------------- ,,south ,,carr ,painted ,red1,rock ,dry,,cairn on ,,bass ,,rock--,bearing ,n4 by ,,beacon4 with ,cross at ,low ,e4 at top4 ,water4 ,,isle of ,,may ,,lighthouse--,bearing ,,ne4 ,,dunbar ,,church ,,tower--,bearing ,,sse4 ,s4 ,,oldham ,,farm-,,house ,,chimney-,,stack-- ,bearing ,w4 ,n4 ---------------------------------------- ------------------------- ,,north ,,carr ,beacon of ,rock ,dry#a ,mile from ,,fifeness--,bearing ,,beacon4 ,stone1 with at ,low from ,,isle of ,,may ,,light ,,nne4 ,iron ,frame ,water4 distant #f ,nautic ,miles4 and ,ball4 ---------------------------------------- ------------------------- ,,beacons ,,and ,,buoys4 ,,district ,,of ,,friths ,,of ,,moray1 ,,cromarty1 ,,inverness1 ,,and ,,dornoch4 ---------------------------------------- ------------------------- ,depth at ,low ,water of ,magnetic ,bearings of ,marks and ,name of ,description ,spring of ,lines of ,intersection ,station4 of ,mark4 ,tides4 ,meeting at the ,station4 ---------------------------------------- ------------------------- ,,covesea ,pyramid of ,rock dry,,covesea ,,skerries ,,lighthouse on ,,skerries ,iron ,pil- at ,low the neighbouring land of ,,beacon4 lars1 with water4 ,,craighead--,bears ,,wsw4 ,w4 open cylin- distant one mile4 dric ,cage1 and a ,cross1 rising to the height of about #ej feet above ,high water4 ---------------------------------------- ------------------------- ,,longman ,cone of ,iron,beach ,,end of ,,kessock ,,south ,,pier-- ,,point ,plates ,dry at ,bearing ,w4 by ,n4 ,n4 ,,beacon4 painted ,low ,black4 water of,,craigtown ,,point--,bearing ,,nw4 ,spring ,w4 ,tides4 ,,meiklemee1 ,,east ,,end ,,buoy--,bearing ,e4 ,n4 ,,bogbain ,,house in line with ,,rigmore ,,house--,bearing ,s4 ,e4 ,,end of ,,longman ,,point--,bearing ,n4 ,w4 distant #dj ,fathoms4 ---------------------------------------- ------------------------- ,,meiklemee #f ,feet ,buoy4#ab ,feet4,,park',s ,,farm-,,house in line with ,,bank ,,buoy4 ,,black4 ,,rigmore ,,house--,bearing ,,ssw4 ,east ,end4 ,middle of space between the ,houses of ,,scorguoy ,,farm-,,yard in line with ,,black ,,mill ,,chimney-- ,bearing ,w4 ,s4 ,,chanonry ,,point ,,lighthouse-- ,bearing ,,ene4 ,e4 ---------------------------------------- ------------------------- ,,middle ,,bank #f ,feet ,buoy4#ab ,feet4,,scorguoy ,,farm-,,yard 7,south ,end71 ,,buoy4 ,black4 in line with ,,black ,,mill ,,chimney-- ,east ,end4 ,bearing ,w4 ,s4 ,,round ,,clump of ,,trees1 ,north of ,,ley',s ,,house1 in line with ,,rigmore ,,house--,bearing ,,sw4 ,s4 ,,chanonry ,,point ,,lighthouse-- ,bearing ,,ene4 ,,meiklemee ,,bank ,,buoy--,bearing ,w4 ,s4 ---------------------------------------- ------------------------- ,,petty ,,bank #f ,feet ,buoy4#ab ,feet4,,dalcross ,,castle in line with ,,buoy4 ,,chequered ,,fishtown ,,farm-,,house--,bearing ,,se4 ,north or ,black and ,s4 ,outer ,edge4 ,white4 ,,extremity of ,,east ,,suter in line with ,,store-,,house1 ,,chanonry ,,point --,bearing ,,ene4 ,n4 ,,munlochy ,,buoy--,bearing ,n4 ---------------------------------------- ------------------------- ,,munlochy #f ,feet ,buoy4#ab ,feet4,,west ,,wing of ,,avoch ,,house1 now in ,,buoy4 ,black4 ruins1 in line with the most ,,western ,,slated ,,house or ,,cottage in ,,avoch--,bearing ,n4 ,w4 ,,north ,,end of ,,fort-,,george in line with ,,chanonry ,,point--,bearing ,,ene4 ,e4 ---------------------------------------- ------------------------- ,,skate ,,bank #f ,feet ,buoy4#ab ,the ,,east ,,wing of ,,kincurdie ,,house ,,buoy4 ,black4 ,feet4 in line with ,,spire of ,,rosemarkie ,east ,end4 ,,kirk--,bearing ,,nne4 ,e4 ,,flagstaff of ,,fort-,,george in line with the ,,outer ,,end of ,,chanonry ,,pier--,bearing ,,ene4 ,e4 ,,dalcross ,,castle in line with ,,cottage on ,,sea-,,cliff--,bearing ,s4 ,e4 ,,munlochy ,,buoy--,bearing ,,wsw4 ,w4 ---------------------------------------- ------------------------- ,,craigmee ,,or #f ,feet ,buoy4#b ,,high ,,part1 or ,,west ,,brow of ,,fort-,,george ,chequered ,fathoms4 ,,altarlie ,,point1 in line with ,,bank ,,buoy4 ,black and ,,chanonry ,,point ,,lighthouse-- ,white4 ,bearing ,,sw4 ,w4 ,,patch of ,,trees at ,west ,end of ,,broomhill ,,wood1 called ,,broomhill ,,bush1 in line with ,,platcock ,,house--,bearing ,,wnw4 ,w4 ---------------------------------------- ------------------------- ,,riff ,,bank #f ,feet ,buoy4#c ,,craighead ,,farm-,,house in line ,,buoy4 ,black4 ,fathoms4 with the most ,,western of the ,west ,end4 ,,three ,,burns--,bearing ,n4 by ,e4 ,e4 ,,broomhill ,,bush 7,east ,end7 in line with the ,,manse of ,,rosemarkie--,bearing ,w4 ,n4 ,,chanonry ,,point ,,lighthouse-- ,bearing ,,wsw4 ,s4 ---------------------------------------- ------------------------- ,,riff ,,bank #f ,feet ,buoy4#c ,,three remarkable ,,trees at ,,north ,,buoy4 ,black4 ,fathoms4 ,,end of ,,craigie ,,wood1 in line ,,middle ,,or with ,,rosemarkie ,,manse--,bearing ,north ,angle4 ,w4 ,s4 ,,gamekeeper',s ,,house at ,end of ,,wood in line with ,,cave on ,,sea-,,shore1 a little ,,east of the ,,three ,,burns--,bearing ,,nw4 ,w4 ,,chanonry ,,point ,,lighthouse-- ,bearing ,,wsw4 ,s4 ---------------------------------------- ------------------------- ,,riff ,,bank #ab ,feet #d ,,castle ,,craig ,,rock in line with ,,buoy4 ,mast-,buoy4 ,fathoms4 ,,stack ,,rock at foot of ,,west ,,suter ,east ,end4 ,black4 --,bearing ,n4 by ,e4 ,e4 ,,store-,,house on ,,chanonry ,,point1 shut in by the ,,north corner of ,,fort-,,george1 and in line with ,,lower part of ,,south ,,brow of ,,ord ,,hill--,bearing ,w4 ,s4 ,,towrie ,,lumb ,,wood in line with ,,craigie ,,wood 7,south ,end7-- ,bearing ,w4 ---------------------------------------- ------------------------- ,,whitenness -- -- -- ,,beacon4 7,in prepara- tion47 ---------------------------------------- ------------------------- ,,navity ,,bank #f ,feet ,buoy4#b ,,trees at end of ,,navity ,,buoy4 ,chequered ,fathoms4 ,,farm-,,house in line with ,,east ,south ,edge4 ,black and ,,bank or ,,cliff of ,,craighouse ,,burn ,white4 --,bearing ,n4 ,e4 ,,extremity of ,,wood on ,,brow of ,,east ,,suter in line with ,lower part of ,,brow of ,,west ,,suter-- ,bearing ,,ne4 by ,e4 ,,chanonry ,,point ,,lighthouse-- ,bearing ,,sw4 by ,w4 ,,riff ,,bank ,,mast ,,buoy--,bearing ,,se4 ,e4 ---------------------------------------- ------------------------- ,,nigg ,,sands #f ,feet ,buoy4#b ,,cromarty ,,gaelic ,,kirk ,,steeple in ,,buoy4 ,black4 ,fathoms4 line with ,,east ,,wing of ,,hotel-- ,east ,end4 ,bearing ,s4 ,e4 ,,face of ,,east ,,suter apparently on a line halfway between ,,ferryhouse and ,,stable--,bearing ,,se4 by ,e4 ---------------------------------------- ------------------------- ,,nigg ,,sands #f ,feet ,buoy4#a ,,farm-,,house of ,,dalney in line ,,buoy4 ,black4 ,fathoms4 with the ,,pigeon-,,house ,east of ,west ,end4 ,,ballintrade--,bearing ,,nne4 ,e4 ,,extremity of ,,west ,,suter in line with ,,cromarty ,,lighthouse-- ,bearing ,,se4 ,e4 ---------------------------------------- ------------------------- ,,newhall #f ,feet ,buoy4#b ,,priesthill ,,farm-,,house in line ,,bank ,,buoy4 ,,chequered ,,fathoms4 with ,,easternmost ,,house in ,east ,end4 ,black and ,,ballintrade--,bearing ,,nne4 ,e4 ,white4 ,,east ,,brow of ,,west ,,suter in line with ,,cromarty ,,gaelic ,,kirk-- ,bearing ,,ese4 ,s4 ,,nigg ,,sands ,,west ,,buoy--,bearing ,,ene4 ,n4 ---------------------------------------- ------------------------- ,,three ,,kings #h ,feet ,buoy4#g ,,eastern ,,trees upon ,top of the ,,rocks ,,buoy4 ,red4 ,fathoms4 ,,high ,,land1 being the most projecting and highest part of ,,sea ,,cliff1 ,west of ,,gilliam ,,burn1 in line with the ,,highest ,,eastern part of ,,three ,,kings ,,rock-- ,bearing ,,wnw4 ,n4 ,,duke of ,,sutherland',s ,,monument in line with ,,west ,,end of ,,long ,,storehouse in ,,shandwick--,bearing ,n4 by ,e4 ,e4 ---------------------------------------- ------------------------- ,,culloden #h ,feet ,buoy4#h ,,brucefield ,,farm-,,house in line ,,rock ,,buoy4 ,,black4 ,,fathoms4 with ,,tarbetness ,,lighthouse ,,flag-,,staff--,bearing ,,wsw4 ,w4 ,,duke of ,,sutherland',s ,,monument in line with ,lower ,corner of ,,wood farthest ,west from ,,dunrobin ,,castle--,bearing ,,nnw4 ---------------------------------------- ------------------------- ,,fairway #ab ,feet ,mast#e ,,west ,,end of ,,bentavie ,,hill in ,,buoy ,,off ,buoy4 ,red4 ,fathoms4 line with ,,trentham ,,farm-,,house-- ,,tain ,,bar4 ,bearing ,,nnw4 ,w4 ,,west ,,brow of ,,east ,,suter in line with ,,meiklerennie ,,farm-,,house-- ,bearing ,,sw4 ,w4 ,,tarbetness ,,lighthouse--,bearing ,,se4 ,e4 ---------------------------------------- ------------------------- ,,tain ,,bar #f ,feet ,buoy4#b ,,remarkable ,,hollow or ,,notch in ,,inner ,,buoy4 ,black4 ,fathoms4 ,,high ,,land ,east of ,,east ,,suter1 in ,,north ,,side4 line with ,,lochslain ,,castle-- ,bearing ,,ssw4 ,w4 ,,lower ,,west ,,brow of ,,cambusmore ,,hill in line with ,,east ,,end of ,,west ,,embo ,,wood--,bearing ,n4 by ,w4 ,w4 ,,tarbetness ,,lighthouse--,bearing ,,ese4 ,s4 ,,fairway ,,buoy off ,,tain ,,bar-- ,bearing ,e4 ,s4 ---------------------------------------- ------------------------- ,,tain ,,bar #f ,feet ,buoy4#d ,,remarkable ,,hollow or ,,notch in ,,inner ,,buoy4 ,chequered ,fathoms4 ,,high ,,land ,,east of ,,east ,,suter in ,,south ,,side4 ,,black ,,and line with ,,meiklerennie ,,farmhouse ,white4 --,bearing ,,ssw4 ,w4 ,,west ,,end of ,,east ,,embo ,,wood in line with ,,embo ,,farmhouse-- ,bearing ,n4 ,w4 ,,fairway ,,buoy off ,,tain ,,bar-- ,bearing ,e4 ,n4 ,,tain ,,bar ,,inner ,,buoy 7,north ,side7 --,bearing ,,ene4 ,n4 ,,dornoch ,,spire--,bearing ,,nnw4 ,w4 ---------------------------------------- ------------------------- ,,beacons ,,and ,,buoys4 ,,frith ,,of ,,clyde ,,district4 ---------------------------------------- ------------------------- ,depth at ,low ,water of ,bearings of ,marks and of ,lines ,name of ,description ,spring of ,intersection ,meeting at ,station4 of ,mark4 ,tides4 the ,station4 ---------------------------------------- ------------------------- ,,fullarton #g ,feet ,buoy4#c ,,clump of ,,trees at ,east side of ,,rock ,,buoy4 ,,red4 ,,fathoms4,,clachlan ,,farm1 just opening from the ,,west ,,brow of ,,holy ,,island-- ,bearing ,n4 by ,e4 ,standing ,stone upon ,,kinross ,,point --,bearing ,w4 ,buoy moored upon ,,ese4 ,tail of ,rock4 ,the shallowest part of ,rock has #h ,feet at ,low water of ,spring ,tides4 ---------------------------------------- ------------------------- ,,arranman',s #h ,feet ,buoy4#h ,west ,end of ,,arranman',s ,,barrels ,,barrels ,red4 ,fathoms4,,shoal--,bearing ,w4 by ,n4 ,,rocks ,,buoy4 ,north-,east ,extremity of ,shoal-- ,bearing ,n4 ,e4 ,,ballyshare ,,house in line with the ,lower ,east ,end of ,,dunacreein ,,rock --,bearing ,,nw4 ,w4 ,the ,buoy is moored abreast of the middle of the ,shoal1 and is distant from the ,low water ,rocks about half a cable's length4 ---------------------------------------- ------------------------- ,,otterard #h ,feet ,buoy4#c ,,clump of ,,trees at ,,ballaminich ,,rock ,,buoy4 ,black4 ,fathoms4,,farm-,,house in line with the lower part of the ,south-eastern ,brow of ,,island ,,davaar--,bearing ,,sw4 ,w4 ,the remarkable ,notch in distant ,hill called ,,balavilan1 in line with ,north ,end of ,green ,patch on the rising ground in ,field south of ,long ,dyke near ,,smerby ,,farm-,,house--,bearing ,,wnw4 ,n4 ,,macrinnan',s ,,point--,bearing ,,wsw4 ,w4 ,the ,buoy is moored upon ,,ese4 ,tail of ,rock4 ,the shallowest part of ,rock at ,low water of ,springs has #ab ,feet4 ---------------------------------------- ------------------------- ,,millbeg ,,bank#f ,feet ,buoy4#b ,,campbelton ,,town-,,house ,,spire in ,,buoy4 ,black4 ,fathoms4line with ,house in ruins on ,,trench ,,point--,bearing ,,wnw4 ,,crossbeg ,,farm-,,house in line with ,lower part or ,mouth of ,,porter',s ,,glen--,bearing ,n4 ,w4 ---------------------------------------- ------------------------- ,,campbelton #f ,feet ,buoy4#b ,west ,corner of ,,gaelic ,,church in ,,harbour ,red4 ,fathoms4line with ,,trench ,,point--,bearing ,,outer ,,buoy4 ,w4 by ,n4 ,n4 ,west ,end of ,,baraskie ,,farm-,,house 7dwelling-house7 in line with ,angle of ,plantation1 and also with the ,corner of the ,second ,field to the ,south of the ,house-- ,bearing ,n4 ,e4 ---------------------------------------- ------------------------- ,,campbelton #f ,feet ,buoy4#a ,,castle ,,hill ,,church in line with ,,harbour ,black4 ,fathoms4high water-mark on ,,trench ,,point ,,inner ,,buoy4 --,bearing ,,wnw4 ,w4 ,north ,end of ,higher ,,glenremisdil ,,farm-,,house in line with ,cottage at ,east ,end of ,,hetly ,,house-- ,bearing ,,sw4 ,s4 ---------------------------------------- ------------------------- ,,millmore ,pyramid of ,beach ,,campbelton ,,north ,,pier-,,head-- ,,beacon4 ,iron ,spars dry at ,bearing ,,nw4 by ,w4 with ,wire ,low ,ball on top4water4 ,,macrinnan',s ,,point--,bearing ,,ene4 ,n4 ---------------------------------------- ------------------------- ,,trench ,,point,pyramid of ,beach ,,campbelton ,,north ,,pier-,,head-- ,,beacon4 ,iron ,spars dry at ,bearing ,,nw4 by ,w4 with ,wire ,low ,ball on top4water4 ,,outer or ,,red ,,buoy 7above described7--,bearing ,,ese4 ,e4 ---------------------------------------- ------------------------- ,,lappock ,tower with ,rock dry,,troon ,,harbour ,,light--,bearing ,s4 ,,beacon4 ,stone ,ball at ,low by ,w4 ,w4 on top1 water4 painted ,red4 ,,beacon on ,,lady ,,isle--,bearing ,,sw4 ,w4 ,,extremity of ,,ardrossan ,,pier-- ,bearing ,,nnw4 ,w4 ---------------------------------------- ------------------------- ,,breast ,,rock ,pyramid of ,rock dry,,turnberry ,,point--,bearing ,,ne4 by ,,beacon4 ,iron ,pil- at ,low ,n4 ,e4 lars1 with water4 cylindric ,,pladda ,,lighthouse--,bearing ,,nnw4 open ,cage1 painted ,red4 ,,ailsa ,,craig 7,highest ,point7-- ,bearing ,w4 ---------------------------------------- ------------------------- ,,loch ,,ryan #g ,feet ,buoy4#c ,mr ,,moore',s ,,pigeon-,,house in line ,,inner ,,buoy4 ,red4 ,fathoms4with ,angle of ,plantation lying to the ,north of ,,corsewall ,,house-- ,bearing ,n4 by ,w4 ,w4 ,east ,end of ,,cairn ,,ryan ,hill ,quarry1 and ,east ,end of ,plantation1 at the foot of the same hill1 in line with ,north ,chimney of ,,mrs ,,begg',s ,,inn1 ,,cairn ,,ryan ,,village--,bearing ,,ne4 ,n4 ,,north ,,end of ,,stranraer ,,pier-- ,bearing ,,ssw4 ,w4 ---------------------------------------- ------------------------- ,,beacon ,,on ,cone of ,iron,dry at ,,loch ,,ryan ,,lighthouse--,bearing ,,the ,,spit ,,of ,plates1 ,low ,,nne4 ,e4 ,,scar ,,point1 painted ,red4water4 ,,off ,,kirkcolm ,,lochnoll ,,houses--,bearing ,,se4 by ,,point1 ,,in ,e4 ,,loch ,,ryan4 ,,stranraer ,,pier ,,end--,bearing ,,ssw4 ,w4 ,,waukmill ,,houses--,bearing ,,sw4 by ,w4 ,,corsewall ,,house in line with ,,the ,,scar ,,off ,,kirkcolm ,,point--,bearing ,,nnw4 ,n4 ---------------------------------------- ------------------------- ,,loch ,,ryan #g ,feet ,buoy1#c ,,portincally ,,farm-,,house in line ,,outer ,,buoy4 ,black4 ,fathoms4with the ,brow of ,,clachan ,,head-- ,bearing ,,nnw4 ,w4 ,mr ,,charles ,m#8,,donald',s ,,house in line with the ,south ,end of ,,general ,,wallace',s ,,porter',s ,,lodge --,bearing ,,se4 ---------------------------------------- ------------------------- ,,laggan1 ,,or ,pyramid of ,rock dry,,corsewall ,,lighthouse--,bearing ,,ne4 ,,ebbstone ,iron,pillars1at ,low by ,e4 ,,rock ,,beacon4with water4 cylindric ,,ailsa ,,craig 7,highest ,point7-- ,open ,cage on ,bearing ,,ne4 ,n4 top1 painted ,red4 ,,laggan ,,point--,bearing ,,sse4 ,e4 ---------------------------------------- ------------------------- ,,beacons ,,and ,,buoys4 ,,loch ,,fyne ,,district4 ---------------------------------------- ------------------------- ,depth at ,low ,water of ,magnetic ,bearings of ,marks and ,name of ,description ,spring ,lines of ,intersection ,station4 of ,mark4 ,tides4 ,meeting at the ,station4 ---------------------------------------- ------------------------- ,,off #h ,feet ,buoy4#b ,,south-,,west ,,extremity of ,,west and ,,ardlamont ,red4 ,fathoms4,,eastern ,,hills upon ,,ardlamont ,,point ,,or ,,point in line with ,,extremity of ,,bradeich ,,point--,bearing ,,nw4 ,w4 ,,rocks1 ,,argyleshire1 ,,highest ,,part of ,,bradeich ,,rocks-- ,,buoy4 ,bearing ,,nnw4 ,w4 ,,south ,,end of ,,inchmarnock ,,island-- ,bearing ,s4 ,w4 ,,extremity of ,,land ,,south of ,,ardlamont ,,point--,bearing ,n4 by ,w4 ,the ,buoy lies about #aae fathoms distant from ,high water-mark upon the ,point1 and about #de fathoms from the highest part of ,bradeich ,rocks4 ,n4,b4--,there is a small ,rock which dries at ,low ,spring ,tides1 about #aj or #ab fathoms outside of the highest main ,rock4 ---------------------------------------- ------------------------- ,,skerna #g ,feet ,buoy4#b ,,south ,,wing of ,sir ,,john ,,ord',s ,,scallaig ,red4 ,fathoms4,,stables in line with ,,north ,,rock1 ,,off ,,extremity of ,,dunchoan ,,island-- ,,entrance ,,to ,bearing ,,ne4 by ,e4 ,,crinan ,,canal1 ,,silver ,,craig',s ,,point1 ,,island ,,argyleshire1 ,,more--,bearing ,,se4 by ,s4 ,e4 ,,buoy4 ,,west ,,wing of ,,ardrishaig ,,hotel in line with ,,lighthouse upon ,,end of ,,ardrishaig ,,pier--,bearing ,n4 ,e4 ,n4,b4--,the ,buoy lies upon the ,south-,west tail of the ,shoal or ,rock4 ---------------------------------------- ------------------------- ,,otter ,,bank ,conical ,iron,gravel ,,auchabolonabaith ,,house 7,east ,,beacon1 ,beacon4 ,beach4 ,wing7 in line with ,,centre of ,,off ,,entrance,to be ,dry at ,,cottage--,bearing ,n4 by ,w4 ,w4 ,,to ,,loch painted ,low ,,fyne1 ,black4 water4 ,,strathlachlan ,,hill in line with ,,argyllshire4 ,,schoolhouse ,,point--,bearing ,,ene4 7,building47 ,,end ,,of ,,liath ,,island--,bearing ,w4 ,s4 ---------------------------------------- ------------------------- ,,west ,,otter ,conical ,iron,gravel ,,end of ,,minard ,,point--,bearing ,,sw4 ,,beacon1 ,beacon4 ,beach4 by ,w4 ,w4 ,,off ,,castle ,to be ,dry at ,,lachlan1 painted ,low ,,end of ,,chapel ,,island--,bearing ,,loch ,,fyne1 ,black4 water4 ,,ene4 ,e4 ,,argyleshire4 7,building47 ,,barneycarry ,,farmhouse in line with ,,north-,,east ,,end of ,,hugh ,,island--,bearing ,,se4 ,e4 ---------------------------------------- ------------------------- ,,beacons ,,and ,,buoys4 ,,oban ,,bay1 ,,argyleshire4 ---------------------------------------- ------------------------- ,depth at ,low ,water of ,magnetic ,bearings of ,marks and ,name of ,description ,spring ,lines of ,intersection ,station4 of ,mark4 ,tides4 ,meeting at the ,station4 ---------------------------------------- ------------------------- ,,skerrat #aj ,feet ,dry at ,,centre of ,,oban ,,free ,,church ,,window ,,rock4 ,buoy1 with ,low- in line with ,,north-,,eastern ,s4 ,w4 ,end4 ,fenders4 water of,,chimney of ,,freemason',s ,,hall-- ,,red4 ,spring ,bearing ,,se4 by ,e4 ,tides4 ,,centre ,,of ,,skerry ,,dhu or ,,black ,,rock 7apparently in middle of ,sound of ,kerrera7 in line with ,,ardincaple ,,point--,bearing ,,wsw4 ,,buoy on ,,north-,,eastern ,,end of ,,skerrat ,,shoal--,bearing ,,ne4 ,e4 distant #aje fathoms4 ---------------------------------------- ------------------------- ,,skerrat #f ,feet ,buoy4#ab ,feet ,,oban ,,free ,,church ,,steeple in line ,,shoal1 ,chequered at ,low with ,,south ,,chimney ,,top of ,,spring ,n4 ,e4 ,end4 ,black and water of,,well ,,cottage--,bearing ,,se4 ,white4 ,spring ,tides4 ,,ardincaple ,,point1 a little ,west of the ,western ,end of ,,skerry ,,dhu or ,,black ,,rock--,bearing ,,wsw4 ,,buoy ,,on ,,skerrat ,,rock--,bearing ,,sw4 ,w4 distant #aje fathoms4 ,n4,b4--,no ,vessel should attempt to pass between those ,buoys4 ---------------------------------------- ------------------------- ,,beacons ,,and ,,buoys4 ,,linnhe ,,loch ,,district1 ,,argyleshire4 ---------------------------------------- ------------------------- ,depth at ,low ,water of ,magnetic ,bearings of ,marks and ,name of ,description ,spring ,lines of ,intersection ,station4 of ,mark4 ,tides4 ,meeting at the ,station4 ---------------------------------------- ------------------------- ,,culchenna #aj ,feet ,mast#d ,,west ,,end of ,,ardgour ,,house in line ,,spit ,,buoy4 ,buoy1 with ,fathoms4with ,,east ,,end of ,,hugh ,,boyd',s ,red ,ball4 ,,cottage--,bearing ,n4 ,e4 ,,john ,,cameron',s ,,cottage in line with ,,end of ,,culchenna ,,point-- ,bearing ,,ne4 ,e4 ,,sallachan ,,point--,bearing ,,nnw4 ,w4 ,,chlavoulin ,,spit ,,buoy--,bearing ,n4 ,e4 ---------------------------------------- ------------------------- ,,chlavoulin #g ,feet ,buoy4#b ,,centre of ,,ardgour ,,house in line ,,spit ,,buoy4 ,black4 ,fathoms4with ,,centre of ,,hugh ,,boyd',s ,,cottage--,bearing ,n4 by ,e4 ,,east ,,end of ,,second ,,wood from ,,corran ,,point in line with ,,barn at ,,east ,,end of ,,hugh ,,campbell',s ,,cottage 7,eastern ,house in ,village of ,chlavoulin7--,bearing ,,ne4 ,e4 ,,corran ,,flat ,,buoy--,bearing ,,ene4 ,e4 ,,end ,,of ,,sallachan ,,point--,bearing ,w4 ---------------------------------------- ------------------------- ,,corran ,,flat #f ,feet ,buoy4#c ,,west ,,end of ,,brow of ,,sallachan ,,buoy4 ,black4 ,fathoms4,,hill covered with ,wood in line with ,,donald ,m#8,,lean',s ,,house-- ,bearing ,,nw4 by ,w4 ,w4 ,,west ,,chimney-,,stack of ,,south ,,corran ,,ferry ,,house in line with ,,white ,,part of ,,rock near ,,high ,,water ,,mark at the ,,end of a ,,dyke-- ,bearing ,e4 ,n4 ,,south ,,brow of ,,stroncrigan ,,hill in line with ,,end of ,,corran ,,cliff-- ,bearing ,,ne4 by ,e4 ,e4 ---------------------------------------- ------------------------- ,,corran ,,bank1#f ,feet ,buoy4#b ,,bunrie ,,point in line with ,,high ,,north-,,west ,chequered ,fathoms4,,water ,,mark on ,,corran ,,point-- ,,end1 ,,buoy4 ,black and ,bearing ,s4 by ,w4 ,w4 ,white4 ,,belfry of ,,corran ,,church--,bearing ,w4 by ,n4 ---------------------------------------- ------------------------- ,,corran ,,bank1#f ,feet ,buoy4#c ,,culchenna ,,point and ,,kintallon ,,south-,,east ,black4 ,fathoms4,,point1 in line with ,,end of ,,cliff ,,end1 ,,buoy4 of ,,corran ,,point--,bearing ,,sw4 by ,s4 ,w4 ,,belfry of ,,corran ,,church--,bearing ,,nw4 by ,w4 ,w4 ,,south ,,keil ,,farmhouse1 in line with ,,arch ,,of ,,bridge ,,on ,,road-- ,bearing ,,nnw4 ,,corran ,,bank ,,north ,,buoy--,bearing ,,nnw4 ---------------------------------------- ------------------------- ,,lochyflat #f ,feet ,buoy4#b ,,south ,,end of ,,wood at ,,stroncrigan ,,east ,,buoy4 ,red4 ,fathoms4,,point1 just clear of ,,cambusnagaul ,,point--,bearing ,,sw4 by ,w4 ,w4 ,,east ,,end of ,,donald ,,cameron',s ,,house in ,,corpach1 in line with ,,north ,,end of ,,old ,,engine ,,house-- ,bearing ,n4 by ,w4 ,w4 ,,south ,,end of ,,free ,,church in line with ,,north ,,end of ,,greyhouse1 or ,,old ,,corpach ,,house--,bearing ,n4 ,e4 ,,entrance of ,,caledonian ,,canal-- ,bearing ,n4 by ,w4 ,w4 ---------------------------------------- ------------------------- ,,lochyflat #f ,feet ,buoy4#c ,,east ,,end of ,,henderson',s ,,house or ,,middle ,,buoy4,red4 ,fathoms4,,croft in line with ,,east ,,end of ,,schoolhouse near ,,cambusnagaul ,,point--,bearing ,w4 ,s4 ,,fish-,,house in line with ,,end of ,,dearg ,,point--,bearing ,n4 by ,w4 ,w4 ,,entrance of ,,caledonian ,,canal-- ,bearing ,n4 ,,north ,,end of ,,wood at ,,banavie at ,,south ,,side of ,,canal in line with ,,clump of ,,trees at ,,east ,,end of ,,john ,,cameron',s ,,cottage in ,,kilcorpach--,bearing ,,ne4 by ,e4 ,e4 ,,buoy on ,,east ,,end of ,,lochyflat-- ,bearing ,,ne4 ,n4 ,m#8,,lean',s ,,rock ,,buoy--,bearing ,,nw4 by ,n4 ---------------------------------------- ------------------------- ,,lochyflat #f ,feet ,buoy4#c ,,cameron',s ,,monument in line with ,,west ,,buoy4 ,red4 ,fathoms4,,end of ,,dearg ,,point--,bearing ,n4 ,e4 ,,north or ,,steep ,,face of ,,donnay ,,hill in line with ,,south ,,wing of ,,old ,,castle of ,,inverlochy--,bearing ,e4 ,s4 ,,lochyflat ,,middle ,,buoy--,bearing ,,ne4 ,m#8,,lean',s ,,rock ,,buoy--,bearing ,n4 by ,e4 ,e4 ,,fort-,,william ,,pier--,bearing ,,ssw4 ,w4 ---------------------------------------- ------------------------- ,,maclean',s #f ,feet ,buoy4#c ,,old ,,engine-,,house in line with ,,rock1 ,black4 ,fathoms4,,high ,,water ,,mark on ,,south ,,end of ,,locheilhead1 ,,island ,,creiah--,bearing ,n4 by ,e4 ,,buoy4 ,e4 ,,north ,,brow of ,,donnay ,,hill in line with ,,alan ,,kennedy',s ,,barn1 ,,southmost ,,house in ,,kilcorpach-- ,bearing ,e4 ,s4 ,,lochyflat ,,west ,,buoy--,bearing ,s4 by ,w4 ,w4 ,,fort-,,william ,,pier--,bearing ,s4 by ,w4 ,w4 ---------------------------------------- ------------------------- ,,new ,,rock1 #f ,feet ,buoy4#c ,,cameron',s ,,monument in line with ,,locheilhead1,chequered ,fathoms4,,end of ,,dearg ,,point--,bearing ,n4 ,,buoy4 ,black and ,e4 ,white4 ,,north ,,end of ,,free ,,church in line with ,,high ,,water ,,mark on ,,east ,,end of ,,island ,,creiah--,bearing ,,ne4 ,n4 ,,centre of ,,donnay ,,hill in line with ,,alan ,,kennedy',s ,,barn--,bearing ,e4 ,s4 ,n4,b4--,depth at ,low ,water of ,spring ,tides on ,rock is #h feet4 ,the ,buoy1 moored in #c fathoms1 swings clear of the ,rock on west side of it4 ---------------------------------------- ------------------------- ,by order of the ,board1 ,,alan ,,stevenson1 ,engineer4 ,edinburgh1 #ast ,january #ahdh4 ,,notice ,,to ,,mariners4 ,,the ,,commissioners ,,of ,,northern ,,lighthouses have resolved to publish1 on #ast ,january annually1 for the use of ,mariners1 a ,descriptive ,list of all the ,lighthouses1 ,beacons1 and ,buoys under their charge1 giving the characteristic appearance and correct bearings of each4 ,,mariners are particularly requested to notice1 that they should ,,never ,,purchase any ,list ,,except ,,that ,,for ,,the ,,year ,,current at the time of purchase4 ,as changes may have taken place1 no reliance can be placed on any ,list which has been published for a preceding year4 ,,publishers are particularly cautioned not to sell any ,list which has been published on a preceding year4 ,arrangements have been made with the ,publishers of the ,board1 that all copies remaining on hand with any ,publisher1 at the close of any year1 will be exchanged for the ,new ,issue2 and all ,publishers are ,,most ,,particularly ,,requested not to retain on hand any copies of a past issue4 ,by ,order of the ,board1 ,,alex4 ,,cuningham1 ,secretary4 ,,northern ,,lights ,,office1 ,,edinburgh1 #ast ,january #ahdh4 ,,appendix1 ,no4 ,,ix4 ,,report ,,to ,,the ,,commissioners ,,of ,,northern ,,lighthouses1 ,,for ,,the ,,year #ahdf2 ,,with ,,appendices4 ,,by ,,alexander ,,cuningham1 ,w4,s41 ,,secretary ,,to ,,the ,,board4 ,the gross amount of ,,duties received from ,shipping in the year to #cast ,december #ahdf1 as per detailed ,state appended hereto 7,no4 ,i41 p4 #dbi71 is #df1jja 3 #aa 3 #b4 ,the ,,commission paid to ,collectors in the same period is #bdja 3 #g 3 #c1 and ,repayments of ,duties erroneously charged1 c41 #bah 3 #af 3 #aj1 making