,libraries47 ,transcriber's ,note ,the punctuation and spelling from the original text have been faithfully preserved4 ,only obvious typographical errors have been corrected4 ,the advertisement from the beginning of the book has been joined with the other advertisements near the end of the book4 ,greek words are spelled out and represented as word4 ,greek letters are represented as a for alpha4 ,,astronomy ,,of ,,to-,,day ,illustration3 ,,the ,,total ,,eclipse ,,of ,,the ,,sun ,,of ,,august #cj,,th1 #aije4 ,the ,corona2 from a water-colour sketch1 made at ,burgos1 in ,spain1 during the total phase1 by the ,french ,artist1 ,mdlle4 ,,andr,e ,,moch4 ,,astronomy ,,of ,,to-,,day ,a ,,popular ,,introduction ,,in ,,non-,,technical ,,language ,by ,,cecil ,g4 ,,dolmage1 ,m4,a41 ,,ll4,d41 ,d4,c4,l4 ,fellow of the ,royal ,astronomical ,society2 ,member of the ,british ,astronomical ,association2 ,member of the ,astronomical ,society of the ,pacific2 ,membre de la ,socit ,astronomique de ,france2 ,membre de la ,socit ,belge d',astronomie ,with a ,frontispiece in ,colour and #de ,illustrations ,diagrams ,,third ,,edition ,,london ,,seeley ,,and ,,co4 ,,limited #ch ,,great ,,russell ,,street #aiaj ,,preface ,the object of this book is to give an account of the science of ,astronomy1 as it is known at the present day1 in a manner acceptable to the general reader4 ,it is too often supposed that it is impossible to acquire any useful knowledge of ,astronomy without much laborious study1 and without adventuring into quite a new world of thought4 ,the reasoning applied to the study of the celestial orbs is1 however1 of no different order from that which is employed in the affairs of everyday life4 ,the science of mathematics is perhaps responsible for the idea that some kind of difference does exist2 but mathematical processes are1 in effect1 no more than ordinary logic in concentrated form1 the shorthand of reasoning1 so to speak4 ,i have attempted in the following pages to take the main facts and theories of ,astronomy out of those mathematical forms which repel the general reader1 and to present them in the ordinary language of our workaday world4 ,the few diagrams introduced are altogether supplementary1 and are not connected with the text by any wearying cross-references4 ,each diagram is complete in itself1 being intended to serve as a pictorial aid1 in case the wording of the text should not have perfectly conveyed the desired meaning4 ,the full page illustrations are also described as adequately as possible at the foot of each4 ,as to the coloured frontispiece1 this must be placed in a category by itself4 ,it is the work of the artist as distinct from the scientist4 ,the book itself contains incidentally a good deal of matter concerned with the ,astronomy of the past1 the introduction of which has been found necessary in order to make clearer the ,astronomy of our time4 ,it would be quite impossible for me to enumerate here the many sources from which information has been drawn4 ,but ,i acknowledge my especial indebtedness to ,professor ,f4,r4 ,moulton's ,introduction to ,astronomy 7,macmillan1 #aijf71 to the works on ,eclipses of the late ,rev4 ,s4,j4 ,johnson and of ,mr4 ,w4,t4 ,lynn1 and to the excellent ,journals of the ,british ,astronomical ,association4 ,further1 for those grand questions concerned with the ,stellar ,universe at large1 ,i owe a very deep debt to the writings of the famous ,american astronomer1 ,professor ,simon ,newcomb1 and of our own countryman1 ,mr4 ,john ,ellard ,gore2 to the latter of whom ,i am under an additional obligation for much valuable information privately rendered4 ,in my search for suitable illustrations1 ,i have been greatly aided by the kindly advice of ,mr4 ,w4 ,h4 ,wesley1 the ,assistant ,secretary of the ,royal ,astronomical ,society4 ,to those who have been so good as to permit me to reproduce pictures and photographs1 ,i desire to record my best thanks as follows3--,to the ,french ,artist1 ,mdlle4 ,andre ,moch2 to the ,astronomer ,royal2 to ,sir ,david ,gill1 ,k4,c4,b41 ,,ll4,d41 ,f4,r4,s42 to the ,council of the ,royal ,astronomical ,society2 to ,professor ,e4,b4 ,frost1 ,director of the ,yerkes ,observatory2 to ,m4,p4 ,puiseux1 of the ,paris ,observatory2 to ,dr4 ,max ,wolf1 of ,heidelberg2 to ,professor ,percival ,lowell2 to the ,rev4 ,theodore ,e4,r4 ,phillips1 ,m4,a41 ,f4,r4,a4,s42 to ,mr4 ,w4,h4 ,wesley2 to the ,warner and ,swasey ,co41 of ,cleveland1 ,ohio1 ,u4,s4,a42 to the publishers of ,knowledge1 and to ,messrs4 ,sampson1 ,low ,co4 ,for permission to reproduce the beautiful photograph of the ,spiral ,nebula in ,canes ,venatici 7,plate ,,xxii471 ,i am indebted to the distinguished astronomer1 the late ,dr4 ,w4,e4 ,wilson1 ,d4,sc41 ,f4,r4,s41 whose untimely death1 ,i regret to state1 occurred in the early part of this year4 ,finally1 my best thanks are due to ,mr4 ,john ,ellard ,gore1 ,f4,r4,a4,s41 ,m4,r4,i4,a41 to ,mr4 ,w4,h4 ,wesley1 and to ,mr4 ,john ,butler ,burke1 ,m4,a41 of ,cambridge1 for their kindness in reading the proof-sheets4 ,,cecil ,g4 ,,dolmage4 ,,london1 ,s4,w41 ,august #d1 #aijh4 ,,prefatory ,,note ,,to ,,the ,,second ,,edition ,the author of this book lived only long enough to hear of the favour with which it had been received1 and to make a few corrections in view of the second edition which it has so soon reached4 ,december #aijh4 ,,contents ,,chapter ,i ,,page ,,the ,,ancient ,,view #ag ,,chapter ,,ii ,,the ,,modern ,,view #bj ,,chapter ,,iii ,,the ,,solar ,,system #bi ,,chapter ,,iv ,,celestial ,,mechanism #ch ,,chapter ,v ,,celestial ,,distances #df ,,chapter ,,vi ,,celestial ,,measurement #ee ,,chapter ,,vii ,,eclipses ,,and ,,kindred ,,phenomena #fa ,,chapter ,,viii ,,famous ,,eclipses ,,of ,,the ,,sun #hc ,,chapter ,,ix ,,famous ,,eclipses ,,of ,,the ,,moon #aja ,,chapter ,x ,,the ,,growth ,,of ,,observation #aje ,,chapter ,,xi ,,spectrum ,,analysis #aba ,,chapter ,,xii ,,the ,,sun #abg ,,chapter ,,xiii ,,the ,,sun--continued #acd ,,chapter ,,xiv ,,the ,,inferior ,,planets #adf ,,chapter ,,xv ,,the ,,earth #aeh ,,chapter ,,xvi ,,the ,,moon #ahc ,,chapter ,,xvii ,,the ,,superior ,,planets #bji ,,chapter ,,xviii ,,the ,,superior ,,planets--continued #bbi ,,chapter ,,xix ,,comets #bdg ,,chapter ,,xx ,,remarkable ,,comets #bei ,,chapter ,,xxi ,,meteors ,,or ,,shooting ,,stars #bff ,,chapter ,,xxii ,,the ,,stars #bgh ,,chapter ,,xxiii ,,the ,,stars--continued #bhg ,,chapter ,,xxiv ,,systems ,,of ,,stars #cjj ,,chapter ,,xxv ,,the ,,stellar ,,universe #cai ,,chapter ,,xxvi ,,the ,,stellar ,,universe--continued #cbi ,,chapter ,,xxvii ,,the ,,beginning ,,of ,,things #ccc ,,chapter ,,xxviii ,,the ,,end ,,of ,,things #cdb ,,index #cea ,,list ,,of ,,illustrations ,,list ,,of ,,plates ,,plate ,,the ,,total ,,eclipse ,,of ,,the ,,sun ,,of ,,august #cj1 #aije ,frontispiece ,i4 ,,the ,,total ,,eclipse ,,of ,,the ,,sun ,,of ,,may #ag1 #ahhb ,to face page #if ,,ii4 ,,great ,,telescope ,,of ,,hevelius #aaj ,,iii4 ,a ,,tubeless1 ,,or ,,aerial ,,telescope #aab ,,iv4 ,,the ,,great ,,yerkes ,,telescope #aah ,v4 ,,the ,,sun1 ,,showing ,,several ,,groups ,,of ,,spots #acd ,,vi4 ,,photograph ,,of ,a ,,sunspot #acf ,,vii4 ,,forms ,,of ,,the ,,solar ,,corona ,,at ,,the ,,epochs ,,of ,,sunspot ,,maximum ,,and ,,sunspot ,,minimum ,,respectively4 7,a7 ,,the ,,total ,,eclipse ,,of ,,the ,,sun ,,of ,,december #bb1 #ahgj4 7,b7 ,,the ,,total ,,eclipse ,,of ,,the ,,sun ,,of ,,may #bh1 #aijj #adb ,,viii4 ,,the ,,moon ,to face page #aif ,,ix4 ,,map ,,of ,,the ,,moon1 ,,showing ,,the ,,principal ,,craters1 ,,mountain ,,ranges ,,and ,,seas #aih ,x4 ,,one ,,of ,,the ,,most ,,interesting ,,regions ,,on ,,the ,,moon #bjj ,,xi4 ,,the ,,moon 7,,showing ,,systems ,,of ,,rays7 #bjd ,,xii4 ,a ,,map ,,of ,,the ,,planet ,,mars #baf ,,xiii4 ,,minor ,,planet ,,trails #bbf ,,xiv4 ,,the ,,planet ,,jupiter #bcj ,,xv4 ,,the ,,planet ,,saturn #bcf ,,xvi4 ,,early ,,representations ,,of ,,saturn #bdb ,,xvii4 ,,donati',s ,,comet #bef ,,xviii4 ,,daniel',s ,,comet ,,of #aijg #beh ,,xix4 ,,the ,,sky ,,around ,,the ,,north ,,pole #bib ,,xx4 ,,orion ,,and ,,his ,,neighbours #bif ,,xxi4 ,,the ,,great ,,globular ,,cluster ,,in ,,the ,,southern ,,constellation ,,of ,,centaurus #cjf ,,xxii4 ,,spiral ,,nebula ,,in ,,the ,,constellation ,,of ,,canes ,,venatici #cad ,,xxiii4 ,,the ,,great ,,nebula ,,in ,,the ,,constellation ,,of ,,andromeda ,to face page #caf ,,xxiv4 ,,the ,,great ,,nebula ,,in ,,the ,,constellation ,,of ,,orion #cah ,,list ,,of ,,diagrams ,,fig4 ,,page #a4 ,,the ,,ptolemaic ,,idea ,,of ,,the ,,universe #ai #b4 ,,the ,,copernican ,,theory ,,of ,,the ,,solar ,,system #ba #c4 ,,total ,,and ,,partial ,,eclipses ,,of ,,the ,,moon #fd #d4 ,,total ,,and ,,partial ,,eclipses ,,of ,,the ,,sun #fg #e4 ,,baily',s ,,beads #gj #f4 ,,map ,,of ,,the ,,world ,,on ,,mercator',s ,,projection1 ,,showing ,a ,,portion ,,of ,,the ,,progress ,,of ,,the ,,total ,,solar ,,eclipse ,,of ,,august #cj1 #aije1 ,,across ,,the ,,surface ,,of ,,the ,,earth #ha #g4 ,,the ,,ring ,,with ,,wings #hg #h4 ,,the ,,various ,,types ,,of ,,telescope #aac #i4 ,,the ,,solar ,,spectrum #abc #aj4 ,a ,,section ,,through ,,the ,,sun1 ,,showing ,,how ,,the ,,prominences ,,rise ,,from ,,the ,,chromosphere #aca #aa4 ,,orbit ,,and ,,phases ,,of ,,an ,,inferior ,,planet #adh #ab4 ,,the ,,black ,,drop #aec #ac4 ,,summer ,,and ,,winter #agf #ad4 ,,orbit ,,and ,,phases ,,of ,,the ,,moon #ahd #ae4 ,,the ,,rotation ,,of ,,the ,,moon ,,on ,,her ,,axis #ahg #af4 ,,laplace',s ,,perennial ,,full ,,moon #aia #ag4 ,,illustrating ,,the ,,author',s ,,explanation ,,of ,,the ,,apparent ,,enlargement ,,of ,,celestial ,,objects #aie #ah4 ,,showing ,,how ,,the ,,tail ,,of ,a ,,comet ,,is ,,directed ,,away ,,from ,,the ,,sun #bdh #ai4 ,,the ,,comet ,,of #ajff1 ,,as ,,represented ,,in ,,the ,,bayeux ,,tapestry #bfc #bj4 ,,passage ,,of ,,the ,,earth ,,through ,,the ,,thickest ,,portion ,,of ,a ,,meteor ,,swarm #bfi ,,astronomy ,,of ,,to-,,day ,,chapter ,i ,,the ,,ancient ,,view ,it is never safe1 as we know1 to judge by appearances1 and this is perhaps more true of astronomy than of anything else4 ,for instance1 the idea which one would most naturally form of the earth and heaven is that the solid earth on which we live and move extends to a great distance in every direction1 and that the heaven is an immense dome upon the inner surface of which the stars are fixed4 ,such must needs have been the idea of the universe held by men in the earliest times4 ,in their view the earth was of paramount importance4 ,the sun and moon were mere lamps for the day and for the night2 and these1 if not gods themselves1 were at any rate under the charge of special deities1 whose task it was to guide their motions across the vaulted sky4 ,little by little1 however1 this simple estimate of nature began to be overturned4 ,difficult problems agitated the human mind4 ,on what1 for instance1 did the solid earth rest1 and what prevented the vaulted heaven from falling in upon men and crushing them out of existence8 ,fantastic myths sprang from the vain attempts to solve these riddles4 ,the ,hindoos1 for example1 imagined the earth as supported by four elephants which stood upon the back of a gigantic tortoise1 which1 in its turn1 floated on the surface of an elemental ocean4 ,the early ,western civilisations conceived the fable of the ,titan ,atlas1 who1 as a punishment for revolt against the ,olympian gods1 was condemned to hold up the expanse of sky for ever and ever4 ,later on glimmerings of the true light began to break in upon men4 ,the ,greek philosophers1 who busied themselves much with such matters1 gradually became convinced that the earth was spherical in shape1 that is to say1 round like a ball4 ,in this opinion we now know that they were right2 but in their other important belief1 viz4 that the earth was placed at the centre of all things1 they were indeed very far from the truth4 ,by the second century of the ,christian era1 the ideas of the early philosophers had become hardened into a definite theory1 which1 though it appears very incorrect to us to-day1 nevertheless demands exceptional notice from the fact that it was everywhere accepted as the true explanation until so late as some four centuries ago4 ,this theory of the universe is known by the name of the ,ptolemaic ,system1 because it was first set forth in definite terms by one of the most famous of the astronomers of antiquity1 ,claudius ,ptolemus ,pelusinensis 7#ajj-agj ,a4,d471 better known as ,ptolemy of ,alexandria4 ,in his system the ,earth occupied the centre2 while around it circled in order outwards the ,moon1 the planets ,mercury and ,venus1 the ,sun1 and then the planets ,mars1 ,jupiter1 and ,saturn4 ,beyond these again revolved the background of the heaven1 upon which it was believed that the stars were fixed-- ,stellis ardentibus aptum1 as ,virgil puts it 7see ,fig4 #a74 ,illustration3 ,,fig4 #a4--,the ,ptolemaic idea of the ,universe4 ,the ,ptolemaic system persisted unshaken for about fourteen hundred years after the death of its author4 ,clearly men were flattered by the notion that their earth was the most important body in nature1 that it stood still at the centre of the universe1 and was the pivot upon which all things revolved4 ,,chapter ,,ii ,,the ,,modern ,,view ,it is still well under four hundred years since the modern1 or ,copernican1 theory of the universe supplanted the ,ptolemaic1 which had held sway during so many centuries4 ,in this new theory1 propounded towards the middle of the sixteenth century by ,nicholas ,copernicus 7#adgc-aedc71 a ,prussian astronomer1 the earth was dethroned from its central position and considered merely as one of a number of planetary bodies which revolve around the sun4 ,as it is not a part of our purpose to follow in detail the history of the science1 it seems advisable to begin by stating in a broad fashion the conception of the universe as accepted and believed in to-day4 ,the ,sun1 the most important of the celestial bodies so far as we are concerned1 occupies the central position2 not1 however1 in the whole universe1 but only in that limited portion which is known as the ,solar ,system4 ,around it1 in the following order outwards1 circle the planets ,mercury1 ,venus1 the ,earth1 ,mars1 ,jupiter1 ,saturn1 ,uranus1 and ,neptune 7see ,fig4 #b1 p4 #ba74 ,at an immense distance beyond the solar system1 and scattered irregularly through the depth of space1 lie the stars4 ,the two first-mentioned members of the solar system1 ,mercury and ,venus1 are known as the ,inferior ,planets2 and in their courses about the sun1 they always keep well inside the path along which our earth moves4 ,the remaining members 7exclusive of the earth7 are called ,superior ,planets1 and their paths lie all outside that of the earth4 ,illustration3 ,,fig4 #b4--,the ,copernican theory of the ,solar ,system4 ,the five planets1 ,mercury1 ,venus1 ,mars1 ,jupiter1 and ,saturn1 have been known from all antiquity4 ,nothing then can bring home to us more strongly the immense advance which has taken place in astronomy during modern times than the fact that it is only #abg years since observation of the skies first added a planet to that time-honoured number4 ,it was indeed on the #acth of ,march #agha1 while engaged in observing the constellation of the ,twins1 that the justly famous ,sir ,william ,herschel caught sight of an object which he did not recognise as having met with before4 ,he at first took it for a comet1 but observations of its movements during a few days showed it to be a planet4 ,this body1 which the power of the telescope alone had thus shown to belong to the solar family1 has since become known to science under the name of ,uranus4 ,by its discovery the hitherto accepted limits of the solar system were at once pushed out to twice their former extent1 and the hope naturally arose that other planets would quickly reveal themselves in the immensities beyond4 ,for a number of years prior to ,herschel's great discovery1 it had been noticed that the distances at which the then known planets circulated appeared to be arranged in a somewhat orderly progression outwards from the sun4 ,this seeming plan1 known to astronomers by the name of ,bode's ,law1 was closely confirmed by the distance of the new planet ,uranus4 ,there still lay1 however1 a broad gap between the planets ,mars and ,jupiter4 ,had another planet indeed circuited there1 the solar system would have presented an appearance of almost perfect order4 ,but the void between ,mars and ,jupiter was unfilled2 the space in which one would reasonably expect to find another planet circling was unaccountably empty4 ,on the first day of the nineteenth century the mystery was however explained1 a body being discovered#a which revolved in the space that had hitherto been considered planetless4 ,but it was a tiny globe hardly worthy of the name of planet4 ,in the following year a second body was discovered revolving in the same space2 but it was even smaller in size than the first4 ,during the ensuing five years two more of these little planets were discovered4 ,then came a pause1 no more such bodies being added to the system until half-way through the century1 when suddenly the discovery of these so-called minor planets began anew4 ,since then additions to this portion of our system have rained thick and fast4 ,the small bodies have received the name of ,asteroids or ,planetoids2 and up to the present time some six hundred of them are known to exist1 all revolving in the previously unfilled space between ,mars and ,jupiter4 ,in the year #ahdf the outer boundary of the solar system was again extended by the discovery that a great planet circulated beyond ,uranus4 ,the new body1 which received the name of ,neptune1 was brought to light as the result of calculations made at the same time1 though quite independently1 by the ,cambridge mathematician ,adams1 and the ,french astronomer ,le ,verrier4 ,the discovery of ,neptune differed1 however1 from that of ,uranus in the following respect4 ,uranus was found merely in the course of ordinary telescopic survey of the heavens4 ,the position of ,neptune1 on the other hand1 was predicted as the result of rigorous mathematical investigations undertaken with the object of fixing the position of an unseen and still more distant body1 the attraction of which1 in passing by1 was disturbing the position of ,uranus in its revolution around the sun4 ,adams actually completed his investigation first2 but a delay at ,cambridge in examining that portion of the sky1 where he announced that the body ought just then to be1 allowed ,france to snatch the honour of discovery1 and the new planet was found by the observer ,galle at ,berlin1 very near the place in the heavens which ,le ,verrier had mathematically predicted for it4 ,nearly fifty years later1 that is to say1 in our own time1 another important planetary discovery was made4 ,one of the recent additions to the numerous and constantly increasing family of the asteroids1 a tiny body brought to light in #ahih1 turned out after all not to be circulating in the customary space between ,mars and ,jupiter1 but actually in that between our earth and ,mars4 ,this body is very small1 not more than about twenty miles across4 ,it has received the name of ,eros 7the ,greek equivalent for ,cupid71 in allusion to its insignificant size as compared with the other leading members of the system4 ,this completes the list of the planets which1 so far1 have revealed themselves to us4 ,whether others exist time alone will show4 ,two or three have been suspected to revolve beyond the path of ,neptune2 and it has even been asserted1 on more than one occasion1 that a planet circulates nearer to the sun than ,mercury4 ,this supposed body1 to which the name of ,vulcan was provisionally given1 is said to have been discovered in #ahei by a ,french doctor named ,lescarbault1 of ,orgres near ,orleans2 but up to the present there has been no sufficient evidence of its existence4 ,the reason why such uncertainty should exist upon this point is easy enough to understand1 when we consider the overpowering glare which fills our atmosphere all around the sun's place in the sky4 ,mercury1 the nearest known planet to the sun1 is for this reason always very difficult to see2 and even when1 in its course1 it gets sufficiently far from the sun to be left for a short time above the horizon after sunset1 it is by no means an easy object to observe on account of the mists which usually hang about low down near the earth4 ,one opportunity1 however1 offers itself from time to time to solve the riddle of an intra-,mercurial planet1 that is to say1 of a planet which circulates within the path followed by ,mercury4 ,the opportunity in question is furnished by a total eclipse of the sun2 for when1 during an eclipse of that kind1 the body of the moon for a few minutes entirely hides the sun's face1 and the dazzling glare is thus completely cut off1 astronomers are enabled to give an unimpeded1 though all too hurried1 search to the region close around4 ,a goodly number of total eclipses of the sun have1 however1 come and gone since the days of ,lescarbault1 and no planet1 so far1 has revealed itself in the intra-,mercurial space4 ,it seems1 therefore1 quite safe to affirm that no globe of sufficient size to be seen by means of our modern telescopes circulates nearer to the sun than the planet ,mercury4 ,next in importance to the planets1 as permanent members of the solar system1 come the relatively small and secondary bodies known by the name of ,satellites4 ,the name satellite is derived from a ,latin word signifying an attendant2 for the bodies so-called move along always in close proximity to their respective primaries1 as the planets which they accompany are technically termed4 ,the satellites cannot be considered as allotted with any particular regularity among the various members of the system2 several of the planets1 for instance1 having a goodly number of these bodies accompanying them1 while others have but one or two1 and some again have none at all4 ,taking the planets in their order of distance outward from the ,sun1 we find that neither ,mercury nor ,venus are provided with satellites2 the ,earth has only one1 viz4 our neighbour the ,moon2 while ,mars has but two tiny ones1 so small indeed that one might imagine them to be merely asteroids1 which had wandered out of their proper region and attached themselves to that planet4 ,for the rest1 so far as we at present know1 ,jupiter possesses seven1#b ,saturn ten1 ,uranus four1 and ,neptune one4 ,it is indeed possible1 nay more1 it is extremely probable1 that the two last-named planets have a greater number of these secondary bodies revolving around them2 but1 unfortunately1 the ,uranian and ,neptunian systems are at such immense distances from us1 that even the magnificent telescopes of to-day can extract very little information concerning them4 ,from the distribution of the satellites1 the reader will notice that the planets relatively near to the sun are provided with few or none1 while the more distant planets are richly endowed4 ,the conclusion1 therefore1 seems to be that nearness to the sun is in some way unfavourable either to the production1 or to the continued existence1 of satellites4 ,a planet and its satellites form a repetition of the solar system on a tiny scale4 ,just as the planets revolve around the sun1 so do these secondary bodies revolve around their primaries4 ,when ,galileo1 in #afaj1 turned his newly invented telescope upon ,jupiter1 he quickly recognised in the four circling moons which met his gaze1 a miniature edition of the solar system4 ,besides the planets and their satellites1 there are two other classes of bodies which claim membership of the solar system4 ,these are ,comets and ,meteors4 ,comets differ from the bodies which we have just been describing in that they appear filmy and transparent1 whereas the others are solid and opaque4 ,again1 the paths of the planets around the sun and of the satellites around their primaries are not actually circles2 they are ovals1 but their ovalness is not of a marked degree4 ,the paths of comets on the other hand are usually very oval2 so that in their courses many of them pass out as far as the known limits of the solar system1 and even far beyond4 ,it should be mentioned that nowadays the tendency is to consider comets as permanent members of the system1 though this was formerly not by any means an article of faith with astronomers4 ,meteors are very small bodies1 as a rule perhaps no larger than pebbles1 which move about unseen in space1 and of which we do not become aware until they arrive very close to the earth4 ,they are then made visible to us for a moment or two in consequence of being heated to a white heat by the friction of rushing through the atmosphere1 and are thus usually turned into ashes and vapour long before they reach the surface of our globe4 ,though occasionally a meteoric body survives the fiery ordeal1 and reaches the earth more or less in a solid state to bury itself deep in the soil1 the majority of these celestial visitants constitute no source of danger whatever for us4 ,any one who will take the trouble to gaze at the sky for a short time on a clear night1 is fairly certain to be rewarded with the view of a meteor4 ,the impression received is as if one of the stars had suddenly left its accustomed place1 and dashed across the heavens1 leaving in its course a trail of light4 ,it is for this reason that meteors are popularly known under the name of shooting stars4 #a ,by the ,italian astronomer1 ,piazzi1 at ,palermo4 #b ,probably eight4 7,see note1 page #bcb47 ,,chapter ,,iii ,,the ,,solar ,,system ,we have seen1 in the course of the last chapter1 that the solar system is composed as follows3--there is a central body1 the sun1 around which revolve along stated paths a number of important bodies known as planets4 ,certain of these planets1 in their courses1 carry along in company still smaller bodies called satellites1 which revolve around them4 ,with regard1 however1 to the remaining members of the system1 viz4 the comets and the meteors1 it is not advisable at this stage to add more to what has been said in the preceding chapter4 ,for the time being1 therefore1 we will devote our attention merely to the sun1 the planets1 and the satellites4 ,of what shape then are these bodies8 ,of one shape1 and that one alone which appears to characterise all solid objects in the celestial spaces3 they are spherical1 which means round like a ball4 ,each of these spherical bodies rotates2 that is to say1 turns round and round1 as a top does when it is spinning4 ,this rotation is said to take place upon an axis1 a statement which may be explained as follows3--,imagine a ball with a knitting-needle run right through its centre4 ,then imagine this needle held pointing in one fixed direction while the ball is turned round and round4 ,well1 it is the same thing with the earth4 ,as it journeys about the sun1 it keeps turning round and round continually as if pivoted upon a mighty knitting needle transfixing it from ,north ,pole to ,south ,pole4 ,in reality1 however1 there is no such material axis to regulate the constant direction of the rotation1 just as there are no actual supports to uphold the earth itself in space4 ,the causes which keep the celestial spheres poised1 and which control their motions1 are far more wonderful than any mechanical device4 ,at this juncture it will be well to emphasise the sharp distinction between the terms rotation and revolution4 ,the term rotation is invariably used by astronomers to signify the motion which a celestial body has upon an axis2 the term revolution1 on the other hand1 is used for the movement of one celestial body around another4 ,speaking of the earth1 for instance1 we say1 that it rotates on its axis1 and that it revolves around the sun4 ,so far1 nothing has been said about the sizes of the members of our system4 ,is there any stock size1 any pattern according to which they may be judged8 ,none whatever6 ,they vary enormously4 ,very much the largest of all is the ,sun1 which is several hundred times larger than all the planets and satellites of the system rolled together4 ,next comes ,jupiter and afterwards the other planets in the following order of size3--,saturn1 ,uranus1 ,neptune1 the ,earth1 ,venus1 ,mars1 and ,mercury4 ,very much smaller than any of these are the asteroids1 of which ,ceres1 the largest1 is less than #ejj miles in diameter4 ,it is1 by the way1 a strange fact that the zone of asteroids should mark the separation of the small planets from the giant ones4 ,the following table1 giving roughly the various diameters of the sun and the principal planets in miles1 will clearly illustrate the great discrepancy in size which prevails in the system4 ,sun #hff1edj miles ,mercury #b1gfe ,venus #g1hbf ,earth #g1iah ,mars #d1ccb ,,zone ,,of ,,asteroids ,jupiter #hg1chj ,saturn #gc1abe ,uranus#c #cd1ijj ,neptune#c #cb1ijj ,it does not seem possible to arrive at any generalisation from the above data1 except it be to state that there is a continuous increase in size from ,mercury to the earth1 and a similar decrease in size from ,jupiter outwards4 ,were ,mars greater than the earth1 the planets could then with truth be said to increase in size up to ,jupiter1 and then to decrease4 ,but the zone of asteroids1 and the relative smallness of ,mars1 negative any attempt to regard the dimensions of the planets as an orderly sequence4 ,next with respect to relative distance from the sun1 ,venus circulates nearly twice as far from it as ,mercury1 the earth nearly three times as far1 and ,mars nearly four times4 ,after this1 just as we found a sudden increase in size1 so do we meet with a sudden increase in distance4 ,jupiter1 for instance1 is about thirteen times as far as ,mercury1 ,saturn about twenty-five times1 ,uranus about forty-nine times1 and ,neptune about seventy-seven4 7,see ,fig4 #b1 p4 #ba47 ,it will thus be seen how enormously the solar system was enlarged in extent by the discovery of the outermost planets4 ,the finding of ,uranus plainly doubled its breadth2 the finding of ,neptune made it more than half as broad again4 ,nothing indeed can better show the import of these great discoveries than to take a pair of compasses and roughly set out the above relative paths in a series of concentric circles upon a large sheet of paper1 and then to consider that the path of ,saturn was the supposed boundary of our solar system prior to the year #agha4 ,we have seen that the usual shape of celestial bodies themselves is spherical4 ,of what form then are their paths1 or orbits1 as these are called8 ,one might be inclined at a venture to answer circular1 but this is not the case4 ,the orbits of the planets cannot be regarded as true circles4 ,they are ovals1 or1 to speak in technical language1 ellipses4 ,their ovalness or ellipticity is1 however1 in each case not by any means of the same degree4 ,some orbits--for instance1 that of the earth--differ only slightly from circles2 while others--those of ,mars or ,mercury1 for example--are markedly elliptic4 ,the orbit of the tiny planet ,eros is1 however1 far and away the most elliptic of all1 as we shall see when we come to deal with that little planet in detail4 ,it has been stated that the sun and planets are always rotating4 ,the various rates at which they do so will1 however1 be best appreciated by a comparison with the rate at which the earth itself rotates4 ,but first of all1 let us see what ground we have1 if any1 for asserting that the earth rotates at all8 ,if we carefully watch the heavens we notice that the background of the sky1 with all the brilliant objects which sparkle in it1 appears to turn once round us in about twenty-four hours2 and that the pivot upon which this movement takes place is situated somewhere near what is known to us as the ,pole ,star4 ,this was one of the earliest facts noted with regard to the sky2 and to the men of old it therefore seems as if the heavens and all therein were always revolving around the earth4 ,it was natural enough for them to take this view1 for they had not the slightest idea of the immense distance of the celestial bodies1 and in the absence of any knowledge of the kind they were inclined to imagine them comparatively near4 ,it was indeed only after the lapse of many centuries1 when men had at last realised the enormous gulf which separated them from even the nearest object in the sky1 that a more reasonable opinion began to prevail4 ,it was then seen that this revolution of the heavens about the earth could be more easily and more satisfactorily explained by supposing a mere rotation of the solid earth about a fixed axis1 pointed in the direction of the polar star4 ,the probability of such a rotation on the part of the earth itself was further strengthened by the observations made with the telescope4 ,when the surfaces of the sun and planets were carefully studied these bodies were seen to be rotating4 ,this being the case1 there could not surely be much hesitation in granting that the earth rotated also2 particularly when it so simply explained the daily movement of the sky1 and saved men from the almost inconceivable notion that the whole stupendous vaulted heaven was turning about them once in every twenty-four hours4 ,if the sun be regularly observed through a telescope1 it will gradually be gathered from the slow displacement of sunspots across its face1 their disappearance at one edge and their reappearance again at the other edge1 that it is rotating on an axis in a period of about twenty-six days4 ,the movement1 too1 of various well-known markings on the surfaces of the planets ,mars1 ,jupiter1 and ,saturn proves to us that these bodies are rotating in periods1 which are about twenty-four hours for the first1 and about ten hours for each of the other two4 ,with regard1 however1 to ,uranus and ,neptune there is much more uncertainty1 as these planets are at such great distances that even our best telescopes give but a confused view of the markings which they display2 still a period of rotation of from ten to twelve hours appears to be accepted for them4 ,on the other hand the constant blaze of sunlight in the neighbourhood of ,mercury and ,venus equally hampers astronomers in this quest4 ,the older telescopic observers considered that the rotation periods of these two planets were about the same as that of the earth2 but of recent years the opinion has been gaining ground that they turn round on their axes in exactly the same time as they revolve about the sun4 ,this question is1 however1 a very doubtful one1 and will be again referred to later on2 but1 putting it on one side1 it will be seen from what we have said above1 that the rotation periods of the other planets of our system are usually about twenty-four hours1 or under4 ,the fact that the rotation period of the sun should run into days need not seem extraordinary when one considers its enormous size4 ,the periods taken by the various planets to revolve around the sun is the next point which has to be considered4 ,here1 too1 it is well to start with the earth's period of revolution as the standard1 and to see how the periods taken by the other planets compare with it4 ,the earth takes about #cfe-a_/d days to revolve around the sun4 ,this period of time is known to us as a year4 ,the following table shows in days and years the periods taken by each of the other planets to make a complete revolution round the sun3-- ,mercury about #hh days4 ,venus #bbf ,mars #a year and #cba days4 ,jupiter #aa years and #cac days4 ,saturn #bi years and #afg days4 ,uranus #hd years and #g days4 ,neptune #afd years and #bhd days4 ,from these periods we gather an important fact1 namely1 that the nearer a planet is to the sun the faster it revolves4 ,compared with one of our years what a long time does an ,uranian1 or ,neptunian1 year seem8 ,for instance1 if a year had commenced in ,neptune about the middle of the reign of ,george ,,ii41 that year would be only just coming to a close2 for the planet is but now arriving back to the position1 with regard to the sun1 which it then occupied4 ,uranus1 too1 has only completed a little more than #a-a_/b of its years since ,herschel discovered it4 ,having accepted the fact that the planets are revolving around the sun1 the next point to be inquired into is3--,what are the positions of their orbits1 or paths1 relatively to each other8 ,suppose1 for instance1 the various planetary orbits to be represented by a set of hoops of different sizes1 placed one within the other1 and the sun by a small ball in the middle of the whole2 in what positions will these hoops have to be arranged so as to imitate exactly the true condition of things8 ,first of all let us suppose the entire arrangement1 ball and hoops1 to be on one level1 so to speak4 ,this may be easily compassed by imagining the hoops as floating1 one surrounding the other1 with the ball in the middle of all1 upon the surface of still water4 ,such a set of objects would be described in astronomical parlance as being in the same plane4 ,suppose1 on the other hand1 that some of these floating hoops are tilted with regard to the others1 so that one half of a hoop rises out of the water and the other half consequently sinks beneath the surface4 ,this indeed is the actual case with regard to the planetary orbits4 ,they do not by any means lie all exactly in the same plane4 ,each one of them is tilted1 or inclined1 a little with respect to the plane of the earth's orbit1 which astronomers1 for convenience1 regard as the level of the solar system4 ,this tilting1 or inclination1 is1 in the larger planets1 greatest for the orbit of ,mercury1 least for that of ,uranus4 ,mercury's orbit is inclined to that of the earth at an angle of about #g1 that of ,venus at a little over #c1 that of ,saturn #b-a_/b2 while in those of ,mars1 ,neptune1 and ,jupiter the inclination is less than #b4 ,but greater than any of these is the inclination of the orbit of the tiny planet ,eros1 viz4 nearly #aa4 ,the systems of satellites revolving around their respective planets being1 as we have already pointed out1 mere miniature editions of the solar system1 the considerations so far detailed1 which regulate the behaviour of the planets in their relations to the sun1 will of necessity apply to the satellites very closely4 ,in one respect1 however1 a system of satellites differs materially from a system of planets4 ,the central body around which planets are in motion is self-luminous1 whereas the planetary body around which a satellite revolves is not4 ,true1 planets shine1 and shine very brightly too2 as1 for instance1 ,venus and ,jupiter4 ,but they do not give forth any light of their own1 as the sun does2 they merely reflect the sunlight which they receive from him4 ,putting this one fact aside1 the analogy between the planetary system and a satellite system is remarkable4 ,the satellites are spherical in form1 and differ markedly in size2 they rotate1 so far as we know1 upon their axes in varying times2 they revolve around their governing planets in orbits1 not circular1 but elliptic2 and these orbits1 furthermore1 do not of necessity lie in the same plane4 ,last of all the satellites revolve around their primaries at rates which are directly comparable with those at which the planets revolve around the sun1 the rule in fact holding good that the nearer a satellite is to its primary the faster it revolves4 #c ,as there seems to be much difference of opinion concerning the diameters of ,uranus and ,neptune1 it should here be mentioned that the above figures are taken from ,professor ,f4,r4 ,moulton's ,introduction to ,astronomy 7#aijf74 ,they are there stated to be given on the authority of ,barnard's many measures at the ,lick ,observatory4 ,,chapter ,,iv ,,celestial ,,mechanism ,as soon as we begin to inquire closely into the actual condition of the various members of the solar system we are struck with a certain distinction4 ,we find that there are two quite different points of view from which these bodies can be regarded4 ,for instance1 we may make our estimates of them either as regards volume--that is to say1 the mere room which they take up2 or as regards mass--that is to say1 the amount of matter which they contain4 ,let us imagine two globes of equal volume2 in other words1 which take up an equal amount of space4 ,one of these globes1 however1 may be composed of material much more tightly put together than in the other2 or of greater density1 as the term goes4 ,that globe is said to be the greater of the two in mass4 ,were such a pair of globes to be weighed in scales1 one globe in each pan1 we should see at once1 by its weighing down the other1 which of the two was composed of the more tightly packed materials2 and we should1 in astronomical parlance1 say of this one that it had the greater mass4 ,volume being merely another word for size1 the order of the members of the solar system1 with regard to their volumes1 will be as follows1 beginning with the greatest3--the ,sun1 ,jupiter1 ,saturn1 ,uranus1 ,neptune1 the ,earth1 ,venus1 ,mars1 and ,mercury4 ,with regard to mass the same order strangely enough holds good4 ,the actual densities of the bodies in question are1 however1 very different4 ,the densest or closest packed body of all is the ,earth1 which is about five and a half times as dense as if it were composed entirely of water4 ,venus follows next1 then ,mars1 and then ,mercury4 ,the remaining bodies1 on the other hand1 are relatively loose in structure4 ,saturn is the least dense of all1 less so than water4 ,the density of the ,sun is a little greater than that of water4 ,this method of estimating is1 however1 subject to a qualification4 ,it must be remembered that in speaking of the ,sun1 for instance1 as being only a little denser than water1 we are merely treating the question from the point of view of an average4 ,certain parts of it in fact will be ever so much denser than water3 those are the parts in the centre4 ,other portions1 for instance1 the outside portions1 will be very much less dense4 ,it will easily be understood that in all such bodies the densest or most compressed portions are to be found towards the centre2 while the portions towards the exterior being less pressed upon1 will be less dense4 ,we now reach a very important point1 the question of ,gravitation4 ,gravitation1 or gravity1 as it is often called1 is the attractive force which1 for instance1 causes objects to fall to the earth4 ,now it seems rather strange that one should say that it is owing to a certain force that things fall towards the earth4 ,all things seem to us to fall so of their own accord1 as if it were quite natural1 or rather most unnatural if they did not4 ,why then require a force to make them fall8 ,the story goes that the great ,sir ,isaac ,newton was set a-thinking on this subject by seeing an apple fall from a tree to the earth4 ,he then carried the train of thought further2 and1 by studying the movements of the moon1 he reached the conclusion that a body even so far off as our satellite would be drawn towards the earth in the same manner4 ,this being the case1 one will naturally ask why the moon herself does not fall in upon the earth4 ,the answer is indeed found to be that the moon is travelling round and round the earth at a certain rapid pace1 and it is this very same rapid pace which keeps her from falling in upon us4 ,any one can test this simple fact for himself4 ,if we tie a stone to the end of a string1 and keep whirling it round and round fast enough1 there will be a strong pull from the stone in an outward direction1 and the string will remain tight all the time that the stone is being whirled4 ,if1 however1 we gradually slacken the speed at which we are making the stone whirl1 a moment will come at length when the string will become limp1 and the stone will fall back towards our hand4 ,it seems1 therefore1 that there are two causes which maintain the stone at a regular distance all the time it is being steadily whirled4 ,one of these is the continual pull inward towards our hand by means of the string4 ,the other is the continual pull away from us caused by the rate at which the stone is travelling4 ,when the rate of whirling is so regulated that these pulls exactly balance each other1 the stone travels comfortably round and round1 and shows no tendency either to fall back upon our hand or to break the string and fly away into the air4 ,it is indeed precisely similar with regard to the moon4 ,the continual pull of the earth's gravitation takes the place of the string4 ,if the moon were to go round and round slower than it does1 it would tend to fall in towards the earth2 if1 on the other hand1 it were to go faster1 it would tend to rush away into space4 ,the same kind of pull which the earth exerts upon the objects at its surface1 or upon its satellite1 the moon1 exists through space so far as we know4 ,every particle of matter in the universe is found in fact to attract every other particle4 ,the moon1 for instance1 attracts the earth also1 but the controlling force is on the side of the much greater mass of the earth4 ,this force of gravity or attraction of gravitation1 as it is also called1 is perfectly regular in its action4 ,its power depends first of all exactly upon the mass of the body which exerts it4 ,the gravitational pull of the sun1 for instance1 reaches out to an enormous distance1 controlling perhaps1 in their courses1 unseen planets circling far beyond the orbit of ,neptune4 ,again1 the strength with which the force of gravity acts depends upon distance in a regularly diminishing proportion4 ,thus1 the nearer an object is to the earth1 for instance1 the stronger is the gravitational pull which it gets from it2 the farther off it is1 the weaker is this pull4 ,if then the moon were to be brought nearer to the earth1 the gravitational pull of the latter would become so much stronger that the moon's rate of motion would have also to increase in due proportion to prevent her from being drawn into the earth4 ,last of all1 the point in a body from which the attraction of gravitation acts1 is not necessarily the centre of the body1 but rather what is known as its centre of gravity1 that is to say1 the balancing point of all the matter which the body contains4 ,it should here be noted that the moon does not actually revolve around the centre of gravity of the earth4 ,what really happens is that both orbs revolve around their common centre of gravity1 which is a point within the body of the earth1 and situated about three thousand miles from its centre4 ,in the same manner the planets and the sun revolve around the centre of gravity of the solar system1 which is a point within the body of the sun4 ,the neatly poised movements of the planets around the sun1 and of the satellites around their respective planets1 will therefore be readily understood to result from a nice balance between gravitation and speed of motion4 ,the mass of the earth is ascertained to be about eighty times that of the moon4 ,our knowledge of the mass of a planet is learned from comparing the revolutions of its satellite or satellites around it1 with those of the moon around the earth4 ,we are thus enabled to deduce what the mass of such a planet would be compared to the earth's mass2 that is to say1 a study1 for instance1 of ,jupiter's satellite system shows that ,jupiter must have a mass nearly three hundred and eighteen times that of our earth4 ,in the same manner we can argue out the mass of the sun from the movements of the planets and other bodies of the system around it4 ,with regard1 however1 to ,venus and ,mercury1 the problem is by no means such an easy one1 as these bodies have no satellites4 ,for information in this latter case we have to rely upon such uncertain evidence as1 for instance1 the slight disturbances caused in the motion of the earth by the attraction of these planets when they pass closest to us1 or their observed effect upon the motions of such comets as may happen to pass near to them4 ,mass and weight1 though often spoken of as one and the same thing1 are by no means so4 ,mass1 as we have seen1 merely means the amount of matter which a body contains4 ,the weight of a body1 on the other hand1 depends entirely upon the gravitational pull which it receives4 ,the force of gravity at the surface of the earth is1 for instance1 about six times as great as that at the surface of the moon4 ,all bodies1 therefore1 weigh about six times as much on the earth as they would upon the moon2 or1 rather1 a body transferred to the moon's surface would weigh only about one-sixth of what it did on the terrestrial surface4 ,it will therefore be seen that if a body of given mass were to be placed upon planet after planet in turn1 its weight would regularly alter according to the force of gravity at each planet's surface4 ,gravitation is indeed one of the greatest mysteries of nature4 ,what it is1 the means by which it acts1 or why such a force should exist at all1 are questions to which so far we have not had even the merest hint of an answer4 ,its action across space appears to be instantaneous4 ,the intensity of gravitation is said in mathematical parlance to vary inversely with the square of the distance4 ,this means that at twice the distance the pull will become only one-quarter as strong1 and not one-half as otherwise might be expected4 ,at four times the distance1 therefore1 it will be one-sixteenth as strong4 ,at the earth's surface a body is pulled by the earth's gravitation1 or falls1 as we ordinarily term it1 through #af feet in one second of time2 whereas at the distance of the moon the attraction of the earth is so very much weakened that a body would take as long as one minute to fall through the same space4 ,newton's investigations showed that if a body were to be placed at rest in space entirely away from the attraction of any other body it would remain always in a motionless condition1 because there would plainly be no reason why it should move in any one direction rather than in another4 ,and1 similarly1 if a body were to be projected in a certain direction and at a certain speed1 it would move always in the same direction and at the same speed so long as it did not come within the gravitational attraction of any other body4 ,the possibility of an interaction between the celestial orbs had occurred to astronomers before the time of ,newton2 for instance1 in the ninth century to the ,arabian ,musa-ben-,shakir1 to ,camillus ,agrippa in #aeec1 and to ,kepler1 who suspected its existence from observation of the tides4 ,horrox also1 writing in #afce1 spoke of the moon as moved by an emanation from the earth4 ,but no one prior to ,newton attempted to examine the question from a mathematical standpoint4 ,notwithstanding the acknowledged truth and far-reaching scope of the law of gravitation--for we find its effects exemplified in every portion of the universe--there are yet some minor movements which it does not account for4 ,for instance1 there are small irregularities in the movement of ,mercury which cannot be explained by the influence of possible intra-,mercurial planets1 and similarly there are slight unaccountable deviations in the motions of our neighbour the ,moon4 ,,chapter ,v ,,celestial ,,distances ,up to this we have merely taken a general view of the solar system--a bird's-eye view1 so to speak1 from space4 ,in the course of our inquiry we noted in a rough way the relative distances at which the various planets move around the sun4 ,but we have not yet stated what these distances actually are1 and it were therefore well now to turn our attention to this important matter4 ,each of us has a fair idea of what a mile is4 ,it is a quarter of an hour's sharp walk1 for instance2 or yonder village or building1 we know1 lies such and such a number of miles away4 ,the measurements which have already been given of the diameters of the various bodies of the solar system appear very great to us1 who find that a walk of a few miles at a time taxes our strength2 but they are a mere nothing when we consider the distances from the sun at which the various planets revolve in their orbits4 ,the following table gives these distances in round numbers4 ,as here stated they are what are called mean distances2 for1 as the orbits are oval1 the planets vary in their distances from the sun1 and we are therefore obliged to strike a kind of average for each case3-- ,mercury about #cf1jjj1jjj miles4 ,venus #fg1bjj1jjj ,earth #ib1ijj1jjj ,mars #ada1ejj1jjj ,jupiter #dhc1cjj1jjj ,saturn #hhf1jjj1jjj ,uranus #a1gha1ijj1jjj ,neptune #b1gia1fjj1jjj ,from the above it will be seen at a glance that we have entered upon a still greater scale of distance than in dealing with the diameters of the various bodies of the system4 ,in that case the distances were limited to thousands of miles2 in this1 however1 we have to deal with millions4 ,a million being ten hundred thousand1 it will be noticed that even the diameter of the huge sun is well under a million miles4 ,how indeed are we to get a grasp of such distances1 when those to which we are ordinarily accustomed--the few miles' walk1 the little stretch of sea or land which we gaze upon around us--are so utterly minute in comparison8 ,the fact is1 that though men may think that they can picture in their minds such immense distances1 they actually can not4 ,in matters like these we unconsciously employ a kind of convention1 and we estimate a thing as being two or three or more times the size of another4 ,more than this we are unable to do4 ,for instance1 our ordinary experience of a mile enables us to judge1 in a way1 of a stretch of several miles1 such as one can take in with a glance2 but in our estimation of a thousand miles1 or even of one hundred1 we are driven back upon a mental trick1 so to speak4 ,in our attempts to realise such immense distances as those in the solar system we are obliged to have recourse to analogies2 to comparisons with other and simpler facts1 though this is at the best a mere self-cheating device4 ,the analogy which seems most suited to our purpose here1 and one which has often been employed by writers1 is borrowed from the rate at which an express train travels4 ,let us imagine1 for instance1 that we possess an express train which is capable of running anywhere1 never stops1 never requires fuel1 and always goes along at sixty miles an hour4 ,suppose we commence by employing it to gauge the size of our own planet1 the earth4 ,let us send it on a trip around the equator1 the span of which is about #bd1jjj miles4 ,at its sixty-miles-an-hour rate of going1 this journey will take nearly #ag days4 ,next let us send it from the earth to the moon4 ,this distance1 #bdj1jjj miles1 being ten times as great as the last1 will of course take ten times as long to cover1 namely1 #agj days2 that is to say1 nearly half a year4 ,again1 let us send it still further afield1 to the sun1 for example4 ,here1 however1 it enters upon a journey which is not to be measured in thousands of miles1 as the others were1 but in millions4 ,the distance from the earth to the sun1 as we have seen in the foregoing table1 is about #ic millions of miles4 ,our express train would take about #agh years to traverse this4 ,having arrived at the sun1 let us suppose that our train makes a tour right round it4 ,this will take more than five years4 ,supposing1 finally1 that our train were started from the sun1 and made to run straight out to the known boundaries of the solar system1 that is to say1 as far as the orbit of ,neptune1 it would take over #ejjj years to traverse the distance4 ,that sixty miles an hour is a very great speed any one1 ,i think1 will admit who has stood upon the platform of a country station while one of the great mail trains has dashed past4 ,but are not the immensities of space appalling to contemplate1 when one realises that a body moving incessantly at such a rate would take so long as #aj1jjj years to traverse merely the breadth of our solar system8 ,ten thousand years6 ,just try to conceive it4 ,why1 it is only a little more than half that time since the ,pyramids were built1 and they mark for us the ,dawn of ,history4 ,and since then half-a-dozen mighty empires have come and gone6 ,having thus concluded our general survey of the appearance and dimensions of the solar system1 let us next inquire into its position and size in relation to what we call the ,universe4 ,a mere glance at the night sky1 when it is free from clouds1 shows us that in every direction there are stars2 and this holds good1 no matter what portion of the globe we visit4 ,the same is really true of the sky by day1 though in that case we cannot actually see the stars1 for their light is quite overpowered by the dazzling light of the sun4 ,we thus reach the conclusion that our earth1 that our solar system in fact1 lies plunged within the midst of a great tangle of stars4 ,what position1 by the way1 do we occupy in this mighty maze8 ,are we at the centre1 or anywhere near the centre1 or where8 ,it has been indeed amply proved by astronomical research that the stars are bodies giving off a light of their own1 just as our sun does2 that they are in fact suns1 and that our sun is merely one1 perhaps indeed a very unimportant member1 of this great universe of stars4 ,each of these stars1 or suns1 besides1 may be the centre of a system similar to what we call our solar system1 comprising planets and satellites1 comets and meteors2--or perchance indeed some further variety of attendant bodies of which we have no example in our tiny corner of space4 ,but as to whether one is right in a conjecture of this kind1 there is up to the present no proof whatever4 ,no telescope has yet shown a planet in attendance upon one of these distant suns2 for such bodies1 even if they do exist1 are entirely out of the range of our mightiest instruments4 ,on what then can we ground such an assumption8 ,merely upon analogy2 upon the common-sense deduction that as the stars have characteristics similar to our particular star1 the sun1 it would seem unlikely that ours should be the only such body in the whole of space which is attended by a planetary system4 ,the ,stars1 using that expression in its most general sense1 do not lie at one fixed distance from us1 set here and there upon a background of sky4 ,there is in fact no background at all4 ,the brilliant orbs are all around us in space1 at different distances from us and from each other2 and we can gaze between them out into the blackness of the void which1 perhaps1 continues to extend unceasingly long after the very outposts of the stellar universe has been left behind4 ,shall we then start our imaginary express train once more1 and send it out towards the nearest of the stars8 ,this would1 however1 be a useless experiment4 ,our express-train method of gauging space would fail miserably in the attempt to bring home to us the mighty gulf by which we are now faced4 ,let us therefore halt for a moment and look back upon the orders of distance with which we have been dealing4 ,first of all we dealt with thousands of miles4 ,next we saw how they shrank into insignificance when we embarked upon millions4 ,we found1 indeed1 that our sixty-mile-an-hour train1 rushing along without ceasing1 would consume nearly the whole of historical time in a journey from the sun to ,neptune4 ,in the spaces beyond the solar system we are faced1 however1 by a new order of distance4 ,from sun to planets is measured in millions of miles1 but from sun to sun is measured in billions4 ,but does the mere stating of this fact convey anything8 ,i fear not4 ,for the word billion runs as glibly off the tongue as million1 and both are so wholly unrealisable by us that the actual difference between them might easily pass unnoticed4 ,let us1 however1 make a careful comparison4 ,what is a million8 ,it is a thousand thousands4 ,but what is a billion8 ,it is a million millions4 ,consider for a moment6 ,a million of millions4 ,that means a million1 each unit of which is again a million4 ,in fact every separate #a in this million is itself a million4 ,here is a way of trying to realise this gigantic number4 ,a million seconds make only eleven and a half days and nights4 ,but a billion seconds will make actually more than thirty thousand years6 ,having accepted this1 let us try and probe with our express train even a little of the new gulf which now lies before us4 ,at our old rate of going it took almost two years to cover a million miles4 ,to cover a billion miles--that is to say1 a million times this distance--would thus take of course nearly two million years4 ,alpha ,centauri1 the nearest star to our earth1 is some twenty-five billions of miles away4 ,our express train would thus take about fifty millions of years to reach it6 ,this shows how useless our illustration1 appropriate though it seemed for interplanetary space1 becomes when applied to the interstellar spaces4 ,it merely gives us millions in return for billions2 and so the mind1 driven in upon itself1 whirls round and round like a squirrel in its revolving cage4 ,there is1 however1 a useful illustration still left us1 and it is the one which astronomers usually employ in dealing with the distances of the stars4 ,the illustration in question is taken from the velocity of light4 ,light travels at the tremendous speed of about #ahf1jjj miles a second4 ,it therefore takes only about a second and a quarter to come to us from the moon4 ,it traverses the #ic1jjj1jjj of miles which separate us from the sun in about eight minutes4 ,it travels from the sun out to ,neptune in about four hours1 which means that it would cross the solar system from end to end in eight4 ,to pass1 however1 across the distance which separates us from ,alpha ,centauri it would take so long as about four and a quarter years6 ,astronomers1 therefore1 agree in estimating the distances of the stars from the point of view of the time which light would take to pass from them to our earth4 ,they speak of that distance which light takes a year to traverse as a light year4 ,according to this notation1 ,alpha ,centauri is spoken of as being about four and a quarter light years distant from us4 ,now as the rays of light coming from ,alpha ,centauri to us are chasing one another incessantly across the gulf of space1 and as each ray left that star some four years before it reaches us1 our view of the star itself must therefore be always some four years old4 ,were then this star to be suddenly removed from the universe at any moment1 we should continue to see it still in its place in the sky for some four years more1 after which it would suddenly disappear4 ,the rays which had already started upon their journey towards our earth must indeed continue travelling1 and reaching us in their turn until the last one had arrived2 after which no more would come4 ,we have drawn attention to ,alpha ,centauri as the nearest of the stars4 ,the majority of the others indeed are ever so much farther4 ,we can only hazard a guess at the time it takes for the rays from many of them to reach our globe4 ,suppose1 for instance1 we see a sudden change in the light of any of these remote stars1 we are inclined to ask ourselves when that change did actually occur4 ,was it in the days of ,queen ,elizabeth1 or at the time of the ,norman ,conquest2 or was it when ,rome was at the height of her glory1 or perhaps ages before that when the ,pyramids of ,egypt were being built8 ,even the last of these suppositions cannot be treated lightly4 ,we have indeed no real knowledge of the distance from us of those stars which our giant telescopes have brought into view out of the depths of the celestial spaces4 ,,chapter ,,vi ,,celestial ,,measurement ,had the telescope never been invented our knowledge of astronomy would be trifling indeed4 ,prior to the year #afaj1 when ,galileo first turned the new instrument upon the sky1 all that men knew of the starry realms was gathered from observation with their own eyes unaided by any artificial means4 ,in such researches they had been very much at a disadvantage4 ,the sun and moon1 in their opinion1 were no doubt the largest bodies in the heavens1 for the mere reason that they looked so6 ,the mighty solar disturbances1 which are now such common-places to us1 were then quite undreamed of4 ,the moon displayed a patchy surface1 and that was all2 her craters and ring-mountains were surprises as yet in store for men4 ,nothing of course was known about the surfaces of the planets4 ,these objects had indeed no particular characteristics to distinguish them from the great host of the stars1 except that they continually changed their positions in the sky while the rest did not4 ,the stars themselves were considered as fixed inalterably upon the vault of heaven4 ,the sun1 moon1 and planets apparently moved about in the intermediate space1 supported in their courses by strange and fanciful devices4 ,the idea of satellites was as yet unknown4 ,comets were regarded as celestial portents1 and meteors as small conflagrations taking place in the upper air4 ,in the entire absence of any knowledge with regard to the actual sizes and distances of the various celestial bodies1 men naturally considered them as small2 and1 concluding that they were comparatively near1 assigned to them in consequence a permanent connection with terrestrial affairs4 ,thus arose the quaint and erroneous beliefs of astrology1 according to which the events which took place upon our earth were considered to depend upon the various positions in which the planets1 for instance1 found themselves from time to time4 ,it must1 however1 be acknowledged that the study of astrology1 fallacious though its conclusions were1 indirectly performed a great service to astronomy by reason of the accurate observations and diligent study of the stars which it entailed4 ,we will now inquire into the means by which the distances and sizes of the celestial orbs have been ascertained1 and see how it was that the ancients were so entirely in the dark in this matter4 ,there are two distinct methods of finding out the distance at which any object happens to be situated from us4 ,one method is by actual measurement4 ,the other is by moving oneself a little to the right or left1 and observing whether the distant object appears in any degree altered in position by our own change of place4 ,one of the best illustrations of this relative change of position which objects undergo as a result of our own change of place1 is to observe the landscape from the window of a moving railway carriage4 ,as we are borne rapidly along we notice that the telegraph posts which are set close to the line appear to fly past us in the contrary direction2 the trees1 houses1 and other things beyond go by too1 but not so fast2 objects a good way off displace slowly2 while some spire1 or tall landmark1 in the far distance appears to remain unmoved during a comparatively long time4 ,actual change of position on our own part is found indeed to be invariably accompanied by an apparent displacement of the objects about us1 such apparent displacement as a result of our own change of position being known as parallax4 ,the dependence between the two is so mathematically exact1 that if we know the amount of our own change of place1 and if we observe the amount of the consequent displacement of any object1 we are enabled to calculate its precise distance from us4 ,thus it comes to pass that distances can be measured without the necessity of moving over them2 and the breadth of a river1 for instance1 or the distance from us of a ship at sea1 can be found merely by such means4 ,it is by the application of this principle to the wider field of the sky that we are able to ascertain the distance of celestial bodies4 ,we have noted that it requires a goodly change of place on our own part to shift the position in which some object in the far distance is seen by us4 ,to two persons separated by1 say1 a few hundred yards1 a ship upon the horizon will appear pretty much in the same direction4 ,they would require1 in fact1 to be much farther apart in order to displace it sufficiently for the purpose of estimating their distance from it4 ,it is the same with regard to the moon4 ,two observers1 standing upon our earth1 will require to be some thousands of miles apart in order to see the position of our satellite sufficiently altered with regard to the starry background1 to give the necessary data upon which to ground their calculations4 ,the change of position thus offered by one side of the earth's surface at a time is1 however1 not sufficient to displace any but the nearest celestial bodies4 ,when we have occasion to go farther afield we have to seek a greater change of place4 ,this we can get as a consequence of the earth's movement around the sun4 ,observations1 taken several days apart1 will show the effect of the earth's change of place during the interval upon the positions of the other bodies of our system4 ,but when we desire to sound the depths of space beyond1 and to reach out to measure the distance of the nearest star1 we find ourselves at once thrown upon the greatest change of place which we can possibly hope for2 and this we get during the long journey of many millions of miles which our earth performs around the sun during the course of each year4 ,but even this last change of place1 great as it seems in comparison with terrestrial measurements1 is insufficient to show anything more than the tiniest displacements in a paltry forty-three out of the entire host of the stars4 ,we can thus realise at what a disadvantage the ancients were4 ,the measuring instruments at their command were utterly inadequate to detect such small displacements4 ,it was reserved for the telescope to reveal them2 and even then it required the great telescopes of recent times to show the slight changes in the position of the nearer stars1 which were caused by the earth's being at one time at one end of its orbit1 and some six months later at the other end--stations separated from each other by a gulf of about one hundred and eighty-six millions of miles4 ,the actual distances of certain celestial bodies being thus ascertainable1 it becomes a matter of no great difficulty to determine the actual sizes of the measurable ones4 ,it is a matter of everyday experience that the size which any object appears to have1 depends exactly upon the distance it is from us4 ,the farther off it is the smaller it looks2 the nearer it is the bigger4 ,if1 then1 an object which lies at a known distance from us looks such and such a size1 we can of course ascertain its real dimensions4 ,take the moon1 for instance4 ,as we have already shown1 we are able to ascertain its distance4 ,we observe also that it looks a certain size4 ,it is therefore only a matter of calculation to find what its actual dimensions should be1 in order that it may look that size at that distance away4 ,similarly we can ascertain the real dimensions of the sun4 ,the planets1 appearing to us as points of light1 seem at first to offer a difficulty2 but1 by means of the telescope1 we can bring them1 as it were1 so much nearer to us1 that their broad expanses may be seen4 ,we fail1 however1 signally with regard to the stars2 for they are so very distant1 and therefore such tiny points of light1 that our mightiest telescopes cannot magnify them sufficiently to show any breadth of surface4 ,instead of saying that an object looks a certain breadth across1 such as a yard or a foot1 a statement which would really mean nothing1 astronomers speak of it as measuring a certain angle4 ,such angles are estimated in what are called degrees of arc2 each degree being divided into sixty minutes1 and each minute again into sixty seconds4 ,popularly considered the moon and sun look about the same size1 or1 as an astronomer would put it1 they measure about the same angle4 ,this is an angle1 roughly1 of thirty-two minutes of arc2 that is to say1 slightly more than half a degree4 ,the broad expanse of surface which a celestial body shows to us1 whether to the naked eye1 as in the case of the sun and moon1 or in the telescope1 as in the case of other members of our system1 is technically known as its disc4 ,,chapter ,,vii ,,eclipses ,,and ,,kindred ,,phenomena ,since some members of the solar system are nearer to us than others1 and all are again much nearer than any of the stars1 it must often happen that one celestial body will pass between us and another1 and thus intercept its light for a while4 ,the moon1 being the nearest object in the universe1 will1 of course1 during its motion across the sky1 temporarily blot out every one of the others which happen to lie in its path4 ,when it passes in this manner across the face of the sun1 it is said to eclipse it4 ,when it thus hides a planet or star1 it is said to occult it4 ,the reason why a separate term is used for what is merely a case of obscuring light in exactly the same way1 will be plain when one considers that the disc of the sun is almost of the same apparent size as that of the moon1 and so the complete hiding of the sun can last but a few minutes at the most2 whereas a planet or a star looks so very small in comparison1 that it is always entirely swallowed up for some time when it passes behind the body of our satellite4 ,the sun1 of course1 occults planets and stars in exactly the same manner as the moon does1 but we cannot see these occultations on account of the blaze of sunlight4 ,by reason of the small size which the planets look when viewed with the naked eye1 we are not able to note them in the act of passing over stars and so blotting them out2 but such occurrences may be seen in the telescope1 for the planetary bodies then display broad discs4 ,there is yet another occurrence of the same class which is known as a transit4 ,this takes place when an apparently small body passes across the face of an apparently large one1 the phenomenon being in fact the exact reverse of an occultation4 ,as there is no appreciable body nearer to us than the moon1 we can never see anything in transit across her disc4 ,but since the planets ,venus and ,mercury are both nearer to us than the sun1 they will occasionally be seen to pass across his face1 and thus we get the well-known phenomena called ,transits of ,venus and ,transits of ,mercury4 ,as the satellites of ,jupiter are continually revolving around him1 they will often pass behind or across his disc4 ,such occultations and transits of satellites can be well observed in the telescope4 ,there is1 however1 a way in which the light of a celestial body may be obscured without the necessity of its being hidden from us by one nearer4 ,it will no doubt be granted that any opaque object casts a shadow when a strong light falls directly upon it4 ,thus the earth1 under the powerful light which is directed upon it from the sun1 casts an extensive shadow1 though we are not aware of the existence of this shadow until it falls upon something4 ,the shadow which the earth casts is indeed not noticeable to us until some celestial body passes into it4 ,as the sun is very large1 and the earth in comparison very small1 the shadow thrown by the earth is comparatively short1 and reaches out in space for only about a million miles4 ,there is no visible object except the moon1 which circulates within that distance from our globe1 and therefore she is the only body which can pass into this shadow4 ,whenever such a thing happens1 her surface at once becomes dark1 for the reason that she never emits any light of her own1 but merely reflects that of the sun4 ,as the moon is continually revolving around the earth1 one would be inclined to imagine that once in every month1 namely at what is called full moon1 when she is on the other side of the earth with respect to the sun1 she ought to pass through the shadow in question4 ,but this does not occur every time1 because the moon's orbit is not quite upon the same plane with the earth's4 ,it thus happens that time after time the moon passes clear of the earth's shadow1 sometimes above it1 and sometimes below it4 ,it is indeed only at intervals of about six months that the moon can be thus obscured4 ,this darkening of her light is known as an eclipse of the moon4 ,it seems a great pity that custom should oblige us to employ the one term eclipse for this and also for the quite different occurrence1 an eclipse of the sun2 in which the sun's face is hidden as a consequence of the moon's body coming directly between it and our eyes4 ,the popular mind seems always to have found it more difficult to grasp the causes of an eclipse of the moon than an eclipse of the sun4 ,as ,mr4 ,j4,e4 ,gore#d puts it3 ,the darkening of the sun's light by the interposition of the moon's body seems more obvious than the passing of the moon through the earth's shadow4 ,eclipses of the moon furnish striking spectacles1 but really add little to our knowledge4 ,they exhibit1 however1 one of the most remarkable evidences of the globular shape of our earth2 for the outline of its shadow when seen creeping over the moon's surface is always circular4 ,illustration3 ,,fig4 #c4--,total and ,partial ,eclipses of the ,moon4 ,the ,moon is here shown in two positions2 i4e4 entirely plunged in the earth's shadow and therefore totally eclipsed1 and only partly plunged in it or partially eclipsed4 ,eclipses of the ,moon1 or ,lunar ,eclipses1 as they are also called1 are of two kinds--,total1 and ,partial4 ,in a total lunar eclipse the moon passes entirely into the earth's shadow1 and the whole of her surface is consequently darkened4 ,this darkening lasts for about two hours4 ,in a partial lunar eclipse1 a portion only of the moon passes through the shadow1 and so only part of her surface is darkened 7see ,fig4 #c74 ,a very striking phenomenon during a total eclipse of the moon1 is that the darkening of the lunar surface is usually by no means so intense as one would expect1 when one considers that the sunlight at that time should be wholly cut off from it4 ,the occasions indeed upon which the moon has completely disappeared from view during the progress of a total lunar eclipse are very rare4 ,on the majority of these occasions she has appeared of a coppery-red colour1 while sometimes she has assumed an ashen hue4 ,the explanations of these variations of colour is to be found in the then state of the atmosphere which surrounds our earth4 ,when those portions of our earth's atmosphere through which the sun's rays have to filter on their way towards the moon are free from watery vapour1 the lunar surface will be tinged with a reddish light1 such as we ordinarily experience at sunset when our air is dry4 ,the ashen colour is the result of our atmosphere being laden with watery vapour1 and is similar to what we see at sunset when rain is about4 ,lastly1 when the air around the earth is thickly charged with cloud1 no light at all can pass2 and on such occasions the moon disappears altogether for the time being from the night sky4 ,eclipses of the ,sun1 otherwise known as ,solar ,eclipses1 are divided into ,total1 ,partial1 and ,annular4 ,a total eclipse of the sun takes place when the moon comes between the sun and the earth1 in such a manner that it cuts off the sunlight entirely for the time being from a portion of the earth's surface4 ,a person situated in the region in question will1 therefore1 at that moment find the sun temporarily blotted out from his view by the body of the moon4 ,since the moon is a very much smaller body than the sun1 and also very much the nearer to us of the two1 it will readily be understood that the portion of the earth from which the sun is seen thus totally eclipsed will be of small extent4 ,in places not very distant from this region1 the moon will appear so much shifted in the sky that the sun will be seen only partially eclipsed4 ,the moon being in constant movement round the earth1 the portion of the earth's surface from which an eclipse is seen as total will be always a comparatively narrow band lying roughly from west to east4 ,this band1 known as the track of totality1 can1 at the utmost1 never be more than about #afe miles in width1 and as a rule is very much less4 ,for about #bjjj miles on either side of it the sun is seen partially eclipsed4 ,outside these limits no eclipse of any kind is visible1 as from such regions the moon is not seen to come in the way of the sun 7see ,fig4 #d 7i471 p4 #fg74 ,it may occur to the reader that eclipses can also take place in the course of which the positions1 where the eclipse would ordinarily be seen as total1 will lie outside the surface of the earth4 ,such an eclipse is thus not dignified with the name of total eclipse1 but is called a partial eclipse1 because from the earth's surface the sun is only seen partly eclipsed at the utmost 7see ,fig4 #d 7ii471 p4 #fg74 ,illustration3 7i47 ,total ,eclipse of the ,sun4 ,illustration3 7ii47 ,partial ,eclipse of the ,sun4 ,,fig4 #d4--,total and ,partial ,eclipses of the ,sun4 ,from the position ,a the ,sun cannot be seen1 as it is entirely blotted out by the ,moon4 ,from ,b it is seen partially blotted out1 because the ,moon is to a certain degree in the way4 ,from ,c no eclipse is seen1 because the ,moon does not come in the way4 ,it is to be noted that in a ,partial ,eclipse of the ,sun1 the position ,a lies outside the surface of the ,earth4 ,an ,annular eclipse is an eclipse which just fails to become total for yet another reason4 ,we have pointed out that the orbits of the various members of the solar system are not circular1 but oval4 ,such oval figures1 it will be remembered1 are technically known as ellipses4 ,in an elliptic orbit the controlling body is situated not in the middle of the figure1 but rather towards one of the ends2 the actual point which it occupies being known as the focus4 ,the sun being at the focus of the earth's orbit1 it follows that the earth is1 at times1 a little nearer to him than at others4 ,the sun will therefore appear to us to vary a little in size1 looking sometimes slightly larger than at other times4 ,it is so1 too1 with the moon1 at the focus of whose orbit the earth is situated4 ,she therefore also appears to us at times to vary slightly in size4 ,the result is that when the sun is eclipsed by the moon1 and the moon at the time appears the larger of the two1 she is able to blot out the sun completely1 and so we can get a total eclipse4 ,but when1 on the other hand1 the sun appears the larger1 the eclipse will not be quite total1 for a portion of the sun's disc will be seen protruding all around the moon like a ring of light4 ,this is what is known as an annular eclipse1 from the ,latin word annulus1 which means a ring4 ,the term is consecrated by long usage1 but it seems an unfortunate one on account of its similarity to the word annual4 ,the ,germans speak of this kind of eclipse as ring-formed1 which is certainly much more to the point4 ,there can never be a year without an eclipse of the sun4 ,indeed there must be always two such eclipses at least during that period1 though there need be no eclipse of the moon at all4 ,on the other hand1 the greatest number of eclipses which can ever take place during a year are seven2 that is to say1 either five solar eclipses and two lunar1 or four solar and three lunar4 ,this general statement refers merely to eclipses in their broadest significance1 and informs us in no way whether they will be total or partial4 ,of all the phenomena which arise from the hiding of any celestial body by one nearer coming in the way1 a total eclipse of the sun is far the most important4 ,it is1 indeed1 interesting to consider how much poorer modern astronomy would be but for the extraordinary coincidence which makes a total solar eclipse just possible4 ,the sun is about #djj times farther off from us than the moon1 and enormously greater than her in bulk4 ,yet the two are relatively so distanced from us as to look about the same size4 ,the result of this is that the moon1 as has been seen1 can often blot out the sun entirely from our view for a short time4 ,when this takes place the great blaze of sunlight which ordinarily dazzles our eyes is completely cut off1 and we are thus enabled1 unimpeded1 to note what is going on in the immediate vicinity of the sun itself4 ,in a total solar eclipse1 the time which elapses from the moment when the moon's disc first begins to impinge upon that of the sun at his western edge until the eclipse becomes total1 lasts about an hour4 ,during all this time the black lunar disc may be watched making its way steadily across the solar face4 ,notwithstanding the gradual obscuration of the sun1 one does not notice much diminution of light until about three-quarters of his disc are covered4 ,then a wan1 unearthly appearance begins to pervade all things1 the temperature falls noticeably1 and nature seems to halt in expectation of the coming of something unusual4 ,the decreasing portion of sun becomes more and more narrow1 until at length it is reduced to a crescent-shaped strip of exceeding fineness4 ,strange1 ill-defined1 flickering shadows 7known as ,shadow ,bands7 may at this moment be seen chasing each other across any white expanse such as a wall1 a building1 or a sheet stretched upon the ground4 ,the western side of the sky has now assumed an appearance dark and lowering1 as if a rainstorm of great violence were approaching4 ,this is caused by the mighty mass of the lunar shadow sweeping rapidly along4 ,it flies onward at the terrific velocity of about half a mile a second4 ,if the gradually diminishing crescent of sun be now watched through a telescope1 the observer will notice that it does not eventually vanish all at once1 as he might have expected4 ,rather1 it breaks up first of all along its length into a series of brilliant dots1 known as ,baily's ,beads4 ,the reason of this phenomenon is perhaps not entirely agreed upon1 but the majority of astronomers incline to the opinion that the so-called beads are merely the last remnants of sunlight peeping between those lunar mountain peaks which happen at the moment to fringe the advancing edge of the moon4 ,the beads are no sooner formed than they rapidly disappear one after the other1 after which no portion of the solar surface is left to view1 and the eclipse is now total 7see ,fig4 #e74 ,illustration3 ,in a total ,eclipse ,in an annular ,eclipse ,,fig4 #e4--;,baily's ,beads4 ,but with the disappearance of the sun there springs into view a new and strange appearance1 ordinarily unseen because of the blaze of sunlight4 ,it is a kind of aureole1 or halo1 pearly white in colour1 which is seen to surround the black disc of the moon4 ,this white radiance is none other than the celebrated phenomenon widely known as the ,solar ,corona4 ,it was once upon a time thought to belong to the moon1 and to be perhaps a lunar atmosphere illuminated by the sunlight shining through it from behind4 ,but the suddenness with which the moon always blots out stars when occulting them1 has amply proved that she possesses no atmosphere worth speaking about4 ,it is now1 however1 satisfactorily determined that the corona belongs to the sun1 for during the short time that it remains in view the black body of the moon can be seen creeping across it4 ,all the time that the total phase 7as it is called7 lasts1 the corona glows with its pale unearthly light1 shedding upon the earth's surface an illumination somewhat akin to full moonlight4 ,usually the planet ,venus and a few stars shine out the while in the darkened heaven4 ,meantime around the observer animal and plant life behave as at nightfall4 ,birds go to roost1 bats fly out1 worms come to the surface of the ground1 flowers close up4 ,in the ,norwegian eclipse of #ahif fish were seen rising to the surface of the water4 ,when the total phase at length is over1 and the moon in her progress across the sky has allowed the brilliant disc of the sun to spring into view once more at the other side1 the corona disappears4 ,there is another famous accompaniment of the sun which partly reveals itself during total solar eclipses4 ,this is a layer of red flame which closely envelops the body of the sun and lies between it and the corona4 ,this layer is known by the name of the ,chromosphere4 ,just as at ordinary times we cannot see the corona on account of the blaze of sunlight1 so are we likewise unable to see the chromosphere because of the dazzling white light which shines through from the body of the sun underneath and completely overpowers it4 ,when1 however1 during a solar eclipse1 the lunar disc has entirely hidden the brilliant face of the sun1 we are still able for a few moments to see an edgewise portion of the chromosphere in the form of a narrow red strip1 fringing the advancing border of the moon4 ,later on1 just before the moon begins to uncover the face of the sun from the other side1 we may again get a view of a strip of chromosphere4 ,the outer surface of the chromosphere is not by any means even4 ,it is rough and billowy1 like the surface of a storm-tossed sea4 ,portions of it1 indeed1 rise at times to such heights that they may be seen standing out like blood-red points around the black disc of the moon1 and remain thus during a good part of the total phase4 ,these projections are known as the ,solar ,prominences4 ,in the same way as the corona1 the chromosphere and prominences were for a time supposed to belong to the moon4 ,this1 however1 was soon found not to be the case1 for the lunar disc was noticed to creep slowly across them also4 ,the total phase1 or totality1 as it is also called1 lasts for different lengths of time in different eclipses4 ,it is usually of about two or three minutes' duration1 and at the utmost it can never last longer than about eight minutes4 ,when totality is over and the corona has faded away1 the moon's disc creeps little by little from the face of the sun1 light and heat returns once more to the earth1 and nature recovers gradually from the gloom in which she has been plunged4 ,about an hour after totality1 the last remnant of moon draws away from the solar disc1 and the eclipse is entirely at an end4 ,the corona1 the chromosphere1 and the prominences are the most important of these accompaniments of the sun which a total eclipse reveals to us4 ,our further consideration of them must1 however1 be reserved for a subsequent chapter1 in which the sun will be treated of at length4 ,every one who has had the good fortune to see a total eclipse of the sun will1 the writer feels sure1 agree with the verdict of ,sir ,norman ,lockyer that it is at once one of the grandest and most awe-inspiring sights which man can witness4 ,needless to say1 such an occurrence used to cause great consternation in less civilised ages2 and that it has not in modern times quite parted with its terrors for some persons1 is shown by the fact that in ,iowa1 in the ,united ,states1 a woman died from fright during the eclipse of #ahfi4 ,to the serious observer of a total solar eclipse every instant is extremely precious4 ,many distinct observations have to be crowded into a time all too limited1 and this in an eclipse-party necessitates constant rehearsals in order that not a moment may be wasted when the longed-for totality arrives4 ,such preparation is very necessary2 for the rarity and uncommon nature of a total eclipse of the sun1 coupled with its exceeding short duration1 tends to flurry the mind1 and to render it slow to seize upon salient points of detail4 ,and1 even after every precaution has been taken1 weather possibilities remain to be reckoned with1 so that success is rather a lottery4 ,above all things1 therefore1 a total solar eclipse is an occurrence for the proper utilisation of which personal experience is of absolute necessity4 ,it was manifestly out of the question that such experience could be gained by any individual in early times1 as the imperfection of astronomical theory and geographical knowledge rendered the predicting of the exact position of the track of totality well-nigh impossible4 ,thus chance alone would have enabled one in those days to witness a total phase1 and the probabilities1 of course1 were much against a second such experience in the span of a life-time4 ,and even in more modern times1 when the celestial motions had come to be better understood1 the difficulties of foreign travel still were in the way2 for it is1 indeed1 a notable fact that during many years following the invention of the telescope the tracks were placed for the most part in far-off regions of the earth1 and ,europe was visited by singularly few total solar eclipses4 ,thus it came to pass that the building up of a body of organised knowledge upon this subject was greatly delayed4 ,nothing perhaps better shows the soundness of modern astronomical theory than the almost exact agreement of the time predicted for an eclipse with its actual occurrence4 ,similarly1 by calculating backwards1 astronomers have discovered the times and seasons at which many ancient eclipses took place1 and valuable opportunities have thus arisen for checking certain disputed dates in history4 ,it should not be omitted here that the ancients were actually able1 in a rough way1 to predict eclipses4 ,the ,chaldean astronomers had indeed noticed very early a curious circumstance1 i4e4 that eclipses tend to repeat themselves after a lapse of slightly more than eighteen years4 ,in this connection it must1 however1 be pointed out1 in the first instance1 that the eclipses which occur in any particular year are in no way associated with those which occurred in the previous year4 ,in other words1 the mere fact that an eclipse takes place upon a certain day this year will not bring about a repetition of it at the same time next year4 ,however1 the nicely balanced behaviour of the solar system1 an equilibrium resulting from ons of orbital ebb and flow1 naturally tends to make the members which compose that family repeat their ancient combinations again and again2 so that after definite lapses of time the same order of things will almost exactly recur4 ,thus1 as a consequence of their beautifully poised motions1 the sun1 the moon1 and the earth tend1 after a period of #ah years and #aj-a_/c days1#e to occupy very nearly the same positions with regard to each other4 ,the result of this is that1 during each recurring period1 the eclipses comprised within it will be repeated in their order4 ,to give examples3-- ,the total solar eclipse of ,august #cj1 #aije1 was a repetition of that of ,august #ai1 #ahhg4 ,the partial solar eclipse of ,february #bc1 #aijf1 corresponded to that which took place on ,february #aa1 #ahhh4 ,the annular eclipse of ,july #aj1 #aijg1 was a recurrence of that of ,june #bh1 #ahhi4 ,in this way we can go on until the eighteen year cycle has run out1 and we come upon a total solar eclipse predicted for ,september #aj1 #aibc1 which will repeat the above-mentioned ones of #aije and #ahhg2 and so on too with the others4 ,from mere observation alone1 extending no doubt over many ages1 those time-honoured watchers of the sky1 the early ,chaldeans1 had arrived at this remarkable generalisation2 and they used it for the rough prediction of eclipses4 ,to the period of recurrence they give the name of ,saros4 ,and here we find ourselves led into one of the most interesting and fascinating by-paths in astronomy1 to which writers1 as a rule1 pay all too little heed4 ,in order not to complicate matters unduly1 the recurrence of solar eclipses alone will first be dealt with4 ,this limitation will1 however1 not affect the arguments in the slightest1 and it will be all the more easy in consequence to show their application to the case of eclipses of the moon4 ,the reader will perhaps have noticed that1 with regard to the repetition of an eclipse1 it has been stated that the conditions which bring it on at each recurrence are reproduced almost exactly4 ,here1 then1 lies the crux of the situation4 ,for it is quite evident that were the conditions exactly reproduced1 the recurrences of each eclipse would go on for an indefinite period4 ,for instance1 if the lapse of a saros period found the sun1 moon1 and earth again in the precise relative situations which they had previously occupied1 the recurrences of a solar eclipse would tend to duplicate its forerunner with regard to the position of the shadow upon the terrestrial surface4 ,but the conditions not being exactly reproduced1 the shadow-track does not pass across the earth in quite the same regions4 ,it is shifted a little1 so to speak2 and each time the eclipse comes round it is found to be shifted a little farther4 ,every solar eclipse has therefore a definite life of its own upon the earth1 lasting about #aaej years1 or #fd saros returns1 and working its way little by little across our globe from north to south1 or from south to north1 as the case may be4 ,let us take an imaginary example4 ,a partial eclipse occurs1 say1 somewhere near the ,north ,pole1 the edge of the partial shadow just grazing the earth1 and the track of totality being as yet cast into space4 ,here we have the beginning of a series4 ,at each saros recurrence the partial shadow encroaches upon a greater extent of earth-surface4 ,at length1 in its turn1 the track of totality begins to impinge upon the earth4 ,this track streaks across our globe at each return of the eclipse1 repeating itself every time in a slightly more southerly latitude4 ,south and south it moves1 passing in turn the ,tropic of ,cancer1 the ,equator1 the ,tropic of ,capricorn1 until it reaches the ,south ,pole2 after which it touches the earth no longer1 but is cast into space4 ,the rear portion of the partial shadow1 in its turn1 grows less and less in extent2 and it too in time finally passes off4 ,our imaginary eclipse series is now no more--its life has ended4 ,we have taken1 as an example1 an eclipse series moving from north to south4 ,we might have taken one moving from south to north1 for they progress in either direction4 ,from the description just given the reader might suppose that1 if the tracks of totality of an eclipse series were plotted upon a chart of the world1 they would lie one beneath another like a set of steps4 ,this is1 however1 not the case1 and the reason is easily found4 ,it depends upon the fact that the saros does not comprise an exact number of days1 but includes1 as we have seen1 one-third of a day in addition4 ,it will be granted1 of course1 that if the number of days was exact1 the same parts of the earth would always be brought round by the axial rotation to front the sun at the moment of the recurrence of the eclipse4 ,but as there is still one-third of a day to complete the saros period1 the earth has yet to make one-third of a rotation upon its axis before the eclipse takes place4 ,thus at every recurrence the track of totality finds itself placed one-third of the earth's circumference to the westward4 ,three of the recurrences will1 of course1 complete the circuit of the globe2 and so the fourth recurrence will duplicate the one which preceded it1 three saros returns1 or #ed years and #a month before4 ,this duplication1 as we have already seen1 will1 however1 be situated in a latitude to the south or north of its predecessor1 according as the eclipse series is progressing in a southerly or northerly direction4 ,lastly1 every eclipse series1 after working its way across the earth1 will return again to go through the same process after some #ab1jjj years2 so that1 at the end of that great lapse of time1 the entire life of every eclipse should repeat itself1 provided that the conditions of the solar system have not altered appreciably during the interval4 ,we are now in a position to consider this gradual southerly or northerly progress of eclipse recurrences in its application to the case of eclipses of the moon4 ,it should be evident that1 just as in solar eclipses the lunar shadow is lowered or raised 7as the case may be7 each time it strikes the terrestrial surface1 so in lunar eclipses will the body of the moon shift its place at each recurrence relatively to the position of the earth's shadow4 ,every lunar eclipse1 therefore1 will commence on our satellite's disc as a partial eclipse at the northern or southern extremity1 as the case may be4 ,let us take1 as an example1 an imaginary series of eclipses of the moon progressing from north to south4 ,at each recurrence the partial phase will grow greater1 its boundary encroaching more and more to the southward1 until eventually the whole disc is enveloped by the shadow1 and the eclipse becomes total4 ,it will then repeat itself as total during a number of recurrences1 until the entire breadth of the shadow has been passed through1 and the northern edge of the moon at length springs out into sunlight4 ,this illuminated portion will grow more and more extensive at each succeeding return1 the edge of the shadow appearing to recede from it until it finally passes off at the south4 ,similarly1 when a lunar eclipse commences as partial at the south of the moon1 the edge of the shadow at each subsequent recurrence finds itself more and more to the northward4 ,in due course the total phase will supervene1 and will persist during a number of recurrences until the southerly trend of the moon results in the uncovering of the lunar surface at the south4 ,thus1 as the boundary of the shadow is left more and more to the northward1 the illuminated portion on the southern side of the moon becomes at each recurrence greater and the darkened portion on the northern side less1 until the shadow eventually passes off at the north4 ,the life of an eclipse of the moon happens1 for certain reasons1 to be much shorter than that of an eclipse of the sun4 ,it lasts during only about #hfj years1 or #dh saros returns4 ,fig4 #f1 p4 #ha1 is a map of the world on ,mercator's ,projection1 showing a portion of the march of the total solar eclipse of ,august #cj1 #aije1 across the surface of the earth4 ,the projection in question has been employed because it is the one with which people are most familiar4 ,this eclipse began by striking the neighbourhood of the ,north ,pole in the guise of a partial eclipse during the latter part of the reign of ,queen ,elizabeth1 and became total on the earth for the first time on the #bdth of ,june #agig4 ,its next appearance was on the #fth of ,july #ahae4 ,it has not been possible to show the tracks of totality of these two early visitations on account of the distortion of the polar regions consequent on the fiction of ,mercator's ,projection4 ,it is therefore made to commence with the track of its third appearance1 viz4 on ,july #ag1 #ahcc4 ,in consequence of those variations in the apparent sizes of the sun and moon1 which result1 as we have seen1 from the variations in their distances from the earth1 this eclipse will change from a total into an annular eclipse towards the end of the twenty-first century4 ,by that time the track will have passed to the southern side of the equator4 ,the track will eventually leave the earth near the ,south ,pole about the beginning of the twenty-sixth century1 and the rear portion of the partial shadow will in its turn be clear of the terrestrial surface by about #bgjj ,a4,d41 when the series comes to an end4 ,illustration3 ,,fig4 #f4--,map of the ,world on ,mercator's ,projection1 showing a portion of the progress of the ,total ,solar ,eclipse of ,august #cj1 #aije1 across the surface of the earth4 #d ,astronomical ,essays 7p4 #dj71 ,london1 #aijg4 #e ,in some cases the periods between the dates of the corresponding eclipses appear to include a greater number of days than ten2 but this is easily explained when allowance is made for intervening leap years 7in each of which an extra day has of course been added71 and also for variations in local time4 ,,chapter ,,viii ,,famous ,,eclipses ,,of ,,the ,,sun ,what is thought to be the earliest reference to an eclipse comes down to us from the ancient ,chinese records1 and is over four thousand years old4 ,the eclipse in question was a solar one1 and occurred1 so far as can be ascertained1 during the twenty-second century ,b4,c4 ,the story runs that the two state astronomers1 ,ho and ,hi by name1 being exceedingly intoxicated1 were unable to perform their required duties1 which consisted in superintending the customary rites of beating drums1 shooting arrows1 and the like1 in order to frighten away the mighty dragon which it was believed was about to swallow up the ,lord of ,day4 ,this eclipse seems to have been only partial2 nevertheless a great turmoil ensued1 and the two astronomers were put to death1 no doubt with the usual celestial cruelty4 ,the next eclipse mentioned in the ,chinese annals is also a solar eclipse1 and appears to have taken place more than a thousand years later1 namely in #ggf ,b4,c4 ,records of similar eclipses follow from the same source2 but as they are mere notes of the events1 and do not enter into any detail1 they are of little interest4 ,curiously enough the ,chinese have taken practically no notice of eclipses of the moon1 but have left us a comparatively careful record of comets1 which has been of value to modern astronomy4 ,the earliest mention of a total eclipse of the sun 7for it should be noted that the ancient ,chinese eclipse above-mentioned was merely partial7 was deciphered in #aije1 on a very ancient ,babylonian tablet1 by ,mr4 ,l4,w4 ,king of the ,british ,museum4 ,this eclipse took place in the year #ajfc ,b4,c4 ,assyrian tablets record three solar eclipses which occurred between three and four hundred years later than this4 ,the first of these was in #gfc ,b4,c42 the total phase being visible near ,nineveh4 ,the next record of an eclipse of the sun comes to us from a ,grecian source4 ,this eclipse took place in #ehe ,b4,c41 and has been the subject of much investigation4 ,herodotus1 to whom we are indebted for the account1 tells us that it occurred during a battle in a war which had been waging for some years between the ,lydians and ,medes4 ,the sudden coming on of darkness led to a termination of the contest1 and peace was afterwards made between the combatants4 ,the historian goes on to state that the eclipse had been foretold by ,thales1 who is looked upon as the ,founder of ,grecian astronomy4 ,this eclipse is in consequence known as the ,eclipse of ,thales4 ,it would seem as if that philosopher were acquainted with the ,chaldean saros4 ,the next solar eclipse worthy of note was an annular one1 and occurred in #dca ,b4,c41 the first year of the ,peloponnesian ,war4 ,plutarch relates that the pilot of the ship1 which was about to convey ,pericles to the ,peloponnesus1 was very much frightened by it2 but ,pericles calmed him by holding up a cloak before his eyes1 and saying that the only difference between this and the eclipse was that something larger than the cloak prevented his seeing the sun for the time being4 ,an eclipse of great historical interest is that known as the ,eclipse of ,agathocles1 which occurred on the morning of the #aeth of ,august1 #caj ,b4,c4 ,agathocles1 ,tyrant of ,syracuse1 had been blockaded in the harbour of that town by the ,carthaginian fleet1 but effected the escape of his squadron under cover of night1 and sailed for ,africa in order to invade the enemy's territory4 ,during the following day he and his vessels experienced a total eclipse1 in which day wholly put on the appearance of night1 and the stars were seen in all parts of the sky4 ,a few solar eclipses are supposed to be referred to in early ,roman history1 but their identity is very doubtful in comparison with those which the ,greeks have recorded4 ,additional doubt is cast upon them by the fact that they are usually associated with famous events4 ,the birth and death of ,romulus1 and the ,passage of the ,rubicon by ,julius ,csar1 are stated indeed to have been accompanied by these marks of the approval or disapproval of the gods6 ,reference to our subject in the ,bible is scanty4 ,amos viii4 #i is thought to refer to the ,nineveh eclipse of #gfc ,b4,c41 to which allusion has already been made2 while the famous episode of ,hezekiah and the shadow on the dial of ,ahaz has been connected with an eclipse which was partial at ,jerusalem in #fhi ,b4,c4 ,the first solar eclipse1 recorded during the ,christian ,era1 is known as the ,eclipse of ,phlegon1 from the fact that we are indebted for the account to a pagan writer of that name4 ,this eclipse took place in ,a4,d4 #bi1 and the total phase was visible a little to the north of ,palestine4 ,it has sometimes been confounded with the darkness of the ,crucifixion1 which event took place near the date in question2 but it is sufficient here to say that the ,crucifixion is well known to have occurred during the ,passover of the ,jews1 which is always celebrated at the full moon1 whereas an eclipse of the sun can only take place at new moon4 ,dion ,cassius1 commenting on the ,emperor ,claudius about the year ,a4,d4 #de1 writes as follows3-- ,as there was going to be an eclipse on his birthday1 through fear of a disturbance1 as there had been other prodigies1 he put forth a public notice1 not only that the obscuration would take place1 and about the time and magnitude of it1 but also about the causes that produce such an event4 ,this is a remarkable piece of information2 for the ,romans1 an essentially military nation1 appear hitherto to have troubled themselves very little about astronomical matters1 and were content1 as we have seen1 to look upon phenomena1 like eclipses1 as mere celestial prodigies4 ,what is thought to be the first definite mention of the solar corona occurs in a passage of ,plutarch4 ,the eclipse to which he refers is probably one which took place in ,a4,d4 #ga4 ,he says that the obscuration caused by the moon has no time to last and no extensiveness1 but some light shows itself round the sun's circumference1 which does not allow the darkness to become deep and complete4 ,no further reference to this phenomenon occurs until near the end of the sixteenth century4 ,it should1 however1 be here mentioned that ,mr4 ,e4,w4 ,maunder has pointed out the probability#f that we have a very ancient symbolic representation of the corona in the winged circle1 winged disc1 or ring with wings1 as it is variously called1 which appears so often upon ,assyrian and ,egyptian monuments1 as the symbol of the ,deity 7,fig4 #g74 ,illustration3 ,,fig4 #g4--,the ,ring with ,wings4 ,the upper is the ,assyrian form of the symbol1 the lower the ,egyptian4 7,from ,knowledge47 ,compare the form of the corona on ,plate ,,vii4 7,b71 p4 #adb4 ,the first solar eclipse recorded to have been seen in ,england is that of ,a4,d4 #ech1 mention of which is found in the ,anglo-,saxon ,chronicle4 ,the track of totality did not1 however1 come near our islands1 for only two-thirds of the sun's disc were eclipsed at ,london4 ,in #hdj a great eclipse took place in ,europe1 which was total for more than five minutes across what is now ,bavaria4 ,terror at this eclipse is said to have hastened the death of ,louis le ,debonnaire1 ,emperor of the ,west1 who lay ill at ,worms4 ,in #hgh--temp4 ,king ,alfred--an eclipse of the sun took place which was total at ,london4 ,from this until #agae no other eclipse was total at ,london itself2 though this does not apply to other portions of ,england4 ,an eclipse1 generally known as the ,eclipse of ,stiklastad1 is said to have taken place in #ajcj1 during the sea-fight in which ,olaf of ,norway is supposed to have been slain4 ,longfellow1 in his ,saga of ,king ,olaf1 has it that ,the ,sun hung red ,as a drop of blood1 but1 as in the case of most poets1 the dramatic value of an eclipse seems to have escaped his notice4 ,in the year #aadj there occurred a total eclipse of the sun1 the last to be visible in ,england for more than five centuries4 ,indeed there have been only two such since--namely1 those of #agae and #agbd1 to which we shall allude in due course4 ,the eclipse of #aadj took place on the #bjth ,march1 and is thus referred to in the ,anglo-,saxon ,chronicle3-- ,in the ,lent1 the sun and the day darkened1 about the noon-tide of the day1 when men were eating1 and they lighted candles to eat by4 ,that was the #acth day before the calends of ,april4 ,men were very much struck with wonder4 ,several of the older historians speak of a fearful eclipse as having taken place on the morning of the ,battle of ,crecy1 #acdf4 ,lingard1 for instance1 in his ,history of ,england1 has as follows3-- ,never1 perhaps1 were preparations for battle made under circumstances so truly awful4 ,on that very day the sun suffered a partial eclipse3 birds1 in clouds1 the precursors of a storm1 flew screaming over the two armies1 and the rain fell in torrents1 accompanied by incessant thunder and lightning4 ,about five in the afternoon the weather cleared up2 the sun in full splendour darted his rays in the eyes of the enemy4 ,calculations1 however1 show that no eclipse of the sun took place in ,europe during that year4 ,this error is found to have arisen from the mistranslation of an obsolete ,french word esclistre 7lightning71 which is employed by ,froissart in his description of the battle4 ,in #aeih an eclipse was total over ,scotland and part of ,north ,germany4 ,it was observed at ,torgau by ,jessenius1 an ,hungarian physician1 who noticed a bright light around the moon during the time of totality4 ,this is said to be the first reference to the corona since that of ,plutarch1 to which we have already drawn attention4 ,mention of ,scotland recalls the fact that an unusual number of eclipses happen to have been visible in that country1 and the occult bent natural to the ,scottish character has traditionalised a few of them in such terms as the ,black ,hour 7an eclipse of #adcc71 ,black ,saturday 7the eclipse of #aeih which has been alluded to above71 and ,mirk ,monday 7#afeb74 ,the track of the last-named also passed over ,carrickfergus in ,ireland1 where it was observed by a certain ,dr4 ,wybord1 in whose account the term corona is first employed4 ,this eclipse is the last which has been total in ,scotland1 and it is calculated that there will not be another eclipse seen as total there until the twenty-second century4 ,an eclipse of the sun which took place on ,may #cj1 #afab1 is recorded as having been seen through a tube4 ,this probably refers to the then recent invention--the telescope4 ,the eclipses which we have been describing are chiefly interesting from an historical point of view4 ,the old mystery and confusion to the beholders seem to have lingered even into comparatively enlightened times1 for we see how late it is before the corona attracts definite attention for the sake of itself alone4 ,it is not a far cry from notice of the corona to that of other accompaniments of a solar eclipse4 ,thus the eclipse of #agjf1 the total phase of which was visible in ,switzerland1 is of great interest2 for it was on this occasion that the famous red prominences seem first to have been noted4 ,a certain ,captain ,stannyan observed this eclipse from ,berne in ,switzerland1 and described it in a letter to ,flamsteed1 the then ,astronomer ,royal4 ,he says the sun's getting out of his eclipse was preceded by a blood-red streak of light from its left limb1 which continued not longer than six or seven seconds of time2 then part of the ,sun's disc appeared all of a sudden1 as bright as ,venus was ever seen in the night1 nay brighter2 and in that very instant gave a ,light and ,shadow to things as strong as ,moonlight uses to do4 ,how little was then expected of the sun is1 however1 shown by ,flamsteed's words1 when communicating this information to the ,royal ,society3-- ,the ,captain is the first man ,i ever heard of that took notice of a ,red ,streak of ,light preceding the ,emersion of the ,sun's body from a total ,eclipse4 ,and ,i take notice of it to you because it infers that the ,moon has an atmosphere2 and its short continuance of only six or seven seconds of time1 tells us that its height is not more than the five or six hundredth part of her diameter4 ,what a change has since come over the ideas of men6 ,the sun has proved a veritable mine of discovery1 while the moon has yielded up nothing new4 ,the eclipse of #agae1 the first total at ,london since that of #hgh1 was observed by the famous astronomer1 ,edmund ,halley1 from the rooms of the ,royal ,society1 then in ,crane ,court1 ,fleet ,street4 ,on this occasion both the corona and a red projection were noted4 ,halley further makes allusion to that curious phenomenon1 which later on became celebrated under the name of ,baily's beads4 ,it was also on the occasion of this eclipse that the earliest recorded drawings of the corona were made4 ,cambridge happened to be within the track of totality2 and a certain ,professor ,cotes of that ,university1 who is responsible for one of the drawings in question1 forwarded them to ,sir ,isaac ,newton together with a letter describing his observations4 ,in #agbd there occurred an eclipse1 the total phase of which was visible from the south-west of ,england1 but not from ,london4 ,the weather was unfavourable1 and the eclipse consequently appears to have been seen by only one person1 a certain ,dr4 ,stukeley1 who observed it from ,haraden ,hill near ,salisbury ,plain4 ,this is the last eclipse of which the total phase was seen in any part of ,england4 ,the next will not be until ,june #bi1 #aibg1 and will be visible along a line across ,north ,wales and ,lancashire4 ,the discs of the sun and moon will just then be almost of the same apparent size1 and so totality will be of extremely short duration2 in fact only a few seconds4 ,london itself will not see a totality until the year #baea--;a circumstance which need hardly distress any of us personally6 ,it is only from the early part of the nineteenth century that serious scientific attention to eclipses of the sun can be dated4 ,an annular eclipse1 visible in #ahcf in the south of ,scotland1 drew the careful notice of ,francis ,baily of ,jedburgh in ,roxburghshire to that curious phenomenon which we have already described1 and which has ever since been known by the name of ,baily's beads4 ,spurred by his observation1 the leading astronomers of the day determined to pay particular attention to a total eclipse1 which in the year #ahdb was to be visible in the south of ,france and the north of ,italy4 ,the public interest aroused on this occasion was also very great1 for the region across which the track of totality was to pass was very populous1 and inhabited by races of a high degree of culture4 ,this eclipse occurred on the morning of the #hth ,july1 and from it may be dated that great enthusiasm with which total eclipses of the sun have ever since been received4 ,airy1 our then ,astronomer ,royal1 observed it from ,turin2 ,arago1 the celebrated director of the ,paris ,observatory1 from ,perpignan in the south of ,france2 ,francis ,baily from ,pavia2 and ,sir ,john ,herschel from ,milan4 ,the corona and three large red prominences were not only well observed by the astronomers1 but drew tremendous applause from the watching multitudes4 ,the success of the observations made during this eclipse prompted astronomers to pay similar attention to that of ,july #bh1 #ahea1 the total phase of which was to be visible in the south of ,norway and ,sweden1 and across the east of ,prussia4 ,this eclipse was also a success1 and it was now ascertained that the red prominences belonged to the sun and not to the moon2 for the lunar disc1 as it moved onward1 was seen to cover and to uncover them in turn4 ,it was also noted that these prominences were merely uprushes from a layer of glowing gaseous matter1 which was seen closely to envelop the sun4 ,the total eclipse of ,july #ah1 #ahfj1 was observed in ,spain1 and photography was for the first time systematically employed in its observation4#g ,in the photographs taken the stationary appearance of both the corona and prominences with respect to the moving moon1 definitely confirmed the view already put forward that they were actual appendages of the sun4 ,the eclipse of ,august #ah1 #ahfh1 the total phase of which lasted nearly six minutes1 was visible in ,india1 and drew thither a large concourse of astronomers4 ,in this eclipse the spectroscope came to the front1 and showed that both the prominences1 and the chromospheric layer from which they rise1 are composed of glowing vapours--chief among which is the vapour of hydrogen4 ,the direct result of the observations made on this occasion was the spectroscopic method of examining prominences at any time in full daylight1 and without a total eclipse4 ,this method1 which has given such an immense impetus to the study of the sun1 was the outcome of independent and simultaneous investigation on the part of the ,french astronomer1 the late ,m4 ,janssen1 and the ,english astronomer1 ,professor 7now ,sir ,norman7 ,lockyer1 a circumstance strangely reminiscent of the discovery of ,neptune4 ,the principles on which the method was founded seem1 however1 to have occurred to ,dr4 7now ,sir ,william7 ,huggins some time previously4 ,the eclipse of ,december #bb1 #ahgj1 was total for a little more than two minutes1 and its track passed across the ,mediterranean4 ,m4 ,janssen1 of whom mention has just been made1 escaped in a balloon from then besieged ,paris1 taking his instruments with him1 and made his way to ,oran1 in ,algeria1 in order to observe it2 but his expectations were disappointed by cloudy weather4 ,the expedition sent out from ,england had the misfortune to be shipwrecked off the coast of ,sicily4 ,but the occasion was redeemed by a memorable observation made by the ,american astronomer1 the late ,professor ,young1 which revealed the existence of what is now known as the ,reversing ,layer4 ,this is a shallow layer of gases which lies immediately beneath the chromosphere4 ,an illustration of the corona1 as it was seen during the above eclipse1 will be found on ,plate ,,vii4 7,a71 p4 #adb4 ,in the eclipse of ,december #ab1 #ahga1 total across ,southern ,india1 the photographs of the corona obtained by ,mr4 ,davis1 assistant to ,lord ,lindsay 7now the ,earl of ,crawford71 displayed a wealth of detail hitherto unapproached4 ,the eclipse of ,july #bi1 #ahgh1 total across the western states of ,north ,america1 was a remarkable success1 and a magnificent view of the corona was obtained by the well-known ,american astronomer and physicist1 the late ,professor ,langley1 from the summit of ,pike's ,peak1 ,colorado1 over #ad1jjj feet above the level of the sea4 ,the coronal streamers were seen to extend to a much greater distance at this altitude than at points less elevated1 and the corona itself remained visible during more than four minutes after the end of totality4 ,it was1 however1 not entirely a question of altitude2 the coronal streamers were actually very much longer on this occasion than in most of the eclipses which had previously been observed4 ,the eclipse of ,may #ag1 #ahhb1 observed in ,upper ,egypt1 is notable from the fact that1 in one of the photographs taken by ,dr4 ,schuster at ,sohag1 a bright comet appeared near the outer limit of the corona 7see ,plate ,i41 p4 #if74 ,the comet in question had not been seen before the eclipse1 and was never seen afterwards4 ,this is the third occasion on which attention has been drawn to a comet merely by a total eclipse4 ,the first is mentioned by ,seneca2 and the second by ,philostorgius1 in an account of an eclipse observed at ,constantinople in ,a4,d4 #dah4 ,a fourth case of the kind occurred in #ahic1 when faint evidences of one of these filmy objects were found on photographs of the corona taken by the ,american astronomer1 ,professor ,schaeberle1 during the total eclipse of ,april #af of that year4 ,the eclipse of ,may #f1 #ahhc1 had a totality of over five minutes1 but the central track unfortunately passed across the ,pacific ,ocean1 and the sole point of land available for observing it from was one of the ,marquesas ,group1 ,caroline ,island1 a coral atoll seven and a half miles long by one and a half broad4 ,nevertheless astronomers did not hesitate to take up their posts upon that little spot1 and were rewarded with good weather4 ,the next eclipse of importance was that of ,april #af1 #ahic4 ,it stretched from ,chili across ,south ,america and the ,atlantic ,ocean to the ,west ,coast of ,africa1 and1 as the weather was fine1 many good results were obtained4 ,photographs were taken at both ends of the track1 and these showed that the appearance of the corona remained unchanged during the interval of time occupied by the passage of the shadow across the earth4 ,it was on the occasion of this eclipse that ,professor ,schaeberle found upon his photographs those traces of the presence of a comet1 to which allusion has already been made4 ,extensive preparations were made to observe the eclipse of ,august #i1 #ahif4 ,totality lasted from two to three minutes1 and the track stretched from ,norway to ,japan4 ,bad weather disappointed the observers1 with the exception of those taken to ,nova ,zembla by ,sir ,george ,baden ,powell in his yacht ,otaria4 ,the eclipse of ,january #bb1 #ahih1 across ,india vi ,bombay and ,benares1 was favoured with good weather1 and is notable for a photograph obtained by ,mrs4 ,e4,w4 ,maunder1 which showed a ray of the corona extending to a most unusual distance4 ,illustration3 ,,plate ,i4 ,,the ,,total ,,eclipse ,,of ,,the ,,sun ,,of ,,may #ag,,th1 #ahhb ,a comet is here shown in the immediate neighbourhood of the corona4 ,drawn by ,mr4 ,w4,h4 ,wesley from the photographs4 7,page #ie7 ,of very great influence in the growth of our knowledge with regard to the sun1 is the remarkable piece of good fortune by which the countries around the ,mediterranean1 so easy of access1 have been favoured with a comparatively large number of total eclipses during the past sixty years4 ,tracks of totality have1 for instance1 traversed the ,spanish peninsula on no less than five occasions during that period4 ,two of these are among the most notable eclipses of recent years1 namely1 those of ,may #bh1 #aijj1 and of ,august #cj1 #aije4 ,in the former the track of totality stretched from the western seaboard of ,mexico1 through the ,southern ,states of ,america1 and across the ,atlantic ,ocean1 after which it passed over ,portugal and ,spain into ,north ,africa4 ,the total phase lasted for about a minute and a half1 and the eclipse was well observed from a great many points along the line4 ,a representation of the corona1 as it appeared on this occasion1 will be found on ,plate ,,vii4 7,b71 p4 #adb4 ,the track of the other eclipse to which we have alluded1 i4e4 that of ,august #cj1 #aije1 crossed ,spain about #bjj miles to the northward of that of #aijj4 ,it stretched from ,winnipeg in ,canada1 through ,labrador1 and over the ,atlantic2 then traversing ,spain1 it passed across the ,balearic ,islands1 ,north ,africa1 and ,egypt1 and ended in ,arabia 7see ,fig4 #f1 p4 #ha74 ,much was to be expected from a comparison between the photographs taken in ,labrador and ,egypt on the question as to whether the corona would show any alteration in shape during the time that the shadow was traversing the intervening space--some #fjjj miles4 ,the duration of the total phase in this eclipse was nearly four minutes4 ,bad weather1 however1 interfered a good deal with the observations4 ,it was not possible1 for instance1 to do anything at all in ,labrador4 ,in ,spain the weather conditions were by no means favourable2 though at ,burgos1 where an immense number of people had assembled1 the total phase was1 fortunately1 well seen4 ,on the whole1 the best results were obtained at ,guelma in ,algeria4 ,the corona on the occasion of this eclipse was a very fine one1 and some magnificent groups of prominences were plainly visible to the naked eye 7see the ,frontispiece74 ,the next total eclipse after that of #aije was one which occurred on ,january #ad1 #aijg4 ,it passed across ,central ,asia and ,siberia1 and had a totality lasting two and a half minutes at most2 but it was not observed as the weather was extremely bad1 a circumstance not surprising with regard to those regions at that time of year4 ,the eclipse of ,january #c1 #aijh1 passed across the ,pacific ,ocean4 ,only two small coral islands--,hull ,island in the ,phoenix ,group1 and ,flint ,island about #djj miles north of ,tahiti--lay in the track4 ,two expeditions set out to observe it1 i4e4 a combined ,american party from the ,lick ,observatory and the ,smithsonian ,institution of ,washington1 and a private one from ,england under ,mr4 ,f4,k4 ,mc,clean4 ,as ,hull ,island afforded few facilities1 both parties installed their instruments on ,flint ,island1 although it was very little better4 ,the duration of the total phase was fairly long--about four minutes1 and the sun very favourably placed1 being nearly overhead4 ,heavy rain and clouds1 however1 marred observation during the first minute of totality1 but the remaining three minutes were successfully utilised1 good photographs of the corona being obtained4 ,the next few years to come are unfortunately by no means favourable from