the nett amount of ,duties for the year #dc1cha 3 #g 3 #a1 as also appears from ,state1 ,no4 ,i41 p4 #dbi4 ,the nett amount of ,duties in the year #ahde was #eb1cia #h #d ,while that received in #ahdf is #dc1cha #g #a ------------- ,making a ,,deficiency in the year of #i1jaj #a #c ,whereof-- ,half-year to #cjth ,june1 #bcej #i #a ,ditto to #cast ,december1 #ffei #ab #b ----------- #i1jaj #a #c ,it is to be observed1 however1 that during the currency of this year1 two reductions in the amount of ,light-duties1 resolved upon by the ,,board1 have come into operation4 #a4 ,the first of these reductions was one halfpenny per ton 7or one-half of the amount leviable by ,statute7 for the ,bell ,rock ,light2 one farthing per ton 7or one-half of the amount leviable7 for each of the ,lights of ,corsewell and ,mull of ,galloway2 and one-eighth of a penny per ton 7or one-fourth of the amount leviable7 for ,pladda ,light4 ,these reductions were in operation during the first half of the year #ahdf4 ,they were estimated to produce a deficiency in the annual ,revenue of #eafj1 which1 for the half-year1 gives #behj4 ,the actual deficiency in the amount levied for the first half of #ahdf1 over that levied in the corresponding period of the preceding year1 was #bcej 3 #i 3 #a1 being still #bcj under the estimated amount4 #b4 ,the ,,board came to the resolution of making such a further reduction as should1 including the previous one1 give an aggregate abatement to the ,coasting ,trade1 for each of the ,lighthouses1 of #ej per cent41 that is1 the amount leviable for each of the ,lights being1 previous to the first reduction1 one halfpenny per ton1 was reduced for the ,coasting ,trade to one farthing per ton2 the amount for the ,bell ,rock and ,skerryvore ,lights1 being one penny1 was reduced to one halfpenny per ton4 ,this reduction commenced on the #ast day of ,july #ahdf1 and has consequently been in operation during the last half of that year4 ,it was estimated to produce a deficiency in the annual revenue of the ,board of #ad1cid 3 #ad 3 #e1 which1 for the half-year1 gives #gaig 3 #i 3 #b4 ,the actual deficiency in the amount levied for the last half of #ahdf1 over that levied in the corresponding period of the preceding year1 was #ffei 3 #ab 3 #b1 being #edj under the estimated amount4 ,it is also proper to observe1 that while there is the above deficiency in ,receipts of the year #ahdf1 as contrasted with #ahde1 of #ijaj #a #c ,there was a surplus ,receipt of the year #ahde1 as contrasted with #ahdd1 amounting to #ffab #ag #h ----------- ,making the ,,deficiency in #ahdf1 as contrasted with the ,,receipts of #ahdd1 upon which the calculations of the ,board were founded1 only #bcig #c #g ,on the other hand1 the greater reduction having been in operation only during half the year1 a greater deficiency in the ,revenue must be looked for in future years4 ,the ,light-,duties in #ahde were contributed by #afc1agd vessels in the ,coasting ,trade1 giving an aggregate tonnage of #ae1eff1dfa1 and by #de1fab vessels in ,oversea ,trade1 giving an aggregate tonnage of #i1cjj1ihc4 ,the ,light-,duties in #ahdf have been contributed by #afc1aff vessels in the ,coasting ,trade1 giving an aggregate tonnage of #ae1ibf1fcd1 and by #ej1cbd vessels in the ,oversea ,trade1 giving an aggregate tonnage of #i1egg1dgh4 ,a contrast of these statements shews an increase in the ,coasting ,trade of #ahdf in tonnage of #cfj1agc1 with eight fewer vessels2 and in the ,oversea ,trade an increase of #dgab vessels1 with a tonnage of #bgf1die4 ,these results 7somewhat singular in their relative amounts7 establish the important fact1 that1 though there is a deficiency in the revenue of the ,board1 it truly arises from the reductions in the ,duties1 and not from any reduction in the ,shipping4 ,for the information of the ,board1 there will be found appended 7p4 #dcc7 a statement shewing the progressive increase of tonnage during the last four years4 ,the amount of ,duties received in the year #ahdf1 as above1 is #df1jja #aa #b ,while the ,ordinary ,expenditure of the ,board has been #cb1jfc #f #c ---------------- ,giving a ,surplus ,receipt for the year to meet ,extraordinary ,expenditure of 7see ,state1 ,no4 ,,ii41 p4 #dcb7 #ac1ich #d #aa ,but the total ,expenditure of the ,board in the ,year has been #fj1cgd #ae #i ,from which if there be deducted the ,gross ,receipts1 per page #dbe1 #dg1hie #h #h ---------------- ,it gives a ,balance superexpended beyond the surplus of the year of #ab1dgi #g #j ,the ,balance on hand at #cast ,march #ahdf was #db1jfi #f #aj ,while that on hand at #cast ,march #ahdg is #bi1ehi #ai #i ---------------- ,difference equal to superexpenditure1 #ab1dgi #g #j ,there has been expended on the various ,works in progress1 prior to the year #ahdf and in that year1 as follows3-- ---------------------------------------- ------------------------- ,prior to #ahdf4 ,in #ahdf4 ,,total4 ---------------------------------------- ------------------------- ,skerryvore ,lighthouse ,works #ic1egf #aj #j #bbg #h #b #ic1hjc #ah #b ,add ,bo-,pheg ,beacon #daf #aj #g #be #aj #a #ddb #j #h ---------------------------------------- --- #ic1iic #j #g #beb #ah #c #id1bde #ah #aj ,covesea ,lighthouse ,works #i1ebc #ag #fa1aji #e #d #aj1fcc #b #aj ,cromarty ,ditto #b1hie #ah #h #cdb #i #c #c1bch #g #aa ,chanonry ,ditto #b1hcb #af #a #dje #g #h #c1bch #c #i ,ardnamurchan ,ditto #bif #b #bb1cdc #ag #f #b1fci #ai #h ,laggan ,spur ,beacon 444 444 #gdh #aj #f #gdh #aj #f ,island ,glass ,new ,buildings and ,inclosures #c1jfd #ae #ca1gig #c #e #d1hfa #ah #h ,nosshead ,lighthouse ,works 444 444 #a1dfg #f #a #a1dfg #f #a ,loch ,ryan ,ditto 444 444 #hbi #ab #i #hbi #ab #i ,pentland ,skerries ,new ,works 444 444 #c1ace #ag #e #c1ace #ag #e ,ditto ,dioptric ,light 444 444 #b1jcg #aa #d #b1jcg #aa #d ,renewal of ,fixed ,lights 444 444 #c1jce #ad #d #c1jce #ad #d ,buoys1 c4 444 444 #a1edi #ad #aa #a1edi #ad #aa ,campbeltown ,beacons 444 444 #ag #d #aj #ag #d #aj ,lappock ,beacon 444 444 #h #ab #e #h #ab #e ,startpoint ,new ,works 444 444 #e #ai #d #e #ai #d ,elie or ,vows ,beacon 444 444 #bje #e #h #bje #e #h ,whiteness ,beacon 444 444 #aeb #e #h #aeb #e #h ,longman's ,point ,ditto 444 444 #afd #ae #f #afd #ae #f ,loch ,ryan ,ditto 444 444 #aeb #e #i #aeb #e #i ,brist ,beacon #gcd #b #i #h #ab #e #gdb #ae #b ,mull of ,kintyre ,dykes and ,road #ehf #ad #d #fdg #ag #i #a1bcd #ab #a ---------------------------------------- ------------------------- ,there has been expended on the new ,steamer 8,pharos10 #ah1igg 3 #f 3 #g4 ,the ,,commissioners have purchased a ,house at ,crail for #aje 3 #ai 3 #d for the use of the ,boatmen attending at the ,isle of ,may4 ,the attention of the ,,commissioners is called to the circumstance that a complete change has been made this year in the mode of stating the ,accounts4 ,the ,accounts are now1 for the first time1 concentrated in the ,secretary's department1 and for every item entered in the subjoined abstract1 reference is now1 and will hereafter1 be made to a page of the ,ledger containing a detailed account vouching the charge4 ,following out this arrangement1 the account has been branched into three heads or divisions4 ,the first head comprises the ordinary expenses of the ,lighthouses4 ,in this branch it has been thought right to state separately1 under the head of the ,isle of ,may1 the interest on the debt to ,government1 being the balance of the price of the ,island4 ,the second head comprises the ordinary expenses of the ,board1 not in the first instance chargeable against any particular ,lighthouse1 but falling to be afterwards allocated in the final view of the ,receipt and ,expenditure of each ,lighthouse4 ,this branch is again subdivided so as to shew-- #a4 ,the ,expense of ,collection4 #b4 ,repayments1 c4 of ,light-,duties overcharged4 #c4 ,the ,expense of the ,establishment1 including ,salaries1 ,stationery1 c4 #d4 ,the ,shipping ,establishment4 #e4 ,beacons and ,buoys--ordinary maintenance4 #f4 ,the ,storehouse1 ,leith4 #g4 ,charities and ,superannuations4 #h4 ,miscellaneous ,payments4 ,the last division of the abstract comprises what is termed the extraordinary expenditure1 that is1 the expense of ,new ,works and others not falling to be allocated upon the ,lighthouses4 99 99 99 99 99 ,in effecting this change1 various payments which appeared in the former abstracts will not now be found in the present1 such as ,rents and ,feu-duties1 which are now charged to the respective ,lighthouses for which they are paid2 the ,storekeeper's ,salary1 which is stated in the ,storehouse ,account2 the ,office-,keeper's1 in the ,office ,account1 c41 and the ,salaries of the ,officers of the ,board will be found under the head of ,edinburgh ,establishment4 ,,abstract of the ,,receipts and ,,payments on ,account of the ,,duties levied for the ,,northern ,,lighthouses for the year #ahdf4 ---------------------------------------- ---------------------------- ,,receipts4 ---------------- ,i4 ,,gross ,,amount of the ,duties received for #ahdf1 per ,state1 ,no4 ,i4 p4 #dbi1 #df1jja #aa #b ,which has been received in the following proportions for each ,lighthouse1 as appears from ,state1 ,no4 ,,ii41 pp4 #dcj-c1 viz43-- ---------------- #a4 ,inchkeith1 #bebd #i #b #b4 ,isle of ,may1 #chbe #h #e #c4 ,bell ,rock1 #ecdb #ae #e #d4 ,girdleness1 #bdeh #d #e #e4 ,buchanness1 #ahhj #a #c #f4 ,kinnairdshead1 #agdd #aa #c #g4 ,tarbetness1 #cbi #ag #d #h4 ,sumburghhead1 #bhf #ah #b #i4 ,startpoint1 #aaed #e #d #aj4 ,pentland ,skerries1 #acgj #aj #e #aa4 ,dunnethead1 #acaa #a #aj #ab4 ,capewrath1 #abgh #i #i #ac4 ,island ,glass1 #fgi #a #aj #ad4 ,barrahead1 #ajfc #c #b #ae4 ,skerryvore1 #bjij #aa #c #af4 ,lismore1 #bci #aa #d #ag4 ,rhinns of ,islay1 #adad #e #h #ah4 ,mull of ,kintyre1 #aedi #j #a #ai4 ,pladda1 #bgfb #ad #c #bj4 ,corsewall1 #bhaa #e #c #ba4 ,mull of ,galloway1 #bhbc #ai #h #bb4 ,little ,ross1 #aahg #g #i #bc4 ,point of ,ayre1 #agee #ag #e #bd4 ,calf of ,man 7two ,lights71 #chci #b #aa #be4 ,covesea ,skerries1 #aic #g #j #bf4 ,cromarty1 #bg #ad #aa #bg4 ,chanonry1 #eg #ae #a ---------------- #df1jja #aa #c ,,deduct fractions short credited by ,bankers1 #j #j #a ---------------- ,as above1#df1jja #aa #b ,,ii4 ,,miscellaneous ,,receipts-- ------- ,folio in ,ledger4 ------- #cb #gc,rent of ,stable behind the ,office1 #ah #j #j #gc ,do4 of ,small ,houses at ,arbroath1 #e #e #j #cc ,proceeds sale of ,regent ,tender1 #dhe #ad #c #cb ,composition of #as4 #f;d4 per pound from the ,trustee on ,andrew ,greig's ,bankrupt ,estate1 on a claim of #cdj1 #aas4 #h;d4 and ,expenses arising from an evasion of ,light-dues1 #bg #j #i #cj ,price of ,lighter sold to ,kirkcaldy ,harbour ,commissioners1 #fj #j #j #gd ,do4 do4 to ,leith ,shipping ,company1 #de #j #j #dj ,do4 of ,horse sold at ,barrahead1 #aj #j #j 444 ,do4 of an ,ass sold at ,inchkeith1 #j #i #f #adi ,do4 of ,articles sold at ,skerryvore1 #abf #e #aj #gc1ge1;,fines imposed on ,light- #cae keepers1 received1 #ac #a #h #gd ,sum received from the ,general ,post-,office1 for the maintenance of the ,harbour ,light at ,portpatrick for the year #ahde1 #acf #aj #i #dj #ge;,interest received from the ,royal ,bank on money deposited1 #iff #i #i ,,sum1 ---------------- #ahic #ag #f ---------------- ,,sums ,,of ,,receipts carried to ,,abstract1 page #dbe1 #dg1hie #h #h ---------------------------------------- --------------------------- ,,payments4 ---------------------------------------- --------------------------- ,folio ,,branch ,i4--,,ordinary ,,expenses of the ,,board1 being the in ,maintenance of the ,lights for the year1 viz3-- ,ledger4 ------- ---------------- #a4 ,,lighthouses-- #cbf #a4 ,inchkeith1 #ehc #e #aj ---------------- #cbg #b4 ,isle of ,may1 #gjb #c #i ,isle of ,may1 ,year's ,interest to ,government1 #bej #j #j ---------------- #ieb #c #i #cee #c4 ,bell ,rock1 #ihi #a #c #cbi #d4 ,girdleness1 #edh #ah #a #ccj #e4 ,buchanness1 #fbc #e #c #cca #f4 ,kinnairdshead1 #egh #aj #j #ccb #g4 ,tarbetness1 #egd #aa #aa #ccc #h4 ,sumburghhead1 #eig #e #c #ccd #i4 ,startpoint1 #cdg #j #h #cce #aj4 ,pentland ,skerries 7two ,lights71 #hea #h #aa #ccf #aa4 ,dunnethead1 #dgj #ai #g #ccg #ab4 ,capewrath1 #ehg #f #aa #cch #ac4 ,island ,glass1 #eae #b #aj #cci #ad4 ,barrahead1 #eid #c #aj #ceg #ae4 ,skerryvore1 #aabb #j #g #cdj #af4 ,lismore1 #eae #ad #b #cda #ag4 ,rhinns of ,islay1 #efi #ab #g #cdb #ah4 ,mull of ,kintyre1 #eed #ag #aj #cdc #ai4 ,pladda1 #ehd #aj #aj #cdd #bj4 ,corsewall1 #dfe #ac #d #cde #ba4 ,mull of ,galloway1 #eag #j #e #cdf #bb4 ,little ,ross1 #eaf #ah #f #cdg #bc4 ,point of ,ayre1 #dji #a #d ---------------- #cdh #bd4 ,calf of ,man 7,high ,tower71 #cid #d #g #ced #be4 ,calf of ,man 7,low ,tower71 #dai #ad #aj ---------------- #hac #ai #e #cea #bf4 ,covesea ,skerries1 #dai #af #h #ceh #bg4 ,cromarty1 #cci #ag #c #cec #bh4 ,chanonry1 #bhd #g #a #cej #bi4 ,loch ,ryan1 #agf #e #g ---------------- ,,sum1--,carried to ,,abstract1 p4 #dbe1 #af1ajc #j #b ,,branch ,,ii4--,,ordinary ,,expenses falling to be allocated upon each ,lighthouse-- #a4 ,,expense of ,,collection-- ---------------- ,to paid ,commission to ,collectors1 per ,state1 ,no4 ,i4 p4 #dbi1 #bdja #g #c ,to paid ,commission to ,bankers1 #aae #c #g ---------------- #beaf #aj #aj #b4 ,,repayments1 c41 of ,,light-,,duties ,,overcharged1 #bah #af #aj #c4 ,,establishment ,,in ,,edinburgh-- ------------------------- ,engineer1 ,salary