the point of view of the eclipse observer4 ,an eclipse will take place on ,june #ag1 #aiji1 the track stretching from ,greenland across the ,north ,polar regions into ,siberia4 ,the geographical situation is1 however1 a very awkward one1 and totality will be extremely short--only six seconds in ,greenland and twenty-three seconds in ,siberia4 ,the eclipse of ,may #i1 #aiaj1 will be visible in ,tasmania4 ,totality will last so long as four minutes1 but the sun will be at the time much too low in the sky for good observation4 ,the eclipse of the following year1 ,april #bh1 #aiaa1 will also be confined1 roughly speaking1 to the same quarter of the earth1 the track passing across the old convict settlement of ,norfolk ,island1 and then out into the ,pacific4 ,the eclipse of ,april #ag1 #aiab1 will stretch from ,portugal1 through ,france and ,belgium into ,north ,germany4 ,it will1 however1 be of practically no service to astronomy4 ,totality1 for instance1 will last for only three seconds in ,portugal2 and1 though ,paris lies in the central track1 the eclipse1 which begins as barely total1 will have changed into an annular one by the time it passes over that city4 ,the first really favourable eclipse in the near future will be that of ,august #ba1 #aiad4 ,its track will stretch from ,greenland across ,norway1 ,sweden1 and ,russia4 ,this eclipse is a return1 after one saros1 of the eclipse of ,august #i1 #ahif4 ,the last solar eclipse which we will touch upon is that predicted for ,june #bi1 #aibg4 ,it has been already alluded to as the first of those in the future to be total in ,england4 ,the central line will stretch from ,wales in a north-easterly direction4 ,stonyhurst ,observatory1 in ,lancashire1 will lie in the track2 but totality there will be very short1 only about twenty seconds in duration4 #f ,knowledge1 vol4 xx4 p4 #i1 ,january #ahig4 #g ,the first photographic representation of the corona had1 however1 been made during the eclipse of #ahea4 ,this was a daguerreotype taken by ,dr4 ,busch at ,knigsberg in ,prussia4 ,,chapter ,,ix ,,famous ,,eclipses ,,of ,,the ,,moon ,the earliest lunar eclipse1 of which we have any trustworthy information1 was a total one which took place on the #aith ,march1 #gba ,b4,c41 and was observed from ,babylon4 ,for our knowledge of this eclipse we are indebted to ,ptolemy1 the astronomer1 who copied it1 along with two others1 from the records of the reign of the ,chaldean king1 ,merodach-,baladan4 ,the next eclipse of the moon worth noting was a total one1 which took place some three hundred years later1 namely1 in #dbe ,b4,c4 ,this eclipse was observed at ,athens1 and is mentioned by ,aristophanes in his play1 ,the ,clouds4 ,plutarch relates that a total eclipse of the moon1 which occurred in #dac ,b4,c41 so greatly frightened ,nicias1 the general of the ,athenians1 then warring in ,sicily1 as to cause a delay in his retreat from ,syracuse which led to the destruction of his whole army4 ,seven years later--namely1 in #djf ,b4,c41 the twenty-sixth year of the ,peloponnesian ,war--there took place another total lunar eclipse of which mention is made by ,xenophon4 ,omitting a number of other eclipses alluded to by ancient writers1 we come to one recorded by ,josephus as having occurred a little before the death of ,herod the ,great4 ,it is probable that the eclipse in question was the total lunar one1 which calculation shows to have taken place on the #aeth ,september #e ,b4,c41 and to have been visible in ,western ,asia4 ,this is very important1 for we are thus enabled to fix that year as the date of the birth of ,christ1 for ,herod is known to have died in the early part of the year following the ,nativity4 ,in those accounts of total lunar eclipses1 which have come down to us from the ,dark and ,middle ,ages1 the colour of the moon is nearly always likened to blood4 ,on the other hand1 in an account of the eclipse of ,january #bc1 ,a4,d4 #gec1 our satellite is described as covered with a horrid black shield4 ,we thus have examples of the two distinct appearances alluded to in ,chapter ,,vii41 i4e4 when the moon appears of a coppery-red colour1 and when it is entirely darkened4 ,it appears1 indeed1 that1 in the majority of lunar eclipses on record1 the moon has appeared of a ruddy1 or rather of a coppery hue1 and the details on its surface have been thus rendered visible4 ,one of the best examples of a bright eclipse of this kind is that of the #aith ,march #ahdh1 when the illumination of our satellite was so great that many persons could not believe that an eclipse was actually taking place4 ,a certain ,mr4 ,foster1 who observed this eclipse from ,bruges1 states that the markings on the lunar disc were almost as visible as on an ordinary dull moonlight night4 ,he goes on to say that the ,british ,consul at ,ghent1 not knowing that there had been any eclipse1 wrote to him for an explanation of the red colour of the moon on that evening4 ,out of the dark eclipses recorded1 perhaps the best example is that of ,may #ah1 #agfa1 observed by ,wargentin at ,stockholm4 ,on this occasion the lunar disc is said to have disappeared so completely1 that it could not be discovered even with the telescope4 ,another such instance is the eclipse of ,june #aj1 #ahaf1 observed from ,london4 ,the summer of that year was particularly wet--a point worthy of notice in connection with the theory that these different appearances are due to the varying state of our earth's atmosphere4 ,sometimes1 indeed1 it has happened that an eclipse of the moon has partaken of both appearances1 part of the disc being visible and part invisible4 ,an instance of this occurred in the eclipse of ,july #ab1 #ahgj1 when the late ,rev4 ,s4,j4 ,johnson1 one of the leading authorities on eclipses1 who observed it1 states that he found one-half the moon's surface quite invisible1 both with the naked eye and with the telescope4 ,in addition to the examples given above1 there are three total lunar eclipses which deserve especial mention4 #a4 ,a4,d4 #gee1 ,november #bc4 ,during the progress of this eclipse the moon occulted the star ,aldebaran in the constellation of ,taurus4 #b4 ,a4,d4 #adic1 ,april #b4 ,this is the celebrated eclipse which is said to have so well served the purposes of ,christopher ,columbus4 ,certain natives having refused to supply him with provisions when in sore straits1 he announced to them that the moon would be darkened as a sign of the anger of heaven4 ,when the event duly came to pass1 the savages were so terrified that they brought him provisions as much as he needed4 #c4 ,a4,d4 #afaj1 ,july #f4 ,the eclipse in question is notable as having been seen through the telescope1 then a recent invention4 ,it was without doubt the first so observed1 but unfortunately the name of the observer has not come down to us4 ,,chapter ,x ,,the ,,growth ,,of ,,observation ,the earliest astronomical observations must have been made in the ,dawn of ,historic ,time by the men who tended their flocks upon the great plains4 ,as they watched the clear night sky they no doubt soon noticed that1 with the exception of the moon and those brilliant wandering objects known to us as the planets1 the individual stars in the heaven remained apparently fixed with reference to each other4 ,these seemingly changeless points of light came in time to be regarded as sign-posts to guide the wanderer across the trackless desert1 or the voyager upon the wide sea4 ,just as when looking into the red coals of a fire1 or when watching the clouds1 our imagination conjures up strange and grotesque forms1 so did the men of old see in the grouping of the stars the outlines of weird and curious shapes4 ,fed with mythological lore1 they imagined these to be rough representations of ancient heroes and fabled beasts1 whom they supposed to have been elevated to the heavens as a reward for great deeds done upon the earth4 ,we know these groupings of stars to-day under the name of the ,constellations4 ,looking up at them we find it extremely difficult to fit in the majority with the figures which the ancients believed them to represent4 ,nevertheless1 astronomy has accepted the arrangement1 for want of a better method of fixing the leading stars in the memory4 ,our early ancestors lived the greater part of their lives in the open air1 and so came to pay more attention in general to the heavenly orbs than we do4 ,their clock and their calendar was1 so to speak1 in the celestial vault4 ,they regulated their hours1 their days1 and their nights by the changing positions of the sun1 the moon1 and the stars2 and recognised the periods of seed-time and harvest1 of calm and stormy weather1 by the rising or setting of certain well-known constellations4 ,students of the classics will recall many allusions to this1 especially in the ,odes of ,horace4 ,as time went on and civilisation progressed1 men soon devised measuring instruments1 by means of which they could note the positions of the celestial bodies in the sky with respect to each other2 and1 from observations thus made1 they constructed charts of the stars4 ,the earliest complete survey of this kind1 of which we have a record1 is the great ,catalogue of stars which was made1 in the second century ,b4,c41 by the celebrated ,greek astronomer1 ,hipparchus1 and in which he is said to have noted down about #ajhj stars4 ,it is unnecessary to follow in detail the tedious progress of astronomical discovery prior to the advent of the telescope4 ,certain it is that1 as time went on1 the measuring instruments to which we have alluded had become greatly improved2 but1 had they even been perfect1 they would have been utterly inadequate to reveal those minute displacements1 from which we have learned the actual distance of the nearest of the celestial orbs4 ,from the early times1 therefore1 until the medival period of our own era1 astronomy grew up upon a faulty basis1 for the earth ever seemed so much the largest body in the universe1 that it continued from century to century to be regarded as the very centre of things4 ,to the ,arabians is due the credit of having kept alive the study of the stars during the dark ages of ,european history4 ,they erected some fine observatories1 notably in ,spain and in the neighbourhood of ,bagdad4 ,following them1 some of the ,oriental peoples embraced the science in earnest2 ,ulugh ,beigh1 grandson of the famous ,tamerlane1 founding1 for instance1 a great observatory at ,samarcand in ,central ,asia4 ,the ,mongol emperors of ,india also established large astronomical instruments in the chief cities of their empire4 ,when the revival of learning took place in the ,west1 the ,europeans came to the front once more in science1 and rapidly forged ahead of those who had so assiduously kept alight the lamp of knowledge through the long centuries4 ,the dethronement of the older theories by the ,copernican system1 in which the earth was relegated to its true place1 was fortunately soon followed by an invention of immense import1 the invention of the ,telescope4 ,it is to this instrument1 indeed1 that we are indebted for our knowledge of the actual scale of the celestial distances4 ,it penetrated the depths of space2 it brought the distant orbs so near1 that men could note the detail on the planets1 or measure the small changes in their positions in the sky which resulted from the movement of our own globe4 ,it was in the year #afji that the telescope was first constructed4 ,a year or so previous to this a spectacle-maker of ,middleburgh in ,holland1 one ,hans ,lippershey1 had1 it appears1 hit upon the fact that distant objects1 when viewed through certain glass lenses suitably arranged1 looked nearer4#h ,news of this discovery reached the ears of ,galileo ,galilei1 of ,florence1 the foremost philosopher of the day1 and he at once applied his great scientific attainments to the construction of an instrument based upon this principle4 ,the result was what was called an optick tube1 which magnified distant objects some few times4 ,it was not much larger than what we nowadays contemptuously refer to as a spy-glass1 yet its employment upon the leading celestial objects instantly sent astronomical science onward with a bound4 ,in rapid succession ,galileo announced world-moving discoveries2 large spots upon the face of the sun2 crater-like mountains upon the moon2 four subordinate bodies1 or satellites1 circling around the planet ,jupiter2 and a strange appearance in connection with ,saturn1 which later telescopic observers found to be a broad flat ring encircling that planet4 ,and more important still1 the magnified image of ,venus showed itself in the telescope at certain periods in crescent and other forms2 a result which ,copernicus is said to have announced should of necessity follow if his system were the true one4 ,the discoveries made with the telescope produced1 as time went on1 a great alteration in the notions of men with regard to the universe at large4 ,it must have been1 indeed1 a revelation to find that those points of light which they called the planets1 were1 after all1 globes of a size comparable with the earth1 and peopled perchance with sentient beings4 ,even to us1 who have been accustomed since our early youth to such an idea1 it still requires a certain stretch of imagination to enlarge1 say1 the ,bright ,star of ,eve1 into a body similar in size to our earth4 ,the reader will perhaps recollect ,tennyson's allusion to this in ,locksley ,hall1 ,sixty ,years ,after3-- ,hesper--,venus--were we native to that splendour or in ,mars1 ,we should see the ,globe we groan in1 fairest of their evening stars4 ,could we dream of wars and carnage1 craft and madness1 lust and spite1 ,roaring ,london1 raving ,paris1 in that point of peaceful light8 ,the form of instrument as devised by ,galileo is called the ,refracting ,telescope1 or ,refractor4 ,as we know it to-day it is the same in principle as his optick tube1 but it is not quite the same in construction4 ,the early object-glass1 or large glass at the end1 was a single convex lens 7see ,fig4 #h1 p4 #aac1 ,galilean72 the modern one is1 on the other hand1 composed of two lenses fitted together4 ,the attempts to construct large telescopes of the ,galilean type met in course of time with a great difficulty4 ,the magnified image of the object observed was not quite pure2 its edges1 indeed1 were fringed with rainbow-like colours4 ,this defect was found to be aggravated with increase in the size of object-glasses4 ,a method was1 however1 discovered of diminishing this colouration1 or chromatic aberration as it is called from the ,greek word chrma 7chroma71 which means colour1 viz4 by making telescopes of great length and only a few inches in width4 ,but the remedy was1 in a way1 worse than the disease2 for telescopes thus became of such huge proportions as to be too unwieldy for use4 ,attempts were made to evade this unwieldiness by constructing them with skeleton tubes 7see ,plate ,,ii41 p4 #aaj71 or1 indeed1 even without tubes at all2 the object-glass in the tubeless or aerial telescope being fixed at the top of a high post1 and the eye-piece1 that small lens or combination of lenses1 which the eye looks directly into1 being kept in line with it by means of a string and manoeuvred about near the ground 7,plate ,,iii41 p4 #aab74 ,the idea of a telescope without a tube may appear a contradiction in terms2 but it is not really so1 for the tube adds nothing to the magnifying power of the instrument1 and is1 in fact1 no more than a mere device for keeping the object-glass and eye-piece in a straight line1 and for preventing the observer from being hindered by stray lights in his neighbourhood4 ,it goes without saying1 of course1 that the image of a celestial object will be more clear and defined when examined in the darkness of a tube4 ,the ancients1 though they knew nothing of telescopes1 had1 however1 found out the merit of a tube in this respect2 for they employed simple tubes1 blackened on the inside1 in order to obtain a clearer view of distant objects4 ,it is said that ,julius ,csar1 before crossing the ,channel1 surveyed the opposite coast of ,britain through a tube of this kind4 ,illustration3 ,,plate ,,ii4 ,,great ,,telescope ,,of ,,hevelius ,this instrument1 #aej feet in length1 with a skeleton tube1 was constructed by the celebrated seventeenth century astronomer1 ,hevelius of ,danzig4 ,from an illustration in the ,machina ,celestis4 7,page #aaj7 ,a few of the most famous of the immensely long telescopes above alluded to are worthy of mention4 ,one of these1 #abc feet in length1 was presented to the ,royal ,society of ,london by the ,dutch astronomer ,huyghens4 ,hevelius of ,danzig constructed a skeleton one of #aej feet in length 7see ,plate ,,ii41 p4 #aaj74 ,bradley used a tubeless one #bab feet long to measure the diameter of ,venus in #agbb2 while one of #fjj feet is said to have been constructed1 but to have proved quite unworkable6 ,such difficulties1 however1 produced their natural result4 ,they set men at work to devise another kind of telescope4 ,in the new form1 called the ,reflecting ,telescope1 or ,reflector1 the light coming from the object under observation was reflected into the eye-piece from the surface of a highly polished concave metallic mirror1 or speculum1 as it was called4 ,it is to ,sir ,isaac ,newton that the world is indebted for the reflecting telescope in its best form4 ,that philosopher had set himself to investigate the causes of the rainbow-like1 or prismatic colours which for a long time had been such a source of annoyance to telescopic observers2 and he pointed out that1 as the colours were produced in the passage of the rays of light through the glass1 they would be entirely absent if the light were reflected from the surface of a mirror instead4 ,the reflecting telescope1 however1 had in turn certain drawbacks of its own4 ,a mirror1 for instance1 can plainly never be polished to such a high degree as to reflect as much light as a piece of transparent glass will let through4 ,further1 the position of the eye-piece is by no means so convenient4 ,it cannot1 of course1 be pointed directly towards the mirror1 for the observer would then have to place his head right in the way of the light coming from the celestial object1 and would thus1 of course1 cut it off4 ,in order to obviate this difficulty1 the following device was employed by ,newton in his telescope1 of which he constructed his first example in #affh4 ,a small1 flat mirror was fixed by thin wires in the centre of the tube of the telescope1 and near to its open end4 ,it was set slant-wise1 so that it reflected the rays of light directly into the eye-piece1 which was screwed into a hole at the side of the tube 7see ,fig4 #h1 p4 #aac1 ,newtonian74 ,although the ,newtonian form of telescope had the immense advantage of doing away with the prismatic colours1 yet it wasted a great deal of light2 for the objection in this respect with regard to loss of light by reflection from the large mirror applied1 of course1 to the small mirror also4 ,in addition1 the position of the flat1 as the small mirror is called1 had the further effect of excluding from the great mirror a certain proportion of light4 ,but the reflector had the advantage1 on the other hand1 of costing less to make than the refractor1 as it was not necessary to procure flawless glass for the purpose4 ,a disc of a certain metallic composition1 an alloy of copper and tin1 known in consequence as speculum metal1 had merely to be cast2 and this had to be ground and polished upon one side only1 whereas a lens has to be thus treated upon both its sides4 ,it was1 therefore1 possible to make a much larger instrument at a great deal less labour and expense4 ,illustration3 ,,plate ,,iii4 ,a ,,tubeless1 ,,or ,,aerial ,,telescope ,from an illustration in the ,opera ,varia of ,christian ,huyghens4 7,page #aaj7 ,illustration3 ,,fig4 #h4--,the various types of ,telescope4 ,all the above telescopes are pointed in the same direction2 that is to say1 the rays of light from the object are coming from the left-hand side4 ,we have given the ,newtonian form as an example of the principle of the reflecting telescope4 ,a somewhat similar instrument had1 however1 been projected1 though not actually constructed1 by ,james ,gregory a few years earlier than ,newton's1 i4e4 in #affc4 ,in this form of reflector1 known as the ,gregorian telescope1 a hole was made in the big concave mirror2 and a small mirror1 also concave1 which faced it at a certain distance1 received the reflected rays1 and reflected them back again through the hole in question into the eye-piece1 which was fixed just behind 7see ,fig4 #h1 p4 #aac1 ,gregorian74 ,the ,gregorian had thus the sentimental advantage of being pointed directly at the object4 ,the hole in the big mirror did not cause any loss of light1 for the central portion in which it was made was anyway unable to receive light through the small mirror being directly in front of it4 ,an adaptation of the ,gregorian was the ,cassegrainian telescope1 devised by ,cassegrain in #afgb1 which differed from it chiefly in the small mirror being convex instead of concave 7see ,fig4 #h1 p4 #aac1 ,cassegrainian74 ,these direct-view forms of the reflecting telescope were much in vogue about the middle of the eighteenth century1 when many beautiful examples of ,gregorians were made by the famous optician1 ,james ,short1 of ,edinburgh4 ,an adaptation of the ,newtonian type of telescope is known as the ,herschelian1 from being the kind favoured by ,sir ,william ,herschel4 ,it is1 however1 only suitable in immense instruments1 such as ,herschel was in the habit of employing4 ,in this form the object-glass is set at a slight slant1 so that the light coming from the object is reflected straight into the eye-piece1 which is fixed facing it in the side of the tube 7see ,fig4 #h1 p4 #aac1 ,herschelian74 ,this telescope has an advantage over the other forms of reflector through the saving of light consequent on doing away with the second reflection4 ,there is1 however1 the objection that the slant of the object-glass is productive of some distortion in the appearance of the object observed2 but this slant is of necessity slight when the length of the telescope is very great4 ,the principle of this type of telescope had been described to the ,french ,academy of ,sciences as early as #agbh by ,le ,maire1 but no one availed himself of the idea until #aggf1 when ,herschel tried it4 ,at first1 however1 he rejected it2 but in #aghf he seems to have found that it suited the huge instruments which he was then making4 ,herschel's largest telescope1 constructed in #aghi1 was about four feet in diameter and forty feet in length4 ,it is generally spoken of as the ,forty-foot ,telescope1 though all other instruments have been known by their diameters1 rather than by their lengths4 ,to return to the refracting telescope4 ,a solution of the colour difficulty was arrived at in #agbi 7two years after ,newton's death7 by an ,essex gentleman named ,chester ,moor ,hall4 ,he discovered that by making a double object-glass1 composed of an outer convex lens and an inner concave lens1 made respectively of different kinds of glass1 i4e4 crown glass and flint glass1 the troublesome colour effects could be1 to a very great extent1 removed4 ,hall's investigations appear to have been rather of an academic nature2 and1 although he is believed to have constructed a small telescope upon these lines1 yet he seems to have kept the matter so much to himself that it was not until the year #ageh that the first example of the new instrument was given to the world4 ,this was done by ,john ,dollond1 founder of the well-known optical firm of ,dollond1 of ,ludgate ,hill1 ,london1 who had1 quite independently1 re-discovered the principle4 ,this ,achromatic telescope1 or telescope free from colour effects1 is the kind ordinarily in use at present1 whether for astronomical or for terrestrial purposes 7see ,fig4 #h1 p4 #aac1 ,achromatic74 ,the expense of making large instruments of this type is very great1 for1 in the object-glass alone1 no less than four surfaces have to be ground and polished to the required curves2 and1 usually1 the two lenses of which it is composed have to fit quite close together4 ,with the object of evading the expense referred to1 and of securing complete freedom from colour effects1 telescopes have even been made1 the object-glasses of which were composed of various transparent liquids placed between thin lenses2 but leakages1 and currents set up within them by changes of temperature1 have defeated the ingenuity of those who devised these substitutes4 ,the solution of the colour difficulty by means of ,dollond's achromatic refractor has not1 however1 ousted the reflecting telescope in its best1 or ,newtonian form1 for which great concave mirrors made of glass1 covered with a thin coating of silver and highly polished1 have been used since about #ahgj instead of metal mirrors4 ,they are very much lighter in weight and cheaper to make than the old specula2 and though the silvering1 needless to say1 deteriorates with time1 it can be renewed at a comparatively trifling cost4 ,also these mirrors reflect much more light1 and give a clearer view1 than did the old metallic ones4 ,when an object is viewed through the type of astronomical telescope ordinarily in use1 it is seen upside down4 ,this is1 however1 a matter of very small moment in dealing with celestial objects2 for1 as they are usually round1 it is really not of much consequence which part we regard as top and which as bottom4 ,such an inversion would1 of course1 be most inconvenient when viewing terrestrial objects4 ,in order to observe the latter we therefore employ what is called a terrestrial telescope1 which is merely a refractor with some extra lenses added in the eye portion for the purpose of turning the inverted image the right way up again4 ,these extra lenses1 needless to say1 absorb a certain amount of light2 wherefore it is better in astronomical observation to save light by doing away with them1 and putting up with the slight inconvenience of seeing the object inverted4 ,this inversion of images by the astronomical telescope must be specially borne in mind with regard to the photographs of the moon in ,chapter ,,xvi4 ,in the year #ahbe the largest achromatic refractor in existence was one of nine and a half inches in diameter constructed by ,fraunhofer for the ,observatory of ,dorpat in ,russia4 ,the largest refractors in the world to-day are in the ,united ,states1 i4e4 the forty-inch of the ,yerkes ,observatory 7see ,plate ,,iv41 p4 #aah71 and the thirty-six inch of the ,lick4 ,the object-glasses of these and of the thirty-inch telescope of the ,observatory of ,pulkowa1 in ,russia1 were made by the great optical house of ,alvan ,clark ,sons1 of ,cambridge1 ,massachusetts1 ,u4,s4,a4 ,the tubes and other portions of the ,yerkes and ,lick telescopes were1 however1 constructed by the ,warner and ,swasey ,co41 of ,cleveland1 ,ohio4 ,the largest reflector1 and so the largest telescope in the world1 is still the six-foot erected by the late ,lord ,rosse at ,parsonstown in ,ireland1 and completed in the year #ahde4 ,it is about fifty-six feet in length4 ,next come two of five feet1 with mirrors of silver on glass2 one of them made by the late ,dr4 ,common1 of ,ealing1 and the other by the ,american astronomer1 ,professor ,g4,w4 ,ritchey4 ,the latter of these is installed in the ,solar ,observatory belonging to ,carnegie ,institution of ,washington1 which is situated on ,mount ,wilson in ,california4 ,the former is now at the ,harvard ,college ,observatory1 and is considered by ,professor ,moulton to be probably the most efficient reflector in use at present4 ,another large reflector is the three-foot made by ,dr4 ,common4 ,it came into the possession of ,mr4 ,crossley of ,halifax1 who presented it to the ,lick ,observatory1 where it is now known as the ,crossley ,reflector4 ,although to the house of ,clark belongs1 as we have seen1 the credit of constructing the object-glasses of the largest refracting telescopes of our time1 it has nevertheless keen competitors in ,sir ,howard ,grubb1 of ,dublin1 and such well-known firms as ,cooke of ,york and ,steinheil of ,munich4 ,in the four-foot reflector1 made in #ahgj for the ,observatory of ,melbourne by the firm of ,grubb1 the ,cassegrainian principle was employed4 ,with regard to the various merits of refractors and reflectors much might be said4 ,each kind of instrument has1 indeed1 its special advantages2 though perhaps1 on the whole1 the most perfect type of telescope is the achromatic refractor4 ,illustration3 ,,plate ,,iv4 ,,the ,,great ,,yerkes ,,telescope ,great telescope at the ,yerkes ,observatory of the ,university of ,chicago1 ,williams ,bay1 ,wisconsin1 ,u4,s4,a4 ,it was erected in #ahif-g1 and is the largest refracting telescope in the world4 ,diameter of object-glass1 #dj inches2 length of telescope1 about #fj feet4 ,the object-glass was made by the firm of ,alvan ,clark and ,sons1 of ,cambridge1 ,massachusetts2 the other portions of the instrument by the ,warner and ,swasey ,co41 of ,cleveland1 ,ohio4 7,page #aag7 ,in connection with telescopes certain devices have from time to time been introduced1 but these merely aim at the convenience of the observer and do not supplant the broad principles upon which are based the various types of instrument above described4 ,such1 for instance1 are the ,siderostat1 and another form of it called the ,coelostat1 in which a plane mirror is made to revolve in a certain manner1 so as to reflect those portions of the sky which are to be observed1 into the tube of a telescope kept fixed4 ,such too are the ,equatorial ,coud of the late ,m4 ,loewy1 ,director of the ,paris ,observatory1 and the ,sheepshanks ,telescope of the ,observatory of ,cambridge1 in which a telescope is separated into two portions1 the eye-piece portion being fixed upon a downward slant1 and the object-glass portion jointed to it at an angle and pointed up at the sky4 ,in these two instruments 7which1 by the way1 differ materially7 an arrangement of slanting mirrors in the tubes directs the journey of the rays of light from the object-glass to the eye-piece4 ,the observer can thus sit at the eye-end of his telescope in the warmth and comfort of his room1 and observe the stars in the same unconstrained manner as if he were merely looking down into a microscope4 ,needless to say1 devices such as these are subject to the drawback that the mirrors employed sap a certain proportion of the rays of light4 ,it will be remembered that we made allusion to loss of light in this way1 when pointing out the advantage in light grasp of the ,herschelian form of telescope1 where only one reflection takes place1 over the ,newtonian in which there are two4 ,it is an interesting question as to whether telescopes can be made much larger4 ,the ,american astronomer1 ,professor ,g4,e4 ,hale1 concludes that the limit of refractors is about five feet in diameter1 but he thinks that reflectors as large as nine feet in diameter might now be made4 ,as regards refractors there are several strong reasons against augmenting their proportions4 ,first of all comes the great cost4 ,secondly1 since the lenses are held in position merely round their rims1 they will bend by their weight in the centres if they are made much larger4 ,on the other hand1 attempts to obviate this1 by making the lenses thicker1 would cause a decrease in the amount of light let through4 ,but perhaps the greatest stumbling-block to the construction of larger telescopes is the fact that the unsteadiness of the air will be increasingly magnified4 ,and further1 the larger the tubes become1 the more difficult will it be to keep the air within them at one constant temperature throughout their lengths4 ,it would1 indeed1 seem as if telescopes are not destined greatly to increase in size1 but that the means of observation will break out in some new direction1 as it has already done in the case of photography and the spectroscope4 ,the direct use of the eye is gradually giving place to indirect methods4 ,we are1 in fact1 now feeling rather than seeing our way about the universe4 ,up to the present1 for instance1 we have not the slightest proof that life exists elsewhere than upon our earth4 ,but who shall say that the twentieth century has not that in store for us1 by which the presence of life in other orbs may be perceived through some form of vibration transmitted across illimitable space8 ,there is no use speaking of the impossible or the inconceivable4 ,after the extraordinary revelations of the spectroscope--nay1 after the astounding discovery of ,rntgen--the word impossible should be cast aside1 and inconceivability cease to be regarded as any criterion4 #h ,the principle upon which the telescope is based appears to have been known theoretically for a long time previous to this4 ,the monk ,roger ,bacon1 who lived in the thirteenth century1 describes it very clearly2 and several writers of the sixteenth century have also dealt with the idea4 ,even ,lippershey's claims to a practical solution of the question were hotly contested at the time by two of his own countrymen1 i4e4 a certain ,jacob ,metius1 and another spectacle-maker of ,middleburgh1 named ,jansen4 ,,chapter ,,xi ,,spectrum ,,analysis ,if white light 7that of the sun1 for instance7 be passed through a glass prism1 namely1 a piece of glass of triangular shape1 it will issue from it in rainbow-tinted colours4 ,it is a common experience with any of us to notice this when the sunlight shines through cut-glass1 as in the pendant of a chandelier1 or in the stopper of a wine-decanter4 ,the same effect may be produced when light passes through water4 ,the ,rainbow1 which we all know so well1 is merely the result of the sunlight passing through drops of falling rain4 ,white light is composed of rays of various colours4 ,red1 orange1 yellow1 green1 blue1 indigo1 and violet1 taken all together1 go1 in fact1 to make up that effect which we call white4 ,it is in the course of the refraction1 or bending of a beam of light1 when it passes in certain conditions through a transparent and denser medium1 such as glass or water1 that the constituent rays are sorted out and spread in a row according to their various colours4 ,this production of colour takes place usually near the edges of a lens2 and1 as will be recollected1 proved very obnoxious to the users of the old form of refracting telescope4 ,it is1 indeed1 a strange irony of fate that this very same production of colour1 which so hindered astronomy in the past1 should have aided it in recent years to a remarkable degree4 ,if sunlight1 for instance1 be admitted through a narrow slit before it falls upon a glass prism1 it will issue from the latter in the form of a band of variegated colour1 each colour blending insensibly with the next4 ,the colours arrange themselves always in the order which we have mentioned4 ,this seeming band is1 in reality1 an array of countless coloured images of the original slit ranged side by side2 the colour of each image being the slightest possible shade different from that next to it4 ,this strip of colour when produced by sunlight is called the ,solar ,spectrum 7see ,fig4 #i1 p4 #abc74 ,a similar strip1 or spectrum1 will be produced by any other light2 but the appearance of the strip1 with regard to preponderance of particular colours1 will depend upon the character of that light4 ,electric light and gas light yield spectra not unlike that of sunlight2 but that of gas is less rich in blue and violet than that of the sun4 ,the ,spectroscope1 an instrument devised for the examination of spectra1 is1 in its simplest form1 composed of a small tube with a narrow slit and prism at one end1 and an eye-piece at the other4 ,if we drop ordinary table salt into the flame of a gas light1 the flame becomes strongly yellow4 ,if1 then1 we observe this yellow flame with the spectroscope1 we find that its spectrum consists almost entirely of two bright yellow transverse lines4 ,chemically considered ordinary table salt is sodium chloride2 that is to say1 a compound of the metal sodium and the gas chlorine4 ,now if other compounds of sodium be experimented with in the same manner1 it will soon be found that these two yellow lines are characteristic of sodium when turned into vapour by great heat4 ,in the same manner it can be ascertained that every element1 when heated to a condition of vapour1 gives as its spectrum a set of lines peculiar to itself4 ,thus the spectroscope enables us to find out the composition of substances when they are reduced to vapour in the laboratory4 ,illustration3 ,,fig4 #i4--,the ,solar ,spectrum4 ,in order to increase the power of a spectroscope1 it is necessary to add to the number of prisms4 ,each extra prism has the effect of lengthening the coloured strip still more1 so that lines1 which at first appeared to be single merely through being crowded together1 are eventually drawn apart and become separately distinguishable4 ,on this principle it has gradually been determined that the sun is composed of elements similar to those which go to make up our earth4 ,further1 the composition of the stars can be ascertained in the same manner2 and we find them formed on a like pattern1 though with certain elements in greater or less proportion as the case may be4 ,it is in consequence of our thus definitely ascertaining that the stars are self-luminous1 and of a sun-like character1 that we are enabled to speak of them as suns1 or to call the sun a star4 ,in endeavouring to discover the elements of which the planets and satellites of our system are composed1 we1 however1 find ourselves baffled1 for the simple reason that these bodies emit no real light of their own4 ,the light which reaches us from them1 being merely reflected sunlight1 gives only the ordinary solar spectrum when examined with the spectroscope4 ,but in certain cases we find that the solar spectrum thus viewed shows traces of being weakened1 or rather of suffering absorption2 and it is concluded that this may be due to the sunlight having had to pass through an atmosphere on its way to and from the surface of the planet from which it is reflected to us4 ,since the sun is found to be composed of elements similar to those which go to make up our earth1 we need not be disheartened at this failure of the spectroscope to inform us of the composition of the planets and satellites4 ,we are justified1 indeed1 in assuming that more or less the same constituents run through our solar system2 and that the elements of which these bodies are composed are similar to those which are found upon our earth and in the sun4 ,the spectroscope supplies us with even more information4 ,it tells us1 indeed1 whether the sun-like body which we are observing is moving away from us or towards us4 ,a certain slight shifting of the lines towards the red or violet end of the spectrum respectively1 is found to follow such movement4 ,this method of observation is known by the name of ,doppler's ,method1#i and by it we are enabled to confirm the evidence which the sunspots give us of the rotation of the sun2 for we find thus that one edge of that body is continually approaching us1 and the other edge is continually receding from us4 ,also1 we can ascertain in the same manner that certain of the stars are moving towards us1 and certain of them away from us4 #i ,the idea1 initiated by ,christian ,doppler at ,prague in #ahdb1 was originally applied to sound4 ,the approach or recession of a source from which sound is coming is invariably accompanied by alterations of pitch1 as the reader has no doubt noticed when a whistling railway-engine has approached him or receded from him4 ,it is to ,sir ,william ,huggins1 however1 that we are indebted for the application of the principle to spectroscopy4 ,this he gave experimental proof of in the year #ahfh4 ,,chapter ,,xii ,,the ,,sun ,the sun is the chief member of our system4 ,it controls the motions of the planets by its immense gravitative power4 ,besides this it is the most important body in the entire universe1 so far as we are concerned2 for it pours out continually that flood of light and heat1 without which life1 as we know it1 would quickly become extinct upon our globe4 ,light and heat1 though not precisely the same thing1 may be regarded1 however1 as next-door neighbours4 ,the light rays are those which directly affect the eye and are comprised in the visible spectrum4 ,we feel the heat rays1 the chief of which are beyond the red portion of the spectrum4 ,they may be investigated with the bolometer1 an instrument invented by the late ,professor ,langley4 ,chemical rays--for instance1 those radiations which affect the photographic plate--are for the most part also outside the visible spectrum4 ,they are1 however1 at the other end of it1 namely1 beyond the violet4 ,such a scale of radiations may be compared to the keyboard of an imaginary piano1 the sound from only one of whose octaves is audible to us4 ,the brightest light we know on the earth is dull compared with the light of the sun4 ,it would1 indeed1 look quite dark if held up against it4 ,it is extremely difficult to arrive at a precise notion of the temperature of the body of the sun4 ,however1 it is far in excess of any temperature which we can obtain here1 even in the most powerful electric furnace4 ,a rough idea of the solar heat may be gathered from the calculation that if the sun's surface were coated all over with a layer of ice #djjj feet thick1 it would melt through this completely in one hour4 ,the sun cannot be a hot body merely cooling2 for the rate at which it is at present giving off heat could not in such circumstances be kept up1 according to ,professor ,moulton1 for more than #cjjj years4 ,further1 it is not a mere burning mass1 like a coal fire1 for instance2 as in that case about a thousand years would show a certain drop in temperature4 ,no perceptible diminution of solar heat having taken place within historic experience1 so far as can be ascertained1 we are driven to seek some more abstruse explanation4 ,the theory which seems to have received most acceptance is that put forward by ,helmholtz in #ahed4 ,his idea was that gravitation produces continual contraction1 or falling in of the outer parts of the sun2 and that this falling in1 in its turn1 generates enough heat to compensate for what is being given off4 ,the calculations of ,helmholtz showed that a contraction of about #ajj feet a year from the surface towards the centre would suffice for the purpose4 ,in recent years1 however1 this estimate has been extended to about #ahj feet4 ,nevertheless1 even with this increased figure1 the shrinkage required is so slight in comparison with the immense girth of the sun1 that it would take a continual contraction at this rate for about #fjjj years1 to show even in our finest telescopes that any change in the size of that body was taking place at all4 ,upon this assumption of continuous contraction1 a time should1 however1 eventually be reached when the sun will have shrunk to such a degree of solidity1 that it will not be able to shrink any further4 ,then1 the loss of heat not being made up for any longer1 the body of the sun should begin to grow cold4 ,but we need not be distressed on this account2 for it will take some #aj1jjj1jjj years1 according to the above theory1 before the solar orb becomes too cold to support life upon our earth4 ,since the discovery of radium it has1 on the other hand1 been suggested1 and not unreasonably1 that radio-active matter may possibly play an important part in keeping up the heat of the sun4 ,but the body of scientific opinion appears to consider the theory of contraction as a result of gravitation1 which has been outlined above1 to be of itself quite a sound explanation4 ,indeed1 the late ,lord ,kelvin is said to have held to the last that it was amply sufficient to account for the underground heat of the earth1 the heat of the sun1 and that of all the stars in the universe4 ,one great difficulty in forming theories with regard to the sun1 is the fact that the temperature and gravitation there are enormously in excess of anything we meet with upon our earth4 ,the force of gravity at the sun's surface is1 indeed1 about twenty-seven times that at the surface of our globe4 ,the earth's atmosphere appears to absorb about one-half of the radiations which come to us from the sun4 ,this absorptive effect is very noticeable when the solar orb is low down in our sky1 for its light and heat are then clearly much reduced4 ,of the light rays1 the blue ones are the most easily absorbed in this way2 which explains why the sun looks red when near the horizon4 ,it has then1 of course1 to shine through a much greater thickness of atmosphere than when high up in the heavens4 ,what astonishes one most about the solar radiation1 is the immense amount of it that is apparently wasted into space in comparison with what falls directly upon the bodies of the solar system4 ,only about the one-hundred-millionth is caught by all the planets together4 ,what becomes of the rest we cannot tell4 ,that brilliant white body of the sun1 which we see1 is enveloped by several layers of gases and vaporous matter1 in the same manner as our globe is enveloped by its atmosphere 7see ,fig4 #aj1 p4 #aca74 ,these are transparent1 just as our atmosphere is transparent2 and so we see the white bright body of the sun right through them4 ,this white bright portion is called the ,photosphere4 ,from it comes most of that light and heat which we see and feel4 ,we do not know what lies under the photosphere1 but1 no doubt1 the more solid portions of the sun are there situated4 ,just above the photosphere1 and lying close upon it1 is a veil of smoke-like haze4 ,next upon this is what is known as the ,reversing ,layer1 which is between #ejj and #ajjj miles in thickness4 ,it is cooler than the underlying photosphere1 and is composed of glowing gases4 ,many of the elements which go to make up our earth are present in the reversing layer in the form of vapour4 ,the ,chromosphere1 of which especial mention has already been made in dealing with eclipses of the sun1 is another layer lying immediately upon the last one4 ,it is between #ejjj and #aj1jjj miles in thickness4 ,like the reversing layer1 it is composed of glowing gases1 chief among which is the vapour of hydrogen4 ,the colour of the chromosphere is1 in reality1 a brilliant scarlet2 but1 as we have already said1 the intensely white light of the photosphere shines through it from behind1 and entirely overpowers its redness4 ,the upper portion of the chromosphere is in violent agitation1 like the waves of a stormy sea1 and from it rise those red prominences which1 it will be recollected1 are such a notable feature in total solar eclipses4 ,illustration3 ,,fig4 #aj4--;,a section through the ,sun1 showing how the prominences rise from the chromosphere4 ,the ,corona lies next in order outside the chromosphere1 and is1 so far as we know1 the outermost of the accompaniments of the sun4 ,this halo of pearly-white light is irregular in outline1 and fades away into the surrounding sky4 ,it extends outwards from the sun to several millions of miles4 ,as has been stated1 we can never see the corona unless1 when during a total solar eclipse1 the moon has1 for the time being1 hidden the brilliant photosphere completely from our view4 ,the solar spectrum is really composed of three separate spectra commingled1 i4e4 those of the photosphere1 of the reversing layer1 and of the chromosphere respectively4 ,if1 therefore1 the photosphere could be entirely removed1 or covered up1 we should see only the spectra of those layers which lie upon it4 ,such a state of things actually occurs in a total eclipse of the sun4 ,when the moon's body has crept across the solar disc1 and hidden the last piece of photosphere1 the solar spectrum suddenly becomes what is technically called reversed1--the dark lines crossing it changing into bright lines4 ,this occurs because a strip of those layers which lie immediately upon the photosphere remains still uncovered4 ,the lower of these layers has therefore been called the reversing layer1 for want of a better name4 ,after a second or two this reversed spectrum mostly vanishes1 and an altered spectrum is left to view4 ,taking into consideration the rate at which the moon is moving across the face of the sun1 and the very short time during which the spectrum of the reversing layer lasts1 the thickness of that layer is estimated to be not more than a few hundred miles4 ,in the same way the last of the three spectra--namely1 that of the chromosphere--remains visible for such a time as allows us to estimate its depth at about ten times that of the reversing layer1 or several thousand miles4 ,when the chromosphere1 in its turn during a total eclipse1 has been covered by the moon1 the corona alone is left4 ,this has a distinct spectrum of its own also2 wherein is seen a strange line in the green portion1 which does not tally with that of any element we are acquainted with upon the earth4 ,this unknown element has received for the time being the name of ,coronium4 ,,chapter ,,xiii ,,the ,,sun--continued ,the various parts of the ,sun will now be treated of in detail4 ,i4 ,,photosphere4 ,the photosphere1 or light-sphere1 from the ,greek phs 7phos71 which means light1 is1 as we have already said1 the innermost portion of the sun which can be seen4 ,examined through a good telescope it shows a finely mottled structure1 as of brilliant granules1 somewhat like rice grains1 with small dark spaces lying in between them4 ,it has been supposed that we have here the process of some system of circulation by which the sun keeps sending forth its radiations4 ,in the bright granules we perhaps see masses of intensely heated matter1 rising from the interior of the sun4 ,the dark interspaces may represent matter which has become cooled and darkened through having parted with its heat and light1 and is falling back again into the solar furnace4 ,the sun spots1 so familiar to every one nowadays1 are dark patches which are often seen to break out in the photosphere 7see ,plate ,v41 p4 #acd74 ,they last during various periods of time2 sometimes only for a few days1 sometimes so long as a month or more4 ,a spot is usually composed of a dark central portion called the umbra1 and a less dark fringe around this called the penumbra 7see ,plate ,,vi41 p4 #acf74 ,the umbra ordinarily has the appearance of a deep hole in the photosphere2 but1 that it is a hole at all1 has by no means been definitely proved4 ,illustration3 ,,plate ,v4 ,,the ,,sun1 ,,showing ,,several ,,groups ,,of ,,spots ,from a photograph taken at the ,royal ,observatory1 ,greenwich4 ,the cross-lines seen on the disc are in no way connected with the ,sun1 but belong to the telescope through which the photograph was taken4 7,page #acd7 ,sun spots are1 as a rule1 some thousands of miles across4 ,the umbra of a good-sized spot could indeed engulf at once many bodies the size of our earth4 ,sun spots do not usually appear singly1 but in groups4 ,the total area of a group of this kind may be of immense extent2 even so great as to cover the one-hundredth part of the whole surface of the sun4 ,very large spots1 when such are present1 may be seen without any telescope2 either through a piece of smoked glass1 or merely with the naked eye when the air is misty1 or the sun low on the horizon4 ,the umbra of a spot is not actually dark4 ,it only appears so in contrast with the brilliant photosphere around4 ,spots form1 grow to a large size in comparatively short periods of time1 and then quickly disappear4 ,they seem to shrink away as a consequence of the photosphere closing in upon them4 ,that the sun is rotating upon an axis1 is shown by the continual change of position of all spots in one constant direction across his disc4 ,the time in which a spot is carried completely round depends1 however1 upon the position which it occupies upon the sun's surface4 ,a spot situated near the equator of the sun goes round once in about twenty-five days4 ,the further a spot is situated from this equator1 the longer it takes4 ,about twenty-seven days is the time taken by a spot situated midway between the equator and the solar poles4 ,spots occur to the north of the sun's equator1 as well as to the south2 though1 since regular observations have been made--that is to say1 during the past fifty years or so--they appear to have broken out a little more frequently in the southern parts4 ,from these considerations it will be seen that the sun does not rotate as the earth does1 but that different portions appear to move at different speeds4 ,whether in the neighbourhood of the solar poles the time of rotation exceeds twenty-seven days we are unable to ascertain1 for spots are not seen in those regions4 ,no explanation has yet been given of this peculiar rotation2 and the most we can say on the subject is that the sun is not by any means a solid body4 ,facul 7,latin1 little torches7 are brilliant patches which appear here and there upon the sun's surface1 and are in some way associated with spots4 ,their displacement1 too1 across the solar face confirms the evidence which the spots give us of the sun's rotation4 ,our proofs of this rotation are still further strengthened by the ,doppler spectroscopic method of observation alluded to in ,chapter ,,xi4 ,as was then stated1 one edge of the sun is thus found to be continually approaching us1 and the other side continually receding from us4 ,the varying rates of rotation1 which the spots and facul give us1 are duly confirmed by this method4 ,illustration3 ,,plate ,,vi4 ,,photograph ,,of ,a ,,sunspot ,this fine picture was taken by the late ,m4 ,janssen4 ,the granular structure of the ,sun's surface is here well represented4 7,from ,knowledge47 7,page #ace7 ,the first attempt to bring some regularity into the question of sunspots was the discovery by ,schwabe1 in #aheb1 that they were subject to a regular variation4 ,as a matter of fact they wax and wane in their number1 and the total area which they cover1 in the course of a period1 or cycle1 of on an average about #aa-a_/d years2 being at one part of this period large and abundant1 and at another few and small4 ,this period of #aa-a_/d years is known as the sun spot cycle4 ,no explanation has yet been given of the curious round of change1 but the period in question seems to govern most of the phenomena connected with the sun4 ,,ii4 ,,reversing ,,layer4 ,this is a layer of relatively cool gases lying immediately upon the photosphere4 ,we never see it directly2 and the only proof we have of its presence is that remarkable reversal of the spectrum already described1 when during an instant or two in a total eclipse1 the advancing edge of the moon1 having just hidden the brilliant photosphere1 is moving across the fine strip which the layer then presents edgewise towards us4 ,the fleeting moments during which this reversed spectrum lasts1 informs us that the layer is comparatively shallow2 little more indeed than about #ejj miles in depth4 ,the spectrum of the reversing layer1 or flash spectrum1 as it is sometimes called on account of the instantaneous character with which the change takes place1 was1 as we have seen1 first noticed by ,young in #ahgj2 and has been successfully photographed since then during several eclipses4 ,the layer itself appears to be in a fairly quiescent state2 a marked contrast to the seething photosphere beneath1 and the agitated chromosphere above4 ,,iii4 ,,the ,,chromosphere4 ,the ,chromosphere--so called from the ,greek chrma 7chroma71 which signifies colour--is a layer of gases lying immediately upon the preceding one4 ,its thickness is1 however1 plainly much the greater of the two2 for whereas the reversing layer is only revealed to us indirectly by the spectroscope1 a portion of the chromosphere may clearly be seen in a total eclipse in the form of a strip of scarlet light4 ,the time which the moon's edge takes to traverse it tells us that it must be about ten times as deep as the reversing layer1 namely1 from #ejjj to #aj1jjj miles in depth4 ,its spectrum shows that it is composed chiefly of hydrogen1 calcium and helium1 in the state of vapour4 ,its red colour is mainly due to glowing hydrogen4 ,the element helium1 which it also contains1 has received its appellation from hlios 7helios71 the ,greek name for the sun2 because1 at the time when it first attracted attention1 there appeared to be no element corresponding to it upon our earth1 and it was consequently imagined to be confined to the sun alone4 ,sir ,william ,ramsay1 however1 discovered it to be also a terrestrial element in #ahie1 and since then it has come into much prominence as one of the products given off by radium4 ,taking into consideration the excessive force of gravity on the sun1 one would expect to find the chromosphere and reversing layer growing gradually thicker in the direction of the photosphere4 ,this1 however1 is not the case4 ,both these layers are strangely enough of the same densities all through2 which makes it suspected that1 in these regions1 the force of gravity may be counteracted by some other force or forces1 exerting a powerful pressure outwards from the sun4 ,,iv4 ,,the ,,prominences4 ,we have already seen1 in dealing with total eclipses1 that the exterior surface of the chromosphere is agitated like a stormy sea1 and from it billows of flame are tossed up to gigantic heights4 ,these flaming jets are known under the name of prominences1 because they were first noticed in the form of brilliant points projecting from behind the rim of the moon when the sun was totally eclipsed4 ,prominences are of two kinds1 eruptive and quiescent4 ,the eruptive prominences spurt up directly from the chromosphere with immense speeds1 and change their shape with great rapidity4 ,quiescent prominences1 on the other hand1 have a form somewhat like trees1 and alter their shape but slowly4 ,in the eruptive prominences glowing masses of gas are shot up to altitudes sometimes as high as #cjj1jjj miles1#aj with velocities even so great as from #ejj to #fjj miles a second4 ,it has been noticed that the eruptive prominences are mostly found in those portions of the sun where spots usually appear1 namely1 in the regions near the solar equator4 ,the quiescent prominences1 on the other hand1 are confined1 as a rule1 to the neighbourhood of the sun's poles4 ,prominences were at first never visible except during total eclipses of the sun4 ,but in the year #ahfh1 as we have already seen1 a method of employing the spectroscope was devised1 by means of which they could be observed and studied at any time1 without the necessity of waiting for an eclipse4 ,a still further development of the spectroscope1 the ,spectroheliograph1 an instrument invented almost simultaneously by ,professor ,hale and the ,french astronomer1 ,m4 ,deslandres1 permits of photographs being taken of the sun1 with the light emanating from only one of its glowing gases at a time4 ,for instance1 we can thus obtain a record of what the glowing hydrogen alone is doing on the solar body at any particular moment4 ,with this instrument it is also possible to obtain a series of photographs1 showing what is taking place upon the sun at various levels4 ,this is very useful in connection with the study of the spots2 for we are1 in consequence1 enabled to gather more evidence on the subject of their actual form than is given us by their highly foreshortened appearances when observed directly in the telescope4 ,v4 ,,corona4 7,latin1 a ,crown47 ,this marvellous halo of pearly-white light1 which displays itself to our view only during the total phase of an eclipse of the sun1 is by no means a layer like those other envelopments of the sun of which we have just been treating4 ,it appears1 on the other hand1 to be composed of filmy matter1 radiating outwards in every direction1 and fading away gradually into space4 ,its structure is noted to bear a strong resemblance to the tails of comets1 or the streamers of the aurora borealis4 ,our knowledge concerning the corona has1 however1 advanced very slowly4 ,we have not1 so far1 been as fortunate with regard to it as with regard to the prominences2 and1 for all we can gather concerning it1 we are still entirely dependent upon the changes and chances of total solar eclipses4 ,all attempts1 in fact1 to apply the spectroscopic method1 so as to observe the corona at leisure in full sunlight in the way in which the prominences can be observed1 have up to the present met with failure4 ,the general form under which the corona appears to our eyes varies markedly at different eclipses4 ,sometimes its streamers are many1 and radiate all round2 at other times they are confined only to the middle portions of the sun1 and are very elongated1 with short feathery-looking wisps adorning the solar poles4 ,it is noticed that this change of shape varies in close accordance with that #aa-a_/d year period during which the sun spots wax and wane2 the many-streamered regular type corresponding to the time of great sunspot activity1 while the irregular type with the long streamers is present only when the spots are few 7see ,plate ,,vii41 p4 #adb74 ,streamers have often been noted to issue from those regions of the sun where active prominences are at the moment in existence2 but it cannot be laid down that this is always the case4 ,no hypothesis has yet been formulated which will account for the structure of the corona1 or for its variation in shape4 ,the great difficulty with regard to theorising upon this subject1 is the fact that we see so much of the corona under conditions of marked foreshortening4 ,assuming1 what indeed seems natural1 that the rays of which it is composed issue in every direction from the solar body1 in a manner which may be roughly imitated by sticking pins all over a ball2 it is plainly impossible to form any definite idea concerning streamers1 which actually may owe most of the shape they present to us1 to the mixing up of multitudes of rays at all kinds of angles to the line of sight4 ,in a word1 we have to try and form an opinion concerning an arrangement which1 broadly speaking1 is spherical1 but which1 on account of its distance1 must needs appear to us as absolutely flat4 ,the most known about the composition of the corona is that it is made up of particles of matter1 mingled with a glowing gas4 ,it is an element in the composition of this gas which1 as has been stated1 is not found to tally with any known terrestrial element1 and has1 therefore1 received the name of coronium for want of a better designation4 ,one definite conclusion appears to be reached with regard to the corona1 i4e4 that the matter of which it is composed1 must be exceedingly rarefied2 as it is not found1 for instance1 to retard appreciably the speed of comets1 on occasions when these bodies pass very close to the sun4 ,a calculation has indeed been made which would tend to show that the particles composing the coronal matter1 are separated from each other by a distance of perhaps between two and three yards6 ,the density of the corona is found not to increase inwards towards the sun4 ,this is what has already been noted with regard to the layers lying beneath it4 ,powerful forces1 acting in opposition to gravity1 must hold sway here also4 ,illustration3 7,a47 ,,the ,,total ,,eclipse ,,of ,,the ,,sun ,,of ,,december #bb,,nd1 #ahgj ,drawn by ,mr4 ,w4,h4 ,wesley from a photograph taken at ,syracuse by ,mr4 ,brothers4 ,this is the type of corona seen at the time of greatest sunspot activity4 ,the coronas of #ahhb 7,plate ,i41 p4 #if7 and of #aije 7,frontispiece7 are of the same type4 7,b47 ,,the ,,total ,,eclipse ,,of ,,the ,,sun ,,of ,,may #bh,,th1 #aijj ,drawn by ,mr4 ,w4,h4 ,wesley from photographs taken by ,mr4 ,e4,w4 ,maunder4 ,this is the type of corona seen when the sunspots are least active4 ,compare the ,ring with ,wings1 ,fig4 #g1 p4 #hg4 ,,plate ,,vii4 ,,forms ,,of ,,the ,,solar ,,corona ,,at ,,the ,,epochs ,,of ,,sunspot ,,maximum ,,and ,,sunspot ,,minimum1 ,,respectively 7,page #ada7 ,the #aa-a_/d year period1 during which the sun spots vary in number and size1 appears to govern the activities of the sun much in the same way that our year does the changing seasonal conditions of our earth4 ,not only1 as we have seen1 does the corona vary its shape in accordance with the said period1 but the activity of the prominences1 and of the facul1 follow suit4 ,further1 this constant round of ebb and flow is not confined to the sun itself1 but1 strangely enough1 affects the earth also4 ,the displays of the aurora borealis1 which we experience here1 coincide closely with it1 as does also the varying state of the earth's magnetism4 ,the connection may be still better appreciated when a great spot1 or group of spots1 has made its appearance upon the sun4 ,it has1 for example1 often been noted that when the solar rotation carries a spot1 or group of spots1 across the middle of the visible surface of the sun1 our magnetic and electrical arrangements are disturbed for the time being4 ,the magnetic needles in our observatories are1 for instance1 seen to oscillate violently1 telegraphic communication is for a while upset1 and magnificent displays of the aurora borealis illumine our night skies4 ,mr4 ,e4,w4 ,maunder1 of ,greenwich ,observatory1 who has made a very careful investigation of this subject1 suspects that1 when elongated coronal streamers are whirled round in our direction by the solar rotation1 powerful magnetic impulses may be projected upon us at the moments when such streamers are pointing towards the earth4 ,some interesting investigations with regard to sunspots have recently been published by ,mrs4 ,e4,w4 ,maunder4 ,in an able paper1 communicated to the ,royal ,astronomical ,society on ,may #aj1 #aijg1 she reviews the ,greenwich ,observatory statistics dealing with the number and extent of the spots which have appeared during the period from #ahhi to #aija--;a whole sunspot cycle4 ,from a detailed study of the dates in question1 she finds that the number of those spots which are formed on the side of the sun turned away from us1 and die out upon the side turned towards us1 is much greater than the number of those which are formed on the side turned towards us and die out upon the side turned away4 ,it used1 for instance1 to be considered that the influence of a planet might produce sunspots2 but these investigations make it look rather as if some influence on the part of the earth tends1 on the contrary1 to extinguish them4 ,mrs4 ,maunder1 so far1 prefers to call the influence thus traced an apparent influence only1 for1 as she very fairly points out1 it seems difficult to attribute a real influence in this matter to the earth1 which is so small a thing in comparison not only with the sun1 but even with many individual spots4 ,the above investigation was to a certain degree anticipated by ,mr4 ,henry ,corder in #ahie2 but ,mrs4 ,maunder's researches cover a much longer period1 and the conclusions deduced are of a wider and more defined nature4 ,with regard to its chemical composition1 the spectroscope shows us that thirty-nine of the elements which are found upon our earth are also to be found in the sun4 ,of these the best known are hydrogen1 oxygen1 helium1 carbon1 calcium1 aluminium1 iron1 copper1 zinc1 silver1 tin1 and lead4 ,some elements of the metallic order have1 however1 not been found there1 as1 for instance1 gold and mercury2 while a few of the other class of element1 such as nitrogen1 chlorine1 and sulphur1 are also absent4 ,it must not1 indeed1 be concluded that the elements apparently missing do not exist at all in the solar body4 ,gold and mercury have1 in consequence of their great atomic weight1 perhaps sunk away into the centre4 ,again1 the fact that we cannot find traces of certain other elements1 is no real proof of their entire absence4 ,some of them may1 for instance1 be resolved into even simpler forms1 under the unusual conditions which exist in the sun2 and so we are unable to trace them with the spectroscope1 the experience of which rests on laboratory experiments conducted1 at best1 in conditions which obtain upon the earth4 #aj ,on ,november #ae1 #aijg1 ,dr4 ,a4 ,rambaut1 ,radcliffe ,observer at ,oxford ,university1 noted a prominence which rose to a height of #cbd1fjj miles4 ,,chapter ,,xiv ,,the ,,inferior ,,planets ,starting from the centre of the solar system1 the first body we meet with is the planet ,mercury4 ,it circulates at an average distance from the sun of about thirty-six millions of miles4 ,the next body to it is the planet ,venus1 at about sixty-seven millions of miles1 namely1 about double the distance of ,mercury from the sun4 ,since our earth comes next again1 astronomers call those planets which circulate within its orbit1 i4e4 ,mercury and ,venus1 the ,inferior ,planets1 while those which circulate outside it they call the ,superior ,planets4#aa ,in studying the inferior planets1 the circumstances in which we make our observations are so very similar with regard to each1 that it is best to take them together4 ,let us begin by considering the various positions of an inferior planet1 as seen from the earth1 during the course of its journeys round the sun4 ,when furthest from us it is at the other side of the sun1 and cannot then be seen owing to the blaze of light4 ,as it continues its journey it passes to the left of the sun1 and is then sufficiently away from the glare to be plainly seen4 ,it next draws in again towards the sun1 and is once more lost to view in the blaze at the time of its passing nearest to us4 ,then it gradually comes out to view on the right hand1 separates from the sun up to a certain distance as before1 and again recedes beyond the sun1 and is for the time being once more lost to view4 ,to these various positions technical names are given4 ,when the inferior planet is on the far side of the sun from us1 it is said to be in ,superior ,conjunction4 ,when it has drawn as far as it can to the left hand1 and is then as east as possible of the sun1 it is said to be at its ,greatest ,eastern ,elongation4 ,again1 when it is passing nearest to us1 it is said to be in ,inferior ,conjunction2 and1 finally1 when it has drawn as far as it can to the right hand1 it is spoken of as being at its ,greatest ,western ,elongation 7see ,fig4 #aa1 p4 #adh74 ,the continual variation in the distance of an interior planet from us1 during its revolution around the sun1 will of course be productive of great alterations in its apparent size4 ,at superior conjunction it ought1 being then farthest away1 to show the smallest disc2 while at inferior conjunction1 being the nearest1 it should look much larger4 ,when at greatest elongation1 whether eastern or western1 it should naturally present an appearance midway in size between the two4 ,illustration3 ,various positions1 and illumination by the ,sun1 of an ,inferior ,planet in the course of its orbit4 ,corresponding views of the same situations of an ,inferior ,planet as seen from the ,earth1 showing consequent phases and alterations in apparent size4 ,,fig4 #aa4--,orbit and ,phases of an ,inferior ,planet4 ,from the above considerations one would be inclined to assume that the best time for studying the surface of an interior planet with the telescope is when it is at inferior conjunction1 or1 nearest to us4 ,but that this is not the case will at once appear if we consider that the sunlight is then falling upon the side away from us1 leaving the side which is towards us unillumined4 ,in superior conjunction1 on the other hand1 the light falls full upon the side of the planet facing us2 but the disc is then so small-looking1 and our view besides is so dazzled by the proximity of the sun1 that observations are of little avail4 ,in the elongations1 however1 the sunlight comes from the side1 and so we see one half of the planet lit up2 the right half at eastern elongation1 and the left half at western elongation4 ,piecing together the results given us at these more favourable views1 we are enabled1 bit by bit1 to gather some small knowledge concerning the surface of an inferior planet4 ,from these considerations it will be seen at once that the inferior planets show various phases comparable to the waxing and waning of our moon in its monthly round4 ,superior conjunction is1 in fact1 similar to full moon1 and inferior conjunction to new moon2 while the eastern and western elongations may be compared respectively to the moon's first and last quarters4 ,it will be recollected how1 when these phases were first seen by the early telescopic observers1 the ,copernican theory was felt to be immensely strengthened2 for it had been pointed out that if this system were the correct one1 the planets ,venus and ,mercury1 were it possible to see them more distinctly1 would of necessity present phases like these when viewed from the earth4 ,it should here be noted that the telescope was not invented until nearly seventy years after the death of ,copernicus4 ,the apparent swing of an inferior planet from side to side of the sun1 at one time on the east side1 then passing into and lost in the sun's rays to appear once more on the west side1 is the explanation of what is meant when we speak of an evening or a morning star4 ,an inferior planet is called an evening star when it is at its eastern elongation1 that is to say1 on the left-hand of the sun2 for1 being then on the eastern side1 it will set after the sun sets1 as both sink in their turn below the western horizon at the close of day4 ,similarly1 when such a planet is at its western elongation1 that is to say1 to the right-hand of the sun1 it will go in advance of him1 and so will rise above the eastern horizon before the sun rises1 receiving therefore the designation of morning star4 ,in very early times1 however1 before any definite ideas had been come to with regard to the celestial motions1 it was generally believed that the morning and evening stars were quite distinct bodies4 ,thus ,venus1 when a morning star1 was known to the ancients under the name of ,phosphorus1 or ,lucifer2 whereas they called it ,hesperus when it was an evening star4 ,since an inferior planet circulates between us and the sun1 one would be inclined to expect that such a body1 each time it passed on the side nearest to the earth1 should be seen as a black spot against the bright solar disc4 ,now this would most certainly be the case were the orbit of an inferior planet in the same plane with the orbit of the earth4 ,but we have already seen how the orbits in the solar system1 whether those of planets or of satellites1 are by no means in the one plane2 and that it is for this very reason that the moon is able to pass time after time in the direction of the sun1 at the epoch known as new moon1 and yet not to eclipse him save after the lapse of several such passages4 ,transits1 then1 as the passages of an inferior planet across the sun's disc are called1 take place1 for the same reason1 only after certain regular lapses of time2 and1 as regards the circumstances of their occurrence1 are on a par with eclipses of the sun4 ,the latter1 however1 happen much more frequently1 because the moon passes in the neighbourhood of the sun1 roughly speaking1 once a month1 whereas ,venus comes to each inferior conjunction at intervals so long apart as a year and a half1 and ,mercury only about every four months4 ,from this it will be further gathered that transits of ,mercury take place much oftener than transits of ,venus4 ,until recent years ,transits of ,venus were phenomena of great importance to astronomers1 for they furnished the best means then available of calculating the distance of the sun from the earth4 ,this was arrived at through comparing the amount of apparent displacement in the planet's path across the solar disc1 when the transit was observed from widely separated stations on the earth's surface4 ,the last transit of ,venus took place in #ahhb1 and there will not be another until the year #bjjd4 ,transits of ,mercury1 on the other hand1 are not of much scientific importance4 ,they are of no interest as a popular spectacle2 for the dimensions of the planet are so small1 that it can be seen only with the aid of a telescope when it is in the act of crossing the sun's disc4 ,the last transit of ,mercury took place on ,november #ad1 #aijg1 and there will be another on ,november #f1 #aiad4 ,the first person known to have observed a transit of an inferior planet was the celebrated ,french philosopher1 ,gassendi4 ,this was the transit of ,mercury which took place on the #gth of ,december #afca4 ,the first time a transit of ,venus was ever seen1 so far as is known1 was on the #bdth of ,november #afci4 ,the observer was a certain ,jeremiah ,horrox1 curate of ,hoole1 near ,preston1 in ,lancashire4 ,the transit in question commenced shortly before sunset1 and his observations in consequence were limited to only about half-an-hour4 ,horrox happened to have a great friend1 one ,william ,crabtree1 of ,manchester1 whom he had advised by letter to be on the look out for the phenomenon4 ,the weather in ,crabtree's neighbourhood was cloudy1 with the result that he only got a view of the transit for about ten minutes before the sun set4 ,that this transit was observed at all is due entirely to the remarkable ability of ,horrox4 ,according to the calculations of the great ,kepler1 no transit could take place that year 7#afci71 as the planet would just pass clear of the lower edge of the sun4 ,horrox1 however1 not being satisfied with this1 worked the question out for himself1 and came to the conclusion that the planet would actually traverse the lower portion of the sun's disc4 ,the event1 as we have seen1 proved him to be quite in the right4 ,horrox is said to have been a veritable prodigy of astronomical skill2 and had he lived longer would1 no doubt1 have become very famous4 ,unfortunately he died about two years after his celebrated transit1 in his twenty-second year only1 according to the accounts4 ,his friend ,crabtree1 who was then also a young man1 is said to have been killed at the battle of ,naseby in #afde4 ,there is an interesting phenomenon in connection with transits which is known as the ,black ,drop4 ,when an inferior planet has just made its way on to the face of the sun1 it is usually seen to remain for a short time as if attached to the sun's edge by what looks like a dark ligament 7see ,fig4 #ab1 p4 #aec74 ,this gives to the planet for the time being an elongated appearance1 something like that of a pear2 but when the ligament1 which all the while keeps getting thinner and thinner1 has at last broken1 the black body of the planet is seen to stand out round against the solar disc4 ,illustration3 ,,fig4 #ab4--,the ,black ,drop4 ,this appearance may be roughly compared to the manner in which a drop of liquid 7or1 preferably1 of some glutinous substance7 tends for a while to adhere to an object from which it is falling4 ,when the planet is in turn making its way off the face of the sun1 the ligament is again seen to form and to attach it to the sun's edge before its due time4 ,the phenomenon of the black drop1 or ligament1 is entirely an illusion1 and1 broadly speaking1 of an optical origin4 ,something very similar will be noticed if one brings one's thumb and forefinger slowly together against a very bright background4 ,this peculiar phenomenon has proved one of the greatest drawbacks to the proper observation of transits1 for it is quite impossible to note the exact instant of the planet's entrance upon and departure from the solar disc in conditions such as these4 ,the black drop seems to bear a family resemblance1 so to speak1 to the phenomenon of ,baily's beads4 ,in the latter instance the lunar peaks1 as they approach the sun's edge1 appear to lengthen out in a similar manner and bridge the intervening space before their time1 thus giving prominence to an effect which otherwise should scarcely be noticeable4 ,the last transit of ,mercury1 which1 as has been already stated1 took place on ,november #ad1 #aijg1 was not successfully observed by astronomers in ,england1 on account of the cloudiness of the weather4 ,in ,france1 however1 ,professor ,moye1 of ,montpellier1 saw it under good conditions1 and mentions that the black drop remained very conspicuous for fully a minute4 ,the transit was also observed in the ,united ,states1 the reports from which speak of the black drop as very troublesome4 ,before leaving the subject of transits it should be mentioned that it was in the capacity of commander of an expedition to ,otaheite1 in the ,pacific1 to observe the transit of ,venus of ,june #c1 #agfi1 that ,captain ,cook embarked upon the first of his celebrated voyages4 ,in studying the surfaces of ,venus and ,mercury with the telescope1 observers are1 needless to say1 very much hindered by the proximity of the sun4 ,venus1 when at the greatest elongations1 certainly draws some distance out of the glare2 but her surface is1 even then1 so dazzlingly bright1 that the markings upon it are difficult to see4 ,mercury1 on the other hand1 is much duller in contrast1 but the disc it shows in the telescope is exceedingly small2 and1 in addition1 when that planet is left above the horizon for a short time after sunset1 as necessarily happens after certain intervals1 the mists near the earth's surface render observation of it very difficult4 ,until about twenty-five years ago1 it was generally believed that both these planets rotated on their axes in about twenty-four hours1 a notion1 no doubt1 originally founded upon an unconscious desire to bring them into some conformity with our earth4 ,but ,schiaparelli1 observing in ,italy1 and ,percival ,lowell1 in the clear skies of ,arizona and ,mexico1 have lately come to the conclusion that both planets rotate upon their axes in the same time as they revolve in their orbits1#ab the result being that they turn one face ever towards the sun in the same manner that the moon turns one face ever towards the earth--a curious state of things1 which will be dealt with more fully when we come to treat of our satellite4 ,the marked difference in the brightness between the two planets has already been alluded to4 ,the surface of ,venus is1 indeed1 about five times as bright as that of ,mercury4 ,the actual brightness of ,mercury is about equivalent to that of our moon1 and astronomers are1 therefore1 inclined to think that it may resemble her in having a very rugged surface and practically no atmosphere4 ,this probable lack of atmosphere is further corroborated by two circumstances4 ,one of these is that when ,mercury is just about to transit the face of the sun1 no ring of diffused light is seen to encircle its disc as would be the case if it possessed an atmosphere4 ,such a lack of atmosphere is1 indeed1 only to be expected from what is known as the ,kinetic ,theory of ,gases4 ,according to this theory1 which is based upon the behaviour of various kinds of gas1 it is found that these elements tend to escape into space from the surface of bodies whose force of gravitation is weak4 ,hydrogen gas1 for example1 tends to fly away from our earth1 as any one may see for himself when a balloon rises into the air4 ,the gravitation of the earth seems1 however1 powerful enough to hold down other gases1 as1 for instance1 those of which the air is chiefly composed1 namely1 oxygen and nitrogen4 ,in due accordance with the ,kinetic theory1 we find the moon and ,mercury1 which are much about the same size1 destitute of atmospheres4 ,mars1 too1 whose diameter is only about double that of the moon1 has very little atmosphere4 ,we find1 on the other hand1 that ,venus1 which is about the same size as our earth1 clearly possesses an atmosphere1 as just before the planet is in transit across the sun1 the outline of its dark body is seen to be surrounded by a bright ring of light4 ,the results of telescopic observation show that more markings are visible on ,mercury than on ,venus4 ,the intense brilliancy of ,venus is1 indeed1 about the same as that of our white clouds when the sun is shining directly upon them4 ,it has1 therefore1 been supposed that the planet is thickly enveloped in cloud1 and that we do not ever see any part of its surface1 except perchance the summit of some lofty mountain projecting through the fleecy mass4 ,with regard to the great brilliancy of ,venus1 it may be mentioned that she has frequently been seen in ,england1 with the naked eye in full sunshine1 when at the time of her greatest brightness4 ,the writer has seen her thus at noonday4 ,needless to say1 the sky at the moment was intensely blue and clear4 ,the orbit of ,mercury is very oval1 and much more so than that of any other planet4 ,the consequence is that1 when ,mercury is nearest to the sun1 the heat which it receives is twice as great as when it is farthest away4 ,the orbit of ,venus1 on the other hand1 is in marked contrast with that of ,mercury1 and is1 besides1 more nearly of a circular shape than that of any of the other planets4 ,venus1 therefore1 always keeps about the same distance from the sun1 and so the heat which she receives during the course of her year can only be subject to very slight variations4 #aa ,in employing the terms ,inferior and ,superior the writer bows to astronomical custom1 though he cannot help feeling that1 in the circumstances1 ,interior and ,exterior would be much more appropriate4 #ab ,this question is1 however1 uncertain1 for some very recent spectroscopic observations of ,venus seem to show a rotation period of about twenty-four hours4 ,,chapter ,,xv ,,the ,,earth ,we have already seen 7in ,chapter ,i47 how1 in very early times1 men naturally enough considered the earth to be a flat plane extending to a very great distance in every direction2 but that1 as years went on1 certain of the ,greek philosophers suspected it to be a sphere4 ,one or two of the latter are1 indeed1 said to have further believed in its rotation about an axis1 and even in its revolution around the sun2 but1 as the ideas in question were founded upon fancy1 rather than upon any direct evidence1 they did not generally attract attention4 ,the small effect1 therefore1 which these theories had upon astronomy1 may well be gathered from the fact that in the ,ptolemaic system the earth was considered as fixed and at the centre of things2 and this belief1 as we have seen1 continued unaltered down to the days of ,copernicus4 ,it was1 indeed1 quite impossible to be certain of the real shape of the earth or the reality of its motions until knowledge became more extended and scientific instruments much greater in precision4 ,we will now consider in detail a few of the more obvious arguments which can be put forward to show that our earth is a sphere4 ,if1 for instance1 the earth were a plane surface1 a ship sailing away from us over the sea would appear to grow smaller and smaller as it receded into the distance1 becoming eventually a tiny speck1 and fading gradually from our view4 ,this1 however1 is not at all what actually takes place4 ,as we watch a vessel receding1 its hull appears bit by bit to slip gently down over the horizon1 leaving the masts alone visible4 ,then1 in their turn1 the masts are seen to slip down in the same manner1 until eventually every trace of the vessel is gone4 ,on the other hand1 when a ship comes into view1 the masts are the first portions to appear4 ,they gradually rise up from below the horizon1 and the hull follows in its turn1 until the whole vessel is visible4 ,again1 when one is upon a ship at sea1 a set of masts will often be seen sticking up alone above the horizon1 and these may shorten and gradually disappear from view without the body of the ship to which they belong becoming visible at all4 ,since one knows from experience that there is no edge at the horizon over which a vessel can drop down1 the appearance which we have been describing can only be explained by supposing that the surface of the earth is always curving gradually in every direction4 ,the distance at which what is known as the horizon lies away from us depends entirely upon the height above the earth's surface where we happen at the moment to be4 ,a ship which has appeared to sink below the horizon for a person standing on the beach1 will be found to come back again into view if he at once ascends a high hill4 ,experiment shows that the horizon line lies at about three miles away for a person standing at the water's edge4 ,the curving of the earth's surface is found1 indeed1 to be at the rate of eight inches in every mile4 ,now it can be ascertained1 by calculation1 that a body curving at this rate in every direction must be a globe about #hjjj miles in diameter4 ,again1 the fact that1 if not stopped by such insuperable obstacles as the polar ice and snow1 those who travel continually in any one direction upon the earth's surface always find themselves back again at the regions from which they originally set out1 is additional ground for concluding that the earth is a globe4 ,we can find still further evidence4 ,for instance1 in an eclipse of the moon the earth's shadow1 when seen creeping across the moon's face1 is noted to be always circular in shape4 ,one cannot imagine how such a thing could take place unless the earth were a sphere4 ,also1 it is found from observation that the sun1 the planets1 and the satellites are1 all of them1 round4 ,this roundness cannot be the roundness of a flat plate1 for instance1 for then the objects in question would sometimes present their thin sides to our view4 ,it happens1 also1 that upon the discs which these bodies show1 we see certain markings shifting along continually in one direction1 to disappear at one side and to reappear again at the other4 ,such bodies must1 indeed1 be spheres in rotation4 ,the crescent and other phases1 shown by the moon and the inferior planets1 should further impress the truth of the matter upon us1 as such appearances can only be caused by the sunlight falling from various directions upon the surfaces of spherical bodies4 ,another proof1 perhaps indeed the weightiest of all1 is the continuous manner in which the stars overhead give place to others as one travels about the surface of the earth4 ,when in northern regions the ,pole ,star and its neighbours--the stars composing the ,plough1 for instance--are over our heads4 ,as one journeys south these gradually sink towards the northern horizon1 while other stars take their place1 and yet others are uncovered to view from the south4 ,the regularity with which these changes occur shows that every point on the earth's surface faces a different direction of the sky1 and such an arrangement would only be possible if the earth were a sphere4 ,the celebrated ,greek philosopher1 ,aristotle1 is known to have believed in the globular shape of the earth1 and it was by this very argument that he had convinced himself that it was so4 ,the idea of the sphericity of the earth does not appear1 however1 to have been generally accepted until the voyages of the great navigators showed that it could be sailed round4 ,the next point we have to consider is the rotation of the earth about its axis4 ,from the earliest times men noticed that the sky and everything in it appeared to revolve around the earth in one fixed direction1 namely1 towards what is called the ,west1 and that it made one complete revolution in the period of time which we know as twenty-four hours4 ,the stars were seen to come up1 one after another1 from below the eastern horizon1 to mount the sky1 and then to sink in turn below the western horizon4 ,the sun was seen to perform exactly the same journey1 and the moon1 too1 whenever she was visible4 ,one or two of the ancient ,greek philosophers perceived that this might be explained1 either by a movement of the entire heavens around the earth1 or by a turning motion on the part of the earth itself4 ,of these diverse explanations1 that which supposed an actual movement of the heavens appealed to them the most1 for they could hardly conceive that the earth should continually rotate and men not be aware of its movement4 ,the question may be compared to what we experience when borne along in a railway train4 ,we see the telegraph posts and the trees and buildings near the line fly past us one after another in the contrary direction4 ,either these must be moving1 or we must be moving2 and as we happen to know that it is1 indeed1 we who are moving1 there can be no question therefore about the matter4 ,but it would not be at all so easy to be sure of this movement were one unable to see the objects close at hand displacing themselves4 ,for instance1 if one is shut up in a railway carriage at night with the blinds down1 there is really nothing to show that one is moving1 except the jolting of the train4 ,and even then it is hard to be sure in which direction one is actually travelling4 ,the way we are situated upon the earth is therefore as follows4 ,there are no other bodies sufficiently near to be seen flying past us in turn2 our earth spins without a jolt2 we and all things around us1 including the atmosphere itself1 are borne along together with precisely the same impetus1 just as all the objects scattered about a railway carriage share in the forward movement of the train4 ,such being the case1 what wonder that we are unconscious of the earth's rotation1 of which we should know nothing at all1 were it not for that slow displacement of the distant objects in the heavens1 as we are borne past them in turn4 ,if the night sky be watched1 it will be soon found that its apparent turning movement seems to take place around a certain point1 which appears as if fixed4 ,this point is known as the north pole of the heavens2 and a rather bright star1 which is situated very close to this hub of movement1 is in consequence called the ,pole ,star4 ,for the dwellers in southern latitudes there is also a point in their sky which appears to remain similarly fixed1 and this is known as the south pole of the heavens4 ,since1 however1 the heavens do not turn round at all1 but the earth does1 it will easily be seen that these apparently stationary regions in the sky are really the points towards which the axis of the earth is directed4 ,the positions on the earth's surface itself1 known as the ,north and ,south ,poles1 are merely the places where the earth's axis1 if there were actually such a thing1 would be expected to jut out4 ,the north pole of the earth will thus be situated exactly beneath the north pole of the heavens1 and the south pole of the earth exactly beneath the south pole of the heavens4 ,we have seen that the earth rotates upon its imaginary axis once in about every twenty-four hours4 ,this means that everything upon the surface of the earth is carried round once during that time4 ,the measurement around the earth's equator is about #bd1jjj miles2 and1 therefore1 an object situated at the equator must be carried round through a distance of about #bd1jjj miles in each twenty-four hours4 ,everything at the equator is thus moving along at the rapid rate of about #ajjj miles an hour1 or between sixteen and seventeen times as fast as an express train4 ,if1 however1 one were to take measurements around the earth parallel to the equator1 one would find these measurements becoming less and less1 according as the poles were approached4 ,it is plain1 therefore1 that the speed with which any point moves1 in consequence of the earth's rotation1 will be greatest at the equator1 and less and less in the direction of the poles2 while at the poles themselves there will be practically no movement1 and objects there situated will merely turn round4 ,the considerations above set forth1 with regard to the different speeds at which different portions of a rotating globe will necessarily be moving1 is the foundation of an interesting experiment1 which gives us further evidence of the rotation of our earth4 ,the measurement around the earth at any distance below the surface1 say1 for instance1 at the depth of a mile1 will clearly be less than a similar measurement at the surface itself4 ,the speed of a point at the bottom of a mine1 which results from the actual rotation of the earth1 must therefore be less than the speed of a point at the surface overhead4 ,this can be definitely proved by dropping a heavy object down a mine shaft4 ,the object1 which starts with the greater speed of the surface1 will1 when it reaches the bottom of the mine1 be found1 as might be indeed expected1 to be a little ahead 7i4e4 to the east7 of the point which originally lay exactly underneath it4 ,the distance by which the object gains upon this point is1 however1 very small4 ,in our latitudes it amounts to about an inch in a fall of #ejj feet4 ,the great speed at which1 as we have seen1 the equatorial regions of the earth are moving1 should result in giving to the matter there situated a certain tendency to fly outwards4 ,sir ,isaac ,newton was the first to appreciate this point1 and he concluded from it that the earth must be bulged a little all round the equator4 ,this is1 indeed1 found to be the case1 the diameter at the equator being nearly twenty-seven miles greater than it is from pole to pole4 ,the reader will1 no doubt1 be here reminded of the familiar comparison in geographies between the shape of the earth and that of an orange4 ,in this connection it is interesting to consider that1 were the earth to rotate seventeen times as fast as it does 7i4e4 in one hour twenty-five minutes1 instead of twenty-four hours71 bodies at the equator would have such a strong tendency to fly outwards that the force of terrestrial gravity acting upon them would just be counterpoised1 and they would virtually have no weight4 ,and1 further1 were the earth to rotate a little faster still1 objects lying loose upon its surface would be shot off into space4 ,the earth is1 therefore1 what is technically known as an oblate spheroid2 that is1 a body of spherical shape flattened at the poles4 ,it follows of course from this1 that objects at the polar regions are slightly nearer to the earth's centre than objects at the equatorial regions4 ,we have already seen that gravitation acts from the central parts of a body1 and that its force is greater the nearer are those central parts4 ,the result of this upon our earth will plainly be that objects in the polar regions will be pulled with a slightly stronger pull1 and will therefore weigh a trifle more than objects in the equatorial regions4 ,this is1 indeed1 found by actual experiment to be the case4 ,as an example of the difference in question1 ,professor ,young1 in his ,manual of ,astronomy1 points out that a man who weighs #aij pounds at the equator would weigh #aia at the pole4 ,in such an experiment the weighing would1 however1 have to be made with a spring balance1 and not with scales2 for1 in the latter case1 the weights used would alter in their weight in exactly the same degree as the objects to be weighed4 ,it used to be thought that the earth was composed of a relatively thin crust1 with a molten interior4 ,scientific men now believe1 on the other hand1 that such a condition cannot after all prevail1 and that the earth must be more or less solid all through1 except perhaps in certain isolated places where collections of molten matter may exist4 ,the atmosphere1 or air which we breathe1 is in the form of a layer of limited depth which closely envelops the earth4 ,actually1 it is a mixture of several gases1 the most important being nitrogen and oxygen1 which between them practically make up the air1 for the proportion of the other gases1 the chief of which is carbonic acid gas1 is exceedingly small4 ,it is hard to picture our earth1 as we know it1 without this atmosphere4 ,deprived of it1 men at once would die2 but even if they could be made to go on living without it by any miraculous means1 they would be like unto deaf beings1 for they would never hear any sound4 ,what we call sounds are merely vibrations set up in the air1 which travel along and strike upon the drum of the ear4 ,the atmosphere is densest near the surface of the earth1 and becomes less and less dense away from it1 as a result of diminishing pressure of air from above4 ,the greater portion of it is accumulated within four or five miles of the earth's surface4 ,it is impossible to determine exactly at what distance from the earth's surface the air ceases altogether1 for it grows continually more and more rarefied4 ,there are1 however1 two distinct methods of ascertaining the distance beyond which it can be said practically not to exist4 ,one of these methods we get from twilight4 ,twilight is1 in fact1 merely light reflected to us from those upper regions of the air1 which still continue to be illuminated by the sun after it has disappeared from our view below the horizon4 ,the time during which twilight lasts1 shows us that the atmosphere must be at least fifty miles high4 ,but the most satisfactory method of ascertaining the height to which the atmosphere extends is from the observation of meteors4 ,it is found that these bodies become ignited1 by the friction of passing into the atmosphere1 at a height of about #ajj miles above the surface of the earth4 ,we thus gather that the atmosphere has a certain degree of density even at this height4 ,it may1 indeed1 extend as far as about #aej miles4 ,the layer of atmosphere surrounding our earth acts somewhat in the manner of the glass covering of a greenhouse1 bottling in the sun's rays1 and thus storing up their warmth for our benefit4 ,were this not so1 the heat which we get from the sun would1 after falling upon the earth1 be quickly radiated again into space4 ,it is owing to the unsteadiness of the air that stars are seen to twinkle4 ,a night when this takes place1 though it may please the average person1 is worse than useless to the astronomer1 for the unsteadiness is greatly magnified in the telescope4 ,this twinkling is1 no doubt1 in a great measure responsible for the conventional points with which ,art has elected to embellish stars1 and which1 of course1 have no existence in fact4 ,the phenomena of ,refraction1#ac namely1 that bending which rays of light undergo1 when passing slant-wise from a rare into a dense transparent medium1 are very marked with regard to the atmosphere4 ,the denser the medium into which such rays pass1 the greater is this bending found to be4 ,since the layer of air around us becomes denser and denser towards the surface of the earth1 it will readily be granted that the rays of light reaching our eyes from a celestial object1 will suffer the greater bending the lower the object happens to be in the sky4 ,celestial objects1 unless situated directly overhead1 are thus not seen in their true places1 and when nearest to the horizon are most out of place4 ,the bending alluded to is upwards4 ,thus the sun and the moon1 for instance1 when we see them resting upon the horizon1 are actually entirely beneath it4 ,when the sun1 too1 is sinking towards the horizon1 the lower edge of its disc will1 for the above reason1 look somewhat more raised than the upper4 ,the result is a certain appearance of flattening2 which may plainly be seen by any one who watches the orb at setting4 ,in observations to determine the exact positions of celestial objects correction has to be made for the effects of refraction1 according to the apparent elevation of these objects in the sky4 ,such effects are least when the objects in question are directly overhead1 for then the rays of light1 coming from them to the eye1 enter the atmosphere perpendicularly1 and not at any slant4 ,a very curious effect1 due to refraction1 has occasionally been observed during a total eclipse of the moon4 ,to produce an eclipse of this kind1 the earth must1 of course1 lie directly between the sun and the moon4 ,therefore1 when we see the shadow creeping over the moon's surface1 the sun should actually be well below the horizon4 ,but when a lunar eclipse happens to come on just about sunset1 the sun1 although really sunk below the horizon1 appears still above it through refraction1 and the eclipsed moon1 situated1 of course1 exactly opposite to it in the sky1 is also lifted up above the horizon by the same cause4 ,pliny1 writing in the first century of the ,christian era1 describes an eclipse of this kind1 and refers to it as a prodigy4 ,the phenomenon is known as a horizontal eclipse4 ,it was1 no doubt1 partly owing to it that the ancients took so long to decide that an eclipse of the moon was really caused by the shadow cast by the earth4 ,plutarch1 indeed1 remarks that it was easy enough to understand that a solar eclipse was caused by the interposition of the moon1 but that one could not imagine by the interposition of what body the moon itself could be eclipsed4 ,in that apparent movement of the heavens about the earth1 which men now know to be caused by the mere rotation of the earth itself1 a slight change is observed to be continually taking place4 ,the stars1 indeed1 are always found to be gradually drawing westward1 i4e4 towards the sun1 and losing themselves one after the other in the blaze of his light1 only to reappear1 however1 on the other side of him after a certain lapse of time4 ,this is equivalent to saying that the sun itself seems always creeping slowly eastward in the heaven4 ,the rate at which this appears to take place is such that the sun finds itself back again to its original position1 with regard to the starry background1 at the end of a year's time4 ,in other words1 the sun seems to make a complete tour of the heavens in the course of a year4 ,here1 however1 we have another illusion1 just as the daily movement of the sky around the earth was an illusion4 ,the truth indeed is1 that this apparent movement of the sun eastward among the stars during a year1 arises merely from a continuous displacement of his position caused by an actual motion of the earth itself around him in that very time4 ,in a word1 it is the earth which really moves around the sun1 and not the sun around the earth4 ,the stress laid upon this fundamental point by ,copernicus1 marks the separation of the modern from the ancient view4 ,not that ,copernicus1 indeed1 had obtained any real proof that the earth is merely a planet revolving around the sun2 but it seemed to his profound intellect that a movement of this kind on the part of our globe was the more likely explanation of the celestial riddle4 ,the idea was not new2 for1 as we have already seen1 certain of the ancient ,greeks 7,aristarchus of ,samos1 for example7 had held such a view2 but their notions on the subject were very fanciful1 and unsupported by any good argument4 ,what ,copernicus1 however1 really seems to have done was to insist upon the idea that the sun occupied the centre1 as being more consonant with common sense4 ,no doubt1 he was led to take up this position by the fact that the sun appeared entirely of a different character from the other members of the system4 ,the one body in the scheme1 which performed the important function of dispenser of light and heat1 would indeed be more likely to occupy a position apart from the rest2 and what position more appropriate for its purposes than the centre6 ,but here ,copernicus only partially solved the difficult question4 ,he unfortunately still clung to an ancient belief1 which as yet remained unquestioned2 i4e4 the great virtue1 one might almost say1 the divineness1 of circular motion4 ,the ancients had been hag-ridden1 so to speak1 by the circle2 and it appeared to them that such a perfectly formed curve was alone fitted for the celestial motions4 ,ptolemy employed it throughout his system4 ,according to him the planets 7which included1 under the ancient view1 both the sun and the moon71 moved around the earth in circles2 but1 as their changing positions in the sky could not be altogether accounted for in this way1 it was further supposed that they performed additional circular movements1 around peculiarly placed centres1 during the course of their orbital revolutions4 ,thus the ,ptolemaic system grew to be extremely complicated2 for astronomers did not hesitate to add new circular movements whenever the celestial positions calculated for the planets were found not to tally with the positions observed4 ,in this manner1 indeed1 they succeeded in doctoring the theory1 so that it fairly satisfied the observations made with the rough instruments of pre-telescopic times4 ,although ,copernicus performed the immense service to astronomy of boldly directing general attention to the central position of the sun1 he unfortunately took over for the new scheme the circular machinery of the ,ptolemaic system4 ,it therefore remained for the famous ,kepler1 who lived about a century after him1 to find the complete solution4 ,just as ,copernicus1 for instance1 had broken free from tradition with regard to the place of the sun2 so did ,kepler1 in turn1 break free from the spell of circular motion1 and thus set the coping-stone to the new astronomical edifice4 ,this astronomer showed1 in fact1 that if the paths of the planets around the sun1 and of the moon around the earth1 were not circles1 but ellipses1 the movements of these bodies about the sky could be correctly accounted for4 ,the extreme simplicity of such an arrangement was far more acceptable than the bewildering intricacy of movement required by the ,ptolemaic theory4 ,the ,copernican system1 as amended by ,kepler1 therefore carried the day2 and was further strengthened1 as we have already seen1 by the telescopic observations of ,galileo and the researches of ,newton into the effects of gravitation4 ,and here a word on the circle1 now fallen from its high estate4 ,the ancients were in error in supposing that it stood entirely apart--the curve of curves4 ,as a matter of fact it is merely a special kind of ellipse4 ,to put it paradoxically1 it is an ellipse which has no ellipticity1 an oval without any ovalness6 ,notwithstanding all this1 astronomy had to wait yet a long time for a definite proof of the revolution of the earth around the sun4 ,the leading argument advanced by ,aristotle1 against the reality of any movement of the earth1 still held good up to about seventy years ago4 ,that philosopher had pointed out that the earth could not move about in space to any great extent1 or the stars would be found to alter their apparent places in the sky1 a thing which had never been observed to happen4 ,centuries ran on1 and instruments became more and more perfect1 yet no displacements of stars were noted4 ,in accepting the ,copernican theory men were therefore obliged to suppose these objects as immeasurably distant4 ,at length1 however1 between the years #ahce and #ahdj1 it was discovered by the ,prussian astronomer1 ,bessel1 that a star known as #fa ,cygni--that is to say1 the star marked in celestial atlases as ,no4 #fa in the constellation of the ,swan--appeared1 during the course of a year1 to perform a tiny circle in the heavens1 such as would result from a movement on our own part around the sun4 ,since then about forty-three stars have been found to show minute displacements of a similar kind1 which cannot be accounted for upon any other supposition than that of a continuous revolution of the earth around the sun4 ,the triumph of the ,copernican system is now at last supreme4 ,if the axis of the earth stood straight up1 so to speak1 while the earth revolved in its orbit1 the sun would plainly keep always on a level with the equator4 ,this is equivalent to stating that1 in such circumstances1 a person at the equator would see it rise each morning exactly in the east1 pass through the zenith1 that is1 the point directly overhead of him1 at midday1 and set in the evening due in the west4 ,as this would go on unchangingly at the equator every day throughout the year1 it should be clear that1 at any particular place upon the earth1 the sun would in these conditions always be seen to move in an unvarying manner across the sky at a certain altitude depending upon the latitude of the place4 ,thus the more north one went upon the earth's surface1 the more southerly in the sky would the sun's path lie2 while at the north pole itself1 the sun would always run round and round the horizon4 ,similarly1 the more south one went from the equator the more northerly would the path of the sun lie1 while at the south pole it would be seen to skirt the horizon in the same manner as at the north pole4 ,the result of such an arrangement would be1 that each place upon the earth would always have one unvarying climate2 in which case there would not exist any of those beneficial changes of season to which we owe so much4 ,the changes of season1 which we fortunately experience1 are due1 however1 to the fact that the sun does not appear to move across the sky each day at one unvarying altitude1 but is continually altering the position of its path2 so that at one period of the year it passes across the sky low down1 and remains above the horizon for a short time only1 while at another it moves high up across the heavens1 and is above the horizon for a much longer time4 ,actually1 the sun seems little by little to creep up the sky during one half of the year1 namely1 from mid-winter to mid-summer1 and then1 just as gradually1 to slip down it again during the other half1 namely1 from mid-summer to mid-winter4 ,it will therefore be clear that every region of the earth is much more thoroughly warmed during one portion of the year than during another1 i4e4 when the sun's path is high in the heavens than when it is low down4 ,once more we find appearances exactly the contrary from the truth4 ,the earth is in this case the real cause of the deception1 just as it was in the other cases4 ,the sun does not actually creep slowly up the sky1 and then slowly dip down it again1 but1 owing to the earth's axis being set aslant1 different regions of the earth's surface are presented to the sun at different times4 ,thus1 in one portion of its orbit1 the northerly regions of the earth are presented to the sun1 and in the other portion the southerly4 ,it follows of course from this1 that when it is summer in the northern hemisphere it is winter in the southern1 and vice vers 7see ,fig4 #ac1 p4 #agf74 ,illustration3 ,,fig4 #ac4--,summer and ,winter4 ,the fact that1 in consequence of this slant of the earth's axis1 the sun is for part of the year on the north side of the equator and part of the year on the south side1 leads to a very peculiar result4 ,the path of the moon around the earth is nearly on the same plane with the earth's path around the sun4 ,the moon1 therefore1 always keeps to the same regions of the sky as the sun4 ,the slant of the earth's axis thus regularly displaces the position of both the sun and the moon to the north and south sides of the equator respectively in the manner we have been describing4 ,were the earth1 however1 a perfect sphere1 such change of position would not produce any effect4 ,we have shown1 however1 that the earth is not a perfect sphere1 but that it is bulged out all round the equator4 ,the result is that this bulged-out portion swings slowly under the pulls of solar and lunar gravitation1 in response to the displacements of the sun and moon to the north and to the south of it4 ,this slow swing of the equatorial regions results1 of course1 in a certain slow change of the direction of the earth's axis1 so that the north pole does not go on pointing continually to the same region of the sky4 ,the change in the direction of the axis is1 however1 so extremely slight1 that it shows up only after the lapse of ages4 ,the north pole of the heavens1 that is1 the region of the sky towards which the north pole of the earth's axis points1 displaces therefore extremely slowly1 tracing out a wide circle1 and arriving back again to the same position in the sky only after a period of about #be1jjj years4 ,at present the north pole of the heavens is quite close to a bright star in the tail of the constellation of the ,little ,bear1 which is consequently known as the ,pole ,star2 but in early ,greek times it was at least ten times as far away from this star as it is now4 ,after some #ab1jjj years the pole will point to the constellation of ,lyra1 and ,vega1 the most brilliant star in that constellation1 will then be considered as the pole star4 ,this slow twisting of the earth's axis is technically known as ,precession1 or the ,precession of the ,equinoxes 7see ,plate ,,xix41 p4 #bib74 ,the slow displacement of the celestial pole appears to have attracted the attention of men in very early times1 but it was not until the second century ,b4,c4 that precession was established as a fact by the celebrated ,greek astronomer1 ,hipparchus4 ,for the ancients this strange cyclical movement had a mystic significance2 and they looked towards the end of the period as the end1 so to speak1 of a dispensation1 after which the life of the universe would begin anew3-- ,magnus ab integro sclorum nascitur ordo4 ,jam redit et ,virgo1 redeunt ,saturnia regna2 4 4 4 4 4 4 ,alter erit tum ,tiphys1 et altera qu vehat ,argo ,delectos heroas2 erunt etiam altera bella1 ,atque iterum ad ,trojam magnus mittetur ,achilles4 ,we have seen that the orbit of the earth is an ellipse1 and that the sun is situated at what is called the focus1 a point not in the middle of the ellipse1 but rather towards one of its ends4 ,therefore1 during the course of the year the distance of the earth from the sun varies4 ,the sun1 in consequence of this1 is about #c1jjj1jjj miles nearer to us in our northern winter than it is in our northern summer1 a statement which sounds somewhat paradoxical4 ,this variation in distance1 large as it appears in figures1 can1 however1 not be productive of much alteration in the amount of solar heat which we receive1 for during the first week in ,january1 when the distance is least1 the sun only looks about one-eighteenth broader than at the commencement of ,july1 when the distance is greatest4 ,the great disparity in temperature between winter and summer depends1 as we have seen1 upon causes of quite another kind1 and varies between such wide limits that the effects of this slight alteration in the distance of the sun from the earth may be neglected for practical purposes4 ,the ,tides are caused by the gravitational pull of the sun and moon upon the water of the earth's surface4 ,of the two1 the moon1 being so much the nearer1 exerts the stronger pull1 and therefore may be regarded as the chief cause of the tides4 ,this pull always draws that portion of the water1 which happens to be right underneath the moon at the time1 into a heap2 and there is also a second heaping of water at the same moment at the contrary side of the earth1 the reasons for which can be shown mathematically1 but cannot be conveniently dealt with here4 ,as the earth rotates on its axis each portion of its surface passes beneath the moon1 and is swelled up by this pull2 the watery portions being1 however1 the only ones to yield visibly4 ,a similar swelling up1 as we have seen1 takes place at the point exactly away from the moon4 ,thus each portion of our globe is borne by the rotation through two tide-areas every day1 and this is the reason why there are two tides during every twenty-four hours4 ,the crest of the watery swelling is known as high tide4 ,the journey of the moon around the earth takes about a month1 and this brings her past each place in turn by about fifty minutes later each day1 which is the reason why high tide is usually about twenty-five minutes later each time4 ,the moon is1 however1 not the sole cause of the tides1 but the sun1 as we have said1 has a part in the matter also4 ,when it is new moon the gravitational attractions of both sun and moon are clearly acting together from precisely the same direction1 and1 therefore1 the tide will be pulled up higher than at other times4 ,at full moon1 too1 the same thing happens2 for1 although the bodies are now acting from opposite directions1 they do not neutralise each other's pulls as one might imagine1 since the sun1 in the same manner as the moon1 produces a tide both under it and also at the opposite side of the earth4 ,thus both these tides are actually increased in height4 ,the exceptionally high tides which we experience at new and full moons are known as ,spring ,tides1 in contradistinction to the minimum high tides1 which are known as ,neap ,tides4 ,the ancients appear to have had some idea of the cause of the tides4 ,it is said that as early as #ajjj ,b4,c4 the ,chinese noticed that the moon exerted an influence upon the waters of the sea4 ,the ,greeks and ,romans1 too1 had noticed the same thing2 and ,csar tells us that when he was embarking his troops for ,britain the tide was high because the moon was full4 ,pliny went even further than this1 in recognising a similar connection between the waters and the sun4 ,from casual observation one is inclined to suppose that the high tide always rises many feet4 ,but that this is not the case is evidenced by the fact that the tides in the midst of the great oceans are only from three to four feet high4 ,however1 in the seas and straits around our ,isles1 for instance1 the tides rise very many feet indeed1 but this is merely owing to the extra heaping up which the large volumes of water undergo in forcing their passage through narrow channels4 ,as the earth1 in rotating1 is continually passing through these tide-areas1 one might expect that the friction thus set up would tend to slow down the rotation itself4 ,such a slowing down1 or tidal drag1 as it is called1 is indeed continually going on2 but the effects produced are so exceedingly minute that it will take many millions of years to make the rotation appreciably slower1 and so to lengthen the day4 ,recently it has been proved that the axis of the earth is subject to a very small displacement1 or rather1 wobbling1 in the course of a period of somewhat over a year4 ,as a consequence of this1 the pole shifts its place through a circle of1 roughly1 a few yards in width during the time in question4 ,this movement is1 perhaps1 the combined result of two causes4 ,one of these is the change of place during the year of large masses of material upon our earth2 such as occurs1 for instance1 when ice and snow melt1 or when atmospheric and ocean currents transport from place to place great bodies of air and water4 ,the other cause is supposed to be the fact that the earth is not absolutely rigid1 and so yields to certain strains upon it4 ,in the course of investigation of this latter point the interesting conclusion has been reached by the famous ,american astronomer1 ,professor ,simon ,newcomb1 that our globe as a whole is a little more rigid than steel4 ,we will bring this chapter to a close by alluding briefly to two strange appearances which are sometimes seen in our night skies4 ,these are known respectively as the ,zodiacal ,light and the ,gegenschein4 ,the ,zodiacal ,light is a faint cone-shaped illumination which is seen to extend upwards from the western horizon after evening twilight has ended1 and from the eastern horizon before morning twilight has begun4 ,it appears to rise into the sky from about the position where the sun would be at that time4 ,the proper season of the year for observing it during the evening is in the spring1 while in autumn it is best seen in the early morning4 ,in our latitudes its light is not strong enough to render it visible when the moon is full1 but in the tropics it is reported to be very bright1 and easily seen in full moonlight4 ,one theory regards it as the reflection of light from swarms of meteors revolving round the sun2 another supposes it to be a very rarefied extension of the corona4 ,the ,gegenschein 7,german for counter-glow7 is a faint oval patch of light1 seen in the sky exactly opposite to the place of the sun4 ,it is usually treated of in connection with the zodiacal light1 and one theory regards it similarly as of meteoric origin4 ,another theory1 however--that of ,mr4 ,evershed--considers it a sort of tail to the earth 7like a comet's tail7 composed of hydrogen and helium--the two lightest gases we know--driven off from our planet in the direction contrary to the sun4 #ac ,every one knows the simple experiment in which a coin lying at the bottom of an empty basin1 and hidden from the eye by its side1 becomes visible when a certain quantity of water has been poured in4 ,this is an example of refraction4 ,the rays of light coming from the coin ought not to reach the eye1 on account of the basin's side being in the way2 yet by the action of the water they are refracted1 or bent over its edge1 in such a manner that they do4 ,,chapter ,,xvi ,,the ,,moon ,what we call the moon's phases are merely the various ways in which we see the sun shining upon her surface during the course of her monthly revolutions around the earth 7see ,fig4 #ad1 p4 #ahd74 ,when she passes in the neighbourhood of the sun all his light falls upon that side which is turned away from us1 and so the side which is turned towards us is unillumined1 and therefore invisible4 ,when in this position the moon is spoken of as new4 ,as she continues her motion around the earth1 she draws gradually to the east of the sun's place in the sky4 ,the sunlight then comes somewhat from the side2 and so we see a small portion of the right side of the lunar disc illuminated4 ,this is the phase known as the crescent moon4 ,as she moves on in her orbit more and more of her illuminated surface is brought into view2 and so the crescent of light becomes broader and broader1 until we get what is called half-moon1 or first quarter1 when we see exactly one-half of her surface lit up by the sun's rays4 ,as she draws still further round yet more of her illuminated surface is brought into view1 until three-quarters of the disc appear lighted up4 ,she is then said to be gibbous4 ,eventually she moves round so that she faces the sun completely1 and the whole of her disc appears illuminated4 ,she is then spoken of as full4 ,when in this position it is clear that she is on the contrary side of the earth to the sun1 and therefore rises about the same time that he is setting4 ,she is now1 in fact1 at her furthest from the sun4 ,illustration3 ,direction from which the sun's rays are coming4 ,various positions and illumination of the mooon by the sun during her revolution around the earth4 ,the corresponding positions as viewed from the earth1 showing the consequent phases4 ,,fig4 #ad4--,orbit and ,phases of the ,moon4 ,after this1 the motion of the moon in her orbit carries her on back again in the direction of the sun4 ,she thus goes through her phases as before1 only these of course are in the reverse order4 ,the full phase is seen to give place to the gibbous1 and this in turn to the half-moon and to the crescent2 after which her motion carries her into the neighbourhood of the sun1 and she is once more new1 and lost to our sight in the solar glare4 ,following this she draws away to the east of the sun again1 and the old order of phases repeat themselves as before4 ,the early ,babylonians imagined that the moon had a bright and a dark side1 and that her phases were caused by the bright side coming more and more into view during her movement around the sky4 ,the ,greeks1 notably ,aristotle1 set to work to examine the question from a mathematical standpoint1 and came to the conclusion that the crescent and other appearances were such as would necessarily result if the moon were a dark body of spherical shape illumined merely by the light of the sun4 ,although the true explanation of the moon's phases has thus been known for centuries1 it is unfortunately not unusual to see pictures--advertisement posters1 for instance--in which stars appear within the horns of a crescent moon6 ,can it be that there are to-day educated persons who believe that the moon is a thing which grows to a certain size and then wastes away again2 who1 in fact1 do not know that the entire body of the moon is there all the while8 ,when the moon shows a very thin crescent1 we are able dimly to see her still dark portion standing out against the sky4 ,this appearance is popularly known as the old moon in the new moon's arms4 ,the dark part of her surface must1 indeed1 be to some degree illumined1 or we should not be able to see it at all4 ,whence then comes the light which illumines it1 since it clearly cannot come from the sun8 ,the riddle is easily solved1 if we consider what kind of view of our earth an observer situated on this darkened part of the moon would at that moment get4 ,he would1 as a matter of fact1 just then see nearly the whole disc of the earth brightly lit up by sunlight4 ,the lunar landscape all around would1 therefore1 be bathed in what to him would be earthlight1 which of course takes the place there of what we call moonlight4 ,if1 then1 we recollect how much greater in size the earth is than the moon1 it should not surprise us that this earthlight will be many times brighter than moonlight4 ,it is considered1 indeed1 to be some twenty times brighter4 ,it is thus