at #ijj1 #fge #j #j ,engineer1 ,salary at #abjj1 #cjj #j #j ---------- #ige #j #j ,secretary1 #ejj #j #j ,accountant1 ,salary to #hth ,july1 when he died1 #hd #ab #j ---------- ,superinten- dent of ,light- keepers1 ,salary at #ade1 #ajh #ae #j ,superinten- dent of ,light- keepers1 ,salary at #baj1 #eb #aj #j ---------- #afa #e #j ---------- ,foreman of ,lightroom repairs1 ,salary at #aaj1 #hb #aj #j ,foreman of ,lightroom repairs1 ,salary at #adj1 #ce #j #j ---------- #aag #aj #j ,engineer's ,clerk1 ,salary 7formerly paid by ,engineer71 #cb #aj #j ,examiner of ,accounts1 from #hth ,january to ,candlemas1 #ag #b #f ,first ,clerk in ,secretary's ,department1 ,salary1 #be #j #j ,second ,clerk in ,secretary's ,department1 ,salary1 #be #j #j ,officer 7now conjoined with ,housekeeper71 ,salary1 #e #j #j ,payments to two ,clerks in ,accountant's ,department1 to cease at ,whitsunday in consequence of the appointments in ,secretary's ,department1 #agd #f #j ,interim ,accountant1 per minute of the ,board1 until ,examiner of ,accounts was appointed1 #aje #j #j ,office1 including ,porter and ,house-,servants' ,wages1 ,house ,expenses1 ,taxes1 ,books for ,library1 c41 #iaj #aj #c #bgi --------------- #cacb #ae #i #d4 ,,shipping ,,establishment----------------- #acb ,pharos ,steam-,vessel1 #cgij #a #aa #acc ,prince of ,wales1 ,bell ,rock ,tender1 #ied #aj #b #ace ,francis1 ,skerryvore ,tender1 #ibj #ag #f #acg ,regent ,tender 7now sold71 #bei #c #g --------------- #eibd #ac #c #e4 ,,beacons and ,,buoys--,expense of ,ordinary ,maintenance1 #ia #g #j #f4 ,,storehouse1 ,,leith1 including ,storekeeper's ,salary1 ,taxes1 ,freight of ,stores1 c41 viz3-- ------------------------- ,salary1 1 #dj #ac #j ,salary1 1 at #ajj per annum1 #be #j #j ---------- #fe #ac #j ,expenses of ,house1 ,packing ,stores1 c41 #ade #i #g #ahd ,freight of ,stores1 #acc #d #c --------------- #cdd #f #aj #g4 ,,charities and ,,superannuations to ,,retired ,,servants of ,,the ,,board1 viz43-- #a4 ,prior to the last ,act of ,parliament-- --------------- ,william ,tweedy1 one year's ,annuity1 #bj #j #j ,mrs ,leask1 one year's ,annuity1 #aj #j #j ,hugh ,rose1 one year's ,annuity1 #bj #j #j ,jane ,walker1 one year's ,annuity1 7died ,march #ac1 #ahdg71 #f #f #j ,euphemia ,poole1 one year's ,annuity1 #e #j #j --------------- #fa #f #j #b4 ,since last ,act1 viz43--------------- ,robert ,stevenson1 ,esq41 late ,engineer1 #ehj #j #j ,matthew ,harvie1 ,light-keeper1 #fi #g #f ,john ,bruce1 late ,officer1 #ac #j #j ,george ,kirk1 ,light- keeper1 #dj #j #j ,john ,watt1 ,light- keeper 7died ,dec4 #ahdf71 #da #ab #f ,william ,heddle1 ,light-keeper1 #ag #ae #j ,robert ,selkirk1 ,light-keeper 7died ,jan4 #ahdg71 #bj #af #d ,andrew ,adamson1 ,light-keeper #dg #j #j ,james ,brown jun41 ,light-keeper #bi #aa #h ,william ,soutar1 ,light-keeper #dh #aj #j ,john ,murray1 late ,boatman1 ,isle of ,may1 #ah #f #h ,david ,lyall1 ,light- keeper1 #dc #j #j ,thomson ,milne1 ,light- keeper #fd #a #j ,david ,laughton1 ,light-keeper #dg #aj #j ,alexander ,burnett1 ,light-keeper #de #j #j ,james ,wallace1 #cd #j #j ,john ,miller 7proportion till date of death71 #aa #ab #j ,mrs ,duncan1 late ,housekeeper1 three-quarters1 #aj #aj #j ,john ,scott1 late ,mate1 ,prince of ,wales1 quarter to ,martinmas last1 #bb #aj #h ,c4 ,cunningham1 ,esq41 late ,secretary1 from #bast ,december to ,candlemas1 #de #g #c --------------- #abdi #i #aa #h4 ,,miscellaneous ,,expenses not appropriated to any ,particular ,head1 #bdbj #ai #e ,being-- --------------- #a4 ,for ,educating ,expectant ,light- keepers1 being their ,travelling ,charges and ,subsistence1 #hd #af #j #b4 ,travelling ,expenses of the ,board1 #abh #ah #aa #c4 ,travelling ,expenses of ,officers on the ,business of the ,board1 #eac #c #i #d4 ,half-yearly ,dinner ,bills1 #fi1 #es41 and #hf 3 #b 3 #f1 #aee #g #f #e4 ,advertising ,reduction of ,duties1 #ij #aj #aj ------------------------- #f4 ,printing ,expenses1 viz41 ,new ,tables1 ,notices1 ,circu- lars1 c41 #agc #e #g ,printing ,expenses1 #ejj vols4 ,collec- tor's ,receipt ,books1 c41 #adf #ai #f ,printing ,expenses1 ,annual ,list of ,light- houses1 c41 #bjg #aj #aj ,printing ,expenses1 8,steven- son on ,lenses10 and ,expenses connected with ,lenses1 #ca #a #e ---------- #eeh #ag #d #g4 ,making ,oil ,casks1 and ,cooperage of old do4 #ade #aa #b #h4 ,postages and ,carriage of ,parcels1 #abj #ah #aj #i4 ,messrs ,cuningham and ,bell1 ,w4,s41 ,law- ,agents1 ,account for ,commissions to and ,bonds by ,collectors1 c41 #acf #d #j #aj4 ,messrs ,spottiswoode and ,robertson1 ,solicitors1 ,london1 #eg #aa #h #aa4 ,gratuity to ,lewis ,proctor1 an occasional ,light- keeper1 who met with a severe ,accident by a fall from the ,lighthouse at ,kinnairdshead1 #cj #j #j #ab4 ,medical ,attendance on ,keepers' ,families at ,insulated ,stations1 #bf #ag #j #ac4 ,paid for ,nomination to ,edinburgh ,royal ,lunatic ,asylum for ,keeper's ,wife at ,chanonry ,lighthouse1 #ab #aj #j #ad4 ,gratuities voted to aged ,light-keepers to meet ,insurances on their ,lives1 #ch #g #a #ae4 ,sundry small ,sums due by ,light- keepers1 connected with ,insurances on their ,lives1 and ,stamps for ,premiums1 #cg #b #h #af4 ,r4 ,w4 ,swinburne and ,co41 ,newcastle1 ,plate-,glass1 #cb #a #f #ag4 ,paid for ,temporary ,lanterns during ,repairs of ,lighthouses1 #fd #ag #g #ah4 ,one ,dozen ,stamped ,receipt-,books for ,keepers' ,salaries1 and ,fees getting same ,stamped in ,london1 #g #a #j #ai4 ,expenses incurred by ,henry ,banks1 tailor1 in visiting the different ,lighthouses1 and taking 8measures0 for ,clothing the ,keepers1 #ch #j #b #bj4 ,periodicals furnished to the ,keepers1 #d #ad #g #ba4 ,a ,copper ,buoy1 #c #af #aa #bb4 ,repairs on ,rankin ,lighter1 #e #b #d #bc4 ,account connected with ,skerryvore ,lighters1 #f #g #j #bd4 ,models of ,dioptric ,light1 #hc #ac #a #be4 ,freight to ,london1 ,leith1 ,edinburgh1 and ,glasgow ,shipping ,company1 #c #a #e #bf4 ,various small items for ,lithographing1 c4 c41 #ce #g #a --------------- ,,sum as on preceding page1 #bdbj #ai #e ---------------- ,carry forward1#ae1ifj #f #j ---------------- ,,ordinary ,,expenses brought forward1 #ae1ifj #f #j ,which have been ,allocated to each ,lighthouse in the proportions following1 as appears from ,state1 ,no4 ,,ii41 pp4 #dcj-c1 viz4-- --------------- #a4 ,inchkeith1 #egg #ae #i #b4 ,isle of ,may1 #ida #h #f #c4 ,bell ,rock1 #igg #ag #i #d4 ,girdleness1 #edd #e #h #e4 ,buchanness1 #fag #d #a #f4 ,kinnairdshead1 #egc #af #aa #g4 ,tarbetness1 #efi #ah #a #h4 ,sumburghhead1 #eia #aa #h #i4 ,startpoint1 #cde #d #d #aj4 ,pentland ,skerries1 #hda #ag #aj #aa4 ,dunnethead1 #dfg #h #d #ab4 ,capewrath1 #eha #ad #g #ac4 ,island ,glass1 #eaj #ae #f #ad4 ,barrahead1 #ehh #ab #g #ae4 ,skerryvore1 #aajh #ai #a #af4 ,lismore1 #eaa #ae #d #ag4 ,rhinns of ,islay1 #efd #ai #f #ah4 ,mull of ,kintyre1 #eej #c #aj #ai4 ,pladda1 #egi #ae #b #bj4 ,corsewall1 #dfb #i #i #ba4 ,mull of ,galloway1 #eab #ad #aa #bb4 ,little ,ross1 #eab #ad #aa #bc4 ,point of ,ayre1 #djf #f #d #bd4 ,calf of ,man 7two ,lights71 #hje #h #g #be4 ,covesea ,skerries1 #dag #c #a #bf4 ,cromarty1 #cch #f #d #bg4 ,chanonry1 #bhc #b #h #bh4 ,loch ,ryan1 #agf #ad #a ,as above1 --------------- #ae1ifj #f #j ,,branch ,,iii4--,,extraordinary ,,expenses not ,allocated to each ,lighthouse3-- ---------------- #ahi ,to paid for new ,steamer ,pharos1 #gedh #ac #g #caj ,expense of ,harbour ,light at ,portpatrick1 #abi #ag #d #ahb ,expense connected with ,skerryvore ,book1 #aii #ah #j #cc ,to paid for ,house in ,crail for use of ,isle of ,may ,boatmen1 and ,fees connected with ,purchase1 #aje #ai #d ---------------- #gihd #h #c ,,expense ,,of ,,new ,,works1 viz43-- --------------- #aej ,skerryvore1 #bbg #h #b #bhg ,bo ,pheg ,beacon1 #be #aj #a #bhd ,covesea1 #aaji #e #d #bif ,cromarty1 #cdb #i #c #bih ,chanonry1 #dje #g #h #cjj ,ardnamurchan1 #bcdc #ag #f #cad ,laggan ,spur ,beacon1 #gdh #aj #f #caf ,island ,glass1 #agig #c #e #cai ,nosshead1 #adfg #f #a #cbb ,loch ,ryan1 #hbi #ab #i #aba ,loch ,ryan1 ,beacon1 #aeb #e #i #cbd ,pentland ,skerries new ,works1 #cace #ag #e #ade ,pentland ,skerries ,dioptric ,light1 #bjcg #aa #d #cjh ,renewal of ,fixed ,lights1 #cjce #ad #d #ajf ,campbeltown ,beacons1 #ag #d #aj 444 ,lapock ,beacon1 #h #ab #e #aag ,startpoint ,new ,works1 #e #ai #d #aah ,elie or ,vow's ,beacon1 #bje #e #h #aai ,whiteness ,beacon1 #aeb #e #h #abj ,longman's ,point ,beacon1 #afd #ae #f #ahd ,brist ,beacon1 #h #ab #e #cjf ,mull of ,kintyre ,dykes and ,road1 #fdg #ag #i #bhf ,buoys1 #adeh #g #aa ,,sum1 --------------- #bj1cbg #a #c ---------------- ,carried to ,,abstract below1 #bh1caa #i #f ---------------------------------------- -------------------- ,,abstract ,,of ,,the ,,preceding ,,account4 ---------------------------------------- ------------------- ,,receipts3-- ,,branch ,i4--,gross ,amount of the ,duties received for #ahdf1 p4 #dah1 #df1jja #aa #b ,,ii4--,miscellaneous ,receipts1 p4 #dai1 #a1hic #ag #f ---------------- #dg1hie #h #h ,,payments3-- ---------------- ,,branch ,i4--,ordinary ,expenses1 being the ,maintenance of ,lights1 c4 p4 #dbj1 #af1ajc #j #b ,,ii4--,ordinary ,expenses1 falling to be allocated upon each ,lighthouse1 p4 #dbd1 #ae1ifj #f #j ,,iii4--,extraordinary ,expenses not allocated to each ,lighthouse1 as above1 #bh1caa #i #f ---------------- #fj1cgd #ae #i ---------------- ,,balance superexpended in #ahdf1 #ab1dgi #g #j ,,balance on hand at #cast ,march #ahdf1 #db1jfi #f #aj ---------------- ,,balance on hand at #cast ,march #ahdg1 #bi1ehi #ai #i ,,whereof-- ---------------- ,in the ,royal ,bank1 #bh1idd #af #h ,in ,secretary's ,account1 #dj #af #aa ---------------- #bh1ihe #ac #g #hi ,balance due by ,peter ,grant1 ,superintendent1 ,nosshead1 #bjc #aj #b #aeg ,balance due by ,master of ,prince of ,wales ,tender1 #ce #c #d #afa ,balance due by ,steward of ,pharos ,steamer1 #cj #ai #b #afd ,balance due by ,master of ,francis1 ,skerryvore ,tender1 #b #ab #e #aff ,balance due by ,superintendent of ,light- keepers1 #aa #aa #b #afh ,balance due by ,foreman of ,light-room ,repairs1 #e #c #e #agb ,balance due by ,buoymaster1 #e #a #f #agf ,balance due by ,store- keeper1 #g #ag #j #ahj ,balance due by ,thomas ,hope1 ,superintendent1 ,island ,glass1 #hg #ag #g #cjg ,balance due by ,master of ,pharos1 #e #aj #h #cah ,balance due by ,james ,scott1 ,superintendent1 ,pentland ,skerries1 #ahh #ab #c ------- ,folio in ,small ,ledger4 ------- #f ,sum due by ,robert ,selkirk's ,representatives1 to be paid when ,insurance money is received1 #aj #j #j #h ,balance due by ,richard ,cumming1 ,light-keeper1 #b #ac #j #i ,balance due by ,james ,laughton1 do41 #c #j #j #aj ,balance due by ,william ,kirk1 do41 #d #ad #f ,equal to ,,balance1 ---------------- #bi1ehi #ai #i ---------------------------------------- --------------------------- ,,edinburgh1 #eth ,may #ahdg4--,prepared and ,reported by 7,signed7 ,,alex4 ,,cuningham1 ,secretary4 99 99 99 99 99 #hd ,george ,street1 ,edinburgh1 #beth ,may #ahdg4 ,in obedience to the ,remit by the ,honourable ,board of ,commissioners of ,northern ,lighthouses1 ,i have carefully audited the ,accounts of the ,board for the year ending #cast ,march #ahdg2 and ,i have to report1 that the ,accounts are clearly and accurately stated--that they are fully vouched--and that1 in my humble opinion1 the ,report of the ,secretary contains a very distinct statement of the ,intromissions of the ,board during the above period4 7,signed7 ,,kenneth ,,mackenzie1 ,accountant4 ,,statements ,,annexed ,,to ,,the ,,secretary',s ,,report ,,for #ahdf4 ,no4 ,i4--,account of ,northern ,light-,duties received in the ,year #ahdf4 ---------------------------------------- ------------- ,gross ,commission ,receipts4 to ,collectors4 ---------------------------------------- ------------- #a4 ,aberdeen1 #bbdc #c #i #aba #aa #h #b4 ,alloa1 #djb #f #a #bc #f #h #c4 ,arbroath1 #bed #b #aa #ab #ag #b #d4 ,ayr1 #aeh #ab #aa #h #a #aj #e4 ,aberystwith1 #f #ag #f #j #f #i #f4 ,arundel1 444 444 #g4 ,banff1 #dfg #g #e #bh #ag #f #h4 ,borrowstounness1 #fge #f #a #dh #aa #i #i4 ,barnstaple1 #a #g #b #j #a #d #aj4 ,beaumaris1 #abc #ag #a #f #ab #g #aa4 ,berwick1 #aba #j #h #f #aa #i #ab4 ,bideford1 #h #ad #aa #j #h #i #ac4 ,boston1 #i #ae #j #j #aj #g #ad4 ,bridgewater1 #ab #j #g #j #aa #aa #ae4 ,bridlington1 #bf #a #c #a #f #a #af4 ,bridport1 #b #ah #j #j #b #aj #ag4 ,bristol1 #abd #ab #g #f #d #f #ah4 ,baltimore1 444 444 #ai4 ,belfast1 #bddf #a #d #abe #f #d #bj4 ,campbeltown1 #hb #ad #i #e #b #a #ba4 ,caernarvon1 #be #ac #aj #a #g #g #bb4 ,cardiff1 #aaj #ai #g #e #aa #j #bc4 ,cardigan1 #a #g #aa #j #a #g #bd4 ,carlisle1 #hd #j #c #d #g #i #be4 ,chepstow1 #j #ad #aa #j #j #i #bf4 ,chester1 #aeh #d #e #h #a #e #bg4 ,chichester1 #b #ae #f #j #c #i #bh4 ,clay1 #a #b #f #j #a #h #bi4 ,colchester1 444 444 #cj4 ,cowes1 444 444 #ca4 ,coleraine1 #aja #e #h #e #a #g #cb4 ,cork1 #gj #ac #a #c #aj #f #cc4 ,dunbar1 #aae #aa #aa #g #a #b #cd4 ,dundee1 #bjfb #i #aj #aje #g #b #ce4 ,dumfries1 #cea #aj #f #bd #ac #j #cf4 ,dartmouth1 444 444 #cg4 ,deal1 444 444 #ch4 ,dover1 #j #h #j #j #j #e #ci4 ,dublin1 #bbef #ag #aj #aad #j #i #dj4 ,drogheda1 #adi #h #b #g #i #e #da4 ,dundalk1 #abj #f #f #f #j #c #db4 ,exeter1 #b #ag #e #j #c #j #dc4 ,fisherrow1 #bai #j #h #ac #ab #d #dd4 ,falmouth1 444 444 #de4 ,faversham1 444 444 #df4 ,fowey1 #b #d #aa #j #c #j #dg4 ,glasgow1 #ceii #af #aj #ahb #ad #d #dh4 ,greenock1 #bfga #j #i #acg #ac #h #di4 ,grangemouth1 #abea #ab #e #fb #aa #f #ej4 ,gainsborough1 #e #ai #h #j #f #i #ea4 ,gloucester1 #fa #ab #aa #c #a #h #eb4 ,goole1 #ca #b #d #a #ab #b #ec4 ,grimsby1 #fd #aa #c #c #d #g #ed4 ,gweek1 444 444 #ee4 ,galway1 #ch #f #j #a #ah #c #ef4 ,hartlepool1 #aec #d #j #g #ac #b #eg4 ,harwich1 444 444 #eh4 ,hull1 #aecb #h #b #gf #ab #e #ei4 ,inverness1 #ibj #ag #a #ef #ab #aa #fj4 ,irvine1 #iae #aj #aj #fc #h #aa #fa4 ,ipswich1 #ag #e #j #j #ag #c #fb4 ,isle of ,man1 #cgc #ah #i #bb #ae #e #fc4 ,kirkcaldy1 #gde #e #e #db #af #b #fd4 ,kirkwall1 #aca #ae #f #g #i #j #fe4 ,leith1 #cbbd #g #c #afa #d #d #ff4 ,lerwick1 #agc #a #a #h #ac #j #fg4 ,lancaster1 #ajg #j #e #f #c #f #fh4 ,leigh1 444 444 #fi4 ,liverpool1 #fghj #ai #e #cdb #h #i #gj4 ,llanelly1 #h #ab #c #j #aa #i #ga4 ,london1 #aidc #h #i #ig #c #d #gb4 ,lyme1 444 444 #gc4 ,lynn1 #gi #g #g #d #ae #b #gd4 ,limerick1 #afj #b #d #h #c #b #ge4 ,londonderry1 #ajeh #b #d #ec #f #f #gf4 ,montrose1 #ceg #ac #b #ah #f #j #gg4 ,maldon1 444 444 #gh4 ,milford1 #ad #d #f #j #ai #g #gi4 ,maryport1 #hg #ag #a #d #e #g #hj4 ,newcastle-on-,tyne1 #baah #af #h #ge #b #i #ha4 ,newhaven1 #a #ad #aj #j #a #i #hb4 ,newport1 #da #b #h #b #a #a #hc4 ,newry1 #bcj #af #b #ac #c #i #hd4 ,perth1 #bge #ad #c #ad #ac #f #he4 ,port-,glasgow1 #dif #h #f #bd #af #c #hf4 ,padstow1 #b #ae #a #j #b #h #hg4 ,penzance1 #a #f #aj #j #a #d #hh4 ,plymouth1 #be #d #i #a #f #b #hi4 ,poole1 #j #aa #f #j #j #g #ij4 ,portsmouth1 #aj #ab #d #j #aj #f #ia4 ,preston1 #efb #a #aa #da #ad #aj #ib4 ,ramsgate1 444 444 #ic4 ,rochester1 #a #ae #a #j #a #aj #id4 ,rye1 #j #ah #c #j #j #aj #ie4 ,ross1 #ab #ag #aj #j #ab #aa #if4 ,stranraer1 #ij #ag #i #d #af #f #ig4 ,stornoway1 #ef #f #aa #b #af #b #ih4 ,scarborough1 #h #ad #aj #j #h #h #ii4 ,seilly1 444 444 #ajj4 ,shoreham1 #j #ai #f #j #j #aa #aja4 ,southampton1 #cj #j #i #a #aj #a #ajb4 ,st ,ives1 #c #i #i #j #e #b #ajc4 ,stockton1 #bbf #ai #b #ab #j #b #ajd4 ,sunderland1 #ijh #ad #i #dg #a #d #aje4 ,swansea1 #bh #d #i #a #ab #c #ajf4 ,sligo1 #cee #j #d #ai #ae #aj #ajg4 ,truro1 #j #aa #j #j #j #i #ajh4 ,tralee1 #i #g #aj #j #i #d #aji4 ,wick1 #cef #ag #i #bj #aj #b #aaj4 ,wigton1 #hc #i #e #e #e #e #aaa4 ,weymouth1 #j #ae #aj #j #j #i #aab4 ,whitby1 #ca #e #aj #a #aa #d #aac4 ,whitehaven1 #cbh #a #i #ah #e #e #aad4 ,woodbridge1 #c #ah #i #j #c #aa #aae4 ,waterford1 #eg #ad #c #b #ag #aj #aaf4 ,westport1 #da #j #f #b #a #j #aag4 ,wexford1 #cb #ai #b #a #ab #aa #aah4 ,yarmouth1 #di #e #f #b #i #e ------------------------------ #df1jja #aa #cbdja #g #c ,,deduct--,amount of fractions short credited by ,bank1 #j #j #a ------------------------------ #df1jja #aa #bbdja #g #c ,,gross ,,receipts1 -------------- ,,deduct--,commission1 #bdja #g #c ,repayments1 #bah #af #aj c41 -------------- ,,nett ,,duties received in year to #cast ,december #ahdf1 ---------------------------------------- ---------------- ---------------------------------------- --------------- ,repayments1 ,nett ,duties c4 ,received4 ---------------------------------------- --------------- #a4 ,aberdeen1 #e #ad #e #baae #ag #h #b4 ,alloa1 #f #ag #i #cgb #a #h #c4 ,arbroath1 #c #ag #g #bcg #h #a #d4 ,ayr1 #a #ae #aj #adh #ae #c #e4 ,aberystwith1 #j #a #j #f #i #i #f4 ,arundel1 444 #g4 ,banff1 #b #ai #c #dce #aj #h #h4 ,borrowstounness1 #i #d #a #fag #aj #c #i4 ,barnstaple1 444 #a #e #aj #aj4 ,beaumaris1 #j #ae #a #aaf #i #e #aa4 ,berwick1 #j #a #h #aad #g #c #ab4 ,bideford1 444 #h #f #b #ac4 ,boston1 #j #e #f #h #ah #aa #ad4 ,bridgewater1 #j #b #aj #aa #e #aj #ae4 ,bridlington1 444 #bd #ae #b #af4 ,bridport1 444 #b #ae #b #ag4 ,bristol1 #j #ad #j #aag #ad #j #ah4 ,baltimore1 444 #ai4 ,belfast1 #ef #ab #aj #bbfd #b #b #bj4 ,campbeltown1 #a #ab #h #gf #j #j #ba4 ,caernarvon1 #j #h #j #bc #ah #c #bb4 ,cardiff1 444 #aje #h #g #bc4 ,cardigan1 444 #a #f #d #bd4 ,carlisle1 #j #aj #e #gi #b #a #be4 ,chepstow1 444 #j #ad #b #bf4 ,chester1 #a #j #j #adi #b #aa #bg4 ,chichester1 444 #b #aa #i #bh4 ,clay1 444 #a #j #i #bi4 ,colchester1 444 #cj4 ,cowes1 444 #ca4 ,coleraine1 444 #if #d #a #cb4 ,cork1 #b #j #i #fe #a #aj #cc4 ,dunbar1 #j #aa #d #ajg #ai #e #cd4 ,dundee1 #g #ae #aj #aidi #f #aj #ce4 ,dumfries1 #b #aj #h #cbd #f #aj #cf4 ,dartmouth1 444 #cg4 ,deal1 444 #ch4 ,dover1 444 #j #g #g #ci4 ,dublin1 #i #af #i #bacc #j #d #dj4 ,drogheda1 444 #ada #ah #i #da4 ,dundalk1 #j #f #h #aac #ai #g #db4 ,exeter1 444 #b #ad #e #dc4 ,fisherrow1 #j #ae #c #bjd #ac #a #dd4 ,falmouth1 444 #de4 ,faversham1 444 #df4 ,fowey1 444 #b #a #aj #dg4 ,glasgow1 #aa #ae #aa #cdje #f #f #dh4 ,greenock1 #g #aj #f #bebe #af #g #di4 ,grangemouth1 #b #af #aj #aahf #d #a #ej4 ,gainsborough1 444 #e #ab #aa #ea4 ,gloucester1 #j #b #j #eh #i #c #eb4 ,goole1 444 #bi #aj #b #ec4 ,grimsby1 444 #fa #f #h #ed4 ,gweek1 444 #ee4 ,galway1 #j #f #j #cf #a #h #ef4 ,hartlepool1 444 #ade #aj #aj #eg4 ,harwich1 444 #eh4 ,hull1 #j #aj #j #adee #e #i #ei4 ,inverness1 #g #a #aa #heg #b #b #fj4 ,irvine1 #c #h #h #hdh #ac #c #fa4 ,ipswich1 #j #b #j #af #e #i #fb4 ,isle of ,man1 #a #ac #i #cdi #i #f #fc4 ,kirkcaldy1 #a #af #b #gjj #ac #a #fd4 ,kirkwall1 #j #i #i #abc #af #i #fe4 ,leith1 #ag #ad #b #cjde #h #i #ff4 ,lerwick1 #j #aa #a #afc #ag #j #fg4 ,lancaster1 #j #ah #h #ii #ah #b #fh4 ,leigh1 444 #fi4 ,liverpool1 #i #ac #aa #fdbh #af #i #gj4 ,llanelly1 444 #h #j #f #ga4 ,london1 444 #ahdf #e #e #gb4 ,lyme1 444 #gc4 ,lynn1 #j #g #b #gd #e #b #gd4 ,limerick1 #j #e #j #aea #ad #b #ge4 ,londonderry1 444 #ajjd #ae #aj #gf4 ,montrose1 #j #aj #c #cch #af #aa #gg4 ,maldon1 444 #gh4 ,milford1 444 #ac #d #aa #gi4 ,maryport1 #b #f #aa #ha #d #g #hj4 ,newcastle-on-,tyne1 #j #ad #h #bjdb #ai #c #ha4 ,newhaven1 444 #a #ac #a #hb4 ,newport1 444 #ci #a #f #hc4 ,newry1 #ad #f #aa #bjc #e #f #hd4 ,perth1 #j #ai #aj #bfj #j #aj #he4 ,port-,glasgow1 #j #ae #g #dgj #af #h #hf4 ,padstow1 #j #e #j #b #g #e #hg4 ,penzance1 444 #a #e #f #hh4 ,plymouth1 #j #a #j #bc #ag #g #hi4 ,poole1 444 #j #aj #aa #ij4 ,portsmouth1 #j #d #i #i #ag #a #ia4 ,preston1 444 #ebj #g #a #ib4 ,ramsgate1 444 #ic4 ,rochester1 444 #a #ac #c #id4 ,rye1 444 #j #ag #e #ie4 ,ross1 #j #d #g #ab #j #d #if4 ,stranraer1 #a #i #c #hd #ab #j #ig4 ,stornoway1 #j #c #f #ec #g #c #ih4 ,scarborough1 444 #h #f #b #ii4 ,seilly1 444 #ajj4 ,shoreham1 444 #j #ah #g #aja4 ,southampton1 444 #bh #aj #h #ajb4 ,st ,ives1 #j #j #a #c #d #f #ajc4 ,stockton1 #e #aa #j #bji #g #aa #ajd4 ,sunderland1 #j #ad #i #hfj #ah #h #aje4 ,swansea1 444 #bf #ab #f #ajf4 ,sligo1 #j #aj #d #ccd #ad #a #ajg4 ,truro1 444 #j #aj #c #ajh4 ,tralee1 #j #b #h #h #ae #aj #aji4 ,wick1 #d #i #a #cca #ah #f #aaj4 ,wigton1 #a #ab #aa #gf #aa #a #aaa4 ,weymouth1 444 #j #ae #a #aab4 ,whitby1 444 #bi #ad #f #aac4 ,whitehaven1 444 #cji #af #d #aad4 ,woodbridge1 444 #c #ad #aj #aae4 ,waterford1 444 #ed #af #e #aaf4 ,westport1 444 #ch #ai #f #aag4 ,wexford1 444 #ca #f #b #aah4 ,yarmouth1 444 #df #af #a -------------------------------- #bah #af #ajdc1cha #g #b ,,deduct--,amount of fractions short credited by ,bank1 #j #j #a -------------------------------- #bah #af #ajdc1cha #g #a ---------------- #df1jja #aa #b ,,deduct--,commission1 ,repayments1 c41 #bfbj #d #a ,,nett ,,duties received---------------- #dc1cha #g #a in year to #cast ,december #ahdf1 ---------------------------------------- ----------------- ,,no4 ,,ii4--,state shewing the ,gross ,receipts on account of each of the ,northern ,lighthouses1 the ,number of ,vessels1 and amount of ,tonnage passing them2--the ,particular ,expenses of the ,lighthouses1 and their ,proportions of the ,general ,expenses1 embracing ,commissions to1 and ,repayments by1 the ,collectors2 ,expenses of the ,shipping ,establishment1 ,salaries to ,officers1 ,experiments1 and other ,general ,expenses2 also the ,ordinary ,expenses of ,beacons and ,buoys1 for the ,year #ahdf4 ---------------------------------------- ----------------------- ,,no4 ,,of ,,vessels4 ,,tonnage4 -------------------------------- ,coast- ,over- ,coast- ,over- ing4 sea4 ing4 sea4 ,,lighthouses4 ---------------------------------------- --------------------- #ae1hgb #b1ffd #a1bch1jeg #bid1ed #a4 ,,inchkeith1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #bj1aja #c1cdi #a1hdc1baj #chc1eaf #b4 ,,isle ,,of ,,may1 ,add for ,leading ,light1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ad1faj #d1dhe #a1bii1hge #fcb1cbh #c4 ,,bell ,,rock1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #g1iae #c1igh #ghh1idg #ehg1igg #d4 ,,girdleness1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #e1bic #d1jab #dai1ihh #eij1dec #e4 ,,buchanness1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #d1hbi #b1hai #cij1aff #edf1hef #f4 ,,kinnairdshead1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #b1bef #bgc #aia1cde #ah1bhb #g4 ,,tarbetness1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #bgi #fdd #cb1adi #aac1eih #h4 ,,sumburghhead1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #cjg #b1cbf #cc1gaj #ebh1fdg #i4 ,,startpoint1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #b1dcd #b1dcj #aha1bhd #ebe1ehbaj4 ,,pentland ,,skerries1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #a1iaa #b1bfg #aci1cgi #ebd1fheaa4 ,,dunnethead1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #a1gjj #b1bca #aca1ach #eag1cccab4 ,,capewrath1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #a1gcd #a1aec #acg1jfj #bbf1idaac4 ,,island ,,glass1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ffi #a1hba #i1eag #dff1jajad4 ,,barrahead1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #eee #a1ghh #eb1eda #dfa1cacae4 ,,skerryvore1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #b1dcj #cd #aei1gai #d1dcfaf4 ,,lismore1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #c1aeb #a1eej #che1ghf #chb1hdaag4 ,,rhinns ,,of ,,islay1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #e1jbc #a1ddj #eji1iad #ceg1fhbah4 ,,mull ,,of ,,kintyre1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ab1cgb #a1icg #a1djc1cei #dej1hdiai4 ,,pladda1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ab1dec #b1ggf #a1djg1iba #fde1ddgbj4 ,,corsewall1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ab1hhd #b1deh #a1fdh1iae #eca1jefba4 ,,mull ,,of ,,galloway1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #i1aie #ih #gbi1iah #ag1dcabb4 ,,little ,,ross1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #i1gcc #a1jcd #hdc1bce #bji1bcgbc4 ,,point ,,of ,,ayre1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ac1hfg #b1eei #a1gfi1dge #edf1bddbd4 ,,calf ,,of ,,man 7#b ,lights71 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #a1eib #aih #acj1jbf #ad1bhhbe4 ,,covesea ,,skerries199 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #bf4 ,,cromarty199 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #bg4 ,,chanonry199 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #bh4 ,,loch ,,ryan199 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 99 ,,note4--,,covesea ,,skerries1 ,,cromarty1 and ,,chanonry1 were not lighted till the #aeth ,may1 to which is owing the small amount of their ,revenue2 and ,,loch ,,ryan was not lighted till the #c;d of ,march subsequent to the period embraced in this ,,state 4 -------------------------------- #afc1affej1cbdae1ibf1fcdi1egg1dgh ,,total1 ---------------------------------------- --------------------- ,the ,surplus amounts as above to ,and the ,deficiency to ,actual ,surplus1 ,,deduct--,fractions short--credited by ,bank1 c41 ,surplus1 as per p4 #dae1 ,,add--,the ,receipts derived from other sources besides ,light-duties1 per p4 #dai1 ,but there has been expended1 besides the amount allocated to the different ,lighthouses above1 as per p4 #dbe1 ,amount superexpended1 per p4 #dbe1 ---------------------------------------- ----------------- ,,gross ,,lighthouses4 ,,receipts4 ---------------------------------------- ----------------- #a4 ,,inchkeith1 #bebd #i #b ,particular ,expense1 #ehc #e #aj ,share of ,general ,expense1 #egg #ae #i ,,total ,,expenditure1 -------------- #aafa #a #g ,,balance1 -------------- #b4 ,,isle ,,of ,,may1 #cfgf #ah #aa ,add for ,leading ,light1 #adh #i #f --------------#chbe #h #e ,particular ,expense1 #ieb #c #i ,share of ,general ,expense1 #ida #h #f ,,total ,,expenditure1 -------------- #ahic #ab #c ,,balance1 -------------- #c4 ,,bell ,,rock1 #ecdb #ae #e ,particular ,expense1 #ihi #a #c ,share of ,general ,expense1 #igg #ag #i ,,total ,,expenditure1 -------------- #aiff #ai #j ,,balance1 -------------- #d4 ,,girdleness1 #bdeh #d #e ,particular ,expense1 #edh #ah #a ,share of ,general ,expense1 #edd #e #h ,,total ,,expenditure1 -------------- #ajic #c #i ,,balance1 -------------- #e4 ,,buchanness1 #ahhj #a #c ,particular ,expense1 #fbc #e #c ,share of ,general ,expense1 #fag #d #a ,,total ,,expenditure1 -------------- #abdj #i #d ,,balance1 -------------- #f4 ,,kinnairdshead1 #agdd #aa #c ,particular ,expense1 #egh #aj #j ,share of ,general ,expense1 #egc #af #aa ,,total ,,expenditure1 -------------- #aaeb #f #aa ,,balance1 -------------- #g4 ,,tarbetness1 #cbi #ag #d ,particular ,expense1 #egd #aa #aa ,share of ,general ,expense1 #efi #ah #a ,,total ,,expenditure1 -------------- #aadd #aj #j ,,balance1 -------------- #h4 ,,sumburghhead1 #bhf #ah #b ,particular ,expense1 #eig #e #c ,share of ,general ,expense1 #eia #aa #h ,,total ,,expenditure1 -------------- #aahh #ag #j ,,balance1 -------------- #i4 ,,startpoint1 #aaed #e #d ,particular ,expense1 #cdg #j #h ,share of ,general ,expense1 #cde #d #d ,,total ,,expenditure1 -------------- #fib #e #j ,,balance1 -------------- #aj4 ,,pentland ,,skerries1 #acgj #aj #e ,particular ,expense1 #hea #h #aa ,share of ,general ,expense1 #hda #ag #aj ,,total ,,expenditure1 -------------- #afic #f #i ,,balance1 -------------- #aa4 ,,dunnethead1 #acaa #a #aj ,particular ,expense1 #dgj #ai #g ,share of ,general ,expense1 #dfg #h #d ,,total ,,expenditure1 -------------- #ich #g #aa ,,balance1 -------------- #ab4 ,,capewrath1 #abgh #i #i ,particular ,expense1 #ehg #f #aa ,share of ,general ,expense1 #eha #ad #g ,,total ,,expenditure1 -------------- #aafi #a #f ,,balance1 -------------- #ac4 ,,island ,,glass1 #fgi #a #aj ,particular ,expense1 #eae #b #aj ,share of ,general ,expense1 #eaj #ae #f ,,total ,,expenditure1 -------------- #ajbe #ah #d ,,balance1 -------------- #ad4 ,,barrahead1 #ajfc #c #b ,particular ,expense1 #eid #c #aj ,share of ,general ,expense1 #ehh #ab #g ,,total ,,expenditure1 -------------- #aahb #af #e ,,balance1 -------------- #ae4 ,,skerryvore1 #bjij #aa #c ,particular ,expense1 #aabb #j #g ,share of ,general ,expense1 #aajh #ai #a ,,total ,,expenditure1 -------------- #bbci #ai #h ,,balance1 -------------- #af4 ,,lismore1 #bci #aa #d ,particular ,expense1 #eae #ad #b ,share of ,general ,expense1 #eaa #ae #d ,,total ,,expenditure1 -------------- #ajbg #i #f ,,balance1 -------------- #ag4 ,,rhinns ,,of ,,islay1 #adad #e #h ,particular ,expense1 #efi #ab #g ,share of ,general ,expense1 #efd #ai #f ,,total ,,expenditure1 -------------- #aacd #ab #b ,,balance1 -------------- #ah4 ,,mull ,,of ,,kintyre1 #aedi #j #a ,particular ,expense1 #eed #ag #aj ,share of ,general ,expense1 #eej #c #aj ,,total ,,expenditure1 -------------- #aaje #a #i ,,balance1 -------------- #ai4 ,,pladda1 #bgfb #ad #c ,particular ,expense1 #ehd #aj #aj ,share of ,general ,expense1 #egi #ae #b ,,total ,,expenditure1 -------------- #aafd #f #j ,,balance1 -------------- #bj4 ,,corsewall1 #bhaa #e #c ,particular ,expense1 #dfe #ac #d ,share of ,general ,expense1 #dfb #i #i ,,total ,,expenditure1 -------------- #ibh #c #a ,,balance1 -------------- #ba4 ,,mull ,,of ,,galloway1 #bhbc #ai #h ,particular ,expense1 #eag #j #e ,share of ,general ,expense1 #eab #ad #aa ,,total ,,expenditure1 -------------- #ajbi #ae #e ,,balance1 -------------- #bb4 ,,little ,,ross1 #aahg #g #i ,particular ,expense1 #eaf #ah #f ,share of ,general ,expense1 #eab #ad #aa ,,total ,,expenditure1 -------------- #ajbi #ac #e ,,balance1 -------------- #bc4 ,,point ,,of ,,ayre1 #agee #ag #e ,particular ,expense1 #dji #a #d ,share of ,general ,expense1 #djf #f #d ,,total ,,expenditure1 -------------- #hae #g #i ,,balance1 -------------- #bd4 ,,calf ,,of ,,man 7#b ,lights71 #chci #b #aa ,particular ,expense1 #hac #ai #e ,share of ,general ,expense1 #hje #h #g ,,total ,,expenditure1 -------------- #afai #h #j ,,balance1 -------------- #be4 ,,covesea ,,skerries199 #aic #g #j ,particular ,expense1 #dai #af #h ,share of ,general ,expense1 #dag #c #a ,,total ,,expenditure1 -------------- #hcf #ai #aj ,,balance1 -------------- #bf4 ,,cromarty199 #bg #ad #aa ,particular ,expense1 #cci #ag #c ,share of ,general ,expense1 #cch #f #d ,,total ,,expenditure1 -------------- #fgh #c #g ,,balance1 -------------- #bg4 ,,chanonry199 #eg #ae #a ,particular ,expense1 #bhd #g #a ,share of ,general ,expense1 #bhc #b #h ,,total ,,expenditure1 -------------- #efg #i #i ,,balance1 -------------- #bh4 ,,loch ,,ryan199 ,particular ,expense1 #agf #e #g ,share of ,general ,expense1 #agf #ad #a ,,total ,,expenditure1 -------------- 99 ,,note4--,,covesea ,,skerries1 ,,cromarty1 and ,,chanonry1 were not lighted till the #aeth ,may1 to which is owing the small amount of their ,revenue2 and ,,loch ,,ryan was not lighted till the #c;d of ,march subsequent to the period embraced in this ,,state 4 ,,total1 ---------------------------------------- ----------------- ,,reconcilement4 ---------------------------------------- ------------------- ,,lighthouses4 ,,surplus4 ,,deficiency4 ---------------------------------------- ------------------- #a4 ,,inchkeith1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #acfc #g #f #b4 ,,isle ,,of ,,may1 ,add for ,leading ,light1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #aica #af #b #c4 ,,bell ,,rock1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ccge #af #e #d4 ,,girdleness1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #acfe #j #h #e4 ,,buchanness1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #fci #aa #aj #f4 ,,kinnairdshead1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #eib #d #f #g4 ,,tarbetness1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #had #ab #g #h4 ,,sumburghhead1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ija #ah #i #i4 ,,startpoint1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #dfb #j #c #aj4 ,,pentland ,,skerries1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #cbb #af #c #aa4 ,,dunnethead1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #cgb #ac #aj #ab4 ,,capewrath1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #aji #h #b #ac4 ,,island ,,glass1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #cdf #af #f #ad4 ,,barrahead1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #aai #ac #b #ae4 ,,skerryvore1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #adj #h #d #af4 ,,lismore1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ghg #ah #b #ag4 ,,rhinns ,,of ,,islay1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #bgi #ac #f #ah4 ,,mull ,,of ,,kintyre1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ddc #ah #c #ai4 ,,pladda1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #aeih #h #c #bj4 ,,corsewall1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ahhc #b #b #ba4 ,,mull ,,of ,,galloway1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #agid #d #c #bb4 ,,little ,,ross1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #aeg #ad #d #bc4 ,,point ,,of ,,ayre1 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #idj #i #h #bd4 ,,calf ,,of ,,man 7#b ,lights71 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #bbai #ad #aj #be4 ,,covesea ,,skerries199 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #fdc #ab #aj #bf4 ,,cromarty199 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #fej #h #h #bg4 ,,chanonry199 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #eji #ad #h #bh4 ,,loch ,,ryan199 ,particular ,expense1 ,share of ,general ,expense1 ,,total ,,expenditure1 #ceb #ai #h 99 ,,note4--,,covesea ,,skerries1 ,,cromarty1 and ,,chanonry1 were not lighted till the #aeth ,may1 to which is owing the small amount of their ,revenue2 and ,,loch ,,ryan was not lighted till the #c;d of ,march subsequent to the period embraced in this ,,state 4 ------------------------------ ,,total1#ai1ebi #e #aeeia #j #j ---------------------------------------- ------------------- ---------------- #ai1ebi #e #a #e1eia #j #j ---------------- #ac1ich #e #j #j #j #a ---------------- #ac1ich #d #aa #a1hic #ag #f ---------------- #ae1hcb #b #e #bh1caa #i #f ---------------- #ab1dgi #g #j ,,note4--,the ,general ,expenses in the above ,,state are allocated to each ,lighthouse in the same proportions as the ,particular ,expenses4 ,the expense of ,beacons and ,buoys is equally divided by the number of ,lighthouses1 and the same amount allocated to each ,lighthouse4 ,no4 ,,iii4--,statement shewing the ,increase in ,tonnage during the ,years #ahdc-dd-de-df1 over #ahdb4 ---------------------------------------- -------------------------- ,the amount of the ,tonnage in #ahdb was in #ahdc ,,increase in #ahdc over #ahdb ----------------------------- ,coasting4 ,oversea4 ,total4 ----------------------------- ,the amount of ,tonnage in #ahdc was #ab1aij1gdeg1aid1icbai1che1fgg in #ahdd #ac1dbe1fadg1gcg1fagba1afc1bca ,,increase in #ahdd over #ahdc ----------------------------- ,,increase in #ahdd over #ahdb ----------------------------- ,coasting4 ,oversea4 ,total4 ----------------------------- ,the amount of ,tonnage in #ahdd was #ac1dbe1fadg1gcg1fagba1afc1bca in #ahde #ae1eff1dfai1cjj1ihcbd1hfg1ddd ,,increase in #ahde over #ahdd ----------------------------- ,,increase in #ahde over #ahdb ----------------------------- ,coasting4 ,oversea4 ,total4 ----------------------------- ,the amount of ,tonnage in #ahde was #ae1eff1dfai1cjj1ihcbd1hfg1ddd in #ahdf #ae1ibf1fcdi1egg1dghbe1ejd1aab ,,increase in #ahdf over #ahde ----------------------------- ,,increase in #ahdf over #ahdb ---------------------------------------- --------------------------- ---------------------------------------- ----------------------- ,coasting4 ,oversea4 ,total4 ----------------------------- ,the amount of the ,tonnage in #ahdb #aa1fbj1agbf1gch1dccah1ceh1fje in #ahdc #ab1aij1gdeg1aid1icbai1che1fgg ----------------------------- #egj1egc #def1dii #a1jbg1jgb ,the amount of ,tonnage in #ahdc was in #ahdd ,,increase in #ahdd over #ahdc #a1bcd1hfi #edb1fhe #a1ggg1eed ----------------------------- #a1hje1ddb #iii1ahd #b1hjd1fbf ,the amount of ,tonnage in #ahdd was in #ahde ,,increase in #ahde over #ahdd #b1adj1hdga1efc1cff #c1gjd1bac ----------------------------- #c1idf1bhib1efb1eej #f1ejh1hci ,the amount of ,tonnage in #ahde was in #ahdf ,,increase in #ahdf over #ahde #cfj1agc #bgf1die #fcf1ffh ----------------------------- #d1cjf1dfbb1hci1jde #g1ade1ejg ---------------------------------------- ------------------------- ,,appendix1 ,no4 ,x4 ,,instructions ,,to ,,the ,,light-,,keepers ,,in ,,the ,,service ,,of ,,the ,,commissioners ,,of ,,northern ,,lighthouses4 #a4 ,the ,lamps shall be kept burning bright and clear every night from sunset to sunrise2 and in order that the greatest degree of light may be maintained throughout the night1 the ,wicks must be trimmed every four hours1 or oftener if necessary2 and the ,keeper who has the first watch shall take care to turn the oil-valves so as to let the oil flow into the ,burner a sufficient time before lighting4 #b4 ,the ,light-keepers shall keep a regular and constant ,watch in the ,light-room throughout the night4 ,the ,first ,watch shall begin at sunset4 ,the ,light-keepers are to take the watches alternately1 in such manner that he who has the first watch one night1 shall have the second watch next night4 ,the length or duration of the watch shall not1 in ordinary cases1 exceed four hours2 but during the period between the months of ,october and ,march1 both inclusive1 the first watch shall change at eight o'clock4 ,the watches shall at all times be so arranged as to have a shift at midnight4 #c4 ,at stations where there is only one ,light-room1 the daily duty shall be laid out in two departments1 and the ,light-keepers shall change from one department to the other every ,saturday night4 #d4 ,,first ,,department4--,the ,light-keeper who has this department1 shall immediately after the morning ,watch1 polish or otherwise cleanse the ,reflectors or ,refractors till they are brought into a proper state of brilliancy2 he shall also thoroughly cleanse the lamps1 and carefully dust the ,chandelier4 ,he shall supply the ,burners with cotton1 the ,lamps with oil1 and shall have every thing connected with the ,apparatus in a state of readiness for lighting in the evening4 #e4 ,,second ,,department4--,the ,light-keeper who has this department shall cleanse the glass of the ,lantern1 lamp-glasses1 copper and brass work and utensils1 the walls1 floors1 and balcony of the ,light-room1 and the apparatus and machinery therewith connected2 together with the ,tower stair1 passage1 doors1 and windows1 from the ,light-room to the ,oil cellar4 #f4 ,for the more effectual cleansing of the glass of the ,lantern1 and management of the ,lamps at the time of lighting1 both ,light-keepers shall be upon watch throughout the first hour of the first watch every night1 during the winter period1 between the first day of ,october and last day of ,march1 when they shall jointly do the duty of the ,light-room during that hour4 ,these changes to and from the double watch shall be intimated by the ,keepers in the ,monthly ,returns for ,october and ,april4 #g4 ,at those stations where there are two ,light-rooms1 each ,light-keeper shall perform the entire duty of both departments in that ,light-room to which he may be especially appointed4 ,but after the first hour of the first ,watch1 the ,light-keeper who has charge of this watch shall perform the whole duty of trimming and attending the ,lights of both ,light-rooms till the expiry of his watch2 and in like manner1 his successor on the watch shall perform the whole duty of both ,light-rooms during his watch4 #h4 ,the ,light-keeper on duty shall on no pretence whatever1 during his watch1 leave the ,light-room and balcony1 or the passage leading from one ,light-room to another1 at stations where there are two ,lights4 ,bells are provided at each ,light-room to enable the ,light-keeper on duty to summon the absent ,light-keeper2 and if at any time the ,light-keeper on duty shall think the presence or assistance of the ,light-keeper not on duty is necessary1 he shall call him by ringing his bell1 which should be immediately answered by the return signal1 and the ,keeper so called1 should repair to the ,light-room without delay4 ,in like manner1 when the watches come to be changed1 the bell shall be rung to call the ,light-keeper next in turn4 ,after which the ,light-keeper