not at all astonishing that we can see the dark portion of the moon illumined merely by sunlight reflected upon it from our earth4 ,the ancients were greatly exercised in their minds to account for this earthlight1 or earthshine1 as it is also called4 ,posidonius 7#ace-ea ,b4,c47 tried to explain it by supposing that the moon was partially transparent1 and that some sunlight consequently filtered through from the other side4 ,it was not1 however1 until the fifteenth century that the correct solution was arrived at4 ,illustration3 ,one side of the moon only is ever presented to the earth4 ,this side is here indicated by the letters ,s4,f4,e4 7side facing earth74 ,by placing the above positions in a row1 we can see at once that the moon makes one complete rotation on her axis in exactly the same time as she revolves around the earth4 ,,fig4 #ae4--,the ,rotation of the ,moon on her ,axis4 ,perhaps the most remarkable thing which one notices about the moon is that she always turns the same side towards us1 and so we never see her other side4 ,one might be led from this to jump to the conclusion that she does not rotate upon an axis1 as do the other bodies which we see2 but1 paradoxical as it may appear1 the fact that she turns one face always towards the earth1 is actually a proof that she does rotate upon an axis4 ,the rotation1 however1 takes place with such slowness1 that she turns round but once during the time in which she revolves around the earth 7see ,fig4 #ae74 ,in order to understand the matter clearly1 let the reader place an object in the centre of a room and walk around it once1 keeping his face turned towards it the whole time1 ,while he is doing this1 it is evident that he will face every one of the four walls of the room in succession4 ,now in order to face each of the four walls of a room in succession one would be obliged to turn oneself entirely round4 ,therefore1 during the act of walking round an object with his face turned directly towards it1 a person at the same time turns his body once entirely round4 ,in the long1 long past the moon must have turned round much faster than this4 ,her rate of rotation has no doubt been slowed down by the action of some force4 ,it will be recollected how1 in the course of the previous chapter1 we found that the tides were tending1 though exceedingly gradually1 to slow down the rotation of the earth upon its axis4 ,but1 on account of the earth's much greater mass1 the force of gravitation exercised by it upon the surface of the moon is1 of course1 much more powerful than that which the moon exercises upon the surface of the earth4 ,the tendency to tidal action on the moon itself must1 therefore1 be much in excess of anything which we here experience4 ,it is1 in consequence1 probable that such a tidal drag1 extending over a very long period of time1 has resulted in slowing down the moon's rotation to its present rate4 ,the fact that we never see but one side of the moon has given rise from time to time to fantastic speculations with regard to the other side4 ,some1 indeed1 have wished to imagine that our satellite is shaped like an egg1 the more pointed end being directed away from us4 ,we are here1 of course1 faced with a riddle1 which is all the more tantalising from its appearing for ever insoluble to men1 chained as they are to the earth4 ,however1 it seems going too far to suppose that any abnormal conditions necessarily exist at the other side of the moon4 ,as a matter of fact1 indeed1 small portions of that side are brought into our view from time to time in consequence of slight irregularities in the moon's movement2 and these portions differ in no way from those which we ordinarily see4 ,on the whole1 we obtain a view of about #fj per cent4 of the entire lunar surface2 that is to say1 a good deal more than one-half4 ,the actual diameter of the moon is about #bafc miles1 which is somewhat more than one-quarter the diameter of the earth4 ,for a satellite1 therefore1 she seems very large compared with her primary1 the earth2 when we consider that ,jupiter's greatest satellite1 although nearly twice as broad as our moon1 has a diameter only one twenty-fifth that of ,jupiter4 ,furthermore1 the moon moves around the earth comparatively slowly1 making only about thirteen revolutions during the entire year4 ,seen from space1 therefore1 she would not give the impression of a circling body1 as other satellites do4 ,her revolutions are1 indeed1 relatively so very slow that she would appear rather like a smaller planet accompanying the earth in its orbit4 ,in view of all this1 some astronomers are inclined to regard the earth and moon rather as a double planet than as a system of planet and satellite4 ,when the moon is full she attracts more attention perhaps than in any of her other phases4 ,the moon1 in order to be full1 must needs be in that region of the heavens exactly opposite to the sun4 ,the sun appears to go once entirely round the sky in the course of a year1 and the moon performs the same journey in the space of about a month4 ,the moon1 when full1 having got half-way round this journey1 occupies1 therefore1 that region of the sky which the sun itself will occupy half a year later4 ,thus in winter the full moon will be found roughly to occupy the sun's summer position in the sky1 and in summer the sun's winter position4 ,it therefore follows that the full moon in winter time is high up in the heavens1 while in summer time it is low down4 ,we thus get the greatest amount of full moonlight when it is the most needed4 ,the great ,french astronomer1 ,laplace1 being struck by the fact that the lesser light did not rule the night to anything like the same extent that the greater light ruled the day1 set to work to examine the conditions under which it might have been made to do so4 ,the result of his speculations showed that if the moon were removed to such a distance that she took a year instead of a month to revolve around the earth2 and if she were started off in her orbit at full moon1 she would always continue to remain full--a great advantage for us4 ,whewell1 however1 pointed out that in order to get the moon to move with the requisite degree of slowness1 she would have to revolve so far from the earth that she would only look one-sixteenth as large as she does at present1 which rather militates against the advantage ,laplace had in mind6 ,finally1 however1 it was shown by ,m4 ,liouville1 in #ahde1 that the position of a perennial full moon1 such as ,laplace dreamed of1 would be unstable--that is to say1 the body in question could not for long remain undisturbed in the situation suggested 7see ,fig4 #af1 p4 #aia74 ,illustration3 ,various positions of ,laplace's ,moon with regard to the earth and sun during the course of a year4 ,the same positions of ,laplace's ,moon1 arranged around the earth1 show that it would make only one revolution in a year4 ,,fig4 #af4--,laplace's ,perennial ,full ,moon4 ,there is a well-known phenomenon called harvest moon1 concerning the nature of which there seems to be much popular confusion4 ,an idea in fact appears to prevail among a good many people that the moon is a harvest moon when1 at rising1 it looks bigger and redder than usual4 ,such an appearance has1 however1 nothing at all to say to the matter2 for the moon always looks larger when low down in the sky1 and1 furthermore1 it usually looks red in the later months of the year1 when there is more mist and fog about than there is in summer4 ,what astronomers actually term the harvest moon is1 indeed1 something entirely different from this4 ,about the month of ,september the slant at which the full moon comes up from below the horizon happens to be such that1 during several evenings together1 she rises almost at the same hour1 instead of some fifty minutes later1 as is usually the case4 ,as the harvest is being gathered in about that time1 it has come to be popularly considered that this is a provision of nature1 according to which the sunlight is1 during several evenings1 replaced without delay by more or less full-moonlight1 in order that harvesters may continue their work straight on into the night1 and not be obliged to break off after sunset to wait until the moon rises4 ,the same phenomenon is almost exactly repeated a month later1 but by reason of the pursuits then carried on it is known as the hunter's moon4 ,in this connection should be mentioned that curious phenomenon above alluded to1 and which seems to attract universal notice1 namely1 that the moon looks much larger when near the horizon--at its rising1 for instance1 than when higher up in the sky4 ,this seeming enlargement is1 however1 by no means confined to the moon4 ,that the sun also looks much larger when low down in the sky than when high up1 seems to strike even the most casual watcher of a sunset4 ,the same kind of effect will1 indeed1 be noted if close attention be paid to the stars themselves4 ,a constellation1 for instance1 appears more spread out when low down in the sky than when high up4 ,this enlargement of celestial objects when in the neighbourhood of the horizon is1 however1 only apparent and not real4 ,it must be entirely an illusion2 for the most careful measurements of the discs of the sun and of the moon fail to show that the bodies are any larger when near the horizon than when high up in the sky4 ,in fact1 if there be any difference in measurements with regard to the moon1 it will be found to be the other way round2 for her disc1 when carefully measured1 is actually the slightest degree greater when high in the sky1 than when low down4 ,the reason for this is that1 on account of the rotundity of the earth's surface1 she is a trifle nearer the observer when overhead of him4 ,this apparent enlargement of celestial objects1 when low down in the sky1 is granted on all sides to be an illusion2 but although the question has been discussed with animation time out of mind1 none of the explanations proposed can be said to have received unreserved acceptance4 ,the one which usually figures in text-books is that we unconsciously compare the sun and moon1 when low down in the sky1 with the terrestrial objects in the same field of view1 and are therefore inclined to exaggerate the size of these orbs4 ,some persons1 on the other hand1 imagine the illusion to have its source in the structure of the human eye2 while others1 again1 put it down to the atmosphere1 maintaining that the celestial objects in question loom large in the thickened air near the horizon1 in the same way that they do when viewed through fog or mist4 ,the writer#ad ventures1 however1 to think that the illusion has its origin in our notion of the shape of the celestial vault4 ,one would be inclined1 indeed1 to suppose that this vault ought to appear to us as the half of a hollow sphere2 but he maintains that it does not so appear1 as a consequence of the manner in which the eyes of men are set quite close together in their heads4 ,if one looks1 for instance1 high up in the sky1 the horizon cannot come within the field of view1 and so there is nothing to make one think that the expanse then gazed upon is other than quite flat--let us say like the ceiling of a room4 ,but1 as the eyes are lowered1 a portion of the encircling horizon comes gradually into the field of view1 and the region of the sky then gazed upon tends in consequence to assume a hollowed-out form4 ,from this it would seem that our idea of the shape of the celestial vault is1 that it is flattened down over our heads and hollowed out all around in the neighbourhood of the horizon 7see ,fig4 #ag1 p4 #aie74 ,now1 as a consequence of their very great distance1 all the objects in the heavens necessarily appear to us to move as if they were placed on the background of the vault2 the result being that the mind is obliged to conceive them as expanded or contracted1 in its unconscious attempts to make them always fill their due proportion of space in the various parts of this abnormally shaped sky4 ,from such considerations the writer concludes that the apparent enlargement in question is merely the natural consequence of the idea we have of the shape of the celestial vault--an idea gradually built up in childhood1 to become later on what is called second nature4 ,and in support of this contention1 he would point to the fact that the enlargement is not by any means confined to the sun and moon1 but is every whit as marked in the case of the constellations4 ,to one who has not noticed this before1 it is really quite a revelation to compare the appearance of one of the large constellations 7,orion1 for instance7 when high up in the sky and when low down4 ,the widening apart of the various stars composing the group1 when in the latter position1 is very noticeable indeed4 ,illustration3 ,,fig4 #ag4--;,illustrating the author's explanation of the apparent enlargement of celestial objects4 ,further1 if a person were to stand in the centre of a large dome1 he would be exactly situated as if he were beneath the vaulted heaven1 and one would consequently expect him to suffer the same illusion as to the shape of the dome4 ,objects fixed upon its background would therefore appear to him under the same conditions as objects in the sky1 and the illusions as to their apparent enlargement should hold good here also4 ,some years ago a ,belgian astronomer1 ,m4 ,stroobant1 in an investigation of the matter at issue1 chanced to make a series of experiments under the very conditions just detailed4 ,to various portions of the inner surface of a large dome he attached pairs of electric lights2 and on placing himself at the centre of the building1 he noticed that1 in every case1 those pairs which were high up appeared closer together than those which were low down6 ,he does not1 however1 seem to have sought for the cause in the vaulted expanse4 ,on the contrary1 he attributed the effect to something connected with our upright stature1 to some physiological reason which regularly makes us estimate objects as larger when in front than when overhead4 ,in connection with this matter1 it may be noted that it always appears extremely difficult to estimate with the eye the exact height above the horizon at which any object 7say a star7 happens to be4 ,even skilled observers find themselves in error in attempting to do so4 ,this seems to bear out the writer's contention that the form under which the celestial vault really appears to us is a peculiar one1 and tends to give rise to false judgments4 ,before leaving this question1 it should also be mentioned that nothing perhaps is more deceptive than the size which objects in the sky appear to present4 ,the full moon looks so like a huge plate1 that it astonishes one to find that a threepenny bit held at arm's length will a long way more than cover its disc4 ,illustration3 ,,plate ,,viii4 ,,the ,,moon ,from a photograph taken at the ,paris ,observatory by ,m4,p4 ,puiseux4 7,page #aig7 ,the moon is just too far off to allow us to see the actual detail on her surface with the naked eye4 ,when thus viewed she merely displays a patchy appearance1#ae and the imaginary forms which her darker markings suggest to the fancy are popularly expressed by the term ,man in the ,moon4 ,an examination of her surface with very moderate optical aid is1 however1 quite a revelation1 and the view we then get is not easily comparable to what we see with the unaided eye4 ,even with an ordinary opera-glass1 an observer will be able to note a good deal of detail upon the lunar disc4 ,if it be his first observation of the kind1 he cannot fail to be struck by the fact to which we have just made allusion1 namely1 the great change which the moon appears to undergo when viewed with magnifying power4 ,cain and his ,dog1 the ,man in the ,moon gathering sticks1 or whatever indeed his fancy was wont to conjure up from the lights and shades upon the shining surface1 have now completely disappeared2 and he sees instead a silvery globe marked here and there with extensive dark areas1 and pitted all over with crater-like formations 7see ,plate ,,viii41 p4 #aif74 ,the dark areas retain even to the present day their ancient name of seas1 for ,galileo and the early telescopic observers believed them to be such1 and they are still catalogued under the mystic appellations given to them in the long ago2 as1 for instance1 ,sea of ,showers1 ,bay of ,rainbows1 ,lake of ,dreams4#af ,the improved telescopes of later times showed1 however1 that they were not really seas 7there is no water on the moon71 but merely areas of darker material4 ,the crater-like formations above alluded to are the lunar mountains4 ,a person examining the moon for the first time with telescopic aid1 will perhaps not at once grasp the fact that his view of lunar mountains must needs be what is called a bird's-eye one1 namely1 a view from above1 like that from a balloon and that he cannot1 of course1 expect to see them from the side1 as he does the mountains upon the earth4 ,but once he has realised this novel point of view1 he will no doubt marvel at the formations which lie scattered as it were at his feet4 ,the type of lunar mountain is indeed in striking contrast to the terrestrial type4 ,on our earth the range-formation is supreme2 on the moon the crater-formation is the rule1 and is so-called from analogy to our volcanoes4 ,a typical lunar crater may be described as a circular wall1 enclosing a central plain1 or floor1 which is often much depressed below the level of the surface outside4 ,these so-called craters1 or ring-mountains1 as they are also termed1 are often of gigantic proportions4 ,for instance1 the central plain of one of them1 known as ,ptolemus1#ag is about #aae miles across1 while that of ,plato is about #fj4 ,the walls of craters often rise to great heights2 which1 in proportion to the small size of the moon1 are very much in excess of our highest terrestrial elevations4 ,nevertheless1 a person posted at the centre of one of the larger craters might be surprised to find that he could not see the encompassing crater-walls1 which would in every direction be below his horizon4 ,this would arise not alone from the great breadth of the crater itself1 but also from the fact that the curving of the moon's surface is very sharp compared with that of our earth4 ,illustration3 ,,plate ,,ix4 ,,map ,,of ,,the ,,moon1 ,,showing ,,the ,,principal ,,craters1 ,,mountain ,,ranges1 ,,and ,,seas ,in this1 as in the other plates of the ,moon1 the ,south will be found at the top of the picture2 such being the view given by the ordinary astronomical telescope1 in which all objects are seen inverted4 7,page #aii7 ,we have mentioned ,ptolemus as among the very large craters1 or ring-mountains1 on the moon4 ,its encompassing walls rise to nearly #ac1jjj feet1 and it has the further distinction of being almost in the centre of the lunar disc4 ,there are1 however1 several others much wider1 but they are by no means in such a conspicuous position4 ,for instance1 ,schickard1 close to the south-eastern border1 is nearly #acj miles in diameter1 and its wall rises in one point to over #aj1jjj feet4 ,grimaldi1 almost exactly at the east point1 is nearly as large as ,schickard4 ,another crater1 ,clavius1 situated near the south point1 is about #adj miles across2 while its neighbour ,bailly--named after a famous ,french astronomer of the eighteenth century--is #ahj1 and the largest of those which we can see 7see ,plate ,,ix41 p4 #aih74 ,many of the lunar craters encroach upon one another2 in fact there is not really room for them all upon the visible hemisphere of the moon4 ,about #cj1jjj have been mapped2 but this is only a small portion1 for according to the ,american astronomer1 ,professor ,w4,h4 ,pickering1 there are more than #bjj1jjj in all4 ,notwithstanding the fact that the crater is the type of mountain associated in the mind with the moon1 it must not be imagined that upon our satellite there are no mountains at all of the terrestrial type4 ,there are indeed many isolated peaks1 but strangely enough they are nearly always to be found in the centres of craters4 ,some of these peaks are of great altitude1 that in the centre of the crater ,copernicus being over #aa1jjj feet high4 ,a few mountain ranges also exist2 the best known of which are styled1 the ,lunar ,alps and ,lunar ,apennines 7see ,plate ,x41 p4 #bjj74 ,since the mass of the moon is only about one-eightieth that of the earth1 it will be understood that the force of gravity which she exercises is much less4 ,it is calculated that1 at her surface1 this is only about one-sixth of what we experience4 ,a man transported to the moon would thus be able to jump six times as high as he can here4 ,a building could therefore be six times as tall as upon our earth1 without causing any more strain upon its foundations4 ,it should not1 then1 be any subject for wonder1 that the highest peaks in the ,lunar ,apennines attain to such heights as #bb1jjj feet4 ,such a height1 upon a comparatively small body like the moon1 for her volume is only one-fiftieth that of the earth1 is relatively very much in excess of the #bi1jjj feet of ,himalayan structure1 ,mount ,everest1 the boast of our planet1 #hjjj miles across6 ,high as are the ,lunar ,apennines1 the highest peaks on the moon are yet not found among them4 ,there is1 for instance1 on the extreme southern edge of the lunar disc1 a range known as the ,leibnitz ,mountains2 several peaks of which rise to a height of nearly #cj1jjj feet1 one peak in particular being said to attain to #cf1jjj feet 7see ,plate ,,ix41 p4 #aih74 ,illustration3 ,,plate ,x4 ,,one ,,of ,,the ,,most ,,interesting ,,regions ,,on ,,the ,,moon ,we have here 7see ,map1 ,plate ,,ix41 p4 #aih7 the mountain ranges of the ,apennines1 the ,caucasus and the ,alps2 also the craters ,plato1 ,aristotle1 ,eudoxus1 ,cassini1 ,aristillus1 ,autolycus1 ,archimedes and ,linn4 ,the crater ,linn is the very bright spot in the dark area at the upper left hand side of the picture4 ,from a photograph taken at the ,paris ,observatory by ,m4,m4 ,loewy and ,puiseux4 7,page #bjj7 ,but the reader will surely ask the question3 ,how is it possible to determine the actual height of a lunar mountain1 if one cannot go upon the moon to measure it8 ,the answer is1 that we can calculate its height from noting the length of the shadow which it casts4 ,any one will allow that the length of a shadow cast by the sun depends upon two things3 firstly1 upon the height of the object which causes the shadow1 and secondly1 upon the elevation of the sun at the moment in the sky4 ,the most casual observer of nature upon our earth can scarcely have failed to notice that shadows are shortest at noonday1 when the sun is at its highest in the sky2 and that they lengthen out as the sun declines towards its setting4 ,here1 then1 we have the clue4 ,to ascertain1 therefore1 the height of a lunar mountain1 we have first to consider at what elevation the sun is at that moment above the horizon of the place where the mountain in question is situated4 ,then1 having measured the actual length in miles of the shadow extended before us1 all that is left is to ask ourselves the question3 ,what height must an object be whose shadow cast by the sun1 when at that elevation in the sky1 will extend to this length8 ,there is no trace whatever of water upon the moon4 ,the opinion1 indeed1 which seems generally held1 is that water has never existed upon its surface4 ,erosions1 sedimentary deposits1 and all those marks which point to a former occupation by water are notably absent4 ,similarly there appears to be no atmosphere on the moon2 or1 at any rate1 such an excessively rare one1 as to be quite inappreciable4 ,of this there are several proofs4 ,for instance1 in a solar eclipse the moon's disc always stands out quite clear-cut against that of the sun4 ,again during occultations1 stars disappear behind the moon with a suddenness1 which could not be the case were there any appreciable atmosphere4 ,lastly1 we see no traces of twilight upon the lunar surface1 nor any softening at the edges of shadows2 both which effects would be apparent if there were an atmosphere4 ,the moon's surface is rough and rocky1 and displays no marks of the weathering that would necessarily follow1 had it possessed anything of an atmosphere in the past4 ,this makes us rather inclined to doubt that it ever had one at all4 ,supposing1 however1 that it did possess an atmosphere in the past1 it is interesting to inquire what may have become of it4 ,in the first place it might have gradually disappeared1 in consequence of the gases which composed it uniting chemically with the materials of which the lunar body is constructed2 or1 again1 its constituent gases may have escaped into space1 in accordance with the principles of that kinetic theory of which we have already spoken4 ,the latter solution seems1 indeed1 the most reasonable of the two1 for the force of gravity at the lunar surface appears too weak to hold down any known gases4 ,this argument seems also to dispose of the question of absence of water2 for ,dr4 ,george ,johnstone ,stoney1 in a careful investigation of the subject1 has shown that the liquid in question1 when in the form of vapour1 will escape from a planet if its mass is less than one-fourth that of our earth4 ,and the mass of the moon is very much less than this2 indeed only the one-eightieth1 as we have already stated4 ,in consequence of this lack of atmosphere1 the condition of things upon the moon will be in marked contrast to what we experience upon the earth4 ,the atmosphere here performs a double service in shielding us from the direct rays of the sun1 and in bottling the heat as a glass-house does4 ,on the moon1 however1 the sun beats down in the day-time with a merciless force2 but its rays are reflected away from the surface as quickly as they are received1 and so the cold of the lunar night is excessive4 ,it has been calculated that the day temperature on the moon may1 indeed1 be as high as our boiling-point1 while the night temperature may be more than twice as low as the greatest cold known in our arctic regions4 ,that a certain amount of solar heat is reflected to us from the moon is shown by the sharp drop in temperature which certain heat-measuring instruments record when the moon becomes obscured in a lunar eclipse4 ,the solar heat which is thus reflected to us by the moon is1 however1 on the whole extremely small2 more light and heat1 indeed1 reach us direct from the sun in half a minute than we get by reflection from the moon during the entire course of the year4 ,with regard to the origin of the lunar craters there has been much discussion4 ,some have considered them to be evidence of violent volcanic action in the dim past2 others1 again1 as the result of the impact of meteorites upon the lunar surface1 when the moon was still in a plastic condition2 while a third theory holds that they were formed by the bursting of huge bubbles during the escape into space of gases from the interior4 ,the question is1 indeed1 a very difficult one4 ,though volcanic action1 such as would result in craters of the size of ,ptolemus1 is hard for us to picture1 and though the lone peaks which adorn the centres of many craters have nothing reminiscent of them in our terrestrial volcanoes1 nevertheless the volcanic theory seems to receive more favour than the others4 ,in addition to the craters there are two more features which demand notice1 namely1 what are known as rays and rills4 ,the rays are long1 light-coloured streaks which radiate from several of the large craters1 and extend to a distance of some hundreds of miles4 ,that they are mere markings on the surface is proved by the fact that they cast no shadows of any kind4 ,one theory is1 that they were originally great cracks which have been filled with lighter coloured material1 welling up from beneath4 ,the rills1 on the other hand1 are actually fissures1 about a mile or so in width and about a quarter of a mile in depth4 ,the rays are seen to the best advantage in connection with the craters ,tycho and ,copernicus 7see ,plate ,,xi41 p4 #bjd74 ,in consequence of its fairly forward position on the lunar disc1 and of the remarkable system of rays which issue from it like spokes from the axle of a wheel1 ,tycho commands especial attention4 ,the late ,rev4 ,t4,w4 ,webb1 a famous observer1 christened it1 very happily1 the metropolitan crater of the moon4 ,illustration3 ,,plate ,,xi4 ,,the ,,moon ,the systems of rays from the craters ,tycho1 ,copernicus and ,kepler are well shown here4 ,from a photograph taken at the ,paris ,observatory by ,m4,p4 ,puiseux4 7,page #bjd7 ,a great deal of attention is1 and has been1 paid by certain astronomers to the moon1 in the hope of finding out if any changes are actually in progress at present upon her surface4 ,sir ,william ,herschel1 indeed1 once thought that he saw a lunar volcano in eruption1 but this proved to be merely the effect of the sunlight striking the top of the crater ,aristarchus1 while the region around it was still in shadow--sunrise upon ,aristarchus1 in fact6 ,no change of any real importance has1 however1 been noted1 although it is suspected that some minor alterations have from time to time taken place4 ,for instance1 slight variations of tint have been noticed in certain areas of the lunar surface4 ,professor ,w4,h4 ,pickering puts forward the conjecture that these may be caused by the growth and decay of some low form of vegetation1 brought into existence by vapours of water1 or carbonic acid gas1 making their way out from the interior through cracks near at hand4 ,again1 during the last hundred years one small crater known as ,linn 7,linnus71 situated in the ,mare ,serenitatis 7,sea of ,serenity71 has appeared to undergo slight changes1 and is even said to have been invisible for a while 7see ,plate ,x41 p4 #bjj74 ,it is1 however1 believed that the changes in question may be due to the varying angles at which the sunlight falls upon the crater2 for it is an understood fact that the irregularities of the moon's motion give us views of her surface which always differ slightly4 ,the suggestion has more than once been put forward that the surface of the moon is covered with a thick layer of ice4 ,this is generally considered improbable1 and consequently the idea has received very little support4 ,it first originated with the late ,mr4 ,s4,e4 ,peal1 an ,english observer of the moon1 and has recently been resuscitated by the ,german observer1 ,herr ,fauth4 ,the most unfavourable time for telescopic study of the moon is when she is full4 ,the sunlight is then falling directly upon her visible hemisphere1 and so the mountains cast no shadows4 ,we thus do not get that impression of hill and hollow which is so very noticeable in the other phases4 ,the first map of the moon was constructed by ,galileo4 ,tobias ,mayer published another in #agge2 while during the nineteenth century greatly improved ones were made by ,beer and ,mdler1 ,schmidt1 ,neison and others4 ,in #aijc1 ,professor ,w4,h4 ,pickering brought out a complete photographic lunar atlas2 and a similar publication has recently appeared1 the work of ,,mm4 ,loewy and ,puiseux of the ,observatory of ,paris4 ,the so-called seas of the moon are1 as we have seen1 merely dark areas1 and there appears to be no proof that they were ever occupied by any liquid4 ,they are for the most part found in the northern portion of the moon2 a striking contrast to our seas and oceans1 which take up so much of the southern hemisphere of the earth4 ,there are many erroneous ideas popularly held with regard to certain influences which the moon is supposed to exercise upon the earth4 ,for instance1 a change in the weather is widely believed to depend upon a change in the moon4 ,but the word change as here used is meaningless1 for the moon is continually changing her phase during the whole of her monthly round4 ,besides1 the moon is visible over a great portion of the earth at the same moment1 and certainly all the places from which it can then be seen do not get the same weather6 ,further1 careful observations1 and records extending over the past one hundred years and more1 fail to show any reliable connection between the phases of the moon and the condition of the weather4 ,it has been stated1 on very good authority1 that no telescope ever shows the surface of the moon as clearly as we could see it with the naked eye were it only #bdj miles distant from us4 ,supposing1 then1 that we were able to approach our satellite1 and view it without optical aid at such comparatively close quarters1 it is interesting to consider what would be the smallest detail which our eye could take in4 ,the question of the limit of what can be appreciated with the naked eye is somewhat uncertain1 but it appears safe to say that at a distance of #bdj miles the minutest speck visible would have to be at least some #fj yards across4 ,atmosphere and liquid both wanting1 the lunar surface must be the seat of an eternal calm2 where no sound breaks the stillness and where change1 as we know it1 does not exist4 ,the sun beats down upon the arid rocks1 and inky shadows lie athwart the valleys4 ,there is no mellowing of the harsh contrasts4 ,we cannot indeed absolutely affirm that ,life has no place at all upon this airless and waterless globe1 since we know not under what strange conditions it may manifest its presence2 and our most powerful telescopes1 besides1 do not bring the lunar surface sufficiently near to us to disprove the existence there of even such large creatures as disport themselves upon our planet4 ,still1 we find it hard to rid ourselves of the feeling that we are in the presence of a dead world4 ,on she swings around the earth month after month1 with one face ever turned towards us1 leaving a certain mystery to hang around that hidden side1 the greater part of which men can never hope to see4 ,the rotation of the moon upon her axis--the lunar day--has become1 as we have seen1 equal to her revolution around the earth4 ,an epoch may likewise eventually be reached in the history of our own planet1 when the length of the terrestrial day has been so slowed down by tidal friction that it will be equal to the year4 ,then will the earth revolve around the central orb1 with one side plunged in eternal night and the other in eternal sunshine4 ,but such a vista need not immediately distress us4 ,it is millions of years forward in time4 #ad ,journal of the ,british ,astronomical ,association1 vol4 x4 7#ahii-aijj71 ,nos4 #a and #c4 #ae ,certain of the ancient ,greeks thought the markings on the moon to be merely the reflection of the seas and lands of our earth1 as in a badly polished mirror4 #af ,mare ,imbrium1 ,sinus ,iridum1 ,lacus ,somniorum4 #ag ,the lunar craters have1 as a rule1 received their names from celebrated persons1 usually men of science4 ,this system of nomenclature was originated by ,riccioli1 in #afea4 ,,chapter ,,xvii ,,the ,,superior ,,planets ,having1 in a previous chapter1 noted the various aspects which an inferior planet presents to our view1 in consequence of its orbit being nearer to the sun than the orbit of the earth1 it will be well here to consider in the same way the case of a superior planet1 and to mark carefully the difference4 ,to begin with1 it should be quite evident that we cannot ever have a transit of a superior planet4 ,the orbit of such a body being entirely outside that of the earth1 the body itself can1 of course1 never pass between us and the sun4 ,a superior planet will be at its greatest distance from us when on the far side of the sun4 ,it is said then to be in conjunction4 ,as it comes round in its orbit it eventually passes1 so to speak1 at the back of us4 ,it is then at its nearest1 or in opposition1 as this is technically termed1 and therefore in the most favourable position for telescopic observation of its surface4 ,being1 besides1 seen by us at that time in the direction of the heavens exactly opposite to where the sun is1 it will thus at midnight be high up in the south side of the sky1 a further advantage to the observer4 ,last of all1 a superior planet cannot show crescent shapes like an interior2 for whether it be on the far side of the sun1 or behind us1 or again to our right or left1 the sunlight must needs appear to fall more or less full upon its face4 ,,the ,,planetoid ,,eros ,the nearest to us of the superior planets is the tiny body1 ,eros1 which1 as has been already stated1 was discovered so late as the year #ahih4 ,in point of view1 however1 of its small size1 it can hardly be considered as a true planet1 and the name planetoid seems much more appropriate to it4 ,eros was not discovered1 like ,uranus1 in the course of telescopic examination of the heavens1 nor yet1 like ,neptune1 as the direct result of difficult calculations1 but was revealed by the impress of its light upon a photographic plate1 which had been exposed for some length of time to the starry sky4 ,since many of the more recent additions to the asteroids have been discovered in the same manner1 we shall have somewhat more to say about this special employment of photography when we come to deal with those bodies later on4 ,the path of ,eros around the sun is so very elliptical1 or1 to use the exact technical term1 so very eccentric1 that the planetoid does not keep all the time entirely in the space between our orbit and that of ,mars1 which latter happens to be the next body in the order of planetary succession outwards4 ,in portions of its journey ,eros1 indeed1 actually goes outside the ,martian orbit4 ,the paths of the planetoid and of ,mars are1 however1 not upon the same plane1 so the bodies always pass clear of each other1 and there is thus as little chance of their dashing together as there would be of trains which run across a bridge at an upper level1 colliding with those which pass beneath it at a lower level4 ,when ,eros is in opposition1 it comes within about #ac-a_/b million miles of our earth1 and1 after the moon1 is therefore by a long way our nearest neighbour in space4 ,it is1 however1 extremely small1 not more1 perhaps1 than twenty miles in diameter1 and is subject to marked variations in brightness1 which do not appear up to the present to meet with a satisfactory explanation4 ,but1 insignificant as is this little body1 it is of great importance to astronomy2 for it happens to furnish the best method known of calculating the sun's distance from our earth--a method which ,galle1 in #ahgb1 and ,sir ,david ,gill1 in #ahgg1 suggested that asteroids might be employed for1 and which has in consequence supplanted the old one founded upon transits of ,venus4 ,the sun's distance is now an ascertained fact to within #ajj1jjj miles1 or less than half the distance of the moon4 ,,the ,,planet ,,mars ,we next come to the planet ,mars4 ,this body rotates in a period of slightly more than twenty-four hours4 ,the inclination1 or slant1 of its axis is about the same as that of the earth1 so that1 putting aside its greater distance from the sun1 the variations of season which it experiences ought to be very much like ours4 ,the first marking detected upon ,mars was the notable one called the ,syrtis ,major1 also known1 on account of its shape1 as the ,hour-,glass ,sea4 ,this observation was made by the famous ,huyghens in #afei2 and1 from the movement of the marking in question across the disc1 he inferred that the planet rotated on its axis in a period of about twenty-four hours4 ,there appears to be very little atmosphere upon ,mars1 the result being that we almost always obtain a clear view of the detail on its surface4 ,indeed1 it is only to be expected from the kinetic theory that ,mars could not retain much of an atmosphere1 as the force of gravity at its surface is less than one-half of what we experience upon the earth4 ,it should here be mentioned that recent researches with the spectroscope seem to show that1 whatever atmosphere there may be upon ,mars1 its density at the surface of the planet cannot be more than the one-fourth part of the density of the air at the surface of the earth4 ,professor ,lowell1 indeed1 thinks it may be more rarefied than that upon our highest mountain-tops4 ,seen with the naked eye1 ,mars appears of a red colour4 ,viewed in the telescope1 its surface is found to be in general of a ruddy hue1 varied here and there with darker patches of a bluish-green colour4 ,these markings are permanent1 and were supposed by the early telescopic observers to imply a distribution of the planet's surface into land and water1 the ruddy portions being considered as continental areas 7perhaps sandy deserts71 and the bluish-green as seas4 ,the similarity to our earth thus suggested was further heightened by the fact that broad white caps1 situated at the poles1 were seen to vary with the planet's seasons1 diminishing greatly in extent during the ,martian summer 7the southern cap in #ahid even disappearing altogether71 and developing again in the ,martian winter4#ah ,readers of ,oliver ,wendell ,holmes will no doubt recollect that poet's striking lines3-- ,the snows that glittered on the disc of ,mars ,have melted1 and the planet's fiery orb ,rolls in the crimson summer of its year4 ,a state of things so strongly analogous to what we experience here1 naturally fired the imaginations of men1 and caused them to look on ,mars as a world like ours1 only upon a much smaller scale4 ,being smaller1 it was concluded to have cooled quicker1 and to be now long past its prime2 and its inhabitants were1 therefore1 pictured as at a later stage of development than the inhabitants of our earth4 ,notwithstanding the strong temptation to assume that the whiteness of the ,martian polar caps is due to fallen snow1 such a solution is1 however1 by no means so simple as it looks4 ,the deposition of water in the form of snow1 or even of hoar frost1 would at least imply that the atmosphere of ,mars should now and then display traces of aqueous vapour1 which it does not appear to do4#ai ,it has1 indeed1 been suggested that the whiteness may not after all be due to this cause1 but to carbonic acid gas 7carbon dioxide71 which is known to freeze at a very low temperature4 ,the suggestion is plainly based upon the assumption that1 as ,mars is so much further from the sun than we are1 it would receive much less heat1 and that the little thus received would be quickly radiated away into space through lack of atmosphere to bottle it in4 ,we now come to those well-known markings1 popularly known as the canals of ,mars1 which have been the subject of so much discussion since their discovery thirty years ago4 ,it was1 in fact1 in the year #ahgg1 when ,mars was in opposition1 and thus at its nearest to us1 that the famous ,italian astronomer1 ,schiaparelli1 announced to the world that he had found that the ruddy areas1 thought to be continents1 were intersected by a network of straight dark lines4 ,these lines1 he reported1 appeared in many cases to be of great length1 so long1 indeed1 as several thousands of miles1 and from about twenty to sixty miles in width4 ,he christened the lines channels1 the ,italian word for which1 canali1 was unfortunately translated into ,english as canals4 ,the analogy1 thus accidentally suggested1 gave rise to the idea that they might be actual waterways4#bj ,in the winter of #ahha-ahhb1 when ,mars was again in opposition1 ,schiaparelli further announced that he had found some of these lines doubled2 that is to say1 certain of them were accompanied by similar lines running exactly parallel at no great distance away4 ,there was at first a good deal of scepticism on the subject of ,schiaparelli's discoveries1 but gradually other observers found themselves seeing both the lines and their doublings4 ,we have in this a good example of a curious circumstance in astronomical observation1 namely1 the fact that when fine detail has once been noted by a competent observer1 it is not long before other observers see the same detail with ease4 ,an immense amount of close attention has been paid to the planet ,mars during recent years by the ,american observer1 ,professor ,percival ,lowell1 at his famous observatory1 #gcjj feet above the sea1 near the town of ,flagstaff1 ,arizona1 ,u4,s4,a4 ,his observations have not1 like those of most astronomers1 been confined merely to oppositions1 but he has systematically kept the planet in view1 so far as possible1 since the year #ahid4 ,the instrumental equipment of his observatory is of the very best1 and the seeing at ,flagstaff is described as excellent4 ,in support of the latter statement1 ,mr4 ,lampland1 of the ,lowell ,observatory1 maintains that the faintest stars shown on charts made at the ,lick ,observatory with the #cf-;inch telescope there1 are perfectly visible with the #bd-;inch telescope at ,flagstaff4 ,professor ,lowell is1 indeed1 generally at issue with the other observers of ,mars4 ,he finds the canals extremely narrow and sharply defined1 and he attributes the blurred and hazy appearance1 which they have presented to other astronomers1 to the unsteady and imperfect atmospheric conditions in which their observations have been made4 ,he assigns to the thinnest a width of two or three miles1 and from fifteen to twenty to the larger4 ,relatively to their width1 however1 he finds their length enormous4 ,many of them are #bjjj miles long1 while one is even as much as #cedj4 ,such lengths as these are very great in comparison with the smallness of the planet4 ,he considers that the canals stand in some peculiar relation to the polar cap1 for they crowd together in its neighbourhood4 ,in place1 too1 of ill-defined condensations1 he sees sharp black spots where the canals meet and intersect1 and to these he gives the name of ,oases4 ,he further lays particular stress upon a dark band of a blue tint1 which is always seen closely to surround the edges of the polar caps all the time that they are disappearing2 and this he takes to be a proof that the white material is something which actually melts4 ,of all substances which we know1 water alone1 he affirms1 would act in such a manner4 ,the question of melting at all may seem strange in a planet which is situated so far from the sun1 and possesses such a rarefied atmosphere4 ,but ,professor ,lowell considers that this very thinness of the atmosphere allows the direct solar rays to fall with great intensity upon the planet's surface1 and that this heating effect is accentuated by the great length of the ,martian summer4 ,in consequence he concludes that1 although the general climate of ,mars is decidedly cold1 it is above the freezing point of water4 ,the observations at ,flagstaff appear to do away with the old idea that the darkish areas are seas1 for numerous lines belonging to the so-called canal system are seen to traverse them4 ,again1 there is no star-like image of the sun reflected from them1 as there would be1 of course1 from the surface of a great sheet of water4 ,lastly1 they are observed to vary in tone and colour with the changing ,martian seasons1 the blue-green changing into ochre1 and later on back again into blue-green4 ,professor ,lowell regards these areas as great tracts of vegetation1 which are brought into activity as the liquid reaches them from the melting snows4 ,illustration3 ,,plate ,,xii4 ,a ,,map ,,of ,,the ,,planet ,,mars ,we see here the ,syrtis ,major 7or ,hour-,glass ,sea71 the polar caps1 several oases1 and a large number of canals1 some of which are double4 ,the ,south is at the top of the picture1 in accordance with the inverted view given by an astronomical telescope4 ,from a drawing by ,professor ,percival ,lowell4 7,page #baf7 ,with respect to the canals1 the ,lowell observations further inform us that these are invisible during the ,martian winter1 but begin to appear in the spring when the polar cap is disappearing4 ,professor ,lowell1 therefore1 inclines to the view that in the middle of the so-called canals there exist actual waterways which serve the purposes of irrigation1 and that what we see is not the waterways themselves1 for they are too narrow1 but the fringe of vegetation which springs up along the banks as the liquid is borne through them from the melting of the polar snows4 ,he supports this by his observation that the canals begin to appear in the neighbourhood of the polar caps1 and gradually grow1 as it were1 in the direction of the planet's equator4 ,it is the idea of life on ,mars which has given this planet such a fascination in the eyes of men4 ,a great deal of nonsense has1 however1 been written in newspapers upon the subject1 and many persons have thus been led to think that we have obtained some actual evidence of the existence of living beings upon ,mars4 ,it must be clearly understood1 however1 that ,professor ,lowell's advocacy of the existence of life upon that planet is by no means of this wild order4 ,at the best he merely indulges in such theories as his remarkable observations naturally call forth4 ,his views are as follows3--,he considers that the planet has reached a time when water has become so scarce that the inhabitants are obliged to employ their utmost skill to make their scanty supply suffice for purposes of irrigation4 ,the changes of tone and colour upon the ,martian surface1 as the irrigation produces its effects1 are similar to what a telescopic observer--say1 upon ,venus--would notice on our earth when the harvest ripens over huge tracts of country2 that is1 of course1 if the earth's atmosphere allowed a clear view of the terrestrial surface--a very doubtful point indeed4 ,professor ,lowell thinks that the perfect straightness of the lines1 and the geometrical manner in which they are arranged1 are clear evidences of artificiality4 ,on a globe1 too1 there is plainly no reason why the liquid which results from the melting of the polar caps should trend at all in the direction of the equator4 ,upon our earth1 for instance1 the transference of water1 as in rivers1 merely follows the slope of the ground1 and nothing else4 ,the ,lowell observations show1 however1 that the ,martian liquid is apparently carried from one pole towards the equator1 and then past it to the other pole1 where it once more freezes1 only to melt again in due season1 and to reverse the process towards and across the equator as before4 ,professor ,lowell therefore holds1 and it seems a strong point in favour of his theory1 that the liquid must1 in some artificial manner1 as by pumping1 for instance1 be helped in its passage across the surface of the planet4 ,a number of attempts have been made to explain the doubling of the canals merely as effects of refraction or reflection2 and it has even been suggested that it may arise from the telescope not being accurately focussed4 ,the actual doubling of the canals once having been doubted1 it was an easy step to the casting of doubt on the reality of the canals themselves4 ,the idea1 indeed1 was put forward that the human eye1 in dealing with detail so very close to the limit of visibility1 may unconsciously treat as an actual line several point-like markings which merely happen to lie in a line4 ,in order to test this theory1 experiments were carried out in #aijb by ,mr4 ,e4,w4 ,maunder of ,greenwich ,observatory1 and ,mr4 ,j4,e4 ,evans of the ,royal ,hospital ,school at ,greenwich1 in which certain schoolboys were set to make drawings of a white disc with some faint markings upon it4 ,the boys were placed at various distances from the disc in question2 and it was found that the drawings made by those who were just too far off to see distinctly1 bore out the above theory in a remarkable manner4 ,recently1 however1 the plausibility of the illusion view has been shaken by photographs of ,mars taken during the opposition of #aije by ,mr4 ,lampland at the ,lowell ,observatory1 in which a number of the more prominent canals come out as straight dark lines4 ,further still1 in some photographs made there quite lately1 several canals are said to appear visibly double4 ,following up the idea alluded to in ,chapter ,,xvi41 that the moon may be covered with a layer of ice1 ,mr4 ,w4,t4 ,lynn has recently suggested that this may be the case on ,mars2 and that1 at certain seasons1 the water may break through along definite lines1 and even along lines parallel to these4 ,this1 he maintains1 would account for the canals becoming gradually visible across the disc1 without the necessity of ,professor ,lowell's pumping theory4 ,and now for the views of ,professor ,lowell himself with regard to the doubling of the canals4 ,from his observations1 he considers that no pairs of railway lines could apparently be laid down with greater parallelism4 ,he draws attention to the fact that the doubling does not take place by any means in every canal2 indeed1 out of #djj canals seen at ,flagstaff1 only fifty-one--or1 roughly1 one-eighth--have at any time been seen double4 ,he lays great stress upon this1 which he considers points strongly against the duplication being an optical phenomenon4 ,he finds that the distance separating pairs of canals is much less in some doubles than in others1 and varies on the whole from #ge to #bjj miles4 ,according to him1 the double canals appear to be confined to within #dj degrees of the equator3 or1 to quote his own words1 they are an equatorial feature of the planet1 confined to the tropic and temperate belts4 ,finally1 he points out that they seem to avoid the blue-green areas4 ,but1 strangely enough1 ,professor ,lowell does not so far attempt to fit in the doubling with his body of theory4 ,he makes the obvious remark that they may be channels and return channels1 and with that he leaves us4 ,the conclusions of ,professor ,lowell have recently been subjected to strenuous criticism by ,professor ,w4,h4 ,pickering and ,dr4 ,alfred ,russel ,wallace4 ,it was ,professor ,pickering who discovered the oases1 and who originated the idea that we did not see the so-called canals themselves1 but only the growth of vegetation along their borders4 ,he holds that the oases are craterlets1 and that the canals are cracks which radiate from them1 as do the rifts and streaks from craters upon the moon4 ,he goes on to suggest that vapours of water1 or of carbonic acid gas1 escaping from the interior1 find their way out through these cracks1 and promote the growth of a low form of vegetation on either side of them4 ,in support of this view he draws attention to the existence of long steam-cracks1 bordered by vegetation1 in the deserts of the highly volcanic island of ,hawaii4 ,we have already seen1 in an earlier chapter1 how he has applied this idea to the explanation of certain changes which are suspected to be taking place upon the moon4 ,in dealing with the ,lowell canal system1 ,professor ,pickering points out that under such a slight atmospheric pressure as exists on ,mars1 the evaporation of the polar caps--supposing them to be formed of snow--would take place with such extraordinary rapidity that the resulting water could never be made to travel along open channels1 but that a system of gigantic tubes or water-mains would have to be employed6 ,as will be gathered from his theories regarding vegetation1 ,professor ,pickering does not deny the existence of a form of life upon ,mars4 ,but he will not hear of civilisation1 or of anything even approaching it4 ,he thinks1 however1 that as ,mars is intermediate physically between the moon and earth1 the form of life which it supports may be higher than that on the moon and lower than that on the earth4 ,in a small book published in the latter part of #aijg1 and entitled ,is ,mars ,habitable8 ,dr4 ,alfred ,russel ,wallace sets himself1 among other things1 to combat the idea of a comparatively high temperature1 such as ,professor ,lowell has allotted to ,mars4 ,he shows the immense service which the water-vapour in our atmosphere exercises1 through keeping the solar heat from escaping from the earth's surface4 ,he then draws attention to the fact that there is no spectroscopic evidence of water-vapour on ,mars#ba2 and points out that its absence is only to be expected1 as ,dr4 ,george ,johnstone ,stoney has shown that it will escape from a body whose mass is less than one-quarter the mass of the earth4 ,the mass of ,mars is1 in fact1 much less than this1 i4e4 only one-ninth4 ,dr4 ,wallace considers1 therefore1 that the temperature of ,mars ought to be extremely low1 unless the constitution of its atmosphere is very different from ours4 ,with regard to the latter statement1 it should be mentioned that the ,swedish physicist1 ,arrhenius1 has recently shown that the carbonic acid gas in our atmosphere has an important influence upon climate4 ,the amount of it in our air is1 as we have seen1 extremely small2 but ,arrhenius shows that1 if it were doubled1 the temperature would be more uniform and much higher4 ,we thus see how futile it is1 with our present knowledge1 to dogmatise on the existence or non-existence of life in other celestial orbs4 ,as to the canals ,dr4 ,wallace puts forward a theory of his own4 ,he contends that after ,mars had cooled to a state of solidity1 a great swarm of meteorites and small asteroids fell in upon it1 with the result that a thin molten layer was formed all over the planet4 ,as this layer cooled1 the imprisoned gases escaped1 producing vents or craterlets2 and as it attempted to contract further upon the solid interior1 it split in fissures radiating from points of weakness1 such1 for instance1 as the craterlets4 ,and he goes on to suggest that the two tiny ,martian satellites1 with which we shall deal next1 are the last survivors of his hypothetical swarm4 ,finally1 with regard to the habitability of ,mars1 ,dr4 ,wallace not only denies it1 but asserts that the planet is absolutely uninhabitable4 ,for a long time it was supposed that ,mars did not possess any satellites4 ,in #ahgg1 however1 during that famous opposition in which ,schiaparelli first saw the canals1 two tiny satellites were discovered at the ,washington ,observatory by an ,american astronomer1 ,professor ,asaph ,hall4 ,these satellites are so minute1 and so near to the planet1 that they can only be seen with very large telescopes2 and even then the bright disc of the planet must be shielded off4 ,they have been christened ,phobos and ,deimos 7,fear and ,dread72 these being the names of the two subordinate deities who1 according to ,homer1 attended upon ,mars1 the god of war4 ,it is impossible to measure the exact sizes of these satellites1 as they are too small to show any discs1 but an estimate has been formed from their brightness4 ,the diameter of ,phobos was at first thought to be six miles1 and that of ,deimos1 seven4 ,as later estimates1 however1 considerably exceed this1 it will1 perhaps1 be not far from the truth to state that they are each roughly about the size of the planetoid ,eros4 ,phobos revolves around ,mars in about #g-a_/b hours1 at a distance of about only #djjj miles from the planet's surface1 and ,deimos in about #cj hours1 at a distance of about #ab1jjj miles4 ,as ,mars rotates on its axis in about #bd hours1 it will be seen that ,phobos makes more than three revolutions while the planet is rotating once--a very interesting condition of things4 ,a strange foreshadowing of the discovery of the satellites of ,mars will be familiar to readers of ,gulliver's ,travels4 ,according to ,dean ,swift's hero1 the astronomers on the ,flying ,island of ,laputa had found two tiny satellites to ,mars1 one of which revolved around the planet in ten hours4 ,the correctness of this guess is extraordinarily close1 though at best it is1 of course1 nothing more than a pure coincidence4 ,it need not be at all surprising that much uncertainty should exist with regard to the actual condition of the surface of ,mars4 ,the circumstances in which we are able to see that planet at the best are1 indeed1 hardly sufficient to warrant us in propounding any hard and fast theories4 ,one of the most experienced of living observers1 the ,american astronomer1 ,professor ,e4,e4 ,barnard1 considers that the view we get of ,mars with the best telescope may be fairly compared with our naked eye view of the moon4 ,since we have seen that a view with quite a small telescope entirely alters our original idea of the lunar surface1 a slight magnification revealing features of whose existence we had not previously the slightest conception1 it does not seem too much to say that a further improvement in optical power might entirely subvert the present notions with regard to the ,martian canals4 ,therefore1 until we get a still nearer view of these strange markings1 it seems somewhat futile to theorise4 ,the lines which we see are perhaps1 indeed1 a foreshortened and all too dim view of some type of formation entirely novel to us1 and possibly peculiar to ,mars4 ,differences of gravity and other conditions1 such as obtain upon different planets1 may perhaps produce very diverse results4 ,the earth1 the moon1 and ,mars differ greatly from one another in size1 gravitation1 and other such characteristics4 ,mountain-ranges so far appear typical of our globe1 and ring-mountains typical of the moon4 ,may not the so-called canals be merely some special formation peculiar to ,mars1 though quite a natural result of its particular conditions and of its past history8 ,,the ,,asteroids 7,,or ,,minor ,,planets7 ,we now come to that belt of small planets which are known by the name of asteroids4 ,in the general survey of the solar system given in ,chapter ,,ii41 we saw how it was long ago noticed that the distances of the planetary orbits from the sun would have presented a marked appearance of orderly sequence1 were it not for a gap between the orbits of ,mars and ,jupiter where no large planet was known to circulate4 ,the suspicion thus aroused that some planet might1 after all1 be moving in this seemingly empty space1 gave rise to the gradual discovery of a great number of small bodies2 the largest of which1 ,ceres1 is less than #ejj miles in diameter4 ,up to the present day some #fjj of these bodies have been discovered2 the four leading ones1 in order of size1 being named ,ceres1 ,pallas1 ,juno1 and ,vesta4 ,all the asteroids are invisible to the naked eye1 with the exception of ,vesta1 which1 though by no means the largest1 happens to be the brightest4 ,it is1 however1 only just visible to the eye under favourable conditions4 ,no trace of an atmosphere has been noted upon any of the asteroids1 but such a state of things is only to be expected from the kinetic theory4 ,for a good many years the discoveries of asteroids were made by means of the telescope4 ,when1 in the course of searching the heavens1 an object was noticed which did not appear upon any of the recognised star charts1 it was kept under observation for several nights to see whether it changed its place in the sky4 ,since asteroids move around the sun in orbits1 just as planets do1 they1 of course1 quickly reveal themselves by their change of position against the starry background4 ,the year #ahia started a new era in the discovery of asteroids4 ,it occurred to the ,heidelberg observer1 ,dr4 ,max ,wolf1 one of the most famous of the hunters of these tiny planets1 that photography might be employed in the quest with success4 ,this photographic method1 to which allusion has already been made in dealing with ,eros1 is an extremely simple one4 ,if a photograph of a portion of the heavens be taken through an equatorial--that is1 a telescope1 moving by machinery1 so as to keep the stars1 at which it is pointed1 always exactly in the field of view during their apparent movement across the sky--the images of these stars will naturally come out in the photograph as sharply defined points4 ,if1 however1 there happens to be an asteroid1 or other planetary body1 in the same field of view1 its image will come out as a short white streak2 because the body has a comparatively rapid motion of its own1 and will1 during the period of exposure1 have moved sufficiently against the background of the stars to leave a short trail1 instead of a dot1 upon the photographic plate4 ,by this method ,wolf himself has succeeded in discovering more than a hundred asteroids 7see ,plate ,,xiii41 p4 #bbf74 ,it was1 indeed1 a little streak of this kind1 appearing upon a photograph taken by the astronomer ,witt1 at ,berlin1 in #ahih1 which first informed the world of the existence of ,eros4 ,illustration3 ,,plate ,,xiii4 ,,minor ,,planet ,,trails ,two trails of minor planets 7asteroids7 imprinted at the same time upon one photographic plate4 ,in the white streak on the left-hand side of the picture we witness the discovery of a new