on duty shall1 at his peril1 remain on guard till he is relieved by the ,light-keeper in person who has the next watch4 #i4 ,should the bell of the ,light-keeper whose turn it is to mount guard1 happen to be in an unserviceable state1 the other house-bell shall be used1 and some of the inmates of that house shall call the ,light-keeper not on duty1 so as by all means to avoid leaving the ,light-room without a constant watch during the night4 #aj4 ,the ,principal ,light-keeper is held responsible for the safety and good order of the ,stores1 ,utensils1 and apparatus of what kind soever1 and for every thing being put to its proper use1 and kept in its proper place4 ,he shall take care that none of the stores or materials are wasted1 and shall observe the strictest economy1 and the most careful management1 yet so as to maintain in every respect the best possible light4 #aa4 ,the ,principal ,light-keeper shall daily serve out the allowance of ,oil and other ,stores for the use of the ,light-room4 ,the oil is to be measured by the ,assistant1 at the sight of the ,principal ,light-keeper4 #ab4 ,the ,light-keepers shall keep a daily ,journal of the quantity of ,oil expended1 the routine of their duty1 and the state of the ,weather1 embodying any other remarks that may occur4 ,these shall be written in the ,journal-,books to be kept at each station for the purpose1 at the periods of the day when they occur1 as they must on no account be trusted to memory4 ,on the first day of each month they shall make up and transmit to the ,engineer a return1 which shall be an accurate copy of the ,journal for the preceding month4 #ac4 ,the ,light-keepers are also required to take notice of any ,shipwreck which shall happen within the district of the ,lighthouse1 and to enter an account thereof1 according to the prescribed form1 in a ,book furnished to each ,station for this purpose2 and in such account he shall state whether the ,light was seen by any one on board the shipwrecked ,vessel and recognised by them1 and how long it was seen before the vessel struck4 ,a copy of this entry shall form the ,shipwreck ,return1 to be forthwith forwarded to the ,engineer4 #ad4 ,a book containing a ,note of the ,vessels passing each ,lighthouse daily shall be kept2 and an annual ,schedule1 shewing the number of vessels in each month1 shall be sent to the ,engineer in the month of ,january4 #ae4 ,the ,monthly and ,shipwreck ,returns are to be written by the ,assistant1 and the accompanying letters by the ,principal ,light-keeper4 ,the whole shall be carefully compared and signed by both ,light-keepers1 as directed by the printed form1 and despatched by post to the ,engineer as soon as possible4 #af4 ,for the purpose of keeping up the practical knowledge of the 8,occasional ,keeper10 he shall be annually called in by the ,principal ,light-keeper to do duty for a fortnight in the month of ,january2 and the same shall be stated in the ,monthly ,letter4 #ag4 ,the ,principal ,light-keeper is held responsible for the regularity of the ,watches throughout the night1 for the cleanliness and good order of the ,reflecting or ,refracting ,apparatus1 ,machinery1 and ,utensils1 and for the due performance of the whole duty of the ,light-room or ,light-rooms1 as the case may be1 whether performed by him personally1 or by the ,assistant4 #ah4 ,the ,principal ,light-keeper is also held responsible for the good order and condition of the ,household ,furniture belonging to the ,lighthouse ,board1 as well in his own as in the ,assistant's house4 ,this duty extends also to the cleanliness of the several apartments1 passages1 stairs1 roofs1 water-cisterns1 store-rooms1 work-shops1 privies1 ash-pits of the dwelling-houses1 offices1 court1 and immediate access to the ,lighthouse4 #ai4 ,the ,light-keepers shall endeavour to keep in good order and repair the ,dykes enclosing the ,lighthouse grounds1 the ,landing-places1 and ,roads leading from thence to the ,lighthouse and the ,drains therewith connected1 together with all other things placed under their charge4 #bj4 ,when stores of any kind are to be landed for the use of the ,lighthouse1 the ,light-keepers shall attend and give their assistance4 ,the ,principal ,light-keeper must1 upon these occasions1 satisfy himself1 as far as possible1 of the quantity and condition of the stores received1 which must be duly entered in the ,store-book and ,monthly ,return-book4 #ba4 ,the ,light-keepers are to make a ,report of the quality of the ,stores1 in the ,monthly ,return for ,march annually1 or earlier should circumstances render this necessary2 and this ,report must proceed upon special trial of the several ,cisterns of ,oil and of the other ,stores in detail1 both at the time of receiving them and after the experience of the winter months4 #bb4 ,at all stations where ,peat ,fuel is in use1 there must be such a quantity of ,peats provided1 that the ,stock of the former year shall be a sufficient supply to the end of the current year4 #bc4 ,should the supply of any of the ,lighthouse ,stores at any time appear to the ,principal ,light-keeper to be getting short1 so as thereby to endanger the regular appearance of the ,light1 he shall immediately intimate the same to the ,engineer1 and he must be guided by prudence in reducing the stated number of ,burners until a supply be received4 #bd4 ,the ,light-keepers are prohibited from carrying on any trade or business whatever4 ,they are also prohibited from having any boarders or lodgers in their dwelling-houses1 and from keeping dogs at the ,lighthouse establishments4 #be4 ,the ,light-keepers are also directed to take care that no smuggled goods are harboured or concealed in any way in or about the ,lighthouse premises or grounds4 #bf4 ,the ,light-keepers have permission to go from home to draw their salaries1 and also to attend church4 ,the ,assistant ,light-keeper1 on all occasions of leave of absence1 must consult the ,principal ,light-keeper as to the proper time for such leave1 and obtain his consent2 in like manner1 the ,principal ,light-keeper shall duly intimate his intention of going from home to the ,assistant ,light-keeper2--it being expressly ordered that only one ,light-keeper shall be absent from the ,lighthouse at one and the same time4 #bg4 ,while the ,principal ,light-keeper is absent1 or is incapacitated for duty by sickness1 the full charge of the ,light-room duty and of the premises shall devolve upon the ,assistant1 who shall in that case have access to the keys of the ,light-room stores1 and be held responsible in all respects as the ,principal ,light-keeper2 and in the case of the incapacity of either ,light-keeper1 the assistance of the ,occasional ,light-keeper shall be immediately called in1 and notice of the same given to the ,engineer4 ,notice of any such occurrences to be taken in the ,monthly ,return1 or by special letter to the ,engineer1 should circumstances render this necessary4 #bh4 ,the ,light-keepers are required to be sober and industrious1 cleanly in their persons and linens1 and orderly in their families4 ,they must conduct themselves with civility to strangers1 by shewing the premises1 at such hours as do not interfere with the proper duties of their office2 it being expressly understood1 that strangers shall not be admitted into the ,light-room after sunset4 ,but no money or other gratuity shall be taken from strangers on any pretence whatever4 #bi4 ,the ,light-keepers are to appear in their ,uniform-dress when any of the ,commissioners or ,principal ,officers visit a station1 and also on ,sunday2--on which day1 at noon1 the weather permitting1 the ,lighthouse flag shall be hoisted by the ,assistant ,light-keeper1 or in his absence by the ,principal ,light-keeper1 when it shall remain displayed until sunset4 #cj4 ,these ,instructions are to be read in the ,light-room by the ,principal ,light-keeper1 in the hearing of his ,assistant1 on the term days1 before drawing his salary2 and notice thereof taken in the ,monthly ,returns4 #ca4 ,in the event of any neglect occurring in the performance of any part of the duties required from a ,light-keeper1 the offending party shall1 jointly with the other ,light-keeper or ,light-keepers at the station1 send immediate notice of the circumstance to the ,engineer2 and in the event of one party refusing or neglecting to concur in giving this intimation1 the others 7whether ,principals or ,assistants7 shall proceed to give the notice in their own names4 #cb4 ,the breach of any of the foregoing ,rules and ,instructions shall subject the ,light-keepers to dismissal1 or to such other punishment as the nature of the offence may require4 #cc4 ,it is recommended that the ,principal ,light-keeper1 or other ,principal ,officer at the respective ,lighthouses for the time being1 shall1 every ,sunday1 perform the service pointed out for the inmates1 by reading a portion of the ,scriptures1 and any other religious book furnished by the ,board1 and the ,prayer composed for their use by the ,rev4 ,dr ,brunton1 one of the ,ministers of ,edinburgh1 or other ,prayers in any work furnished by the ,board4 ,for this purpose1 the ,principal ,light-keeper shall invite the families to assemble at noon in the ,visiting ,officer's room4 #cd4 ,the ,light-keepers are to observe that the above general ,regulations are without prejudice to any more special ,instructions which may be made applicable to any particular ,lighthouse1 or to such orders as may from time to time be issued by the ,engineer4 ,,alan ,,stevenson1 ,engineer for ,northern ,lighthouses4 ,,northern ,,lights ,,office1 ,,edinburgh1 #afth ,june #ahdg4 ,,edinburgh1 #afth ,june #ahdg4 ,,the ,,commissioners having considered the preceding ,,rules and ,,instructions1 approve of the same1 direct them to be substituted for those now in use1 appoint them to be signed by the ,engineer1 and copies of them and of this ,minute to be issued to the present ,light-keepers2 direct a copy to be delivered in future to each ,light-keeper at the time of his appointment1 that they may understand that they are placed under the department and superintendence of the ,engineer1 who is held responsible for the strict observance of the ,rules and ,instructions1 and for their general good conduct2 that the ,engineer has power1 in case of neglect or disobedience1 instantly to suspend and remove any of the ,light-keepers1 and to report the case to the ,commissioners1 by whom it will be considered1 and the offending party subjected to dismissal1 or such other punishment as the offence may merit4 ,in case of a punishment less than dismissal1 that circumstance1 as well as the general conduct of the ,light-keeper1 will always be taken into consideration when any application may be made for superannuated allowance4 ,extracted from the ,minutes by ,,alex4 ,,cuningham1 ,sec4 ,,edinburgh3 ,,printed ,,by ,,neill ,,and ,,company1 ,,old ,,fishmarket4 ,illustration3 ,,plate ,i ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,,chart ,shewing the ,situation of the ,,skerryvore ,,lighthouse ,stevensons ,account of ,skerryvore ,lighthouse ,illustration3 ,,plate ,,ii4 ,engraved by ,w4 ,a4 ,k4 ,johnston4 ,edinburgh4 ,,chart of the ,,position of the ,,skerryvore ,,rocks ,,foulground from a ,survey made for the ,,commissioners ,,of ,,northern ,,light ,,houses ,,james ,,ritson ,,surveyor #ahdf4 ,stevenson's ,account of the ,skerryvore ,lighthouse4 ,illustration3 ,,plate ,stevenson's ,account of ,skerryvore ,lighthouse4 ,james ,andrews1 ,delt4 ,william ,miller1 ,sculpt4 ,,plan ,,of ,,skerryvore ,,rock ,,at ,,low ,,water ,,of ,,spring ,,tides4 ,shewing the site of the ,lighthouse ,tower1 ,barracks1 ,cranes1 fresh ,water ,tanks1 ,railway c4 ,ilustration3 ,no4 ,,iii4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,james ,andrews1 ,delt4 ,william ,miller1 ,sculpt4 ,,plan ,,of ,,skerryvore ,,rock ,,at ,,high ,,water ,,of ,,spring ,,tides4 ,illustration3 ,,plate ,,iv4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,james ,andrews1 ,delt4 ,g4 ,aikman ,sc ,,curves ,,for ,,lighthouse ,,towers ,,parabola ,,conchoid ,,logarithmic ,,hyperbola ,illustration3 ,w4 ,a4 ,k4 ,johnston ,sculpt4 ,,marine ,,dynamometer1 ,,small ,,size1 ,,length #ah ,,inches4 ,illustration3 ,,plate ,v4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,walter ,ferrier ,delt4 ,g4 ,aikman ,sculpt4 ,,temporary ,,barrack4 ,barrack ,room for ,workmen ,engineer ,foreman's ,apartments ,kitchen ,provision ,store ,store for ,coals c4 ,illustration3 ,,plate ,,vi4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,walter ,ferrier ,delt4 ,g4 ,aikman ,sculpt4 ,elevation ,fig4 #a ,,temporary ,,barrack4 ,,top ,,fixtures4 ,plan ,fig4 #b ,illustration3 ,,plate ,,vii4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,james ,andrews1 ,delt4 ,william ,miller1 ,sculpt4 ,,elevation4 ,illustration3 ,,plate ,,viii4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,james ,andrews1 ,delt4 ,william ,miller1 ,sculpt4 ,,section4 #hdth4 ,course #idth4 ,course #cb;d4 ,course #bhth4 ,course #ast4 ,course #aith4 ,course ,illustration3 ,,plate ,,ix4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,g4 ,h4 ,slight ,delt4 ,w4 ,h4 ,lizars ,sculpt4 ,,balance ,,crane ,,used ,,at ,,skerryvore4 ,elevation ,plan ,section shewing ,rollers ,plan of ,rollers ,plan of ,pedestal ,frame ,circle ,end view of ,crane ,illustration3 ,,plate ,x4 ,engraved by ,w4 ,a4 ,k4 ,johnston1 ,edinburgh4 ,,plan of ,,establishment at ,,hynish1 ,,island ,,of ,,tyree4 ,,shewing ,,the ,,pier1 ,,dock1 ,,reservoir1 ,,lightkeepers ,,and ,,seamens ,,houses c4 ,,note ,the ,soundings are marked in a fractional form thus in which the figures in the place of the ,numerator indicate the depth at high water of spring tides and those in the place of the ,denominator the depth at low water of spring tides1 the rise of tide being #ab feet4 ,stevensons account of the ,skerryvore ,light ,house ,illustration3 ,,plate ,,xi4 ,walter ,ferrier1 ,delt4 ,william ,miller1 ,sculpt4 ,,hynish ,,dock4 ,elevation4 ,section across ,gates4 ,,single ,,boom ,illustration3 ,,plate ,,xii ,j4 ,l4 ,kerr1 delt4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,annular ,,lens ,,of ,,first ,,order ,,scale th44 ,,full ,,size ,,plan ,,section ,,through ,a4,b4 ,,table ,,of ,,elements ,,of ,,lens ,,in ,,millim,,tres ---------------------------------------- ,,co-,,ordinates ,,to ,,centres ,,of ,,radius ,,radius ,,curvature ,,of ,,of ---------------- ,no,,periphery,,curvature x y --------------------------------------- #a #adj4jj #dhc4ej #ded4gi #jj4jj #b #bjh4ae #edc4fj #dhh4ee #ac4jh #c #bfb4dj #eih4fb #eac4ch #ca4gb #d #cji4bj #fei4gg #edj4ga #eg4jj #e #cej4ej #gai4hd #efe4bg #hd4hf #f #chg4dd #ggi4dh #ehh4jj #aad4ic #g #dbb4bc #hdf4de #fad4ce #aea4ej #h #def4bc #iaa4cj #fcf4ij #ahi4ee #i #dij4jj #ihj4cj #ffj4aa #bej4ag #aj #ebc4cc #ajeg4gj #fhc4da #bhj4fj #aa #eec4cc #aacf4ja #gab4gi #cbh4jj --------------------------------------- ,illustration3 ,,plate ,,xiii ,g4 ,h4 ,slight ,delt4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,revolving ,,dioptric ,,apparatus ,,first ,,order4 ,,one ,,twentieth ,,of ,,full ,,size4 ,illustration3 ,,plate ,,xiv4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,g4 ,aikman1 ,sculpt4 ,,revolving ,,dioptric ,,light ,,of ,,the ,,first ,,order4 ,plan ,illustration3 ,,plate ,,xv4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,g4 ,aikman1 ,sculpt4 ,,fixed ,,dioptric ,,light ,,of ,,the ,,first ,,order4 ,vertical ,section4 ,illustration3 ,,plate4 ,,xvi4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,j4 ,andrews ,delt4 ,w4 ,h4 ,lizars ,sculpt4 #ast4 ,,order of ,,lights4 ,,concave ,,mirrors4 ,illustration3 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,plate ,,xvii4 ,,fixed ,,catadioptric ,,light ,,of #ast4 ,,order ,,one ,,nineteenth ,,of ,,full ,,size ,,references4 ,a ,b ,c4 ,,catadioptric ,,zones4 ,d ,e ,f4 ,,compound ,,dioptric ,,belt ,,with ,,diagonal ,,joints ,c ,n ,m4 ,a ,b ,c4 ,,lower ,,catadioptric ,,zones ,,one ,,division ,,being ,,left ,,out ,,for ,,free ,,access ,,to ,,the ,,lamp4 ,f4 ,,focus ,,with ,,flame ,,of ,,lamp4 ,,references4 ,x ,x ,x4 ,,diagonal ,,supports ,,for ,,the ,,upper ,,catadioptric ,,zones4 ,h ,h4 ,,service ,,table ,,on ,,which ,,the ,,lamp ,,rests ,,where ,,the ,,keeper ,,stands ,,to ,,trim ,,the ,,burner4 ,r ,r4 ,,diagonal ,,frame ,,for ,,carrying ,,the ,,apparatus4 ,james ,andrews1 ,delt4 ,william ,miller1 ,sc4 ,illustration3 ,,plate ,,xviii4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,g4 ,h4 ,slight ,delt4 ,w4 ,h4 ,lizars ,sculpt4 #ast4 ,,order of ,,lights4 ,,fixed ,,catadioptric ,,apparatus4 ,illustration3 ,,plate ,,xix4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,catadioptric ,,apparatus4 ,,fourth ,,order ,illustration3 ,,plate ,,xx ,stevenson's ,account of ,skerryvore ,lighthouse4 ,walter ,h4 ,ferrier1 delt4 ,engraved by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,,mechanical ,,lamp for ,,dioptric ,,lights of ,,first ,,order4 ,a ,,wick ,,holders ,b ,,glass ,,holder ,c ,,screw ,,to ,,rack ,d ,,for ,,raising ,,wick ,d ,,rack ,,for ,do4 ,e ,,pipe ,,supplying ,,oil ,,to ,,wicks ,f ,,collar ,,supporting ,,burners ,g ,,drip ,,cup ,h ,,return ,,pipe ,,for ,,oil ,,overflowing ,,burner ,i ,,valve ,,box ,j ,,crank ,,rods ,,for ,,working ,,leather ,,valves ,k ,,hinge ,,of ,,lid ,l ,,lid ,,of ,,cistern ,m ,,oil ,,cistern ,n ,,suction ,,pipe ,o ,,winding ,,arbour ,,for ,,machine ,p ,,box ,,for ,,machinery ,q ,,screw ,,for ,,adjusting ,,level ,,of ,,burner ,r ,,service ,,table ,s ,,coupling ,,screw ,,for ,,oil ,,tube ,t ,,universal ,,joints ,,for ,,connecting ,,rod ,u ,,crane ,,for ,,emptying ,,cistern ,v ,,connecting ,,rod ,,for ,,cranks ,illustration3 ,,plate ,,xxi ,stevenson's ,account of ,skerryvore ,lighthouse4 ,walter ,h4 ,ferrier1 delt4 ,engraved by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,,mechanical ,,lamp4 ,,enlarged ,,views ,,of ,,oil ,,pumps4 ,,elevation ,j ,,supports ,,of ,,burner ,p ,,crank ,,rods ,,for ,,leather ,,valves ,m ,n ,,supports ,,for ,,crank ,,rods ,l ,,coupling ,t ,,universal ,,joint ,p ,,connecting ,,rod ,,for ,,cranks ,s ,,suction ,,pipe ,o ,,square ,,tray ,,for ,,overflowing ,,oil ,q ,,lid ,,of ,,oil ,,cistern ,i ,,oil ,,tube ,,plans ,,and ,,sections ,,in ,,reference ,,to ,,opposite ,,plate4 ,,section ,,on ,,line ,a4 ,b4 ,,section ,,of ,,discharging ,,chest ,e4 ,,plan ,,of ,,upper ,,side ,,of ,,pump ,,chamber ,,at ,f4 ,f4 ,,plan ,,of ,,valves ,,at ,f4 ,f4 ,,and ,h4 ,h4 ,,section ,,on ,,line ,c4 ,d4 ,,plan ,,and ,,section ,,of ,,plate ,k4 ,,plan ,,of ,,lower ,,side ,,of ,,pump ,,chamber ,,at ,h4 ,h4 ,illustration3 ,,plate ,,xxii ,walter ,h4 ,ferrier1 delt4 ,engraved by ,w4 ,a4 ,k4 ,johnston1 ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,mechanical ,,lamp ,,enlarged ,,views ,,of ,,oil ,,pumps4 ,,elevation ,,front ,,view ,,of ,,leather ,,pistons ,,and ,,levers ,,working ,,into ,,pump ,j ,,supports ,,of ,,burner ,p ,,crank ,,rods ,,for ,,leather ,,valves ,m ,n ,,supports ,,for ,,crank ,,rods ,l ,,coupling ,t ,,universal ,,joint ,r ,,connecting ,,rod ,,for ,,cranks ,s ,,suction ,,pipe ,o ,,square ,,tray ,,for ,,overflowing ,,oil ,q ,,lid ,,of ,,oil ,,cistern ,i ,,oil ,,tube ,,plan ,illustration3 ,,plate ,,xxiii ,walter ,h4 ,ferrier ,delt4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,clockwork ,,movement ,,of ,,mechanical ,,lamp ,,plan ,,of ,,clockwork ,,side ,,view ,,of ,,clockwork ,illustration3 ,,plate ,,xxiv ,james ,andrews1 delt4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,clockwork ,,movement ,,and ,,burner ,,of ,,mechanical ,,lamp ,,section ,,of ,,burners ,,elevation ,,of ,,wickholder ,,elevation ,,of ,,inner ,,tube ,,of ,,glass ,,gallery ,,plan ,,of ,,burners ,,plan ,,of ,,the ,,lower ,,side ,,of ,,burners ,,shewing ,,the ,,handles ,,of ,,the ,,racks ,,for ,,elevating ,,the ,,wicks ,a4 ,,universal ,,joint ,,of ,,pump ,,rod ,b4 ,,regulator ,c4 ,,chain ,,barrel ,d4 ,,chain ,e4 ,,driving ,,wheel ,f4 ,,bevel ,,wheels ,,for ,,horizontal ,,motion ,g4 ,,wheel ,,with ,,cogs ,,for ,,lifting ,,bell-,,hammer ,h4 ,,hammer ,,for ,,striking ,,alarum ,,bell ,i4 ,,alarum ,,bell ,,which ,,repeats ,,while ,,the ,,pump ,,is ,,working ,k4 ,,endless ,,screw ,,on ,,axis ,,of ,,regulator ,l4 ,,winding ,,arbour ,,end ,,view ,,of ,,clockwork ,illustration3 ,,plate ,,xxv4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,g4 ,aikman1 ,sculpt4 ,,flame ,,for #ast4 ,,order ,,of ,,dioptric ,,lights at full size4 ,illustration3 ,,plate ,,xxvi ,james ,andrews ,delt4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,lantern #a,,st4 ,,order ,,of ,,lights4 ,,parapet ,,wall ,,elevation ,,side ,,view ,,of ,,upper ,,parts ,,of ,,astragals ,,elevation ,,plan ,,of ,,horizontal ,,parts ,,of ,,astragals ,,enlarged ,,sections ,,of ,,astragals ,,enlarged ,,section ,,of ,,cornice ,,elevation ,,side ,,view ,,of ,,lower ,,parts ,,of ,,astragals ,,enlarged ,,section ,,of ,,sole ,,plate ,,astragal ,illustration3 ,,plate ,,xxvii4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,james ,andrews1 ,delt4 ,william ,miller1 ,sculpt4 ,,ardnamurchan ,,lighthouse4 ,illustration3 ,,plate ,,xxviii4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,h4 ,g4 ,slight delt4 ,g4 ,aikman ,sculpt4 ,,ardnamurchan ,,lighthouse4 ,,plan ,illustration3 ,,plate ,,xxix ,james ,andrews ,delt4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,floating ,,light ,,vessel ,reduced from ,drawings in possession of ,honble4 ,corporation of ,trinity ,house ,deptford ,strond4 ,,dimensions ,ft4 ,in4 ,length between the perpendiculars #hjj ,breadth moulded #bjf ,do4 extreme #baj ,depth in hold #ajh ,burthen in ,tons #aeh ,illustration3 ,,plate ,,xxx ,g4 ,h4 ,slight ,delt4 ,engraved by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,,elevation ,,of ,,covesea ,,skerries ,,beacon4 ,n4 ,b4 ,the ,letters refer to those in ,plate ,,xxxi4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,illustration3 ,,plate ,,xxxi ,g4 ,h4 ,slight4 ,delt4 ,engraved by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,,covesea ,,skerries ,,beacon ,plan on c d ,plan on a b ,section showing connection of cage with main ,pillars ,plan on e f ,section showing connection of ,pillars ,section showing attachment of ,pillars to the ,sole plates and its connection with ,rocks by ,bats ,connecting ,plate ,plan on g h ,stevenson's ,account of ,skerryvore ,lighthouse4 ,illustration3 ,,plate ,,xxxii ,james ,andrews ,delt4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse ,,stone ,,beacon ,,elevation ,,section ,,iron ,,beacon ,,elevation ,,section ,illustration3 ,,plate ,,xxxiii ,james ,andrews ,delt4 ,engd4 by ,w4 ,a4 ,k4 ,johnston ,edinr4 ,stevenson's ,account of ,skerryvore ,lighthouse4 ,,buoys ,,mast ,,buoy ,,can ,,buoy ,,cask ,,buoy ,,nun ,,buoy ,,for ,,wrecks ,,spherical ,,buoy ,,nelson ,,buoy ,,river ,,ribble ,,fairway ,,buoy ,,river ,,tay ,transcriber's ,notes ,inconsistent1 archaic spelling1 hyphenation1 typography etc4 have been retained1 also in proper and geographic names and in numbering of illustrations and plates1 except as listed under ,changes below4 ,depending on the hard- and software used and their settings not all elements may display as intended4 ,the book regularly refers to a book published by the author's father3 ,an ,account of the ,bell ,rock ,light-,house by ,robert ,stevenson1 which is available at ,project ,gutenberg3 https3_/_/www4gutenberg4org_/ebooks_/#dh dad4 ,page xi3 the errata have already been corrected in the text2 see also under ,changes made below4 ,page #adi1 444 the same mass of ,mull stone would weigh #dbeb tons 4443 possibly an error for #daeb tons 7which would make the calculation correct74 ,page #agd3 444 somewhat on the same plan as that which is described in the ,appendix 4443 it is not clear to which ,appendix this refers2 possibly the reference is to ,plate ,,xxxi4 ,page #beb ff43 ,figures #ei and #fj are identical4 ,page #bga ff43 ,figures #ga and #gb are identical4 ,page #bgf1 ,see fig4 #gc and the following paragraph3 the description appears to refer to ,fig4 #ga_/gb rather than to fig4 #gc4 ,page #cfb1 ,conversely1 n is the origin of the co-ordinates for the grinding centre ,o of the interior convex refracting surface ,,bc1 4443 in the illustration 7,fig4 #aaj7 this appears to be a lower case o4 ,page #chi1 entries for ,may #ad and #ae1 #ahdd3 the order as given here is the one printed in the source document2 the reason for the inverse order is not clear4 ,page #dbb1 item ,charities 4c1 number #b3 ,since last ,act3 there appears to be a discrepancy between the individual amounts paid out and the sub-total given4 ,changes made3 ,footnotes1 illustrations and tables have been moved outside text paragraphs2 marginalia have been moved to directly above the paragraphs they refer to4 ,some of the wider tables have been split into chunks in order to fit the available width2 such split tables may be recombined into single tables 7hence there are occasional blank lines and columns in these split tables74 ,in certain tables1 ,do4 or do4 have been replaced with the dittoed text4 ,some obvious minor typographical and punctuation errors have been corrected silently4 ,some minor oddities in text lay-out have been changed silently for easier readability4 ,repeated table and column headers1 carry_/brought forward1 subtotals etc4 on page transitions in lists and tables have been removed1 except partly on the transition from page #dbc to #dbd4 ,suter and ,souter have been standardised to ,suter4 ,page xi3 the errata listed have already been corrected in the text4 ,the amount ,l4#ic1cjf 3 #h 3 #aj does not occur on line #f of page #agh2 the amount ,l4#ij1bfh1 #ab 3 #a that does occur on line #g of that page has been replaced by ,l4#hf1igg 3 #ag 3 #g as given in the ,appendix 7page #chd74 ,page #fa1 ,footnote #ac3 ,g,m 444 will be ----1 by which expression 444 ,g,m changed to ,g,m 444 will be -----1 by which expression 4444 ,g,m ,page #bca3 ,in these figures1 n n shews the reflector flame 444 changed to ,in these figures1 n n shews the reflector frame 4444 ,page #bfg3 ,franois ,soliel1 whom ,i urged 444 changed to ,franois ,soleil1 whom ,i urged 4442 444 the light derived from the accessary part 444 changed to 444 the light derived from the accessory part 4444 ,page #bha3 ,,oa 4 cos 4 ,,oax4 changed to ,,oa 4 cos ,,oax4 ,page #bhd3 ,f is the small flame in the focus 444 changed to ,e is the small flame in the focus 4444 ,page #dac1 entry ,the ,commission paid to ,collectors 4443 #bdja 3 #g 3 #j changed to #bdja 3 #g 3 #c cf4 page #dbi4 ,page #dcj1 entry #i4 ,startpoint1 ,balance3 #dfb #j #h changed to #dfb #j #c4 ,page #cee3 444 forming a flat parallelopepid 444 changed to 444 forming a flat parallelopiped 4444 ,page #cii1 entry ,drum ,sand ,west ,buoy1 ,south ,point3 ,bear changed to ,bearing4