minor planet4 ,the streak on the right was made by a body already known--the minor planet ,fiducia4 ,this photograph was taken by ,dr4 ,max ,wolf1 at ,heidelberg1 on the #dth of ,november1 #aija1 with the aid of a #af-;inch telescope4 ,the time of exposure was two hours4 7,page #bbg7 ,it has been calculated that the total mass of the asteroids must be much less than one-quarter that of the earth4 ,they circulate as a rule within a space of some #cj1jjj1jjj miles in breadth1 lying about midway between the paths of ,mars and ,jupiter4 ,two or three1 however1 of the most recently discovered of these small bodies have been found to pass quite close to ,jupiter4 ,the orbits of the asteroids are by no means in the one plane1 that of ,pallas being the most inclined to the plane of the earth's orbit4 ,it is actually three times as much inclined as that of ,eros4 ,two notable theories have been put forward to account for the origin of the asteroids4 ,the first is that of the celebrated ,german astronomer1 ,olbers1 who was the discoverer of ,pallas and ,vesta4 ,he suggested that they were the fragments of an exploded planet4 ,this theory was for a time generally accepted1 but has now been abandoned in consequence of certain definite objections4 ,the most important of these objections is that1 in accordance with the theory of gravitation1 the orbits of such fragments would all have to pass through the place where the explosion originally occurred4 ,but the wide area over which the asteroids are spread points rather against the notion that they all set out originally from one particular spot4 ,another objection is that it does not appear possible that1 within a planet already formed1 forces could originate sufficiently powerful to tear the body asunder4 ,the second theory is that for some reason a planet here failed in the making4 ,possibly the powerful gravitational action of the huge body of ,jupiter hard by1 disturbed this region so much that the matter distributed through it was never able to collect itself into a single mass4 #ah ,sir ,william ,herschel was the first to note these polar changes4 #ai ,quite recently1 however1 ,professor ,lowell has announced that his observer1 ,mr4 ,e4,c4 ,slipher1 finds with the spectroscope faint traces of water vapour in the ,martian atmosphere4 #bj ,in a somewhat similar manner the term crater1 as applied to the ring-mountain formation on the moon1 has evidently given a bias in favour of the volcanic theory as an explanation of that peculiar structure4 #ba ,mr4 ,slipher's results 7see note #b1 page #bac7 were not then known4 ,,chapter ,,xviii ,,the ,,superior ,,planets--continued ,the planets1 so far1 have been divided into inferior and superior4 ,such a division1 however1 refers merely to the situation of their orbits with regard to that of our earth4 ,there is1 indeed1 another manner in which they are often classed1 namely1 according to size4 ,on this principle they are divided into two groups2 one group called the ,terrestrial ,planets1 or those which have characteristics like our earth1 and the other called the ,major ,planets1 because they are all of very great size4 ,the terrestrial planets are ,mercury1 ,venus1 the earth1 and ,mars4 ,the major planets are the remainder1 namely1 ,jupiter1 ,saturn1 ,uranus1 and ,neptune4 ,as the earth's orbit is the boundary which separates the inferior from the superior planets1 so does the asteroidal belt divide the terrestrial from the major planets4 ,we found the division into inferior and superior useful for emphasising the marked difference in aspect which those two classes present as seen from our earth2 the inferior planets showing phases like the moon when viewed in the telescope1 whereas the superior planets do not4 ,but the division into terrestrial and major planets is the more far-reaching classification of the two1 for it includes the whole number of planets1 whereas the other arrangement necessarily excludes the earth4 ,the members of each of these classes have many definite characteristics in common4 ,the terrestrial planets are all of them relatively small in size1 comparatively near together1 and have few or no satellites4 ,they are1 moreover1 rather dense in structure4 ,the major planets1 on the other hand1 are huge bodies1 circulating at great distances from each other1 and are1 as a rule1 provided with a number of satellites4 ,with respect to structure1 they may be fairly described as being loosely put together4 ,further1 the markings on the surfaces of the terrestrial planets are permanent1 whereas those on the major planets are continually shifting4 ,,the ,,planet ,,jupiter ,jupiter is the greatest of the major planets4 ,it has been justly called the ,giant planet1 for both in volume and in mass it exceeds all the other planets put together4 ,when seen through the telescope it exhibits a surface plentifully covered with markings1 the most remarkable being a series of broad parallel belts4 ,the chief belt lies in the central parts of the planet1 and is at present about #aj1jjj miles wide4 ,it is bounded on either side by a reddish brown belt of about the same width4 ,bright spots also appear upon the surface of the planet1 last for a while1 and then disappear4 ,the most notable of the latter is one known as the ,great ,red ,spot4 ,this is situated a little beneath the southern red belt1 and appeared for the first time about thirty years ago4 ,it has undergone a good many changes in colour and brightness1 and is still faintly visible4 ,this spot is the most permanent marking which has yet been seen upon ,jupiter4 ,in general1 the markings change so often that the surface which we see is evidently not solid1 but of a fleeting nature akin to cloud 7see ,plate ,,xiv41 p4 #bcj74 ,illustration3 ,,plate ,,xiv4 ,,the ,,planet ,,jupiter ,the ,giant ,planet as seen at #aa4cj p4m41 on the #aath of ,january1 #aijh1 with a #ab-a_/b-;inch reflecting telescope4 ,the extensive oval marking in the upper portion of the disc is the ,great ,red ,spot4 ,the ,south is at the top of the picture1 the view being the inverted one given by an astronomical telescope4 ,from a drawing by the ,rev4 ,theodore ,e4,r4 ,phillips1 ,m4,a41 ,f4,r4,a4,s41 ,director of the ,jupiter ,section of the ,british ,astronomical ,association4 7,page #bca7 ,observations of ,jupiter's markings show that on an average the planet rotates on its axis in a period of about #i hours #ed minutes4 ,the mention here of an average with reference to the rotation will1 no doubt1 recall to the reader's mind the similar case of the sun1 the different portions of which rotate with different velocities4 ,the parts of ,jupiter which move quickest take #i hours #ej minutes to go round1 while those which move slowest take #i hours #eg minutes4 ,the middle portions rotate the fastest1 a phenomenon which the reader will recollect was also the case with regard to the sun4 ,jupiter is a very loosely packed body4 ,its density is on an average only about #a-a_/b times that of water1 or about one-fourth the density of the earth2 but its bulk is so great that the gravitation at that surface which we see is about #b-a_/b times what it is on the surface of the earth4 ,in accordance1 therefore1 with the kinetic theory1 we may expect the planet to retain an extensive layer of gases around it2 and this is confirmed by the spectroscope1 which gives evidence of the presence of a dense atmosphere4 ,all things considered1 it may be safely inferred that the interior of ,jupiter is very hot1 and that what we call its surface is not the actual body of the planet1 but a voluminous layer of clouds and vapours driven upwards from the heated mass underneath4 ,the planet was indeed formerly thought to be self-luminous2 but this can hardly be the case1 for those portions of the surface which happen to lie at any moment in the shadows cast by the satellites appear to be quite black4 ,again1 when a satellite passes into the great shadow cast by the planet it becomes entirely invisible1 which would not be the case did the planet emit any perceptible light of its own4 ,in its revolutions around the sun1 ,jupiter is attended1 so far as we know1 by seven#bb satellites4 ,four of these were among the first celestial objects which ,galileo discovered with his optick tube1 and he named them the ,medicean ,stars in honour of his patron1 ,cosmo de ,medici4 ,being comparatively large bodies they might indeed just be seen with the naked eye1 were it not for the overpowering glare of the planet4 ,it was only in quite recent times1 namely1 in #ahib1 that a fifth satellite was added to the system of ,jupiter4 ,this body1 discovered by ,professor ,e4,e4 ,barnard1 is very small4 ,it circulates nearer to the planet than the innermost of ,galileo's moons2 and1 on account of the glare1 is a most difficult object to obtain a glimpse of1 even in the best of telescopes4 ,in ,december #aijd and ,january #aije respectively1 two more moons were added to the system1 these being found by photography1 by the ,american astronomer1 ,professor ,c4,d4 ,perrine4 ,both the bodies in question revolve at a greater distance from the planet than the outermost of the older known satellites4 ,galileo's moons1 though the largest bodies of ,jupiter's satellite system1 are1 as we have already pointed out1 very small indeed when compared with the planet itself4 ,the diameters of two of them1 ,europa and ,io1 are1 however1 about the same as that of our moon1 while those of the other two1 ,callisto and ,ganymede1 are more than half as large again4 ,the recently discovered satellites are1 on the other hand1 insignificant2 that found by ,barnard1 for example1 being only about #ajj miles in diameter4 ,of the four original satellites ,io is the nearest to ,jupiter1 and1 seen from the planet1 it would show a disc somewhat larger than that of our moon4 ,the others would appear somewhat smaller4 ,however1 on account of the great distance of the sun1 the entire light reflected to ,jupiter by all the satellites should be very much less than what we get from our moon4 ,barnard's satellite circles around ,jupiter at a distance less than our moon is from us1 and in a period of about #ab hours4 ,galileo's four satellites revolve in periods of about #b1 #c-a_/b1 #g1 and #af-a_/b days respectively1 at distances lying roughly between a quarter of a million and one million miles4 ,perrine's two satellites are at a distance of about seven million miles1 and take about nine months to complete their revolutions4 ,the larger satellites1 when viewed in the telescope1 exhibit certain defined markings2 but the bodies are so far away from us1 that only those details which are of great extent can be seen4 ,the satellite ,io1 according to ,professor ,barnard1 shows a darkish disc1 with a broad white belt across its middle regions4 ,mr4 ,douglass1 one of the observers at the ,lowell ,observatory1 has noted upon ,ganymede a number of markings somewhat resembling those seen on ,mars1 and he concludes1 from their movement1 that this satellite rotates on its axis in about seven days4 ,professor ,barnard1 on the other hand1 does not corroborate this1 though he claims to have discovered bright polar caps on both ,ganymede and ,callisto4 ,in an earlier chapter we dealt at length with eclipses1 occultations1 and transits1 and endeavoured to make clear the distinction between them4 ,the system of ,jupiter's satellites furnishes excellent examples of all these phenomena4 ,the planet casts a very extensive shadow1 and the satellites are constantly undergoing obscuration by passing through it4 ,such occurrences are plainly comparable to our lunar eclipses4 ,again1 the satellites may1 at one time1 be occulted by the huge disc of the planet1 and at another time seen in transit over its face4 ,a fourth phenomenon is what is known as an eclipse of the planet by a satellite1 which is the exact equivalent of what we style on the earth an eclipse of the sun4 ,in this last case the shadow1 cast by the satellite1 appears as a round black spot in movement across the planet's surface4 ,in the passages of these attendant bodies behind the planet1 into its shadow1 or across its face1 respectively1 it occasionally happens that ,galileo's four satellites all disappear from view1 and the planet is then seen for a while in the unusual condition of being apparently without its customary attendants4 ,an instance of this phenomenon took place on the #crd of ,october #aijg4 ,on that occasion1 the satellites known as ,i4 and ,,iii4 7i4e4 ,io and ,ganymede7 were eclipsed1 that is to say1 obscured by passing into the planet's shadow2 ,satellite ,,iv4 7,callisto7 was occulted by the planet's disc2 while ,satellite ,,ii4 7,europa71 being at the same moment in transit across the planet's face1 was invisible against that brilliant background4 ,a number of instances of this kind of occurrence are on record4 ,galileo1 for example1 noted one on the #aeth of ,march #afaa1 while ,herschel observed another on the #bcrd of ,may #ahjb4 ,it was indirectly to ,jupiter's satellites that the world was first indebted for its knowledge of the velocity of light4 ,when the periods of revolution of the satellites were originally determined1 ,jupiter happened1 at the time1 to be at his nearest to us4 ,from the periods thus found tables were made for the prediction of the moments at which the eclipses and other phenomena of the satellites should take place4 ,as ,jupiter1 in the course of his orbit1 drew further away from the earth1 it was noticed that the disappearances of the satellites into the shadow of the planet occurred regularly later than the time predicted4 ,in the year #afge1 ,roemer1 a ,danish astronomer1 inferred from this1 not that the predictions were faulty1 but that light did not travel instantaneously4 ,it appeared1 in fact1 to take longer to reach us1 the greater the distance it had to traverse4 ,thus1 when the planet was far from the earth1 the last ray given out by the satellite1 before its passage into the shadow1 took a longer time to cross the intervening space1 than when the planet was near4 ,modern experiments in physics have quite confirmed this1 and have proved for us that light does not travel across space in the twinkling of an eye1 as might hastily be supposed1 but actually moves1 as has been already stated1 at the rate of about #ahf1jjj miles per second4 ,,the ,,planet ,,saturn ,seen in the telescope the planet ,saturn is a wonderful and very beautiful object4 ,it is distinguished from all the other planets1 in fact from all known celestial bodies1 through being girt around its equator by what looks like a broad1 flat ring of exceeding thinness4 ,this1 however1 upon closer examination1 is found to be actually composed of three concentric rings4 ,the outermost of these is nearly of the same brightness as the body of the planet itself4 ,the ring which comes immediately within it is also bright1 and is separated from the outer one all the way round by a relatively narrow space1 known as ,cassini's division1 because it was discovered by the celebrated ,french astronomer1 ,j4,d4 ,cassini1 in the year #afge4 ,inside the second ring1 and merging insensibly into it1 is a third one1 known as the crape ring1 because it is darker in hue than the others and partly transparent1 the body of ,saturn being visible through it4 ,the inner boundary of this third and last ring does not adjoin the planet1 but is everywhere separated from it by a definite space4 ,this ring was discovered independently#bc in #ahej by ,bond in ,america and ,dawes in ,england4 ,illustration3 ,,plate ,,xv4 ,,the ,,planet ,,saturn ,from a drawing made by ,professor ,barnard with the ,great ,lick ,telescope4 ,the black band fringing the outer ring1 where it crosses the disc1 is portion of the shadow which the rings cast upon the planet4 ,the black wedge-shaped mark1 where the rings disappear behind the disc at the left-hand side1 is portion of the shadow which the planet casts upon the rings4 7,page #bcg7 ,as distinguished from the crape ring1 the bright rings must have a considerable closeness of texture2 for the shadow of the planet may be seen projected upon them1 and their shadows in turn projected upon the surface of the planet 7see ,plate ,,xv41 p4 #bcf74 ,according to ,professor ,barnard1 the entire breadth of the ring system1 that is to say1 from one side to the other of the outer ring1 is #agb1caj miles1 or somewhat more than double the planet's diameter4 ,in the varying views which we get of ,saturn1 the system of the rings is presented to us at very different angles4 ,sometimes we are enabled to gaze upon its broad expanse2 at other times1 however1 its thin edge is turned exactly towards us1 an occurrence which takes place after intervals of about fifteen years4 ,when this happened in #ahib the rings are said to have disappeared entirely from view in the great ,lick telescope4 ,we thus get an idea of their small degree of thickness1 which would appear to be only about #ej miles4 ,the last time the system of rings was exactly edgewise to the earth was on the #crd of ,october #aijg4 ,the question of the composition of these rings has given rise to a good deal of speculation4 ,it was formerly supposed that they were either solid or liquid1 but in #aheg it was proved by ,clerk ,maxwell that a structure of this kind would not be able to stand4 ,he showed1 however1 that they could be fully explained by supposing them to consist of an immense number of separate solid particles1 or1 as one might otherwise put it1 extremely small satellites1 circling in dense swarms around the middle portions of the planet4 ,it is therefore believed that we have here the materials ready for the formation of a satellite or satellites2 but that the powerful gravitative action1 arising through the planet's being so near at hand1 is too great ever to allow these materials to aggregate themselves into a solid mass4 ,there is1 as a matter of fact1 a minimum distance from the body of any planet within which it can be shown that a satellite will be unable to form on account of gravitational stress4 ,this is known as ,roche's limit1 from the name of a ,french astronomer who specially investigated the question4 ,there thus appears to be a certain degree of analogy between ,saturn's rings and the asteroids4 ,empty spaces1 too1 exist in the asteroidal zone1 the relative position of one of which bears a striking resemblance to that of ,cassini's division4 ,it is suggested1 indeed1 that this division had its origin in gravitational disturbances produced by the attraction of the larger satellites1 just as the empty spaces in the asteroidal zone are supposed to be the result of perturbations caused by the ,giant ,planet hard by4 ,it has long been understood that the system of the rings must be rotating around ,saturn1 for if they were not in motion his intense gravitational attraction would quickly tear them in pieces4 ,this was at length proved to be the fact by the late ,professor ,keeler1 ,director of the ,lick ,observatory1 who from spectroscopic observations found that those portions of the rings situated near to the planet rotated faster than those farther from it4 ,this directly supports the view that the rings are composed of satellites2 for1 as we have already seen1 the nearer a satellite is to its primary the faster it will revolve4 ,on the other hand1 were the rings solid1 their outer portions would move the fastest2 as we have seen takes place in the body of the earth1 for example4 ,the mass of the ring system1 however1 must be exceedingly small1 for it does not appear to produce any disturbances in the movements of ,saturn's satellites4 ,from the kinetic theory1 therefore1 one would not expect to find any atmosphere on the rings1 and the absence of it is duly shown by spectroscopic observations4 ,the diameter of ,saturn1 roughly speaking1 is about one-fifth less than that of ,jupiter4 ,the planet is very flattened at the poles1 this flattening being quite noticeable in a good telescope4 ,for instance1 the diameter across the equator is about #gf1dgj miles1 while from pole to pole it is much less1 namely1 #fi1ggj4 ,the surface of ,saturn bears a strong resemblance to that of ,jupiter4 ,its markings1 though not so well defined1 are of the same belt-like description2 and from observation of them it appears that the planet rotates on an average in a little over ten hours4 ,the rotation is in fact of the same peculiar kind as that of the sun and ,jupiter2 but the difference of speed at which the various portions of ,saturn go round are even more marked than in the case of the ,giant ,planet4 ,the density of ,saturn is less than that of ,jupiter2 so that it must be largely in a condition of vapour1 and in all probability at a still earlier stage of planetary evolution4 ,up to the present we know of as many as ten satellites circling around ,saturn1 which is more than any other planet of the solar system can lay claim to4 ,two of these1 however1 are very recent discoveries2 one1 ,phoebe1 having been found by photography in ,august #ahih1 and the other1 ,themis1 in #aijd1 also by the same means4 ,for both of these we are indebted to ,professor ,w4,h4 ,pickering4 ,themis is said to be the faintest object in the solar system4 ,it cannot be seen1 even with the largest telescope in existence2 a fact which should hardly fail to impress upon one the great advantage the photographic plate possesses in these researches over the human eye4 ,the most important of the whole ,saturnian family of satellites are the two known as ,titan and ,japetus4 ,these were discovered respectively by ,huyghens in #afee and by ,cassini in #afga4 ,japetus is about the same size as our moon2 while the diameter of ,titan1 the largest of the satellites1 is about half as much again4 ,titan takes about sixteen days to revolve around ,saturn1 while ,japetus takes more than two months and a half4 ,the former is about three-quarters of a million miles distant from the planet1 and the latter about two and a quarter millions4 ,to ,sir ,william ,herschel we are indebted for the discovery of two more satellites1 one of which he found on the evening that he used his celebrated #dj-;foot telescope for the first time4 ,the ninth satellite1 ,phoebe1 one of the two discovered by ,professor ,pickering1 is perhaps the most remarkable body in the solar system1 for all the other known members of that system perform their revolutions in one fixed direction1 whereas this satellite revolves in the contrary direction4 ,in consequence of the great distance of ,saturn1 the sun1 as seen from the planet1 would appear so small that it would scarcely show any disc4 ,the planet1 indeed1 only receives from the sun about one-ninetieth of the heat and light which the earth receives4 ,owing to this diminished intensity of illumination1 the combined light reflected to ,saturn by the whole of its satellites must be very small4 ,with the sole exception of ,jupiter1 not one of the planets circulating nearer to the sun could be seen from ,saturn1 as they would be entirely lost in the solar glare4 ,for an observer upon ,saturn1 ,jupiter would1 therefore1 fill much the same position as ,venus does for us1 regularly displaying phases and being alternately a morning and an evening star4 ,it is rather interesting to consider the appearances which would be produced in our skies were the earth embellished with a system of rings similar to those of ,saturn4 ,in consequence of the curving of the terrestrial surface1 they would not be seen at all from within the ,arctic or ,antarctic circles1 as they would be always below the horizon4 ,from the equator they would be continually seen edgewise1 and so would appear merely as line of light stretching right across the heaven and passing through the zenith4 ,but the dwellers in the remaining regions would find them very objectionable1 for they would cut off the light of the sun during lengthy periods of time4 ,saturn was a sore puzzle to the early telescopic observers4 ,they did not for a long time grasp the fact that it was surrounded by a ring--so slow is the human mind to seek for explanations out of the ordinary course of things4 ,the protrusions of the ring on either side of the planet1 at first looked to ,galileo like two minor globes placed on opposite sides of it1 and slightly overlapping the disc4 ,he therefore informed ,kepler that ,saturn consists of three stars in contact with one another4 ,yet he was genuinely puzzled by the fact that the two attendant bodies 7as he thought them7 always retained the same position with regard to the planet's disc1 and did not appear to revolve around it1 nor to be in any wise shifted as a consequence of the movements of our earth4 ,about a year and a half elapsed before he again examined ,saturn2 and1 if he was previously puzzled1 he was now thoroughly amazed4 ,it happened just then to be one of those periods when the ring is edgewise towards the earth1 and of course he only saw a round disc like that of ,jupiter4 ,what1 indeed1 had become of the attendant orbs8 ,was some demon mocking him8 ,had ,saturn devoured his own children8 ,he was1 however1 fated to be still more puzzled1 for soon the minor orbs reappeared1 and1 becoming larger and larger as time went on1 they ended by losing their globular appearance and became like two pairs of arms clasping the planet from each side6 7see ,plate ,,xvi41 p4 #bdb74 ,galileo went to his grave with the riddle still unsolved1 and it remained for the famous ,dutch astronomer1 ,huyghens1 to clear up the matter4 ,it was1 however1 some little time before he hit upon the real explanation4 ,having noticed that there were dark spaces between the strange appendages and the body of the planet1 he imagined ,saturn to be a globe fitted with handles at each side2 ans these came to be called1 from the ,latin ansa1 which means a handle4 ,at length1 in the year #afef1 he solved the problem1 and this he did by means of that #abc-;foot tubeless telescope1 of which mention has already been made4 ,the ring happened then to be at its edgewise period1 and a careful study of the behaviour of the ans when disappearing and reappearing soon revealed to ,huyghens the true explanation4 ,illustration3 ,,plate ,,xvi4 ,,early ,,representations ,,of ,,saturn ,from an illustration in the ,systema ,saturnium of ,christian ,huyghens4 7,page #bdb7 ,,the ,,planets ,,uranus ,,and ,,neptune ,we have already explained 7in ,chapter ,,ii47 the circumstances in which both ,uranus and ,neptune were discovered4 ,it should1 however1 be added that after the discovery of ,uranus1 that planet was found to have been already noted upon several occasions by different observers1 but always without the least suspicion that it was other than a mere faint star4 ,again1 with reference to the discovery of ,neptune1 it may here be mentioned that the apparent amount by which that planet had pulled ,uranus out of its place upon the starry background was exceedingly small--so small1 indeed1 that no eye could have detected it without the aid of a telescope6 ,of the two predictions of the place of ,neptune in the sky1 that of ,le ,verrier was the nearer4 ,indeed1 the position calculated by ,adams was more than twice as far out4 ,but ,adams was by a long way the first in the field with his results1 and only for unfortunate delays the prize would certainly have fallen to him4 ,for instance1 there was no star-map at ,cambridge1 and ,professor ,challis1 the director of the observatory there1 was in consequence obliged to make a laborious examination of the stars in the suspected region4 ,on the other hand1 all that ,galle had to do was to compare that part of the sky where ,le ,verrier told him to look with the ,berlin star-chart which he had by him4 ,this he did on ,september #bc1 #ahdf1 with the result that he quickly noted an eighth magnitude star which did not figure in that chart4 ,by the next night this star had altered its position in the sky1 thus disclosing the fact that it was really a planet4 ,six days later ,professor ,challis succeeded in finding the planet1 but of course he was now too late4 ,on reviewing his labours he ascertained that he had actually noted down its place early in ,august1 and had he only been able to sift his observations as he made them1 the discovery would have been made then4 ,later on it was found that ,neptune had only just missed being discovered about fifty years earlier4 ,in certain observations made during #agie1 the famous ,french astronomer1 ,lalande1 found that a star1 which he had mapped in a certain position on the #hth of ,may of that year1 was in a different position two days later4 ,the idea of a planet does not appear to have entered his mind1 and he merely treated the first observation as an error6 ,the reader will1 no doubt1 recollect how the discovery of the asteroids was due in effect to an apparent break in the seemingly regular sequence of the planetary orbits outwards from the sun4 ,this curious sequence of relative distances is usually known as ,bode's ,law1 because it was first brought into general notice by an astronomer of that name4 ,it had1 however1 previously been investigated mathematically by ,titius in #aggb4 ,long before this1 indeed1 the unnecessarily wide space between the orbits of ,mars and ,jupiter had attracted the attention of the great ,kepler to such a degree1 that he predicted that a planet would some day be found to fill the void4 ,notwithstanding the service which the so-called ,law of ,bode has indirectly rendered to astronomy1 it has strangely enough been found after all not to rest upon any scientific foundation4 ,it will not account for the distance from the sun of the orbit of ,neptune1 and the very sequence seems on the whole to be in the nature of a mere coincidence4 ,neptune is invisible to the naked eye2 ,uranus is just at the limit of visibility4 ,both planets are1 however1 so far from us that we can get but the poorest knowledge of their condition and surroundings4 ,uranus1 up to the present1 is known to be attended by four satellites1 and ,neptune by one4 ,the planets themselves are about equal in size2 their diameters1 roughly speaking1 being about one-half that of ,saturn4 ,some markings have1 indeed1 been seen upon the disc of ,uranus1 but they are very indistinct and fleeting4 ,from observation of them1 it is assumed that the planet rotates on its axis in a period of some ten to twelve hours4 ,no definite markings have as yet been seen upon ,neptune1 which body is described by several observers as resembling a faint planetary nebula4 ,with regard to their physical condition1 the most that can be said about these two planets is that they are probably in much the same vaporous state as ,jupiter and ,saturn4 ,on account of their great distance from the sun they can receive but little solar heat and light4 ,seen from ,neptune1 in fact1 the sun would appear only about the size of ,venus at her best1 though of a brightness sufficiently intense to illumine the ,neptunian landscape with about seven hundred times our full moonlight4 #bb ,mr4 ,p4 ,melotte1 of ,greenwich ,observatory1 while examining a photograph taken there on ,february #bh1 #aijh1 discovered upon it a very faint object which it is firmly believed will prove to be an eighth satellite of ,jupiter4 ,this object was afterwards found on plates exposed as far back as ,january #bg4 ,it has since been photographed several times at ,greenwich1 and also at ,heidelberg 7by ,dr4 ,max ,wolf7 and at the ,lick ,observatory4 ,its movement is probably retrograde1 like that of ,phoebe 7p4 #bdj74 #bc ,in the history of astronomy two salient points stand out4 ,the first of these is the number of independent discoveries which have taken place2 such1 for instance1 as in the cases of ,le ,verrier and ,adams with regard to ,neptune1 and of ,lockyer and ,janssen in the matter of the spectroscopic method of observing solar prominences4 ,the other is the great amount of anticipation4 ,copernicus1 as we have seen1 was anticipated by the ,greeks2 ,kepler was not actually the first who thought of elliptic orbits2 others before ,newton had imagined an attractive force4 ,both these points furnish much food for thought6 ,,chapter ,,xix ,,comets ,the reader has1 no doubt1 been struck by the marked uniformity which exists among those members of the solar system with which we have dealt up to the present4 ,the sun1 the planets1 and their satellites are all what we call solid bodies4 ,the planets move around the sun1 and the satellites around the planets1 in orbits which1 though strictly speaking1 ellipses1 are yet not in any instance of a very oval form4 ,two results naturally follow from these considerations4 ,firstly1 the bodies in question hide the light coming to us from those further off1 when they pass in front of them4 ,secondly1 the planets never get so far from the sun that we lose sight of them altogether4 ,with the objects known as ,comets it is1 however1 quite the contrary4 ,these objects do not conform to our notions of solidity4 ,they are so transparent that they can pass across the smallest star without dimming its light in the slightest degree4 ,again1 they are only visible to us during a portion of their orbits4 ,a comet may be briefly described as an illuminated filmy-looking object1 made up usually of three portions--a head1 a nucleus1 or brighter central portion within this head1 and a tail4 ,the heads of comets vary greatly in size2 some1 indeed1 appear quite small1 like stars1 while others look even as large as the moon4 ,occasionally the nucleus is wanting1 and sometimes the tail also4 ,illustration3 ,,fig4 #ah4--,showing how the ,tail of a ,comet is directed away from the ,sun4 ,these mysterious visitors to our skies come up into view out of the immensities beyond1 move towards the sun at a rapidly increasing speed1 and1 having gone around it1 dash away again into the depths of space4 ,as a comet approaches the sun1 its body appears to grow smaller and smaller1 while1 at the same time1 it gradually throws out behind it an appendage like a tail4 ,as the comet moves round the central orb this tail is always directed away from the sun2 and when it departs again into space the tail goes in advance4 ,as the comet's distance from the sun increases1 the tail gradually shrinks away and the head once more grows in size 7see ,fig4 #ah74 ,in consequence of these changes1 and of the fact that we lose sight of comets comparatively quickly1 one is much inclined to wonder what further changes may take place after the bodies have passed beyond our ken4 ,the orbits of comets are1 as we have seen1 very elliptic4 ,in some instances this ellipticity is so great as to take the bodies out into space to nearly six times the distance of ,neptune from the sun4 ,for a long time1 indeed1 it was considered that comets were of two kinds1 namely1 those which actually belonged to the solar system1 and those which were merely visitors to it for the first and only time--rushing in from the depths of space1 rapidly circuiting the sun1 and finally dashing away into space again1 never to return4 ,on the contrary1 nowadays1 astronomers are generally inclined to regard comets as permanent members of the solar system4 ,the difficulty1 however1 of deciding absolutely whether the orbits of comets are really always closed curves1 that is to say1 curves which must sooner or later bring the bodies back again towards the sun1 is1 indeed1 very great4 ,comets1 in the first place1 are always so diffuse1 that it is impossible to determine their exact position1 or1 rather1 the exact position of that important point within them1 known as the centre of gravity4 ,secondly1 that stretch of its orbit along which we can follow a comet1 is such a very small portion of the whole path1 that the slightest errors of observation which we make will result in considerably altering our estimate of the actual shape of the orbit4 ,comets have been described as so transparent that they can pass across the sky without dimming the lustre of the smallest stars1 which the thinnest fog or mist would do4 ,this is1 indeed1 true of every portion of a comet except the nucleus1 which is1 as its name implies1 the densest part4 ,and yet1 in contrast to this ghostlike character1 is the strange fact that when comets are of a certain brightness they may actually be seen in full daylight4 ,as might be gathered from their extreme tenuity1 comets are so exceedingly small in mass that they do not appear to exert any gravitational attraction upon the other bodies of our system4 ,it is1 indeed1 a known fact that in the year #ahhf a comet passed right amidst the satellites of ,jupiter without disturbing them in the slightest degree4 ,the attraction of the planet1 on the other hand1 so altered the comet's orbit1 as to cause it to revolve around the sun in a period of seven years1 instead of twenty-seven1 as had previously been the case4 ,also1 in #aggi1 the comet known as ,lexell's passed quite close to ,jupiter1 and its orbit was so changed by that planet's attraction that it has never been seen since4 ,the density of comets must1 as a rule1 be very much less than the one-thousandth part of that of the air at the surface of our globe2 for1 if the density of the comet were even so small as this1 its mass would not be inappreciable4 ,if comets are really undoubted members of the solar system1 the circumstances in which they were evolved must have been different from those which produced the planets and satellites4 ,the axial rotations of both the latter1 and also their revolutions1 take place in one certain direction2#bd their orbits1 too1 are ellipses which do not differ much from circles1 and which1 furthermore1 are situated fairly in the one plane4 ,comets1 on the other hand1 do not necessarily travel round the sun in the same fixed direction as the planets4 ,their orbits1 besides1 are exceedingly elliptic2 and1 far from keeping to one plane1 or even near it1 they approach the sun from all directions4 ,broadly speaking1 comets may be divided into two distinct classes1 or families4 ,in the first class1 the same orbit appears to be shared in common by a series of comets which travel along it1 one following the other4 ,the comets which appeared in the years #affh1 #ahdc1 #ahhj1 #ahhb1 and #ahhg are instances of a number of different bodies pursuing the same path around the sun4 ,the members of a comet family of this kind are observed to have similar characteristics4 ,the idea is that such comets are merely portions of one much larger cometary body1 which became broken up by the gravitational action of other bodies in the system1 or through violent encounter with the sun's surroundings4 ,the second class is composed of comets which are supposed to have been seized by the gravitative action of certain planets1 and thus forced to revolve in short ellipses around the sun1 well within the limits of the solar system4 ,these comets are1 in consequence1 spoken of as captures4 ,they move around the sun in the same direction as the planets do4 ,jupiter has a fairly large comet family of this kind attached to him4 ,as a result of his overpowering gravitation1 it is imagined that during the ages he must have attracted a large number of these bodies on his own account1 and1 perhaps1 have robbed other planets of their captures4 ,his family at present numbers about thirty4 ,of the other planets1 so far as we know1 ,saturn possesses a comet family of two1 ,uranus three1 and ,neptune six4 ,there are1 indeed1 a few comets which appear as if under the influence of some force situated outside the known bounds of the solar system1 a circumstance which goes to strengthen the idea that other planets may revolve beyond the orbit of ,neptune4 ,the terrestrial planets1 on the other hand1 cannot have comet families2 because the enormous gravitative action of the sun in their vicinity entirely overpowers the attractive force which they exert upon those comets which pass close to them4 ,besides this1 a comet1 when in the inner regions of the solar system1 moves with such rapidity1 that the gravitational pull of the planets there situated is not powerful enough to deflect it to any extent4 ,it must not be presumed1 however1 that a comet once captured should always remain a prisoner4 ,further disturbing causes might unsettle its newly acquired orbit1 and send it out again into the celestial spaces4 ,with regard to the matter of which comets are composed1 the spectroscope shows the presence in them of hydrocarbon compounds 7a notable characteristic of these bodies71 and at times1 also1 of sodium and iron4 ,some of the light which we get from comets is1 however1 merely reflected sunlight4 ,the fact that the tails of comets are always directed away from the sun1 has given rise to the idea that this is caused by some repelling action emanating from the sun itself1 which is continually driving off the smallest particles4 ,two leading theories have been formulated to account for the tails themselves upon the above assumption4 ,one of these1 first suggested by ,olbers in #ahab1 and now associated with the name of the ,russian astronomer1 the late ,professor ,brdikhine1 who carefully worked it out1 presumes an electrical action emanating from the sun2 the other1 that of ,arrhenius1 supposes a pressure exerted by the solar light in its radiation outwards into space4 ,it is possible1 indeed1 that repelling forces of both these kinds may be at work together4 ,minute particles are probably being continually produced by friction and collisions among the more solid parts in the heads of comets4 ,supposing that such particles are driven off altogether1 one may therefore assume that the so-called captured comets are disintegrating at a comparatively rapid rate4 ,kepler long ago maintained that comets die1 and this actually appears to be the case4 ,the ordinary periodic ones1 such1 for instance1 as ,encke's ,comet1 are very faint1 and becoming fainter at each return4 ,certain of these comets have1 indeed1 failed altogether to reappear4 ,it is notable that the members of ,jupiter's comet family are not very conspicuous objects4 ,they have small tails1 and even in some cases have none at all4 ,the family1 too1 does not contain many members1 and yet one cannot but suppose that ,jupiter1 on account of his great mass1 has had many opportunities for making captures adown the ages4 ,of the two theories to which allusion has above been made1 that of ,brdikhine has been worked out so carefully1 and with such a show of plausibility1 that it here calls for a detailed description4 ,it appears besides to explain the phenomena of comets' tails so much more satisfactorily than that of ,arrhenius1 that astronomers are inclined to accept it the more readily of the two4 ,according to ,brdikhine's theory the electrical repulsive force1 which he assumes for the purposes of his argument1 will drive the minutest particles of the comet in a direction away from the sun much more readily than the gravitative action of that body will pull them towards it4 ,this may be compared to the ease with which fine dust may be blown upwards1 although the earth's gravitation is acting upon it all the time4 ,the researches of ,brdikhine1 which began seriously with his investigation of ,coggia's ,comet of #ahgd1 led him to classify the tails of comets in three types4 ,presuming that the repulsive force emanating from the sun did not vary1 he came to the conclusion that the different forms assumed by cometary tails must be ascribed to the special action of this force upon the various elements which happen to be present in the comet4 ,the tails which he classes as of the first type1 are those which are long and straight and point directly away from the sun4 ,examples of such tails are found in the comets of #ahaa1 #ahdc1 and #ahfa4 ,tails of this kind1 he thinks1 are in all probability formed of hydrogen4 ,his second type comprises those which are pointed away from the sun1 but at the same time are considerably curved1 as was seen in the comets of ,donati and ,coggia4 ,these tails are formed of hydrocarbon gas4 ,the third type of tail is short1 brush-like1 and strongly bent1 and is formed of the vapour of iron1 mixed with that of sodium and other elements4 ,it should1 however1 be noted that comets have occasionally been seen which possess several tails of these various types4 ,we will now touch upon a few of the best known comets of modern times4 ,the comet of #afhj was the first whose orbit was calculated according to the laws of gravitation4 ,this was accomplished by ,newton1 and he found that the comet in question completed its journey round the sun in a period of about #fjj years4 ,in #afhb there appeared a great comet1 which has become famous under the name of ,halley's ,comet1 in consequence of the profound investigations made into its motion by the great astronomer1 ,edmund ,halley4 ,he fixed its period of revolution around the sun at about seventy-five years1 and predicted that it would reappear in the early part of #agei4 ,he did not1 however1 live to see this fulfilled1 but the comet duly returned--the first body of the kind to verify such a prediction--and was detected on ,christmas ,day1 #ageh1 by ,george ,palitzch1 an amateur observer living near ,dresden4 ,halley also investigated the past history of the comet1 and traced it back to the year #adef4 ,the orbit of ,halley's comet passes out slightly beyond the orbit of ,neptune4 ,at its last visit in #ahce1 this comet passed comparatively close to us1 namely1 within five million miles of the earth4 ,according to the calculations of ,messrs ,p4,h4 ,cowell and ,a4,c4,d4 ,crommelin of ,greenwich ,observatory1 its next return will be in the spring of #aiaj2 the nearest approach to the earth taking place about ,may #ab4 ,on the #bfth of ,march1 #ahaa1 a great comet appeared1 which remained visible for nearly a year and a half4 ,it was a magnificent object2 the tail being about #ajj millions of miles in length1 and the head about #abg1jjj miles in diameter4 ,a detailed study which he gave to this comet prompted ,olbers to put forward that theory of electrical repulsion which1 as we have seen1 has since been so carefully worked out by ,brdikhine4 ,olbers had noticed that the particles expelled from the head appeared to travel to the end of the tail in about eleven minutes1 thus showing a velocity per second very similar to that of light4 ,the discovery in #ahai of the comet known as ,encke's1 because its orbit was determined by an astronomer of that name1 drew attention for the first time to ,jupiter's comet family1 and1 indeed1 to short-period comets in general4 ,this comet revolves around the sun in the shortest known period of any of these bodies1 namely1 #c-a_/c years4 ,encke predicted that it would return in #ahbb4 ,this duly occurred1 the comet passing at its nearest to the sun within three hours of the time indicated2 being thus the second instance of the fulfilment of a prediction of the kind4 ,a certain degree of irregularity which ,encke's ,comet displays in the dates of its returns to the sun1 has been supposed to indicate that it passes in the course of its orbit through some retarding medium1 but no definite conclusions have so far been arrived at in this matter4 ,a comet1 which appeared in #ahbf1 goes by the name of ,biela's ,comet1 because of its discovery by an ,austrian military officer1 ,wilhelm von ,biela4 ,this comet was found to have a period of between six and seven years4 ,certain calculations made by ,olbers showed that1 at its return in #ahcb1 it would pass through the earth's orbit4 ,the announcement of this gave rise to a panic2 for people did not wait to inquire whether the earth would be anywhere near that part of its orbit when the comet passed4 ,the panic1 however1 subsided when the ,french astronomer1 ,arago1 showed that at the moment in question the earth would be some #ej millions of miles away from the point indicated6 ,illustration3 ,,plate ,,xvii4 ,,donati',s ,,comet ,from a drawing made on ,october #ith1 #aheh1 by ,g4,p4 ,bond1 of ,harvard ,college ,observatory1 ,u4,s4,a4 ,a good illustration of ,brdikhine's theory3 note the straight tails of his first type1 and the curved tail of his second4 7,page #beg7 ,in #ahdf1 shortly after one of its returns1 ,biela's ,comet divided into two portions4 ,at its next appearance 7#aheb7 these portions had separated to a distance of about #a-a_/b millions of miles from each other4 ,this comet1 or rather its constituents1 have never since been seen4 ,perhaps the most remarkable comet of recent times was that of #aheh1 known as ,donati's1 it having been discovered at ,florence by the ,italian astronomer1 ,g4,b4 ,donati4 ,this comet1 a magnificent object1 was visible for more than three months with the naked eye4 ,its tail was then #ed millions of miles in length4 ,it was found to revolve around the sun in a period of over #bjjj years1 and to go out in its journey to about #e-a_/b times the distance of ,neptune4 ,its motion is retrograde1 that is to say1 in the contrary direction to the usual movement in the solar system4 ,a number of beautiful drawings of ,donati's ,comet were made by the ,american astronomer1 ,g4,p4 ,bond4 ,one of the best of these is reproduced on ,plate ,,xvii41 p4 #bef4 ,in #ahfa there appeared a great comet4 ,on the #cjth of ,june of that year the earth and moon actually passed through its tail2 but no effects were noticed1 other than a peculiar luminosity in the sky4 ,in the year #ahha there appeared another large comet1 known as ,tebbutt's ,comet1 from the name of its discoverer4 ,this was the first comet of which a satisfactory photograph was obtained4 ,the photograph in question was taken by the late ,m4 ,janssen4 ,the comet of #ahhb was of vast size and brilliance4 ,it approached so close to the sun that it passed through some #ajj1jjj miles of the solar corona4 ,though its orbit was not found to have been altered by this experience1 its nucleus displayed signs of breaking up4 ,some very fine photographs of this comet were obtained at the ,cape of ,good ,hope by ,mr4 7now ,sir ,david7 ,gill4 ,the comet of #ahhi was followed with the telescope nearly up to the orbit of ,saturn1 which seems to be the greatest distance at which a comet has ever been seen4 ,the first discovery of a comet by photographic means#be was made by ,professor ,barnard in #ahib2 and1 since then1 photography has been employed with marked success in the detection of small periodic comets4 ,the best comet seen in the ,northern hemisphere since that of #ahhb1 appears to have been ,daniel's ,comet of #aijg 7see ,plate ,,xviii41 p4 #beh74 ,this comet was discovered on ,june #i1 #aijg1 by ,mr4 ,z4 ,daniel1 at ,princeton ,observatory1 ,new ,jersey1 ,u4,s4,a4 ,it became visible to the naked eye about mid-,july of that year1 and reached its greatest brilliancy about the end of ,august4 ,it did not1 however1 attract much popular attention1 as its position in the sky allowed it to be seen only just before dawn4 #bd ,with the exception1 of course1 of such an anomaly as the retrograde motion of the ninth satellite of ,saturn4 #be ,if we except the case of the comet which was photographed near the solar corona in the eclipse of #ahhb4 ,illustration3 ,,plate ,,xviii4 ,,daniel',s ,,comet ,,of #aijg ,from a photograph taken1 on ,august #aath1 #aijg1 by ,dr4 ,max ,wolf1 at the ,astrophysical ,observatory1 ,heidelberg4 ,the instrument used was a #bh-;inch reflecting telescope1 and the time of exposure was fifteen minutes4 ,as the telescope was guided to follow the moving comet1 the stars have imprinted themselves upon the photographic plate as short trails4 ,this is clearly the opposite to what is depicted on ,plate ,,xiii4 7,page #beh7 ,,chapter ,,xx ,,remarkable ,,comets ,if eclipses were a cause of terror in past ages1 comets appear to have been doubly so4 ,their much longer continuance in the sight of men had no doubt something to say to this1 and also the fact that they arrived without warning2 it not being then possible to give even a rough prediction of their return1 as in the case of eclipses4 ,as both these phenomena were occasional1 and out of the ordinary course of things1 they drew exceptional attention as unusual events always do2 for it must be allowed that quite as wonderful things exist1 but they pass unnoticed merely because men have grown accustomed to them4 ,for some reason the ancients elected to class comets along with meteors1 the aurora borealis1 and other phenomena of the atmosphere1 rather than with the planets and the bodies of the spaces beyond4 ,the sudden appearance of these objects led them to be regarded as signs sent by the gods to announce remarkable events1 chief among these being the deaths of monarchs4 ,shakespeare has reminded us of this in those celebrated lines in ,julius ,csar3-- ,when beggars die there are no comets seen1 ,the heavens themselves blaze forth the death of princes4 ,numbed by fear1 the men of old blindly accepted these presages of fate2 and did not too closely question whether the threatened danger was to their own nation or to some other1 to their ruler or to his enemy4 ,now and then1 as in the case of the ,roman ,emperor ,vespasian1 there was a cynical attempt to apply some reasoning to the portent4 ,that emperor1 in alluding to the comet of ,a4,d4 #gi1 is reported to have said3 ,this hairy star does not concern me2 it menaces rather the ,king of the ,parthians1 for he is hairy and ,i am bald4 ,vespasian1 all the same1 died shortly afterwards6 ,pliny1 in his natural history1 gives several instances of the terrible significance which the ancients attached to comets4 ,a comet1 he says1 is ordinarily a very fearful star2 it announces no small effusion of blood4 ,we have seen an example of this during the civil commotion of ,octavius4 ,a very brilliant comet appeared in #cga ,b4,c41 and about the same time an earthquake caused ,helic and ,bura1 two towns in ,achaia1 to be swallowed up by the sea4 ,the following remark made by ,seneca concerning it shows that the ancients did not consider comets merely as precursors1 but even as actual causes of fatal events3 ,this comet1 so anxiously observed by every one1 because of the great catastrophe which it produced as soon as it appeared1 the submersion of ,bura and ,helic4 ,comets are by no means rare visitors to our skies1 and very few years have elapsed in historical times without such objects making their appearance4 ,in the ,dark and ,middle ,ages1 when ,europe was split up into many small kingdoms and principalities1 it was1 of course1 hardly possible for a comet to appear without the death of some ruler occurring near the time4 ,critical situations1 too1 were continually arising in those disturbed days4 ,the end of ,louis le ,debonnaire was hastened1 as the reader will1 no doubt1 recollect1 by the great eclipse of #hdj2 but it was firmly believed that a comet which had appeared a year or two previously presaged his death4 ,the comet of #aeef is reported to have influenced the abdication of the ,emperor ,charles ,v42 but curiously enough1 this event had already taken place before the comet made its appearance6 ,such beliefs1 no doubt1 had a very real effect upon rulers of a superstitious nature1 or in a weak state of health4 ,for instance1 ,gian ,galeazzo ,visconti1 ,duke of ,milan1 was sick when the comet of #adjb appeared4 ,after seeing it1 he is said to have exclaimed3 ,i render thanks to ,god for having decreed that my death should be announced to men by this celestial sign4 ,his malady then became worse1 and he died shortly afterwards4 ,it is indeed not improbable that such superstitious fears in monarchs were fanned by those who would profit by their deaths1 and yet did not wish to stain their own hands with blood4 ,evil though its effects may have been1 this morbid interest which past ages took in comets has proved of the greatest service to our science4 ,had it not been believed that the appearance of these objects was attended with far-reaching effects1 it is very doubtful whether the old chroniclers would have given themselves the trouble of alluding to them at all2 and thus the modern investigators of cometary orbits would have lacked a great deal of important material4 ,we will now mention a few of the most notable comets which historians have recorded4 ,a comet which appeared in #cdd ,b4,c4 was thought to betoken the success of the expedition undertaken in that year by ,timoleon of ,corinth against ,sicily4 ,the gods by an extraordinary prodigy announced his success and future greatness3 a burning torch appeared in the heavens throughout the night and preceded the fleet of ,timoleon until it arrived off the coast of ,sicily4 ,the comet of #dc ,b4,c4 was generally believed to be the soul of ,csar on its way to heaven4 ,josephus tells us that in ,a4,d4 #fi several prodigies1 and amongst them a comet in the shape of a sword1 announced the destruction of ,jerusalem4 ,this comet is said to have remained over the city for the space of a year6 ,a comet which appeared in ,a4,d4 #ccf was considered to have announced the death of the ,emperor ,constantine4 ,but perhaps the most celebrated comet of early times was the one which appeared in ,a4,d4 #ajjj4 ,that year was1 in more than one way1 big with portent1 for there had long been a firm belief that the ,christian era could not possibly run into four figures4 ,men1 indeed1 steadfastly believed that when the thousand years had ended1 the millennium would immediately begin4 ,therefore they did not reap neither did they sow1 they toiled not1 neither did they spin1 and the appearance of the comet strengthened their convictions4 ,the fateful year1 however1 passed by without anything remarkable taking place2 but the neglect of husbandry brought great famine and pestilence over ,europe in the years which followed4 ,in ,april #ajff1 that year fraught with such immense consequences for ,england1 a comet appeared4 ,no one doubted but that it was a presage of the success of the ,conquest1 and perhaps1 indeed1 it had its due weight in determining the minds and actions of the men who took part in the expedition4 ,nova stella1 novus rex 7a new star1 a new sovereign7 was a favourite proverb of the time4 ,the chroniclers1 with one accord1 have delighted to relate that the ,normans1 guided by a comet1 invaded ,england4 ,a representation of this object appears in the ,bayeux ,tapestry 7see ,fig4 #ai1 p4 #bfc74bf ,illustration3 ,,fig4 #ai4--,the comet of #ajff1 as represented in the ,bayeux ,tapestry4 7,from the ,world of ,comets47 ,we have mentioned ,halley's ,comet of #afhb1 and how it revisits the neighbourhood of the earth at intervals of seventy-six years4 ,the comet of #ajff has for many years been supposed to be ,halley's ,comet on one of its visits4 ,the identity of these two1 however1 was only quite recently placed beyond all doubt by the investigations of ,messrs ,cowell and ,crommelin4 ,this comet appeared also in #adef1 when ,john ,huniades was defending ,belgrade against the ,turks led by ,mahomet ,,ii41 the conqueror of ,constantinople1 and is said to have paralysed both armies with fear4 ,the ,middle ,ages have left us descriptions of comets1 which show only too well how the imagination will run riot under the stimulus of terror4 ,for instance1 the historian1 ,nicetas1 thus describes the comet of the year #aahb3 ,after the ,romans were driven from ,constantinople a prognostic was seen of the excesses and crimes to which ,andronicus was to abandon himself4 ,a comet appeared in the heavens similar to a writhing serpent2 sometimes it extended itself1 sometimes it drew itself in2 sometimes1 to the great terror of the spectators1 it opened a huge mouth2 it seemed that1 as if thirsting for human blood1 it was upon the point of satiating itself4 ,and1 again1 the celebrated ,ambrose ,par1 the father of surgery1 has left us the following account of the comet of #aebh1 which appeared in his own time3 ,this comet1 said he1 was so horrible1 so frightful1 and it produced such great terror in the vulgar1 that some died of fear1 and others fell sick4 ,it appeared to be of excessive length1 and was of the colour of blood4 ,at the summit of it was seen the figure of a bent arm1 holding in its hand a great sword1 as if about to strike4 ,at the end of the point there were three stars4 ,on both sides of the rays of this comet were seen a great number of axes1 knives1 blood-coloured swords1 among which were a great number of hideous human faces1 with beards and bristling hair4 ,par1 it is true1 was no astronomer2 yet this shows the effect of the phenomenon1 even upon a man of great learning1 as undoubtedly he was4 ,it should here be mentioned that nothing very remarkable happened at or near the year #aebh4 ,concerning the comet of #afhj1 the extraordinary story got about that1 at ,rome1 a hen had laid an egg on which appeared a representation of the comet6 ,but the superstitions with regard to comets were now nearing their end4 ,the last blow was given by ,halley1 who definitely proved that they obeyed the laws of gravitation1 and circulated around the sun as planets do2 and further announced that the comet of #afhb had a period of seventy-six years1 which would cause it to reappear in the year #agei4 ,we have seen how this prediction was duly verified4 ,we have seen1 too1 how this comet appeared again in #ahce1 and how it is due to return in the early part of #aiaj4 #bf ,with regard to the words ,isti mirant stella in the figure1 ,mr4 ,w4,t4 ,lynn suggests that they may not1 after all1 be the grammatically bad ,latin which they appear1 but that the legend is really ,isti mirantur stellam1 the missing letters being supposed to be hidden by the building and the comet4 ,,chapter ,,xxi ,,meteors ,,or ,,shooting ,,stars ,any one who happens to gaze at the sky for a short time on a clear night is pretty certain to be rewarded with a view of what is popularly known as a shooting star4 ,such an object1 however1 is not a star at all1 but has received its appellation from an analogy2 for the phenomenon gives to the inexperienced in these matters an impression as if one of the many points of light1 which glitter in the vaulted heaven1 had suddenly become loosened from its place1 and was falling towards the earth4 ,in its passage across the sky the moving object leaves behind a trail of light which usually lasts for a few moments4 ,shooting stars1 or meteors1 as they are technically termed1 are for the most part very small bodies1 perhaps no larger than peas or pebbles1 which1 dashing towards our earth from space beyond1 are heated to a white heat1 and reduced to powder by the friction resulting from their rapid passage into our atmosphere4 ,this they enter at various degrees of speed1 in some cases so great as #de miles a second4 ,the speed1 of course1 will depend greatly upon whether the earth and the meteors are rushing towards each other1 or whether the latter are merely overtaking the earth4 ,in the first of these cases the meteors will naturally collide with the atmosphere with great force2 in the other case they will plainly come into it with much less rapidity4 ,as has been already stated1 it is from observations of such bodies that we are enabled to estimate1 though very imperfectly1 the height at which the air around our globe practically ceases1 and this height is imagined to be somewhere about #ajj miles4 ,fortunate1 indeed1 is it for us that there is a goodly layer of atmosphere over our heads1 for1 were this not so1 these visitors from space would strike upon the surface of our earth night and day1 and render existence still more unendurable than many persons choose to consider it4 ,to what a bombardment must the moon be continually subject1 destitute as she is of such an atmospheric shield6 ,it is only in the moment of their dissolution that we really learn anything about meteors1 for these bodies are much too small to be seen before they enter our atmosphere4 ,the dbris arising from their destruction is wafted over the earth1 and1 settling down eventually upon its surface1 goes to augment the accumulation of that humble domestic commodity which men call dust4 ,this continual addition of material tends1 of course1 to increase the mass of the earth1 though the effect thus produced will be on an exceedingly small scale4 ,the total number of meteors moving about in space must be practically countless4 ,the number which actually dash into the earth's atmosphere during each year is1 indeed1 very great4 ,professor ,simon ,newcomb1 the well-known ,american astronomer1 has estimated that1 of the latter1 those large enough to be seen with the naked eye cannot be in all less than #adf1jjj1jjj1jjj per annum4 ,ten times more numerous still are thought to be those insignificant ones which are seen to pass like mere sparks of light across the field of an observer's telescope4 ,until comparatively recent times1 perhaps up to about a hundred years ago1 it was thought that meteors were purely terrestrial phenomena which had their origin in the upper regions of the air4 ,it1 however1 began to be noticed that at certain periods of the year these moving objects appeared to come from definite areas of the sky4 ,considerations1 therefore1 respecting their observed velocities1 directions1 and altitudes1 gave rise to the theory that they are swarms of small bodies travelling around the sun in elongated elliptical orbits1 all along the length of which they are scattered1 and that the earth1 in its annual revolution1 rushing through the midst of such swarms at the same epoch each year1 naturally entangles many of them in its atmospheric net4 ,the dates at which the earth is expected to pass through the principal meteor-swarms are now pretty well known4 ,these swarms are distinguished from one another by the direction of the sky from which the meteors seem to arrive4 ,many of the swarms are so wide that the earth takes days1 and even weeks1 to pass through them4 ,in some of these swarms1 or streams1 as they are also called1 the meteors are distributed with fair evenness along the entire length of their orbits1 so that the earth is greeted with a somewhat similar shower at each yearly encounter4 ,in others1 the chief portions are bunched together1 so that1 in certain years1 the display is exceptional 7see ,fig4 #bj1 p4 #bfi74 ,that part of the heavens from which a shower of meteors is seen to emanate is called the radiant1 or radiant point1 because the foreshortened view we get of the streaks of light makes it appear as if they radiated outwards from this point4 ,in observations of these bodies the attention of astronomers is directed to registering the path and speed of each meteor1 and to ascertaining the position of the radiant4 ,it is from data such as these that computations concerning the swarms and their orbits are made4 ,illustration3 ,,fig4 #bj4--,passage of the ,earth through the thickest portion of a ,meteor ,swarm4 ,the ,earth and the ,meteors are here represented as approaching each other from opposite directions4 ,for the present state of knowledge concerning meteors1 astronomy is largely indebted to the researches of ,mr4 ,w4,f4 ,denning1 of ,bristol1 and of the late ,professor ,a4,s4 ,herschel4 ,during the course of each year the earth encounters a goodly number of meteor-swarms4 ,three of these1 giving rise to fine displays1 are very well known--the ,perseids1 or ,august ,meteors1 and the ,leonids and ,bielids1 which appear in ,november4 ,of the above three the ,leonid display is by far the most important1 and the high degree of attention paid to it has laid the foundation of meteoric astronomy in much the same way that the study of the fascinating corona has given such an impetus to our knowledge of the sun4 ,the history of this shower of meteors may be traced back as far as ,a4,d4 #ijb1 which was known as the ,year of the ,stars4 ,it is related that in that year1 on the night of ,october #abth--the shower now comes about a month later--whilst the ,moorish ,king1 ,ibrahim ,ben ,ahmed1 lay dying before ,cosenza1 in ,calabria1 a multitude of falling stars scattered themselves across the sky like rain1 and the beholders shuddered at what they considered a dread celestial portent4 ,we have1 however1 little knowledge of the subsequent history of the ,leonids until #afih1 since which time the maximum shower has appeared with considerable regularity at intervals of about thirty-three years4 ,but it was not until #agii that they sprang into especial notice4 ,on the #aath ,november in that year a splendid display was witnessed at ,cumana1 in ,south ,america1 by the celebrated travellers1 ,humboldt and ,bonpland4 ,finer still1 and surpassing all displays of the kind ever seen1 was that of ,november #ab1 #ahcc1 when the meteors fell thick as snowflakes1 #bdj1jjj being estimated to have appeared during seven hours4 ,some of them were even so bright as to be seen in full daylight4 ,the radiant from which the meteors seem to diverge was ascertained to be situated in the head of the constellation of the ,lion1 or ,sickle of ,leo1 as it is popularly termed1 whence their name--,leonids4 ,it was from a discussion of the observations then made that the ,american astronomer1 ,olmsted1 concluded that these meteors sprang upon us from interplanetary space1 and were not1 as had been hitherto thought1 born of our atmosphere4 ,later on1 in #ahcg1 ,olbers formulated the theory that the bodies in question travelled around the sun in an elliptical orbit1 and at the same time he established the periodicity of the maximum shower4 ,the periodic time of recurrence of this maximum1 namely1 about thirty-three years1 led to eager expectancy as #ahff drew near4 ,hopes were then fulfilled1 and another splendid display took place1 of which ,sir ,robert ,ball1 who observed it1 has given a graphic description in his ,story of the ,heavens4 ,the display was repeated upon a smaller scale in the two following years4 ,the ,leonids were henceforth deemed to hold an anomalous position among meteor swarms4 ,according to theory the earth cut through their orbit at about the same date each year1 and so a certain number were then seen to issue from the radiant4 ,but1 in addition1 after intervals of thirty-three years1 as has been seen1 an exceptional display always took place2 and this state of things was not limited to one year alone1 but was repeated at each meeting for about three years running4 ,the further assumption was1 therefore1 made that the swarm was much denser in one portion of the orbit than elsewhere1#bg and that this congested part was drawn out to such an extent that the earth could pass through the crossing place during several annual meetings1 and still find it going by like a long procession 7see ,fig4 #bj1 p4 #bfi74 ,in accordance with this ascertained period of thirty-three years1 the recurrence of the great ,leonid shower was timed to take place on the #aeth of ,november #ahii4 ,but there was disappointment then1 and the displays which occurred during the few years following were not of much importance4 ,a good deal of comment was made at the time1 and theories were accordingly put forward to account for the failure of the great shower4 ,the most probable explanation seems to be1 that the attraction of one of the larger planets--,jupiter perhaps--has diverted the orbit somewhat from its old position1 and the earth does not in consequence cut through the swarm in the same manner as it used to do4 ,the other ,november display alluded to takes place between the #bcrd and #bgth of that month4 ,it is called the ,andromedid ,shower1 because the meteors appear to issue from the direction of the constellation of ,andromeda1 which at that period of the year is well overhead during the early hours of the night4 ,these meteors are also known by the name of ,bielids1 from a connection which the orbit assigned to them appears to have with that of the well-known comet of ,biela4 ,m4 ,egenitis1 ,director of the ,observatory of ,athens1 accords to the ,bielids a high antiquity4 ,he traces the shower back to the days of the ,emperor ,justinian4 ,theophanes1 the ,chronicler of that epoch1 writing of the famous revolt of ,nika in the year ,a4,d4 #ecb1 says3--,during the same year a great fall of stars came from the evening till the dawn4 ,m4 ,egenitis notes another early reference to these meteors in ,a4,d4 #geb1 during the reign of the ,eastern ,emperor1 ,constantine ,copronymous4 ,writing of that year1 ,nicephorus1 a ,patriarch of ,constantinople1 has as follows3--,all the stars appeared to be detached from the sky1 and to fall upon the earth4 ,the ,bielids1 however1 do not seem to have attracted particular notice until the nineteenth century4 ,attention first began to be riveted upon them on account of their suspected connection with ,biela's comet4 ,it appeared that the same orbit was shared both by that comet and the ,bielid swarm4 ,it will be remembered that the comet in question was not seen after its appearance in #aheb4 ,since that date1 however1 the ,bielid shower has shown an increased activity2 which was further noticed to be especially great in those years in which the comet1 had it still existed1 would be due to pass near the earth4 ,the third of these great showers to which allusion has above been made1 namely1 the ,perseids1 strikes the earth about the #ajth of ,august2 for which reason it is known on the ,continent under the name of the tears of ,st4 ,lawrence1 the day in question being sacred to that ,saint4 ,this shower is traceable back many centuries1 even as far as the year ,a4,d4 #haa4 ,the name given to these meteors1 ,perseids1 arises from the fact that their radiant point is situated in the constellation of ,perseus4 ,this shower is1 however1 not by any means limited to the particular night of ,august #ajth1 for meteors belonging to the swarm may be observed to fall in more or less varying quantities from about ,july #hth to ,august #bbnd4 ,the ,perseid meteors sometimes fall at the rate of about sixty per hour4 ,they are noted for their great rapidity of motion1 and their trails besides often persist for a minute or two before being disseminated4 ,unlike the other well-known showers1 the radiants of which are stationary1 that of the ,perseids shifts each night a little in an easterly direction4 ,the orbit of the ,perseids cuts that of the earth almost perpendicularly4 ,the bodies are generally supposed to be the result of the disintegration of an ancient comet which travelled in the same orbit4 ,tuttle's ,comet1 which passed close to the earth in #ahfb1 also belongs to this orbit2 and its period of revolution is calculated to be #aca years4 ,the ,perseids appear to be disseminated all along this great orbit1 for we meet them in considerable quantities each year4 ,the bodies in question are in general particularly small4 ,the swarm has1 however1 like most others1 a somewhat denser portion1 and through this the earth passed in #ahdh4 ,the aphelion1 or point where the far end of the orbit turns back again towards the sun1 is situated right away beyond the path of ,neptune1 at a distance of forty-eight times that of the earth from the sun4 ,the comet of #aecb also belongs to the ,perseid orbit4 ,it revisited the neighbourhood of the earth in #affa1 and should have returned in #aghi4 ,but we have no record of it in that year2 for which omission the then politically disturbed state of ,europe may account4 ,if not already disintegrated1 this comet is due to return in #aiai4 ,this supposed connection between comets and meteor-swarms must be also extended to the case of the ,leonids4 ,these meteors appear to travel along the same track as ,tempel's ,comet of #ahff4 ,it is considered that the attractions of the various bodies of the solar system upon a meteor swarm must eventually result in breaking up the bunched portion1 so that in time the individual meteors should become distributed along the whole length of the orbit4 ,upon this assumption the ,perseid swarm1 in which the meteors are fairly well scattered along its path1 should be of greater age than the ,leonid4 ,as to the ,leonid swarm itself1 ,le ,verrier held that it was first brought into the solar system in ,a4,d4 #abf1 having been captured from outer space by the gravitative action of the planet ,uranus4 ,the acknowledged theory of meteor swarms has naturally given rise to an idea1 that the sunlight shining upon such a large collection of particles ought to render a swarm visible before its collision with the earth's atmosphere4 ,several attempts have therefore been made to search for approaching swarms by photography1 but1 so far1 it appears without success4 ,it has also been proposed1 by ,mr4 ,w4,h4,s4 ,monck1 that the stars in those regions from which swarms are due1 should be carefully watched1 to see if their light exhibits such temporary diminutions as would be likely to arise from the momentary interposition of a cloud of moving particles4 ,between ten and fifteen years ago it happened that several well-known observers1 employed in telescopic examination of the sun and moon1 reported that from time to time they had seen small dark bodies1 sometimes singly1 sometimes in numbers1 in passage across the discs of the luminaries4 ,it was concluded that these were meteors moving in space beyond the atmosphere of the earth4 ,the bodies were called dark meteors1 to emphasise the fact that they were seen in their natural condition1 and not in that momentary one in which they had hitherto been always seen2 i4e4 when heated to white heat1 and rapidly vaporised1 in the course of their passage through the upper regions of our air4 ,this discovery gave promise of such assistance to meteor theories1 that calculations were made from the directions in which they had been seen to travel1 and the speeds at which they had moved1 in the hope that some information concerning their orbits might be revealed4 ,but after a while some doubt began to be thrown upon their being really meteors1 and eventually an ,australian observer solved the mystery4 ,he found that they were merely tiny particles of dust1 or of the black coating on the inner part of the tube of the telescope1 becoming detached from the sides of the eye-piece and falling across the field of view4 ,he was led to this conclusion by having noted that a gentle tapping of his instrument produced the dark bodies in great numbers6 ,thus the opportunity of observing meteors beyond our atmosphere had once more failed4 ,meteorites1 also known as rolites and fireballs1 are usually placed in quite a separate category from meteors4 ,they greatly exceed the latter in size1 are comparatively rare1 and do not appear in any way connected with the various showers of meteors4 ,the friction of their passage through the atmosphere causes them to shine with a great light2 and if not shattered to pieces by internal explosions1 they reach the ground to bury themselves deep in it with a great rushing and noise4 ,when found by uncivilised peoples1 or savages1 they are1 on account of their celestial origin1 usually regarded as objects of wonder and of worship1 and thus have arisen many mythological legends and deifications of blackened stones4 ,on the other hand1 when they get into the possession of the civilised1 they are subjected to careful examinations and tests in chemical laboratories4 ,the bodies are1 as a rule1 composed of stone1 in conjunction with iron1 nickel1 and such elements as exist in abundance upon our earth2 though occasionally specimens are found which are practically pure metal4 ,in the museums of the great capitals of both ,continents are to be seen some fine collections of meteorites4 ,several countries--,greenland and ,mexico1 for instance--contain in the soil much meteoric iron1 often in masses so large as to baffle all attempts at removal4 ,blocks of this kind have been known to furnish the natives in their vicinity for many years with sources of workable iron4 ,the largest meteorite in the world is one known as the ,anighito meteorite4 ,it was brought to the ,united ,states by the explorer ,peary1 who found it at ,cape ,york in ,greenland4 ,he estimates its weight at from #ij to #ajj tons4 ,one found in ,mexico1 called the ,bacubirito1 comes next1 with an estimated weight of #bg-a_/b tons4 ,the third in size is the ,willamette meteorite1 found at ,willamette in ,oregon in #aijb4 ,it measures #aj #f-a_/b #d-a_/b feet1 and weighs about #ae-a_/b tons4 #bg ,the gem of the meteor ring1 as it has been termed4 ,,chapter ,,xxii ,,the ,,stars ,in the foregoing chapters we have dealt at length with those celestial bodies whose nearness to us brings them into our especial notice4 ,the entire room1 however1 taken up by these bodies1 is as a mere point in the immensities of star-filled space4 ,the sun1 too1 is but an ordinary star2 perhaps quite an insignificant one#bh in comparison with the majority of those which stud that background of sky against which the planets are seen to perform their wandering courses4 ,dropping our earth and the solar system behind1 let us go afield and explore the depths of space4 ,we have seen how1 in very early times1 men portioned out the great mass of the so-called fixed stars into divisions known as constellations4 ,the various arrangements1 into which the brilliant points of light fell as a result of perspective1 were noticed and roughly compared with such forms as were familiar to men upon the earth4 ,imagination quickly saw in them the semblances of heroes and of mighty fabled beasts2 and1 around these monstrous shapes1 legends were woven1 which told how the great deeds done in the misty dawn of historical time had been enshrined by the gods in the sky as an example and a memorial for men4 ,though the centuries have long outlived such fantasies1 yet the constellation figures and their ancient names have been retained to this day1 pretty well unaltered for want of any better arrangement4 ,the ,great and ,little ,bears1 ,cassiopeia1 ,perseus1 and ,andromeda1 ,orion and the rest1 glitter in our night skies just as they did centuries and centuries ago4 ,many persons seem to despair of gaining any real knowledge of astronomy1 merely because they are not versed in recognising the constellations4 ,for instance1 they will say3--,what is the use of my reading anything about the subject8 ,why1 ,i believe ,i couldn't even point out the ,great ,bear1 were ,i asked to do so6 ,but if such persons will only consider for a moment that what we call the ,great ,bear has no existence in fact1 they need not be at all disheartened4 ,could we but view this familiar constellation from a different position in space1 we should perhaps be quite unable to recognise it4 ,mountain masses1 for instance1 when seen from new directions1 are often unrecognisable4 ,it took1 as we have seen1 a very long time for men to acknowledge the immense distances of the stars from our earth4 ,their seeming unchangeableness of position was1 as we have seen1 largely responsible for the idea that the earth was immovable in space4 ,it is a wonder that the ,copernican system ever gained the day in the face of this apparent fixity of the stars4 ,as time went on1 it became indeed necessary to accord to these objects an almost inconceivable distance1 in order to account for the fact that they remained apparently quite undisplaced1 notwithstanding the journey of millions of miles which the earth was now acknowledged to make each year around the sun4 ,in the face of the gradual and immense improvement in telescopes1 this apparent immobility of the stars was1 however1 not destined to last4 ,the first ascertained displacement of a star1 namely that of #fa ,cygni1 noted by ,bessel in the year #ahch1 definitely proved to men the truth of the ,copernican system4 ,since then some forty more stars have been found to show similar tiny displacements4 ,we are1 therefore1 in possession of the fact1 that the actual distances of a few out of the great host can be calculated4 ,to mention some of these4 ,the nearest star to the earth1 so far as we yet know1 is ,alpha ,centauri1 which is distant from us about #be billions of miles4 ,the light from this star1 travelling at the stupendous rate of about #ahf1jjj miles per second1 takes about #d-a_/d years to reach our earth1 or1 to speak astronomically1 ,alpha ,centauri is about #d-a_/d light years distant from us4 ,sirius--the brightest star in the whole sky--is at twice this distance1 i4e4 about #h-a_/b light years4 ,vega is about #cj light years distant from us1 ,capella about #cb1 and ,arcturus about #ajj4 ,the displacements1 consequent on the earth's movement1 have1 however1 plainly nothing to say to any real movements on the part of the stars themselves4 ,the old idea was that the stars were absolutely fixed2 hence arose the term fixed stars--a term which1 though inaccurate1 has not yet been entirely banished from the astronomical vocabulary4 ,but careful observations extending over a number of years have shown slight changes of position among these bodies2 and such alterations cannot be ascribed to the revolution of the earth in its orbit1 for they appear to take place in every direction4 ,these evidences of movement are known as proper motions1 that is to say1 actual motions in space proper to the stars themselves4 ,stars which are comparatively near to us show1 as a rule1 greater proper motions than those which are farther off4 ,it must not1 however1 be concluded that these proper motions are of any very noticeable amounts4 ,they are1 as a matter of fact1 merely upon the same apparently minute scale as other changes in the heavens2 and would largely remain unnoticed were it not for the great precision of modern astronomical instruments4 ,one of the swiftest moving of the stars is a star of the sixth magnitude in the constellation of the ,great ,bear2 which is known as #ahcj ,groombridge1 because this was the number assigned to it in a catalogue of stars made by an astronomer of that name4 ,it is popularly known as the ,runaway ,star1 a name given to it by ,professor ,newcomb4 ,its speed is estimated to be at least #ach miles per second4 ,it may be actually moving at a much greater rate1 for it is possible that we see its path somewhat foreshortened4 ,a still greater proper motion--the greatest1 in fact1 known--is that of an eighth magnitude star in the southern hemisphere1 in the constellation of ,pictor4 ,nothing1 indeed1 better shows the enormous distance of the stars from us1 and the consequent inability of even such rapid movements to alter the appearance of the sky during the course of ages1 than the fact that it would take more than two centuries for the star in question to change its position in the sky by a space equal to the apparent diameter of the moon2 a statement which is equivalent to saying that1 were it possible to see this star with the naked eye1 which it is not1 at least twenty-five years would have to elapse before one would notice that it had changed its place at all6 ,both the stars just mentioned are very faint4 ,that in ,pictor is1 as has been said1 not visible to the naked eye4 ,it appears besides to be a very small body1 for ,sir ,david ,gill finds a parallax which makes it only as far off from us as ,sirius4 ,the ,groombridge star1 too1 is just about the limit of ordinary visibility4 ,it is1 indeed1 a curious fact that the fainter stars seem1 on the average1 to be moving more rapidly than the brighter4 ,investigations into proper motions lead us to think that every one of the stars must be moving in space in some particular direction4 ,to take a few of the best known4 ,sirius and ,vega are both approaching our system at a rate of about #aj miles per second1 ,arcturus at about #e miles per second1 while ,capella is receding from us at about #ae miles per second4 ,of the twin brethren1 ,castor and ,pollux1 ,castor is moving away from us at about #d-a_/b miles per second1 while ,pollux is coming towards us at about #cc miles per second4 ,much of our knowledge of proper motions has been obtained indirectly by means of the spectroscope1 on the ,doppler principle already treated of1 by which we are enabled to ascertain whether a source from which light is coming is approaching or receding4 ,the sun being1 after all1 a mere star1 it will appear only natural for it also to have a proper motion of its own4 ,this is indeed the case2 and it is rushing along in space at a rate of between ten and twelve miles per second1 carrying with it its whole family of planets and satellites1 of comets and meteors4 ,the direction in which it is advancing is towards a point in the constellation of ,lyra1 not far from its chief star ,vega4 ,this is shown by the fact that the stars about the region in question appear to be opening out slightly1 while those in the contrary portion of the sky appear similarly to be closing together4 ,sir ,william ,herschel was the first to discover this motion of the sun through space2 though in the idea that such a movement might take place he seems to have been anticipated by ,mayer in #agfj1 by ,michell in #agfg1 and by ,lalande in #aggf4 ,a suggestion has been made that our solar system1 in its motion through the celestial spaces1 may occasionally pass through regions where abnormal magnetic conditions prevail1 in consequence of which disturbances may manifest themselves throughout the system at the same instant4 ,thus the sun may be getting the credit of producing what it merely reacts to in common with the rest of its family4 ,but this suggestion1 plausible though it may seem1 will not explain why the magnetic disturbances experienced upon our earth show a certain dependence upon such purely local facts1 as the period of the sun's rotation1 for instance4 ,one would very much like to know whether the movement of the sun is along a straight line1 or in an enormous orbit around some centre4 ,the idea has been put forward that it may be moving around the centre of gravity of the whole visible stellar universe4 ,mdler1 indeed1 propounded the notion that ,alcyone--the chief star in the group known as the ,pleiades--occupied this centre1 and that everything revolved around it4 ,he went even further to proclaim that here was the ,place of the ,almighty1 the ,mansion of the ,eternal6 ,but ,mdler's ideas upon this point have long been shelved4 ,to return to the general question of the proper motion of stars4 ,in several instances these motions appear to take place in groups1 as if certain stars were in some way associated together4 ,for example1 a large number of the stars composing the ,pleiades appear to be moving through space in the same direction4 ,also1 of the seven stars composing the ,plough1 all but two--the star at the end of its handle1 and that one of the pointers1 as they are called1 which is the nearer to the pole star--have a common proper motion1 i4e4 are moving in the same direction and nearly at the same rate4 ,further still1 the well-known ,dutch astronomer1 ,professor ,kapteyn1 of ,groningen1 has lately reached the astonishing conclusion that a great part of the visible universe is occupied by two vast streams of stars travelling in opposite directions4 ,in both these great streams1 the individual bodies are found1 besides1 to be alike in design1 alike in chemical constitution1 and alike in the stage of their development4 ,a fable related by the ,persian astronomer1 ,al ,sufi 7tenth century1 ,a4,d47 shows well the changes in the face of the sky which proper motions are bound to produce after great lapses of time4 ,according to this fable the stars ,sirius and ,procyon were the sisters of the star ,canopus4 ,canopus married ,rigel 7another star17 but1 having murdered her1 he fled towards the ,south ,pole1 fearing the anger of his sisters4 ,the fable goes on to relate1 among other things1 that ,sirius followed him across the ,milky ,way4 ,mr4 ,j4 ,e4 ,gore1 in commenting on the story1 thinks that it may be based upon a tradition of ,sirius having been seen by the men of the ,stone ,age on the opposite side of the ,milky ,way to that on which it now is4 ,sirius is in that portion of the heavens from which the sun is advancing4 ,its proper motion is such that it is gaining upon the earth at the rate of about ten miles per second1 and so it must overtake the sun after the lapse of great ages4 ,vega1 on the other hand1 is coming towards us from that part of the sky towards which the sun is travelling4 ,it should be about half a million years before the sun and ,vega pass by one another4 ,those who have specially investigated this question say that1 as regards the probability of a near approach1 it is much more likely that ,vega will be then so far to one side of the sun1 that her brightness will not be much greater than it is at this moment4 ,considerations like these call up the chances of stellar collisions4 ,such possibilities need not1 however1 give rise to alarm2 for the stars1 as a rule1 are at such great distances from each other1 that the probability of relatively near approaches is slight4 ,we thus see that the constellations do not in effect exist1 and that there is in truth no real background to the sky4 ,we find further that the stars are strewn through space at immense distances from each other1 and are moving in various directions hither and thither4 ,the sun1 which is merely one of them1 is moving also in a certain direction1 carrying the solar system along with it4 ,it seems1 therefore1 but natural to suppose that many a star may be surrounded by some planetary system in a way similar to ours1 which accompanies it through space in the course of its celestial journeyings4 #bh ,vega1 for instance1 shines one hundred times more brightly than the sun would do1 were it to be removed to the distance at which that star is from us4 ,,chapter ,,xxiii ,,the ,,stars--continued ,the stars appear to us to be scattered about the sky without any orderly arrangement4 ,further1 they are of varying degrees of brightness2 some being extremely brilliant1 whilst others can but barely be seen4 ,the brightness of a star may arise from either of two causes4 ,on the one hand1 the body may be really very bright in itself2 on the other hand1 it may be situated comparatively near to us4 ,sometimes1 indeed1 both these circumstances may come into play together4 ,since variation in brightness is the most noticeable characteristic of the stars1 men have agreed to class them in divisions called magnitudes4 ,this term1 it must be distinctly understood1 is employed in such classification without any reference whatever to actual size1 being merely taken to designate roughly the amount of light which we receive from a star4 ,the twenty brightest stars in the sky are usually classed in the first magnitude4 ,in descending the scale1 each magnitude will be noticed to contain1 broadly speaking1 three times as many stars as the one immediately above it4 ,thus the second magnitude contains #fe1 the third #aij1 the fourth #dbe1 the fifth #aajj1 and the sixth #cbjj4 ,the last of these magnitudes is about the limit of the stars which we are able to see with the naked eye4 ,adding1 therefore1 the above numbers together1 we find that1 without the aid of the telescope1 we cannot see more than about #ejjj stars in the entire sky--northern and southern hemispheres included4 ,quite a small telescope will1 however1 allow us to see down to the ninth magnitude1 so that the total number of stars visible to us with such very moderate instrumental means will be well over #ajj1jjj4 ,it must not1 however1 be supposed that the stars included within each magnitude are all of exactly the same brightness4 ,in fact1 it would be difficult to say if there exist in the whole sky two stars which send us precisely the same amount of light4 ,in arranging the magnitudes1 all that was done was to make certain broad divisions1 and to class within them such stars as were much on a par with regard to brightness4 ,it may here be noted that a standard star of the first magnitude gives us about one hundred times as much light as a star of the sixth magnitude1 and about one million times as much as one of the sixteenth magnitude--which is near the limit of what we can see with the very best telescope4 ,though the first twenty stars in the sky are popularly considered as being of the first magnitude1 yet several of them are much brighter than an average first magnitude star would be4 ,for instance1 ,sirius--the brightest star in the whole sky--is equal to about eleven first magnitude stars1 like1 say1 ,aldebaran4 ,in consequence of such differences1 astronomers are agreed in classifying the brightest of them as brighter than the standard first magnitude star4 ,on this principle ,sirius would be about two and a half magnitudes above the first4 ,this notation is usefully employed in making comparisons between the amount of light which we receive from the sun1 and that which we get from an individual star4 ,thus the sun will be about twenty-seven and a half magnitudes above the first magnitude4 ,the range1 therefore1 between the light which we receive from the sun 7considered merely as a very bright star7 and the first magnitude stars is very much greater than that between the latter and the faintest star which can be seen with the telescope1 or even registered upon the photographic plate4 ,to classify stars merely by their magnitudes1 without some definite note of their relative position in the sky1 would be indeed of little avail4 ,we must have some simple method of locating them in the memory1 and the constellations of the ancients here happily come to our aid4 ,a system combining magnitudes with constellations was introduced by ,bayer in #afjc1 and is still adhered to4 ,according to this the stars in each constellation1 beginning with the brightest star1 are designated by the letters of the ,greek alphabet taken in their usual order4 ,for example1 in the constellation of ,canis ,major1 or the ,greater ,dog1 the brightest star is the well-known ,sirius1 called by the ancients the ,dog ,star2 and this star1 in accordance with ,bayer's method1 has received the ,greek letter a 7alpha71 and is consequently known as ,alpha ,canis ,majoris4#bi ,as soon as the ,greek letters are used up in this way the ,roman alphabet is brought into requisition1 after which recourse is had to ordinary numbers4 ,notwithstanding this convenient arrangement1 some of the brightest stars are nearly always referred to by certain proper names given to them in old times4 ,for instance1 it is more usual to speak of ,sirius1 ,arcturus1 ,vega1 ,capella1 ,procyon1 ,aldebaran1 ,regulus1 and so on1 than of a ,canis ,majoris1 a ,botis1 a ,lyr1 a ,aurig1 a ,canis ,minoris1 a ,tauri1 a ,leonis1 c4 c4 ,in order that future generations might be able to ascertain what changes were taking place in the face of the sky1 astronomers have from time to time drawn up catalogues of stars4 ,these lists have included stars of a certain degree of brightness1 their positions in the sky being noted with the utmost accuracy possible at the period4 ,the earliest known catalogue of this kind was made1 as we have seen1 by the celebrated ,greek astronomer1 ,hipparchus1 about the year #abe ,b4,c4 ,it contained #ajhj stars4 ,it was revised and brought up to date by ,ptolemy in ,a4,d4 #aej4 ,another celebrated list was that drawn up by the ,persian astronomer1 ,al ,sufi1 about the year ,a4,d4 #ifd4 ,in it #ajbb stars were noted down4 ,a catalogue of #ajje stars was made in #aehj by the famous ,danish astronomer1 ,tycho ,brahe4 ,among modern catalogues that of ,argelander 7#agii-ahge7 contained as many as #cbd1aih stars4 ,it was extended by ,schnfeld so as to include a portion of the ,southern ,hemisphere1 in which way #acc1fei more stars were added4 ,in recent years a project was placed on foot of making a photographic survey of the sky1 the work to be portioned out among various nations4 ,a great part of this work has already been brought to a conclusion4 ,about #ae1jjj1jjj stars will appear upon the plates2 but1 so far1 it has been proposed to catalogue only about a million and a quarter of the brightest of them4 ,this idea of surveying the face of the sky by photography sprang indirectly from the fine photographs which ,sir ,david ,gill took1 when at the ,cape of ,good ,hope1 of the ,comet of #ahhb4 ,the immense number of star-images which had appeared upon his plates suggested the idea that photography could be very usefully employed to register the relative positions of the stars4 ,the arrangement of seven stars known as the ,plough is perhaps the most familiar configuration in the sky 7see ,plate ,,xix41 p4 #bib74 ,in the ,united ,states it is called the ,dipper1 on account of its likeness to the outline of a saucepan1 or ladle4 ,charles' ,wain was the old ,english name for it1 and readers of ,csar will recollect it under ,septentriones1 or the ,seven ,stars1 a term which that writer uses as a synonym for the ,north4 ,though identified in most persons' minds with ,ursa ,major1 or the ,great ,bear1 the ,plough is actually only a small portion of that famous constellation4 ,six out of the seven stars which go to make up the well-known figure are of the second magnitude1 while the remaining one1 which is the middle star of the group1 is of the third4 ,the ,greek letters1 as borne by the individual stars of the ,plough1 are a plain transgression of ,bayer's method as above described1 for they have certainly not been allotted here in accordance with the proper order of brightness4 ,for instance1 the third magnitude star1 just alluded to as being in the middle of the group1 has been marked with the ,greek letter d 7,delta72 and so is made to take rank before the stars composing what is called the handle of the ,plough1 which are all of the second magnitude4 ,sir ,william ,herschel long ago drew attention to the irregular manner in which ,bayer's system had been applied4 ,it is1 indeed1 a great pity that this notation was not originally worked out with greater care and correctness2 for1 were it only reliable1 it would afford great assistance to astronomers in judging of what changes in relative brightness have taken place among the stars4 ,though we may speak of using the constellations as a method of finding our way about the sky1 it is1 however1 to certain marked groupings in them of the brighter stars that we look for our sign-posts4 ,most of the constellations contain a group or so of noticeable stars1 whose accidental arrangement dimly recalls the outline of some familiar geometrical figure and thus arrests the attention4#cj ,for instance1 in an almost exact line with the two front stars of the ,plough1 or pointers as they are called1#ca and at a distance about five times as far away as the interval between them1 there will be found a third star of the second magnitude4 ,this is known as ,polaris1 or the ,pole ,star1 for it very nearly occupies that point of the heaven towards which the north pole of the earth's axis is at present directed 7see ,plate ,,xix41 p4 #bib74 ,thus during the apparently daily rotation of the heavens1 this star looks always practically stationary4 ,it will1 no doubt1 be remembered how ,shakespeare has put into the mouth of ,julius ,csar these memorable words3-- ,but ,i am constant as the northern star1 ,of whose true-fix'd and resting quality ,there is no fellow in the firmament4 ,illustration3 ,,plate ,,xix4 ,,the ,,sky ,,around ,,the ,,north ,,pole ,we see here the ,plough1 the ,pole ,star1 ,ursa ,minor1 ,auriga1 ,cassiopeia's ,chair1 and ,lyra4 ,also the ,circle of ,precession1 along which the ,pole makes a complete revolution in a period of #be1hfh years1 and the ,temporary ,star discovered by ,tycho ,brahe in the year #aegb4 7,page #bia7 ,on account of the curvature of the earth's surface1 the height at which the ,pole ,star is seen above the horizon at any place depends regularly upon the latitude2 that is to say1 the distance of the place in question from the equator4 ,for instance1 at the north pole of the earth1 where the latitude is greatest1 namely1 #ij1 the ,pole ,star will appear directly overhead2 whereas in ,england1 where the latitude is about #ej1 it will be seen a little more than half way up the northern sky4 ,at the equator1 where the latitude is nil1 the ,pole ,star will be on the horizon due north4 ,in consequence of its unique position1 the ,pole ,star is of very great service in the study of the constellations4 ,it is a kind of centre around which to hang our celestial ideas--a starting point1 so to speak1 in our voyages about the sky4 ,according to the constellation figures1 the ,pole ,star is in ,ursa ,minor1 or the ,little ,bear1 and is situated at the end of the tail of that imaginary figure 7see ,plate ,,xix41 p4 #bib74 ,the chief stars of this constellation form a group not unlike the ,plough1 except that the handle is turned in the contrary direction4 ,the ,americans1 in consequence1 speak of it as the ,little ,dipper4 ,before leaving this region of the sky1 it will be well to draw attention to the second magnitude star z in the ,great ,bear 7,zeta ,urs ,majoris71 which is the middle star in the handle of the ,plough4 ,this star is usually known as ,mizar1 a name given to it by the ,arabians4 ,a person with good eyesight can see quite near to it a fifth magnitude star1 known under the name of ,alcor4 ,we have here a very good example of that deception in the estimation of objects in the sky1 which has been alluded to in an earlier chapter4 ,alcor is indeed distant from ,mizar by about one-third the apparent diameter of the moon1 yet no one would think so6 ,on the other side of ,polaris from the ,plough1 and at about an equal apparent distance1 will be found a figure in the form of an irregular ,w1 made up of second and third magnitude stars4 ,this is the well-known ,cassiopeia's ,chair--portion of the constellation of ,cassiopeia 7see ,plate ,,xix41 p4 #bib74 ,on either side of the ,pole ,star1 about midway between the ,plough and ,cassiopeia's ,chair1 but a little further off from it than these1 are the constellations of ,auriga and ,lyra 7see ,plate ,,xix41 p4 #bib74 ,the former constellation will be easily recognised1 because its chief features are a brilliant yellowish first magnitude star1 with one of the second magnitude not far from it4 ,the first magnitude star is ,capella1 the other is b ,aurig4 ,lyra contains only one first magnitude star--,vega1 pale blue in colour4 ,this star has a certain interest for us from the fact that1 as a consequence of that slow shift of direction of the earth's axis known as ,precession1 it will be very near the north pole of the heavens in some #ab1jjj years1 and so will then be considered the pole star 7see ,plate ,,xix41 p4 #bib74 ,the constellation of ,lyra itself1 it must also be borne in mind1 occupies that region of the heavens towards which the solar system is travelling4 ,the handle of the ,plough points roughly towards the constellation of ,botes1 in which is the brilliant first magnitude star ,arcturus4 ,this star is of an orange tint4 ,between ,botes and ,lyra lie the constellations of ,corona ,borealis 7or the ,northern ,crown7 and ,hercules4 ,the chief feature of ,corona ,borealis1 which is a small constellation1 is a semicircle of six small stars1 the brightest of which is of the second magnitude4 ,the constellation of ,hercules is very extensive1 but contains no star brighter than the third magnitude4 ,near to ,lyra1 on the side away from ,hercules1 are the constellations of ,cygnus and ,aquila4 ,of the two1 the former is the nearer to the ,pole ,star1 and will be recognised by an arrangement of stars widely set in the form of a cross1 or perhaps indeed more like the framework of a boy's kite4 ,the position of ,aquila will be found through the fact that three of its brightest stars are almost in a line and close together4 ,the middle of these is ,altair1 a yellowish star of the first magnitude4 ,at a little distance from ,ursa ,major1 on the side away from the ,pole ,star1 is the constellation of ,leo1 or the ,lion4 ,its chief feature is a series of seven stars1 supposed to form the head of that animal4 ,the arrangement of these stars is1 however1 much more like a sickle1 wherefore this portion of the constellation is usually known as the ,sickle of ,leo4 ,at the end of the handle of the sickle is a white first magnitude star--,regulus4 ,the reader will1 no doubt1 recollect that it is from a point in the ,sickle of ,leo that the ,leonid meteors appear to radiate4 ,the star second in brightness in the constellation of ,leo is known as ,denebola4 ,this star1 now below the second magnitude1 seems to have been very much brighter in the past4 ,it is noted1 indeed1 as a brilliant first magnitude star by ,al ,sufi1 that famous ,persian astronomer who lived1 as we have seen1 in the tenth century4 ,ptolemy also notes it as of the first magnitude4 ,in the neighbourhood of ,auriga1 and further than it from the ,pole ,star1 are several remarkable constellations--,taurus1 ,orion1 ,gemini1 ,canis ,minor1 and ,canis ,major 7see ,plate ,,xx41 p4 #bif74 ,the first of these1 ,taurus 7or the ,bull71 contains two conspicuous star groups--the ,pleiades and the ,hyades4 ,the ,pleiades are six or seven small stars quite close together1 the majority of which are of the fourth magnitude4 ,this group is sometimes occulted by the moon4 ,the way in which the stars composing it are arranged is somewhat similar to that in the ,plough1 though of course on a scale ever so much smaller4 ,the impression which the group itself gives to the casual glance is thus admirably pictured in ,tennyson's ,locksley ,hall3-- ,many a night ,i saw the ,pleiads1 rising through the mellow shade1 ,glitter like a swarm of fire-flies tangled in a silver braid4 ,illustration3 ,,plate ,,xx4 ,,orion ,,and ,,his ,,neighbours ,we see here that magnificent region of the sky which contains the brightest star of all--,sirius4 ,note also especially the ,milky ,way1 the ,pleiades1 the ,hyades1 and the ,belt and ,sword of ,orion4 7,page #bif7 ,the group of the ,hyades occupies the head of the ,bull1 and is much more spread out than that of the ,pleiades4 ,it is composed besides of brighter stars1 the brightest being one of the first magnitude1 ,aldebaran4 ,this star is of a red colour1 and is sometimes known as the ,eye of the ,bull4 ,the constellation of ,orion is easily recognised as an irregular quadrilateral formed of four bright stars1 two of which1 ,betelgeux 7reddish7 and ,rigel 7brilliant white71 are of the first magnitude4 ,in the middle of the quadrilateral is a row of three second magnitude stars1 known as the ,belt of ,orion4 ,jutting off from this is another row of stars called the ,sword of ,orion4 ,the constellation of ,gemini1 or the ,twins1 contains two bright stars--,castor and ,pollux--close to each other4 ,pollux1 though marked with the ,greek letter b1 is the brighter of the two1 and nearly of the standard first magnitude4 ,just further from the ,pole than ,gemini1 is the constellation of ,canis ,minor1 or the ,lesser ,dog4 ,its chief star is a white first magnitude one--,procyon4 ,still further again from the ,pole than ,canis ,minor is the constellation of ,canis ,major1 or the ,greater ,dog4 ,it contains the brightest star in the whole sky1 the first magnitude star ,sirius1 bluish-white in colour1 also known as the ,dog ,star4 ,this star is almost in line with the stars forming the ,belt of ,orion1 and is not far from that constellation4 ,taken in the following order1 the stars ,capella1 b ,aurig1 ,castor1 ,pollux1 ,procyon1 and ,sirius1 when they are all above the horizon at the same time1 form a beautiful curve stretching across the heaven4 ,the groups of stars visible in the southern skies have by no means the same fascination for us as those in the northern4 ,the ancients were in general unacquainted with the regions beyond the equator1 and so their scheme of constellations did not include the sky around the ,south ,pole of the heavens4 ,in modern times1 however1 this part of the celestial expanse was also portioned out into constellations for the purpose of easy reference2 but these groupings plainly lack that simplicity of conception and legendary interest which are so characteristic of the older ones4 ,the brightest star in the southern skies is found in the constellation of ,argo1 and is known as ,canopus4 ,in brightness it comes next to ,sirius1 and so is second in that respect in the entire heaven4 ,it does not1 however1 rise above the ,english horizon4 ,of the other southern constellations1 two call for especial notice1 and these adjoin each other4 ,one is ,centaurus 7or the ,centaur71 which contains the two first magnitude stars1 a and b ,centauri4 ,the first of these1 ,alpha ,centauri1 comes next in brightness to ,canopus1 and is notable as being the nearest of all the stars to our earth4 ,the other constellation is called ,crux1 and contains five stars set in the form of a rough cross1 known as the ,southern ,cross4 ,the brightest of these1 a ,crucis1 is of the first magnitude4 ,owing to the ,precession of the ,equinoxes1 which1 as we have seen1 gradually shifts the position of the ,pole among the stars1 certain constellations used to be visible in ancient times in more northerly latitudes than at present4 ,for instance1 some five thousand years ago the ,southern ,cross rose above the ,english horizon1 and was just visible in the latitude of ,london4 ,it has1 however1 long ago even ceased to be seen in the ,south of ,europe4 ,the constellation of ,crux happens to be situated in that remarkable region of the southern skies1 in which are found the stars ,canopus and ,alpha ,centauri1 and also the most brilliant portion of the ,milky ,way4 ,it is believed to be to this grand celestial region that allusion is made in the ,book of ,job 7ix4 #i71 under the title of the ,chambers of the ,south4 ,the ,cross must have been still a notable feature in the sky of ,palestine in the days when that ancient poem was written4 ,there is no star near enough to the southern pole of the heavens to earn the distinction of ,south ,polar ,star4 ,the ,galaxy1 or ,milky ,way 7see ,plate ,,xx41 p4 #bif71 is a broad band of diffused light which is seen to stretch right around the sky4 ,the telescope1 however1 shows it to be actually composed of a great host of very faint stars--too faint1 indeed1 to be separately distinguished with the naked eye4 ,along a goodly stretch of its length it is cleft in two2 while near the south pole of the heavens it is entirely cut across by a dark streak4 ,in this rapid survey of the face of the sky1 we have not been able to do more than touch in the broadest manner upon some of the most noticeable star groups and a few of the most remarkable stars4 ,to go any further is not a part of our purpose2 our object being to deal with celestial bodies as they actually are1 and not in those groupings under which they display themselves to us as a mere result of perspective4 #bi ,attention must here be drawn to the fact that the name of the constellation is always put in the genitive case4 #cj ,the early peoples1 as we have seen1 appear to have been attracted by those groupings of the stars which reminded them in a way of the figures of men and animals4 ,we moderns1 on the other hand1 seek almost instinctively for geometrical arrangements4 ,this is1 perhaps1 symptomatic of the evolution of the race4 ,in the growth of the individual we find1 for example1 something analogous4 ,a child1 who has been given pencil and paper1 is almost certain to produce grotesque drawings of men and animals2 whereas the idle and half-conscious scribblings which a man may make upon his blotting-paper are usually of a geometrical character4 #ca ,because the line joining them points in the direction of the ,pole ,star4 ,,chapter ,,xxiv ,,systems ,,of ,,stars ,many stars are seen comparatively close together4 ,this may plainly arise from two reasons4 ,firstly1 the stars may happen to be almost in the same line of sight2 that is to say1 seen in nearly the same direction2 and though one star may be ever so much nearer to us than the other1 the result will give all the appearance of a related pair4 ,a seeming arrangement of two stars in this way is known as a double1 or double star2 or1 indeed1 to be very precise1 an optical double4 ,secondly1 in a pair of stars1 both bodies may be about the same distance from us1 and actually connected as a system like1 for instance1 the moon and the earth4 ,a pairing of stars in this way1 though often casually alluded to as a double star1 is properly termed a binary1 or binary system4 ,but collocations of stars are by no means limited to two4 ,we find1 indeed1 all over the sky such arrangements in which there are three or more stars2 and these are technically known as triple or multiple stars respectively4 ,further1 groups are found in which a great number of stars are closely massed together1 such a massing together of stars being known as a cluster4 ,the ,pole ,star 7,polaris7 is a double star1 one of the components being of a little below the second magnitude1 and the other a little below the ninth4 ,they are so close together that they appear as one star to the naked eye1 but they may be seen separate with a moderately sized telescope4 ,the brighter star is yellowish1 and the faint one white4 ,this brighter star is found by means of the spectroscope to be actually composed of three stars so very close together that they cannot be seen separately even with a telescope4 ,it is thus a triple star1 and the three bodies of which it is composed are in circulation about each other4 ,two of them are darker than the third4 ,the method of detecting binary stars by means of the spectroscope is an application of ,doppler's principle4 ,it will1 no doubt1 be remembered that1 according to the principle in question1 we are enabled1 from certain shiftings of the lines in the spectrum of a luminous body1 to ascertain whether that body is approaching us or receding from us4 ,now there are certain stars which always appear single even in the largest telescopes1 but when the spectroscope is directed to them a spectrum with two sets of lines is seen4 ,such stars must1 therefore1 be double4 ,further1 if the shiftings of the lines1 in a spectrum like this1 tell us that the component stars are making small movements to and from us which go on continuously1 we are therefore justified in concluding that these are the orbital revolutions of a binary system greatly compressed by distance4 ,such connected pairs of stars1 since they cannot be seen separately by means of any telescope1 no matter how large1 are known as spectroscopic binaries4 ,in observations of spectroscopic binaries we do not always get a double spectrum4 ,indeed1 if one of the components be below a certain magnitude1 its spectrum will not appear at all2 and so we are left in the strange uncertainty as to whether this component is merely faint or actually dark4 ,it is1 however1 from the shiftings of the lines in the spectrum of the other component that we see that an orbital movement is going on1 and are thus enabled to conclude that two bodies are here connected into a system1 although one of these bodies resolutely refuses directly to reveal itself even to the all-conquering spectroscope4 ,mizar1 that star in the handle of the ,plough to which we have already drawn attention1 will be found with a small telescope to be a fine double1 one of the components being white and the other greenish4 ,actually1 however1 as the ,american astronomer1 ,professor ,f4,r4 ,moulton1 points out1 these stars are so far from each other that if we could be transferred to one of them we should see the other merely as an ordinary bright star4 ,the spectroscope shows that the brighter of these stars is again a binary system of two huge suns1 the components revolving around each other in a period of about twenty days4 ,this discovery made by ,professor ,e4,c4 ,pickering1 the first of the kind by means of the spectroscope1 was announced in #ahhi from the ,harvard ,observatory in the ,united ,states4 ,a star close to ,vega1 known as e 7,epsilon7 ,lyr 7see ,plate ,,xix41 p4 #bib71 is a double1 the components of which may be seen separately with the naked eye by persons with very keen eyesight4 ,if this star1 however1 be viewed with the telescope1 the two companions will be seen far apart2 and it will be noticed that each of them is again a double4 ,by means of the spectroscope ,capella is shown to be really composed of two stars 7one about twice as bright as the other7 situated very close together and forming a binary system4 ,sirius is also a binary system2 but it is what is called a visual one1 for its component stars may be seen separately in very large telescopes4 ,its double1 or rather binary1 nature1 was discovered in #ahfb by the celebrated optician ,alvan ,g4 ,clark1 while in the act of testing the #ah-;inch refracting telescope1 then just constructed by his firm1 and now at the ,dearborn ,observatory1 ,illinois1 ,u4,s4,a4 ,the companion is only of the tenth magnitude1 and revolves around ,sirius in a period of about fifty years1 at a mean distance equal to about that of ,uranus from the sun4 ,seen from ,sirius1 it would shine only something like our full moon4 ,it must be self-luminous and not a mere planet2 for ,mr4 ,gore has shown that if it shone only by the light reflected from ,sirius1 it would be quite invisible even in the ,great ,yerkes ,telescope4 ,procyon is also a binary1 its companion having been discovered by ,professor ,j4,m4 ,schaeberle at the ,lick ,observatory in #ahif4 ,the period of revolution in this system is about forty years4 ,observations by ,mr4 ,t4 ,lewis of ,greenwich seem1 however1 to point to the companion being a small nebula rather than a star4 ,the star 7,eta7 ,cassiopei 7see ,plate ,,xix41 p4 #bib71 is easily seen as a fine double in telescopes of moderate size4 ,it is a binary system1 the component bodies revolving around their common centre of gravity in a period of about two hundred years4 ,this system is comparatively near to us1 i4e4 about nine light years1 or a little further off than ,sirius4 ,in a small telescope the star ,castor will be found double1 the components1 one of which is brighter than the other1 forming a binary system4 ,the fainter of these was found by ,belopolsky1 with the spectroscope1 to be composed of a system of two stars1 one bright and the other either dark or not so bright1 revolving around each other in a period of about three days4 ,the brighter component of ,castor is also a spectroscopic binary1 with a period of about nine days2 so that the whole of what we see with the naked eye as ,castor1 is in reality a remarkable system of four stars in mutual orbital movement4 ,alpha ,centauri--the nearest star to the earth--is a visual binary1 the component bodies revolving around each other in a period of about eighty-one years4 ,the extent of this system is about the same as that of ,sirius4 ,viewed from each other1 the bodies would shine only like our sun as seen from ,neptune4 ,among the numerous binary stars the orbits of some fifty have been satisfactorily determined4 ,many double stars1 for which this has not yet been done1 are1 however1 believed to be1 without doubt1 binary4 ,in some cases a parallax has been found2 so that we are enabled to estimate in miles the actual extent of such systems1 and the masses of the bodies in terms of the sun's mass4 ,most of the spectroscopic binaries appear to be upon a smaller scale than the telescopic ones4 ,some are1 indeed1 comparatively speaking1 quite small4 ,for instance1 the component stars forming b ,aurig are about eight million miles apart1 while in z ,geminorum1 the distance between the bodies is only a little more than a million miles4 ,spectroscopic binaries are probably very numerous4 ,professor ,w4,w4 ,campbell1 ,director of the ,lick ,observatory1 estimates1 for instance1 that1 out of about every half-a-dozen stars1 one is a spectroscopic binary4 ,it is only in the case of binary systems that we can discover the masses of stars at all4 ,these are ascertained from their movements with regard to each other under the influence of their mutual gravitative attractions4 ,in the case of simple stars we have clearly nothing of the kind to judge by2 though1 if we can obtain a parallax1 we may hazard a guess from their brightness4 ,binary stars were incidentally discovered by ,sir ,william ,herschel4 ,in his researches to get a stellar parallax he had selected a number of double stars for test purposes1 on the assumption that1 if one of such a pair were much nearer than the other1 it might show a displacement with regard to its neighbour as a direct consequence of the earth's orbital movement around the sun4 ,he1 however1 failed entirely to obtain any parallaxes1 the triumph in this being1 as we have seen1 reserved for ,bessel4 ,but in some of the double stars which he had selected1 he found certain alterations in the relative positions of the bodies1 which plainly were not a consequence of the earth's motion1 but showed rather that there was an actual circling movement of the bodies themselves under their mutual attractions4 ,it is to be noted that the existence of such connected pairs had been foretold as probable by the ,rev4 ,john ,michell1 who lived a short time before ,herschel4 ,the researches into binary systems--both those which can be seen with the eye and those which can be observed by means of the spectroscope1 ought to impress upon us very forcibly the wide sway of the law of gravitation4 ,of star clusters about #ajj are known1 and such systems often contain several thousand stars4 ,they usually cover an area of sky somewhat smaller than the moon appears to fill4 ,in most clusters the stars are very faint1 and1 as a rule1 are between the twelfth and sixteenth magnitudes4 ,it is difficult to say whether these are actually small bodies1 or whether their faintness is due merely to their great distance from us1 since they are much too far off to show any appreciable parallactic displacement4 ,mr4 ,gore1 however1 thinks there is good evidence to show that the stars in clusters are really close1 and that the clusters themselves fill a comparatively small space4 ,one of the finest examples of a cluster is the great globular one1 in the constellation of ,hercules1 discovered by ,halley in #agad4 ,it contains over #ejjj stars1 and upon a clear1 dark night is visible to the naked eye as a patch of light4 ,in the telescope1 however1 it is a wonderful object4 ,there are also fine clusters in the constellations of ,auriga1 ,pegasus1 and ,canes ,venatici4 ,in the southern heavens there are some magnificent examples of globular clusters4 ,this hemisphere seems1 indeed1 to be richer in such objects than the northern4 ,for instance1 there is a great one in the constellation of the ,centaur1 containing some #fjjj stars 7see ,plate ,,xxi41 p4 #cjf74 ,illustration3 ,,plate ,,xxi4 ,,the ,,great ,,globular ,,cluster ,,in ,,the ,,southern ,,constellation ,,of ,,centaurus ,from a photograph taken at the ,cape ,observatory1 on ,may #bdth1 #aijc4 ,time of exposure1 #a hour4 7,page #cjf7 ,certain remarkable groups of stars1 of a nature similar to clusters1 though not containing such faint or densely packed stars as those we have just alluded to1 call for a mention in this connection4 ,the best example of such star groups are the ,pleiades and the ,hyades 7see ,plate ,,xx41 p4 #bif71 ,coma ,berenices1 and ,prsepe 7or the ,beehive71 the last-named being in the constellation of ,cancer4 ,stars which alter in their brightness are called ,variable ,stars1 or variables4 ,the first star whose variability attracted attention is that known as ,omicron ,ceti1 namely1 the star marked with the ,greek letter o 7,omicron7 in the constellation of ,cetus1 or the ,whale1 a constellation situated not far from ,taurus4 ,this star1 the variability of which was discovered by ,fabricius in #aeif1 is also known as ,mira1 or the ,wonderful1 on account of the extraordinary manner in which its light varies from time to time4 ,the star known by the name of ,algol1#cb popularly called the ,demon ,star--whose astronomical designation is b 7,beta7 ,persei1 or the star second in brightness in the constellation of ,perseus--was discovered by ,goodricke1 in the year #aghc1 to be a variable star4 ,in the following year b ,lyr1 the star in ,lyra next in order of brightness after ,vega1 was also found by the same observer to be a variable4 ,it may be of interest to the reader to know that ,goodricke was deaf and dumb1 and that he died in #aghf at the early age of twenty-one years6 ,it was not1 however1 until the close of the nineteenth century that much attention was paid to variable stars4 ,now several hundreds of these are known1 thanks chiefly to the observations of1 amongst others1 ,professor ,s4,c4 ,chandler of ,boston1 ,u4,s4,a41 ,mr4 ,john ,ellard ,gore of ,dublin1 and ,dr4 ,a4,w4 ,roberts of ,south ,africa4 ,this branch of astronomy has not1 indeed1 attracted as much popular attention as it deserves1 no doubt because the nature of the work required does not call for the glamour of an observatory or a large telescope4 ,the chief discoveries with regard to variable stars have been made by the naked eye1 or with a small binocular4 ,the amount of variation is estimated by a comparison with other stars4 ,as in many other branches of astronomy1 photography is now employed in this quest with marked success2 and lately many variable stars have been found to exist in clusters and nebul4 ,it was at one time considered that a variable star was in all probability a body1 a portion of whose surface had been relatively darkened in some manner akin to that in which sun spots mar the face of the sun2 and that when its axial rotation brought the less illuminated portions in turn towards us1 we witnessed a consequent diminution in the star's general brightness4 ,herschel1 indeed1 inclined to this explanation1 for his belief was that all the stars bore spots like those of the sun4 ,it appears preferably thought nowadays that disturbances take place periodically in the atmosphere or surroundings of certain stars1 perhaps through the escape of imprisoned gases1 and that this may be a fruitful cause of changes of brilliancy4 ,the theory in question will1 however1 apparently account for only one class of variable star1 namely1 that of which ,mira ,ceti is the best-known example4 ,the scale on which it varies in brightness is very great1 for it changes from the second to the ninth magnitude4 ,for the other leading type of variable star1 ,algol1 of which mention has already been made1 is the best instance4 ,the shortness of the period in which the changes of brightness in such stars go their round1 is the chief characteristic of this latter class4 ,the period of ,algol is a little under three days4 ,this star when at its brightest is of about the second magnitude1 and when least bright is reduced to below the third magnitude2 from which it follows that its light1 when at the minimum1 is only about one-third of what it is when at the maximum4 ,it seems definitely proved by means of the spectroscope that variables of this kind are merely binary stars1 too close to be separated by the telescope1 which1 as a consequence of their orbits chancing to be edgewise towards us1 eclipse each other in turn time after time4 ,if1 for instance1 both components of such a pair are bright1 then when one of them is right behind the other1 we will not1 of course1 get the same amount of light as when they are side by side4 ,if1 on the other hand1 one of the components happens to be dark or less luminous and the other bright1 the manner in which the light of the bright star will be diminished when the darker star crosses its face should easily be understood4 ,it is to the second of these types that ,algol is supposed to belong4 ,the ,algol system appears to be composed of a body about as broad as our sun1 which regularly eclipses a brighter body which has a diameter about half as great again4 ,since the companion of ,algol is often spoken of as a dark body1 it were well here to point out that we have no evidence at all that it is entirely devoid of light4 ,we have already found1 in dealing with spectroscopic binaries1 that when one of the component stars is below a certain magnitude#cc its spectrum will not be seen2 so one is left in the glorious uncertainty as to whether the body in question is absolutely dark1 or darkish1 or faint1 or indeed only just out of range of the spectroscope4 ,it is thought probable by good authorities that the companion of ,algol is not quite dark1 but has some inherent light of its own4 ,it is1 of course1 much too near ,algol to be seen with the largest telescope4 ,there is in fact a distance of only from two to three millions of miles between the bodies1 from which ,mr4 ,gore infers that they would probably remain unseparated even in the largest telescope which could ever be constructed by man4 ,the number of known variables of the ,algol type is1 so far1 small2 not much indeed over thirty4 ,in some of them the components are believed to revolve touching each other1 or nearly so4 ,an extreme example of this is found in the remarkable star ,v4 ,puppis1 an ,algol variable of the southern hemisphere4 ,both its components are bright1 and the period of light variation is about one and a half days4 ,dr4 ,a4 ,w4 ,roberts finds that the bodies are revolving around each other in actual contact4 ,temporary stars are stars which have suddenly blazed out in regions of the sky where no star was previously seen1 and have faded away more or less gradually4 ,it was the appearance of such a star1 in the year #acd ,b4,c41 which prompted ,hipparchus to make his celebrated catalogue1 with the object of leaving a record by which future observers could note celestial changes4 ,in #aegb another star of this kind flashed out in the constellation of ,cassiopeia 7see ,plate ,,xix41 p4 #bib71 and was detected by ,tycho ,brahe4 ,it became as bright as the planet ,venus1 and eventually was visible in the day-time4 ,two years later1 however1 it disappeared1 and has never since been seen4 ,in #afjd ,kepler recorded a similar star in the constellation of ,ophiuchus which grew to be as bright as ,jupiter4 ,it also lasted for about two years1 and then faded away1 leaving no trace behind4 ,it is rarely1 however1 that temporary stars attain to such a brilliance2 and so possibly in former times a number of them may have appeared1 but not have risen to a sufficient magnitude to attract attention4 ,even now1 unless such a star becomes clearly visible to the naked eye1 it runs a good chance of not being detected4 ,a curious point1 worth noting1 with regard to temporary stars is that the majority of them have appeared in the ,milky ,way4 ,these sudden visitations have in our day received the name of ,nov2 that is to say1 ,new ,stars4 ,two1 in recent years1 attracted a good deal of attention4 ,the first of these1 known as ,nova ,aurig1 or the ,new ,star in the constellation of ,auriga1 was discovered by ,dr4 ,t4,d4 ,anderson at ,edinburgh in ,january #ahib4 ,at its greatest brightness it attained to about the fourth magnitude4 ,by ,april it had sunk to the twelfth1 but during ,august it recovered to the ninth magnitude4 ,after this last flare-up it gradually faded away4 ,the startling suddenness with which temporary stars usually spring into being is the groundwork upon which theories to account for their origin have been erected4 ,that numbers of dark stars1 extinguished suns1 so to speak1 may exist in space1 there is a strong suspicion2 and it is just possible that we have an instance of one dark stellar body in the companion of ,algol4 ,that such dark stars might be in rapid motion is reasonable to assume from the already known movements of bright stars4 ,two dark bodies might1 indeed1 collide together1 or a collision might take place between a dark star and a star too faint to be seen even with the most powerful telescope4 ,the conflagration produced by the impact would thus appear where nothing had been seen previously4 ,again1 a similar effect might be produced by a dark body1 or a star too faint to be seen1 being heated to incandescence by plunging in its course through a nebulous mass of matter1 of which there are many examples lying about in space4 ,the last explanation1 which is strongly reminiscent of what takes place in shooting stars1 appears more probable than the collision theory4 ,the flare-up of new stars continues1 indeed1 only for a comparatively short time2 whereas a collision between two bodies would1 on the other hand1 produce an enormous nebula which might take even millions of years to cool down4 ,we have1 indeed1 no record of any such sudden appearance of a lasting nebula4 ,the other temporary star1 known as ,nova ,persei1 or the new star in the constellation of ,perseus1 was discovered early in the morning of ,february #bb1 #aija1 also by ,dr4 ,anderson4 ,a day later it had grown to be brighter than ,capella4 ,photographs which had been taken1 some three days previous to its discovery1 of the very region of the sky in which it had burst forth1 were carefully examined1 and it was not found in these4 ,at the end of two days after its discovery ,nova ,persei had lost one-third of its light4 ,during the ensuing six months it passed through a series of remarkable fluctuations1 varying in brightness between the third and fifth magnitudes4 ,in the month of ,august it was seen to be surrounded by luminous matter in the form of a nebula1 which appeared to be gradually spreading to some distance around4 ,taking into consideration the great way off at which all this was taking place1 it looked as if the new star had ejected matter which was travelling outward with a velocity equivalent to that of light4 ,the remarkable theory was1 however1 put forward by ,professor ,kapteyn and the late ,dr4 ,w4,e4 ,wilson that there might be after all no actual transmission of matter2 but that perhaps the real explanation was the gradual illumination of hitherto invisible nebulous matter1 as a consequence of the flare-up which had taken place about six months before4 ,it was1 therefore1 imagined that some dark body moving through space at a very rapid rate had plunged through a mass of invisible nebulous matter1 and had consequently become heated to incandescence in its passage1 very much like what happens to a meteor when moving through our atmosphere4 ,the illumination thus set up temporarily in one point1 being transmitted through the nebulous wastes around with the ordinary velocity of light1 had gradually rendered this surrounding matter visible4 ,on the assumptions required to fit in with such a theory1 it was shown that ,nova ,persei must be at a distance from which light would take about three hundred years in coming to us4 ,the actual outburst of illumination1 which gave rise to this temporary star1 would therefore have taken place about the beginning of the reign of ,james ,i4 ,some recent investigations with regard to ,nova ,persei have1 however1 greatly narrowed down the above estimate of its distance from us4 ,for instance1 ,bergstrand proposes a distance of about ninety-nine light years2 while the conclusions of ,mr4 ,f4,w4 ,very would bring it still nearer1 i4e4 about sixty-five light years4 ,the last celestial objects with which we have here to deal are the ,nebul4 ,these are masses of diffused shining matter scattered here and there through the depths of space4 ,nebul are of several kinds1 and have been classified under the various headings of ,spiral1 ,planetary1 ,ring1 and ,irregular4 ,a typical spiral nebula is composed of a disc-shaped central portion1 with long curved arms projecting from opposite sides of it1 which give an impression of rapid rotatory movement4 ,the discovery of spiral nebul was made by ,lord ,rosse with his great #f-;foot reflector4 ,two good examples of these objects will be found in ,ursa ,major1 while there is another fine one in ,canes ,venatici 7see ,plate ,,xxii41 p4 #cad71 a constellation which lies between ,ursa ,major and ,botes4 ,but the finest spiral of all1 perhaps the most remarkable nebula known to us1 is the ,great ,nebula in the constellation of ,andromeda1 7see ,plate ,,xxiii41 p4 #caf7--;a constellation just further from the pole than ,cassiopeia4 ,when the moon is absent and the night clear this nebula can be easily seen with the naked eye as a small patch of hazy light4 ,it is referred to by ,al ,sufi4 ,illustration3 ,,plate ,,xxii4 ,,spiral ,,nebula ,,in ,,the ,,constellation ,,of ,,canes ,,venatici ,from a photograph by the late ,dr4 ,w4,e4 ,wilson1 ,d4,sc41 ,f4,r4,s4 7,page #cad7 ,spiral nebul are white in colour1 whereas the other kinds of nebula have a greenish tinge4 ,they are also by far the most numerous2 and the late ,professor ,keeler1 who considered this the normal type of nebula1 estimated that there were at least #abj1jjj of such spirals within the reach of the ,crossley reflector of the ,lick ,observatory4 ,professor ,perrine has indeed lately raised this estimate to half a million1 and thinks that with more sensitive photographic plates and longer exposures the number of spirals would exceed a million4 ,the majority of these objects are very small1 and appear to be distributed over the sky in a fairly uniform manner4 ,planetary nebul are small faint roundish objects which1 when seen in the telescope1 recall the appearance of a planet1 hence their name4 ,one of these nebul1 known astronomically as ,g4,c4 #dcgc1 has recently been found to be rushing through space towards the earth at a rate of between thirty and forty miles per second4 ,it seems strange1 indeed1 that any gaseous mass should move at such a speed6 ,what are known as ring nebul were until recently believed to form a special class4 ,these objects have the appearance of mere rings of nebulous matter4 ,much doubt has1 however1 been thrown upon their being rings at all2 and the best authorities regard them merely as spiral nebul1 of which we happen to get a foreshortened view4 ,very few examples are known1 the most famous being one in the constellation of ,lyra1 usually known as the ,annular ,nebula in ,lyra4 ,this object is so remote from us as to be entirely invisible to the naked eye4 ,it contains a star of the fifteenth magnitude near to its centre4 ,from photographs taken with the ,crossley reflector1 ,professor ,schaeberle finds in this nebula evidences of spiral structure4 ,it may here be mentioned that the ,great ,nebula in ,andromeda1 which has now turned out to be a spiral1 had in earlier photographs the appearance of a ring4 ,there also exist nebul of irregular form1 the most notable being the ,great ,nebula in the constellation of ,orion 7see ,plate ,,xxiv41 p4 #cah74 ,it is situated in the centre of the ,sword of ,orion 7see ,plate ,,xx41 p4 #bif74 ,in large telescopes it appears as a magnificent object1 and in actual dimensions it must be much on the same scale as the ,andromeda ,nebula4 ,the spectroscope tells us that it is a mass of glowing gas4 ,the ,trifid ,nebula1 situated in the constellation of ,sagittarius1 is an object of very strange shape4 ,three dark clefts radiate from its centre1 giving it an appearance as if it had been torn into shreds4 ,the ,dumb-bell ,nebula1 a celebrated object1 so called from its likeness to a dumb-bell1 turns out1 from recent photographs taken by ,professor ,schaeberle1 which bring additional detail into view1 to be after all a great spiral4 ,there is a nest1 or rather a cluster of nebul in the constellation of ,coma ,berenices2 over a hundred of these objects being here gathered into a space of sky about the size of our full moon4 ,illustration3 ,,plate ,,xxiii4 ,,the ,,great ,,nebula ,,in ,,the ,,constellation ,,of ,,andromeda ,from a photograph taken at the ,yerkes ,observatory4 7,page #cad7 ,the spectroscope informs us that spiral nebul are composed of partially-cooled matter4 ,their colour1 as we have seen1 is white4 ,nebul of a greenish tint are1 on the other hand1 found to be entirely in a gaseous condition4 ,just as the solar corona contains an unknown element1 which for the time being has been called ,coronium1 so do the gaseous nebul give evidence of the presence of another unknown element4 ,to this ,sir ,william ,huggins has given the provisional name of ,nebulium4 ,the ,magellanic ,clouds are two patches of nebulous-looking light1 more or less circular in form1 which are situated in the southern hemisphere of the sky4 ,they bear a certain resemblance to portions of the ,milky ,way1 but are1 however1 not connected with it4 ,they have received their name from the celebrated navigator1 ,magellan1 who seems to have been one of the first persons to draw attention to them4 ,nubecul is another name by which they are known1 the larger cloud being styled nubecula major and the smaller one nubecula minor4 ,they contain within them stars1 clusters1 and gaseous nebul4 ,no parallax has yet been found for any object which forms part of the nubecul1 so it is very difficult to estimate at what distance from us they may lie4 ,they are1 however1 considered to be well within our stellar universe4 ,having thus brought to a conclusion our all too brief review of the stars and the nebul--of the leading objects in fine which the celestial spaces have revealed to man--we will close this chapter with a recent summation by ,sir ,david ,gill of the relations which appear to obtain between these various bodies4 ,huggins's spectroscope1 he says1 has shown that many nebul are not stars at all2 that many well-condensed nebul1 as well as vast patches of nebulous light in the sky1 are but inchoate masses of luminous gas4 ,evidence upon evidence has accumulated to show that such nebul consist of the matter out of which stars 7i4e4 suns7 have been and are being evolved4 ,the different types of star spectra form such a complete and gradual sequence 7from simple spectra resembling those of nebul onwards through types of gradually increasing complexity7 as to suggest that we have before us1 written in the cryptograms of these spectra1 the complete story of the evolution of suns from the inchoate nebula onwards to the most active sun 7like our own71 and then downward to the almost heatless and invisible ball4 ,the period during which human life has existed upon our globe is probably too short--even if our first parents had begun the work--to afford observational proof of such a cycle of change in any particular star2 but the fact of such evolution1 with the evidence before us1 can hardly be doubted4#cd #cb ,the name ,al gl1 meaning the ,demon1 was what the old ,arabian astronomers called it1 which looks very much as if they had already noticed its rapid fluctuations in brightness4 #cc ,mr4 ,gore thinks that the companion of ,algol may be a star of the sixth magnitude4 #cd ,presidential ,address to the ,british ,association for the ,advancement of ,science 7,leicester1 #aijg71 by ,sir ,david ,gill1 ,k4,c4,b41 ,,ll4,d41 ,f4,r4,s41 c4 c4 ,illustration3 ,,plate ,,xxiv4 ,,the ,,great ,,nebula ,,in ,,the ,,constellation ,,of ,,orion ,from a photograph taken at the ,yerkes ,observatory4 7,page #caf7 ,,chapter ,,xxv ,,the ,,stellar ,,universe ,the stars appear fairly evenly distributed all around us1 except in one portion of the sky where they seem very crowded1 and so give one an impression of being very distant4 ,this portion1 known as the ,milky ,way1 stretches1 as we have already said1 in the form of a broad band right round the entire heavens4 ,in those regions of the sky most distant from the ,milky ,way the stars appear to be thinly sown1 but become more and more closely massed together as the ,milky ,way is approached4 ,this apparent distribution of the stars in space has given rise to a theory which was much favoured by ,sir ,william ,herschel1 and which is usually credited to him1 although it was really suggested by one ,thomas ,wright of ,durham in #agej2 that is to say1 some thirty years or more before ,herschel propounded it4 ,according to this1 which is known as the ,disc or ,grindstone ,theory1 the stars are considered as arranged in space somewhat in the form of a thick disc1 or grindstone1 close to the central parts of which our solar system is situated4#ce ,thus we should see a greater number of stars when we looked out through the length of such a disc in any direction1 than when we looked out through its breadth4 ,this theory was1 for a time1 supposed to account quite reasonably for the ,milky ,way1 and for the gradual increase in the number of stars in its vicinity4 ,it is quite impossible to verify directly such a theory1 for we know the actual distance of only about forty-three stars4 ,we are unable1 therefore1 definitely to assure ourselves whether1 as the grindstone theory presupposes1 the stellar universe actually reaches out very much further from us in the direction of the ,milky ,way than in the other parts of the sky4 ,the theory is clearly founded upon the supposition that the stars are more or less equal in size1 and are scattered through space at fairly regular distances from each other4 ,brightness1 therefore1 had been taken as implying nearness to us1 and faintness great distance4 ,but we know to-day that this is not the case1 and that the stars around us are1 on the other hand1 of various degrees of brightness and of all orders of size4 ,some of the faint stars--for instance1 the galloping star in ,pictor--are indeed nearer to us than many of the brighter ones4 ,sirius1 on the other hand1 is twice as far off from us as a ,centauri1 and yet it is very much brighter2 while ,canopus1 which in brightness is second only to ,sirius out of the whole sky1 is too far off for its distance to be ascertained6 ,it must be remembered that no parallax had yet been found for any star in the days of ,herschel1 and so his estimations of stellar distances were necessarily of a very circumstantial kind4 ,he did not1 however1 continue always to build upon such uncertain ground2 but1 after some further examination of the ,milky ,way1 he gave up his idea that the stars were equally disposed in space1 and eventually abandoned the grindstone theory4 ,since we have no means of satisfactorily testing the matter1 through finding out the various distances from us at which the stars are really placed1 one might just as well go to the other extreme1 and assume that the thickening of stars in the region of the ,milky ,way is not an effect of perspective at all1 but that the stars in that part of the sky are actually more crowded together than elsewhere--a thing which astronomers now believe to be the case4 ,looked at in this way1 the shape of the stellar universe might be that of a globe-shaped aggregation of stars1 in which the individuals are set at fairly regular distances from each other2 the whole being closely encircled by a belt of densely packed stars4 ,it must1 however1 be allowed that the gradual increase in the number of stars towards the ,milky ,way appears a strong argument in favour of the grindstone theory2 yet the belt theory1 as above detailed1 seems to meet with more acceptance4 ,there is1 in fact1 one marked circumstance which is remarkably difficult of explanation by means of the grindstone theory4 ,this is the existence of vacant spaces--holes1 so to speak1 in the groundwork of the ,milky ,way4 ,for instance1 there is a cleft running for a good distance along its length1 and there is also a starless gap in its southern portion4 ,it seems rather improbable that such a great number of stars could have arranged themselves so conveniently1 as to give us a clear view right out into empty space through such a system in its greatest thickness2 as if1 in fact1 holes had been bored1 and clefts made1 from the boundary of the disc clean up to where our solar system lies4 ,sir ,john ,herschel long ago drew attention to this point very forcibly4 ,it is plain that such vacant spaces can1 on the other hand1 be more simply explained as mere holes in a belt2 and the best authorities maintain that the appearance of the ,milky ,way confirms a view of this kind4 ,whichever theory be indeed the correct one1 it appears at any rate that the stars do not stretch out in every direction to an infinite distance2 but that the stellar system is of limited extent1 and has in fact a boundary4 ,in the first place1 ,science has no grounds for supposing that light is in any way absorbed or destroyed merely by its passage through the ether1 that imponderable medium which is believed to transmit the luminous radiations through space4 ,this of course is tantamount to saying that all the direct light from all the stars should reach us1 excepting that little which is absorbed in its passage through our own atmosphere4 ,if stars1 and stars1 and stars existed in every direction outwards without end1 it can be proved mathematically that in such circumstances there could not remain the tiniest space in the sky without a star to fill it1 and that therefore the heavens would always blaze with light1 and the night would be as bright as the noonday4#cf ,how very far indeed this is from being the case1 may be gathered from an estimate which has been made of the general amount of light which we receive from the stars4 ,according to this estimate the sky is considered as more or less dark1 the combined illumination sent to us by all the stars being only about the one-hundreth part of what we get from the full moon4#cg ,secondly1 it has been suggested that although light may not suffer any extinction or diminution from the ether itself1 still a great deal of illumination may be prevented from reaching us through myriads of extinguished suns1 or dark meteoric matter lying about in space4 ,the idea of such extinguished suns1 dark stars in fact1 seems however to be merely founded upon the sole instance of the invisible companion of ,algol2 but1 as we have seen1 there is no proof whatever that it is a dark body4 ,again1 some astronomers have thought that the dark holes in the ,milky ,way1 ,coal ,sacks1 as they are called1 are due to masses of cool1 or partially cooled matter1 which cuts off the light of the stars beyond4 ,the most remarkable of these holes is one in the neighbourhood of the ,southern ,cross1 known as the ,coal ,sack in ,crux4 ,but ,mr4 ,gore thinks that the cause of the holes is to be sought for rather in what ,sir ,william ,herschel termed clustering power1 i4e4 a tendency on the part of stars to accumulate in certain places1 thus leaving others vacant2 and the fact that globular and other clusters are to be found very near to such holes certainly seems corroborative of this theory4 ,in summing up the whole question1 ,professor ,newcomb maintains that there does not appear any evidence of the light from the ,milky ,way stars1 which are apparently the furthest bodies we see1 being intercepted by dark bodies or dark matter4 ,as far as our telescopes can penetrate1 he holds that we see the stars just as they are4 ,also1 if there did exist an infinite number of stars1 one would expect to find evidence in some direction of an overpoweringly great force1--the centre of gravity of all these bodies4 ,it is noticed1 too1 that although the stars increase in number with decrease in magnitude1 so that as we descend in the scale we find three times as many stars in each magnitude as in the one immediately above it1 yet this progression does not go on after a while4 ,there is1 in fact1 a rapid falling off in numbers below the twelfth magnitude2 which looks as if1 at a certain distance from us1 the stellar universe were beginning to thin out4 ,again1 it is estimated1 by ,mr4 ,gore and others1 that only about #ajj millions of stars are to be seen in the whole of the sky with the best optical aids4 ,this shows well the limited extent of the stellar system1 for the number is not really great4 ,for instance1 there are from fifteen to sixteen times as many persons alive upon the earth at this moment6 ,last of all1 there appears to be strong photographic evidence that our sidereal system is limited in extent4 ,two photographs taken by the late ,dr4 ,isaac ,roberts of a region rich in stellar objects in the constellation of ,cygnus1 clearly show what has been so eloquently called the darkness behind the stars4 ,one of these photographs was taken in #ahie1 and the other in #ahih4 ,on both occasions the state of the atmosphere was practically the same1 and the sensitiveness of the films was of the same degree4 ,the exposure in the first case was only one hour2 in the second it was about two hours and a half4 ,and yet both photographs show exactly the same stars1 even down to the faintest4 ,from this one would gather that the region in question1 which is one of the most thickly star-strewn in the ,milky ,way1 is penetrable right through with the means at our command4 ,dr4 ,roberts himself in commenting upon the matter drew attention to the fact1 that many astronomers seemed to have tacitly adopted the assumption that the stars extend indefinitely through space4 ,from considerations such as these the foremost astronomical authorities of our time consider themselves justified in believing that the collection of stars around us is finite2 and that although our best telescopes may not yet be powerful enough to penetrate to the final stars1 still the rapid decrease in numbers as space is sounded with increasing telescopic power1 points strongly to the conclusion that the boundaries of the stellar system may not lie very far beyond the uttermost to which we can at present see4 ,is it possible then to make an estimate of the extent of this stellar system8 ,whatever estimates we may attempt to form cannot however be regarded as at all exact1 for we know the actual distances of such a very few only of the nearest of the stars4 ,but our knowledge of the distances even of these few1 permits us to assume that the stars close around us may be situated1 on an average1 at about eight light-years from each other2 and that this holds good of the stellar spaces1 with the exception of the encircling girdle of the ,milky ,way1 where the stars seem actually to be more closely packed together4 ,this girdle further appears to contain the greater number of the stars4 ,arguing along these lines1 ,professor ,newcomb reaches the conclusion that the farthest stellar bodies which we see are situated at about between #cjjj and #djjj light-years from us4 ,starting our inquiry from another direction1 we can try to form an estimate by considering the question of proper motions4 ,it will be noticed that such motions do not depend entirely upon the actual speed of the stars themselves1 but that some of the apparent movement arises indirectly from the speed of our own sun4 ,the part in a proper motion which can be ascribed to the movement of our solar system through space is clearly a displacement in the nature of a parallax--,sir ,william ,herschel called it ,systematic ,parallax2 so that knowing the distance which we move over in a certain lapse of time1 we are able to hazard a guess at the distances of a good many of the stars4 ,an inquiry upon such lines must needs be very rough1 and is plainly based upon the assumption that the stars whose distances we attempt to estimate are moving at an average speed much like that of our own sun1 and that they are not runaway stars of the #ahcj ,groombridge order4 ,be that as it may1 the results arrived at by ,professor ,newcomb from this method of reasoning are curiously enough very much on a par with those founded on the few parallaxes which we are really certain about2 with the exception that they point to somewhat closer intervals between the individual stars1 and so tend to narrow down our previous estimate of the extent of the stellar system4 ,thus far we get1 and no farther4 ,our solar system appears to lie somewhere near the centre of a great collection of stars1 separated each one from the other1 on an average1 by some #dj billions of miles2 the whole being arranged in the form of a mighty globular cluster4 ,light from the nearest of these stars takes some four years to come to us4 ,it takes about #ajjj times as long to reach us from the confines of the system4 ,this globe of stars is wrapt around closely by a stellar girdle1 the individual stars in which are set together more densely than those in the globe itself4 ,the entire arrangement appears to be constructed upon a very regular plan4 ,here and there1 as ,professor ,newcomb points out1 the aspect of the heavens differs in small detail2 but generally it may be laid down that the opposite portions of the sky1 whether in the ,milky ,way itself1 or in those regions distant from it1 show a marked degree of symmetry4 ,the proper motions of stars in corresponding portions of the sky reveal the same kind of harmony1 a harmony which may even be extended to the various colours of the stars4 ,the stellar system1 which we see disposed all around us1 appears in fine to bear all the marks of an organised whole4 ,the older astronomers1 to take ,sir ,william ,herschel as an example1 supposed some of the nebul to be distant universes4 ,sir ,william was led to this conclusion by the idea he had formed that1 when his telescopes failed to show the separate stars of which he imagined these objects to be composed1 he must put down the failure to their stupendous distance from us4 ,for instance1 he thought the ,orion ,nebula1 which is now known to be made up of glowing gas1 to be an external stellar system4 ,later on1 however1 he changed his mind upon this point1 and came to the conclusion that shining fluid would better account both for this nebula1 and for others which his telescopes had failed to separate into component stars4 ,the old ideas with regard to external systems and distant universes have been shelved as a consequence of recent research4 ,all known clusters and nebul are now firmly believed to lie within our stellar system4 ,this view of the universe of stars as a sort of island in the immensities1 does not1 however1 give us the least idea about the actual extent of space itself4 ,whether what is called space is really infinite1 that is to say1 stretches out unendingly in every direction1 or whether it has eventually a boundary somewhere1 are alike questions which the human mind seems utterly unable to picture to itself4 #ce ,the ,ptolemaic idea dies hard6 #cf ,even the ,milky ,way itself is far from being a blaze of light1 which shows that the stars composing it do not extend outwards indefinitely4 #cg ,mr4 ,gore has recently made some remarkable deductions1 with regard to the amount of light which we get from the stars4 ,he considers that most of this light comes from stars below the sixth magnitude2 and consequently1 if all the stars visible to the naked eye were to be blotted out1 the glow of the night sky would remain practically the same as it is at present4 ,going to the other end of the scale1 he thinks also that the combined light which we get from all the stars below the seventeenth magnitude is so very small1 that it may be neglected in such an estimation4 ,he finds1 indeed1 that if there are stars so low as the twentieth magnitude1 one hundred millions of them would only be equal in brightness to a single first-magnitude star like ,vega4 ,on the other hand1 it is possible that the light of the sky at night is not entirely due to starlight1 but that some of it may be caused by phosphorescent glow4 ,,chapter ,,xxvi ,,the ,,stellar ,,universe--continued ,it is very interesting to consider the proper motions of stars with reference to such an isolated stellar system as has been pictured in the previous chapter4 ,these proper motions are so minute as a rule1 that we are quite unable to determine whether the stars which show them are moving along in straight lines1 or in orbits of immense extent4 ,it would1 in fact1 take thousands of years of careful observation to determine whether the paths in question showed any degree of curving4 ,in the case of the more distant stars1 the accurate observations which have been conducted during the last hundred years have not so far revealed any proper motions with regard to them2 but one cannot escape the conclusion that these stars move as the others do4 ,if space outside our stellar system is infinite in extent1 and if all the stars within that system are moving unchecked in every conceivable direction1 the result must happen that after immense ages these stars will have drawn apart to such a distance from each other1 that the system will have entirely disintegrated1 and will cease to exist as a connected whole4 ,eventually1 indeed1 as ,professor ,newcomb points out1 the stars will have separated so far from each other that each will be left by itself in the midst of a black and starless sky4 ,if1 however1 a certain proportion of stars have a speed sufficiently slow1 they will tend under mutual attraction to be brought to rest by collisions1 or forced to move in orbits around each other4 ,but those stars which move at excessive speeds1 such1 for instance1 as #ahcj ,groombridge1 or the star in the southern constellation of ,pictor1 seem utterly incapable of being held back in their courses by even the entire gravitative force of our stellar system acting as a whole4 ,these stars must1 therefore1 move eventually right through the system and pass out again into the empty spaces beyond4 ,add to this2 certain investigations1 made into the speed of #ahcj ,groombridge1 furnish a remarkable result4 ,it is calculated1 indeed1 that had this star been falling through infinite space for ever1 pulled towards us by the combined gravitative force of our entire system of stars1 it could not have gathered up anything like the speed with which it is at present moving4 ,no force1 therefore1 which we can conjure out of our visible universe1 seems powerful enough either to have impressed upon this runaway star the motion which it now has1 or to stay it in its wild course4 ,what an astounding condition of things6 ,speculations like this call up a suspicion that there may yet exist other universes1 other centres of force1 notwithstanding the apparent solitude of our stellar system in space4 ,it will be recollected that the idea of this isolation is founded upon such facts as1 that the heavens do not blaze with light1 and that the stars gradually appear to thin out as we penetrate the system with increasing telescopic power4 ,but perchance there is something which hinders us from seeing out into space beyond our cluster of stars2 which prevents light1 in fact1 from reaching us from other possible systems scattered through the depths beyond4 ,it has1 indeed1 been suggested by ,mr4 ,gore#ch that the light-transmitting ether may be after all merely a kind of atmosphere of the stars2 and that it may1 therefore1 thin off and cease a little beyond the confines of our stellar system1 just as the air thins off and practically ceases at a comparatively short distance from the earth4 ,a clashing together of solid bodies outside our atmosphere could plainly send us no sound1 for there is no air extending the whole way to bear to our ears the vibrations thus set up2 so light emitted from any body lying beyond our system of stars1 would not be able to come to us if the ether1 whose function it is to convey the rays of light1 ceased at or near the confines of that system4 ,perchance we have in this suggestion the key to the mystery of how our sun and the other stellar bodies maintain their functions of temperature and illumination4 ,the radiations of heat and light arriving at the limits of this ether1 and unable to pass any further1 may be thrown back again into the system in some altered form of energy4 ,but these1 at best1 are mere airy and fascinating speculations4 ,we have1 indeed1 no evidence whatever that the luminiferous ether ceases at the boundary of the stellar system4 ,if1 therefore1 it extends outwards infinitely in every direction1 and if it has no absorbing or weakening effect on the vibrations which it transmits1 we cannot escape from the conclusion that practically all the rays of light ever emitted by all the stars must chase one another eternally through the never-ending abysses of space4 #ch ,planetary and ,stellar ,studies1 by ,john ,ellard ,gore1 ,f4,r4,a4,s41 ,m4,r4,i4,a41 ,london1 #ahhh4 ,,chapter ,,xxvii ,,the ,,beginning ,,of ,,things ,,laplace',s ,,nebular ,,hypothesis ,dwelling upon the fact that all the motions of revolution and rotation in the solar system1 as known in his day1 took place in the same direction and nearly in the same plane1 the great ,french astronomer1 ,laplace1 about the year #agif1 put forward a theory to account for the origin and evolution of that system4 ,he conceived that it had come into being as a result of the gradual contraction1 through cooling1 of an intensely heated gaseous lens-shaped mass1 which had originally occupied its place1 and had extended outwards beyond the orbit of the furthest planet4 ,he did not1 however1 attempt to explain how such a mass might have originated6 ,he went on to suppose that this mass1 in some manner1 perhaps by mutual gravitation among its parts1 had acquired a motion of rotation in the same direction as the planets now revolve4 ,as this nebulous mass parted with its heat by radiation1 it contracted towards the centre4 ,becoming smaller and smaller1 it was obliged to rotate faster and faster in order to preserve its equilibrium4 ,meanwhile1 in the course of contraction1 rings of matter became separated from the nucleus of the mass1 and were left behind at various intervals4 ,these rings were swept up into subordinate masses similar to the original nebula4 ,these subordinate masses also contracted in the same manner1 leaving rings behind them which1 in turn1 were swept up to form satellites4 ,saturn's ring was considered1 by ,laplace1 as the only portion of the system left which still showed traces of this evolutionary process4 ,it is even probable that it may have suggested the whole of the idea to him4 ,laplace was1 however1 not the first philosopher who had speculated along these lines concerning the origin of the world4 ,nearly fifty years before1 in #agej to be exact1 ,thomas ,wright1 of ,durham1 had put forward a theory to account for the origin of the whole sidereal universe4 ,in his theory1 however1 the birth of our solar system was treated merely as an incident4 ,shortly afterwards the subject was taken up by the famous ,german philosopher1 ,kant1 who dealt with the question in a still more ambitious manner1 and endeavoured to account in detail for the origin of the solar system as well as of the sidereal universe4 ,something of the trend of such theories may be gathered from the remarkable lines in ,tennyson's ,princess3-- ,this world was once a fluid haze of light1 ,till toward the centre set the starry tides1 ,and eddied into suns1 that wheeling cast ,the planets4 ,the theory1 as worked out by ,kant1 was1 however1 at the best merely a tour de force of philosophy4 ,laplace's conception was much less ambitious1 for it did not attempt to explain the origin of the entire universe1 but only of the solar system4 ,being thus reasonably limited in its scope1 it more easily obtained credence4 ,the arguments of ,laplace were further founded upon a mathematical basis4 ,the great place which he occupied among the astronomers of that time caused his theory to exert a preponderating influence on scientific thought during the century which followed4 ,a modification of ,laplace's theory is the ,meteoritic ,hypothesis of ,sir ,norman ,lockyer4 ,according to the views of that astronomer1 the material of which the original nebula was composed is presumed to have been in the meteoric1 rather than in the gaseous1 state4 ,sir ,norman ,lockyer holds1 indeed1 that nebul are1 in reality1 vast swarms of meteors1 and the light they emit results from continual collisions between the constituent particles4 ,the ,french astronomer1 ,faye1 also proposed to modify ,laplace's theory by assuming that the nebula broke up into rings all at once1 and not in detail1 as ,laplace had wished to suppose4 ,the hypothesis of ,laplace fits in remarkably well with the theory put forward in later times by ,helmholtz1 that the heat of the sun is kept up by the continual contraction of its mass4 ,it could thus have only contracted to its present size from one very much larger4 ,plausible1 however1 as ,laplace's great hypothesis appears on the surface1 closer examination shows several vital objections1 a few of those set forth by ,professor ,moulton being here enumerated-- ,although ,laplace held that the orbits of the planets were sufficiently near to being in the one plane to support his views1 yet later investigators consider that their very deviations from this plane are a strong argument against the hypothesis4 ,again1 it is thought that if the theory were the correct explanation1 the various orbits of the planets would be much more nearly circular than they are4 ,it is also thought that such interlaced paths1 as those in which the asteroids and the little planet ,eros move1 are most unlikely to have been produced as a result of ,laplace's nebula4 ,further1 while each of the rings was sweeping up its matter into a body of respectable dimensions1 its gravitative power would have been for the time being so weak1 through being thus spread out1 that any lighter elements1 as1 for instance1 those of the gaseous order1 would have escaped into space in accordance with the principles of the kinetic theory4 ,the idea that rings would at all be left behind at certain intervals during the contraction of the nebula is1 perhaps1 one of the weakest points in ,laplace's hypothesis4 ,mathematical investigation does not go to show that the rings1 presuming they could be left behind during the contraction of the mass1 would have aggregated into planetary bodies4 ,indeed1 it rather points to the reverse4 ,lastly1 such a discovery as that the ninth satellite of ,saturn revolves in a retrograde direction--that is to say1 in a direction contrary to the other revolutions and rotations in our solar system--appears directly to contradict the hypothesis4 ,although ,laplace's hypothesis seems to break down under the keen criticism to which it has been subjected1 yet astronomers have not relinquished the idea that our solar system has probably had its origin from a nebulous mass4 ,but the apparent failure of the ,laplacian theory is emphasised by the fact1 that not a single example of a nebula1 in the course of breaking up into concentric rings1 is known to exist in the entire heaven4 ,indeed1 as we saw in ,chapter ,,xxiv41 there seems to be no reliable example of even a ring nebula at all4 ,mr4 ,gore has pointed this out very succinctly in his recently published work1 ,astronomical ,essays1 where he says3--,to any one who still persists in maintaining the hypothesis of ring formation in nebul1 it may be said that the whole heavens are against him4 ,the conclusions of ,keeler already alluded to1 that the spiral is the normal type of nebula1 has led during the past few years to a new theory by the ,american astronomers1 ,professors ,chamberlin and ,moulton4 ,in the detailed account of it which they have set forth1 they show that those anomalies which were stumbling-blocks to ,laplace's theory do not contradict theirs4 ,to deal at length with this theory1 to which the name of ,planetesimal ,hypothesis has been given1 would not be possible in a book of this kind4 ,but it may be of interest to mention that the authors of the theory in question remount the stream of time still further than did ,laplace1 and seek to explain the origin of the spiral nebul themselves in the following manner3-- ,having begun by assuming that the stars are moving apparently in every direction with great velocities1 they proceed to point out that sooner or later1 although the lapse of time may be extraordinarily long1 collisions or near approaches between stars are bound to occur4 ,in the case of collisions the chances are against the bodies striking together centrally1 it being very much more likely that they will hit each other rather towards the side4 ,the nebulous mass formed as a result of the disintegration of the bodies through their furious impact would thus come into being with a spinning movement1 and a spiral would ensue4 ,again1 the stars may not actually collide1 but merely approach near to each other4 ,if very close1 the interaction of gravitation will give rise to intense strains1 or tides1 which will entirely disintegrate the bodies1 and a spiral nebula will similarly result4 ,as happens upon our earth1 two such tides would rise opposite to each other2 and1 consequently1 it is a noticeable fact that spiral nebul have almost invariably two opposite branches 7see ,plate ,,xxii41 p #cad74 ,even if not so close1 the gravitational strains set up would produce tremendous eruptions of matter2 and in this case1 a spiral movement would also be generated4 ,on such an assumption the various bodies of the solar system may be regarded as having been ejected from parent masses4 ,the acceptance of the ,planetesimal ,hypothesis in the place of the ,hypothesis of ,laplace will not1 as we have seen1 by any means do away with the probability that our solar system1 and similar systems1 have originated from a nebulous mass4 ,on the contrary it puts that idea on a firmer footing than before4 ,the spiral nebul which we see in the heavens are on a vast scale1 and may represent the formation of stellar systems and globular clusters4 ,our solar system may have arisen from a small spiral4 ,we will close these speculations concerning the origin of things with a short sketch of certain investigations made in recent years by ,sir ,george ,h4 ,darwin1 of ,cambridge ,university1 into the question of the probable birth of our moon4 ,he comes to the conclusion that at least fifty-four millions of years ago the earth and moon formed one body1 which had a diameter of a little over #hjjj miles4 ,this body rotated on an axis in about five hours1 namely1 about five times as fast as it does at present4 ,the rapidity of the rotation caused such a tremendous strain that the mass was in a condition of1 what is called1 unstable equilibrium2 very little more1 in fact1 being required to rend it asunder4 ,the gravitational pull of the sun1 which1 as we have already seen1 is in part the cause of our ordinary tides1 supplied this extra strain1 and a portion of the mass consequently broke off1 which receded gradually from the rest and became what we now know as the moon4 ,sir ,george ,darwin holds that the gravitational action of the sun will in time succeed in also disturbing the present apparent harmony of the earth-moon system1 and will eventually bring the moon back towards the earth1 so that after the lapse of great ages they will re-unite once again4 ,in support of this theory of the terrestrial origin of the moon1 ,professor ,w4,h4 ,pickering has put forward a bold hypothesis that our satellite had its origin in the great basin of the ,pacific4 ,this ocean is roughly circular1 and contains no large land masses1 except the ,australian ,continent4 ,he supposes that1 prior to the moon's birth1 our globe was already covered with a slight crust4 ,in the tearing away of that portion which was afterwards destined to become the moon the remaining area of the crust was rent in twain by the shock2 and thus were formed the two great continental masses of the ,old and ,new ,worlds4 ,these masses floated apart across the fiery ocean1 and at last settled in the positions which they now occupy4 ,in this way ,professor ,pickering explains the remarkable parallelism which exists between the opposite shores of the ,atlantic4 ,the fact of this parallelism had1 however1 been noticed before2 as1 for example1 by the late ,rev4 ,s4,j4 ,johnson1 in his book ,eclipses1 ,past and ,future1 where we find the following passage3-- ,if we look at our maps we shall see the parts of one ,continent that jut out agree with the indented portions of another4 ,the prominent coast of ,africa would fit in the opposite opening between ,north and ,south ,america1 and so in numerous other instances4 ,a general rending asunder of the ,world would seem to have taken place when the foundations of the great deep were broken up4 ,although ,professor ,pickering's theory is to a certain degree anticipated in the above words1 still he has worked out the idea much more fully1 and given it an additional fascination by connecting it with the birth of the moon4 ,he points out1 in fact1 that there is a remarkable similarity between the lunar volcanoes and those in the immediate neighbourhood of the ,pacific ,ocean4 ,he goes even further to suggest that ,australia is another portion of the primal crust which was detached out of the region now occupied by the ,indian ,ocean1 where it was originally connected with the south of ,india or the east of ,africa4 ,certain objections to the theory have been put forward1 one of which is that the parallelism noticed between the opposite shores of the ,atlantic is almost too perfect to have remained through some sixty millions of years down to our own day1 in the face of all those geological movements of upheaval and submergence1 which are perpetually at work upon our globe4 ,professor ,pickering1 however1 replies to this objection by stating that many geologists believe that the main divisions of land and water on the earth are permanent1 and that the geological alterations which have taken place since these were formed have been merely of a temporary and superficial nature4 ,,chapter ,,xxviii ,,the ,,end ,,of ,,things ,we have been trying to picture the beginning of things4 ,we will now try to picture the end4 ,in attempting this1 we find that our theories must of necessity be limited to the earth1 or at most to the solar system4 ,the time-honoured expression ,end of the ,world really applies to very little beyond the end of our own earth4 ,to the people of past ages it1 of course1 meant very much more4 ,for them1 as we have seen1 the earth was the centre of everything2 and the heavens and all around were merely a kind of minor accompaniment1 created1 as they no doubt thought1 for their especial benefit4 ,in the ancient view1 therefore1 the beginning of the earth meant the beginning of the universe1 and the end of the earth the extinction of all things4 ,the belief1 too1 was general that this end would be accomplished through fire4 ,in the modern view1 however1 the birth and death of the earth1 or indeed of the solar system1 might pass as incidents almost unnoticed in space4 ,they would be but mere links in the chain of cosmic happenings4 ,a number of theories have been forward from time to time prognosticating the end of the earth1 and consequently of human life4 ,we will conclude with a recital of a few of them1 though which1 if any1 is the true one1 the ,last ,men alone can know4 ,just as a living creature may at any moment die in the fulness of strength through sudden malady or accident1 or1 on the other hand1 may meet with death as a mere consequence of old age1 so may our globe be destroyed by some sudden cataclysm1 or end in slow processes of decay4 ,barring accidents1 therefore1 it would seem probable that the growing cold of the earth1 or the gradual extinction of the sun1 should after many millions of years close the chapter of life1 as we know it4 ,on the former of these suppositions1 the decrease of temperature on our globe might perhaps be accelerated by the thinning of the atmosphere1 through the slow escape into space of its constituent gases1 or their gradual chemical combination with the materials of the earth4 ,the subterranean heat entirely radiated away1 there would no longer remain any of those volcanic elevating forces which so far have counteracted the slow wearing down of the land surface of our planet1 and thus what water remained would in time wash over all4 ,if this preceded the growing cold of the sun1 certain strange evolutions of marine forms of life would be the last to endure1 but these1 too1 would have to go in the end4 ,should1 however1 the actual process be the reverse of this1 and the sun cool down the quicker1 then man would1 as a consequence of his scientific knowledge1 tend in all probability to outlive the other forms of terrestrial life4 ,in such a vista we can picture the regions of the earth towards the north and south becoming gradually more and more uninhabitable through cold1 and human beings withdrawing before the slow march of the icy boundary1 until the only regions capable of habitation would lie within the tropics4 ,in such a struggle between man and destiny science would be pressed to the uttermost1 in the devising of means to counteract the slow diminution of the solar heat and the gradual disappearance of air and water4 ,by that time the axial rotation of our globe might possibly have been slowed down to such an extent that one side alone of its surface would be turned ever towards the fast dying sun4 ,and the mind's eye can picture the last survivors of the human race1 huddled together for warmth in a glass-house somewhere on the equator1 waiting for the end to come4 ,the mere idea of the decay and death of the solar system almost brings to one a cold shudder4 ,all that sun's light and heat1 which means so much to us1 entirely a thing of the past4 ,a dark1 cold ball rushing along in space1 accompanied by several dark1 cold balls circling ceaselessly around it4 ,one of these a mere cemetery1 in which there would be no longer any recollection of the mighty empires1 the loves and hates1 and all that teeming play of life which we call ,history4 ,tombstones of men and of deeds1 whirling along forgotten in the darkness and silence4 ,sic transit gloria mundi4 ,in that brilliant flight of scientific fancy1 the ,time ,machine1 ,mr4 ,h4,g4 ,wells has pictured the closing years of the earth in some such long-drawn agony as this4 ,he has given us a vision of a desolate beach by a salt and almost motionless sea4 ,foul monsters of crab-like form crawl slowly about1 beneath a huge hull of sun1 red and fixed in the sky4 ,the rocks around are partly coated with an intensely green vegetation1 like the lichen in caves1 or the plants which grow in a perpetual twilight4 ,and the air is now of an exceeding thinness4 ,he dips still further into the future1 and thus predicts the final form of life3-- ,i saw again the moving thing upon the shoal--there was no mistake now that it was a moving thing--against the red water of the sea4 ,it was a round thing1 the size of a football perhaps1 or it may be bigger1 and tentacles trailed down from it2 it seemed black against the weltering blood-red water1 and it was hopping fitfully about4 ,what a description of the ,heir of all the ,ages6 ,to picture the end of our world as the result of a cataclysm of some kind1 is1 on the other hand1 a form of speculation as intensely dramatic as that with which we have just been dealing is unutterably sad4 ,it is not so many years ago1 for instance1 that men feared a sudden catastrophe from the possible collision of a comet with our earth4 ,the unreasoning terror with which the ancients were wont to regard these mysterious visitants to our skies had1 indeed1 been replaced by an apprehension of quite another kind4 ,for instance1 as we have seen1 the announcement in #ahcb that ,biela's ,comet1 then visible1 would cut through the orbit of the earth on a certain date threw many persons into a veritable panic4 ,they did not stop to find out the real facts of the case1 namely1 that1 at the time mentioned1 the earth would be nearly a month's journey from the point indicated6 ,it is1 indeed1 very difficult to say what form of damage the earth would suffer from such a collision4 ,in #ahfa it passed1 as we have seen1 through the tail of the comet without any noticeable result4 ,but the head of a comet1 on the other hand1 may1 for aught we know1 contain within it elements of peril for us4 ,a collision with this part might1 for instance1 result in a violent bombardment of meteors4 ,but these meteors could not be bodies of any great size1 for the masses of comets are so very minute that one can hardly suppose them to contain any large or dense constituent portions4 ,the danger1 however1 from a comet's head might after all be a danger to our atmosphere4 ,it might precipitate1 into the air1 gases which would asphyxiate us or cause a general conflagration4 ,it is scarcely necessary to point out that dire results would follow upon any interference with the balance of our atmosphere4 ,for instance1 the well-known ,french astronomer1 ,m4 ,camille ,flammarion1#ci has imagined the absorption of the nitrogen of the air in this way2 and has gone on to picture men and animals reduced to breathing only oxygen1 first becoming excited1 then mad1 and finally ending in a perfect saturnalia of delirium4 ,lastly1 though we have no proof that stars eventually become dark and cold1 for human time has so far been all too short to give us even the smallest evidence as to whether heat and light are diminishing in our own sun1 yet it seems natural to suppose that such bodies must at last cease their functions1 like everything else which we know of4 ,we may1 therefore1 reasonably presume that there are dark bodies scattered in the depths of space4 ,we have1 indeed1 a suspicion of at least one1 though perhaps it partakes rather of a planetary nature1 namely1 that dark body which continually eclipses ,algol1 and so causes the temporary diminution of its light4 ,as the sun rushes towards the constellation of ,lyra such an extinguished sun may chance to find itself in his path2 just as a derelict hulk may loom up out of the darkness right beneath the bows of a vessel sailing the great ocean4 ,unfortunately a collision between the sun and a body of this kind could not occur with such merciful suddenness4 ,a tedious warning of its approach would be given from that region of the heavens whither our system is known to be tending4 ,as the dark object would become visible only when sufficiently near our sun to be in some degree illuminated by his rays1 it might run the chance at first of being mistaken for a new planet4 ,if such a body were as large1 for instance1 as our own sun1 it should1 according to ,mr4 ,gore's calculations1 reveal itself to the telescope some fifteen years before the great catastrophe4 ,steadily its disc would appear to enlarge1 so that1 about nine years after its discovery1 it would become visible to the naked eye4 ,at length the doomed inhabitants of the earth1 paralysed with terror1 would see their relentless enemy shining like a second moon in the northern skies4 ,rapidly increasing in apparent size1 as the gravitational attractions of the solar orb and of itself interacted more powerfully with diminishing distance1 it would at last draw quickly in towards the sun and disappear in the glare4 ,it is impossible for us to conceive anything more terrible than these closing days1 for no menace of catastrophe which we can picture could bear within it such a certainty of fulfilment4 ,it appears1 therefore1 useless to speculate on the probable actions of men in their now terrestrial prison4 ,hope1 which so far had buoyed them up in the direst calamities1 would here have no place4 ,humanity1 in the fulness of its strength1 would await a wholesale execution from which there could be no chance at all of a reprieve4 ,observations of the approaching body would have enabled astronomers to calculate its path with great exactness1 and to predict the instant and character of the impact4 ,eight minutes after the moment allotted for the collision the resulting tide of flame would surge across the earth's orbit1 and our globe would quickly pass away in vapour4 ,and what then8 ,a nebula1 no doubt2 and after untold ages the formation possibly from it of a new system1 rising phoenix-like from the vast crematorium and filling the place of the old one4 ,a new central sun1 perhaps1 with its attendant retinue of planets and satellites4 ,and teeming life1 perchance1 appearing once more in the fulness of time1 when temperature in one or other of these bodies had fallen within certain limits1 and other predisposing conditions had supervened4 ,the world's great age begins anew1 ,the golden years return1 ,the earth doth like a snake renew ,her winter weeds outworn3 ,heaven smiles1 and faiths and empires gleam ,like wrecks of a dissolving dream4 ,a brighter ,hellas rears its mountains ,from waves serener far2 ,a new ,peneus rolls his fountains ,against the morning star2 ,where fairer ,tempes bloom1 there sleep ,young ,cyclads on a sunnier deep4 ,a loftier ,argo cleaves the main1 ,fraught with a later prize2 ,another ,orpheus sings again1 ,and loves1 and weeps1 and dies2 ,a new ,ulysses leaves once more ,calypso for his native shore4 99 99 99 99 99 ,oh cease6 must hate and death return8 ,cease6 must men kill and die8 ,cease6 drain not to its dregs the urn ,of bitter prophecy6 ,the world is weary of the past1-- ,oh might it die or rest at last6 #ci ,see his work1 ,la ,fin du ,monde1 wherein the various ways by which our world may come to an end are dealt with at length1 and in a profoundly interesting manner4 ,,index ,achromatic telescope1 #aae1 #aaf ,adams1 #bd1 #bcf1 #bdc ,aerial telescopes1 #aaj1 #aaa ,agathocles1 ,eclipse of1 #he ,agrippa1 ,camillus1 #dd ,ahaz1 dial of1 #he ,air1 #aff ,airy1 ,sir ,g4,b41 #ib ,al gl1 #cjg ,al ,sufi1 #bhd1 #bij1 #bif1 #cae ,alcor1 #bid ,alcyone1 #bhd ,aldebaran1 #ajc1 #bhh1 #bij1 #big ,algol1 #cjg1 #cji-caj1 #cab1 #cbc1 #cdg ,alpha1 ,centauri1 #eb-ec1 #bhj1 #bih-bii1 #cjd1 #cbj ,alpha ,crucis1 #bih ,alps1 ,lunar1 #bjj ,altair1 #bie ,altitude of objects in sky1 #aif ,aluminium1 #ade ,amos viii4 #i1 #he ,anderson1 ,t4,d41 #caa-cab ,andromeda 7constellation71 #bgi1 #cad2 ,great ,nebula in1 #cad1 #caf ,andromedid meteors1 #bgb ,anglo-,saxon ,chronicle1 #hg-hh ,anighito meteorite1 #bgg ,annular eclipse1 #fe-fh1 #hj1 #ib1 #ii ,annular ,nebula in ,lyra1 #cae-caf ,annulus1 #fh ,ans1 #bdb-bdc ,anticipation in discovery1 #bcf-bcg ,apennines1 ,lunar1 #bjj ,aphelion1 #bgd ,apparent enlargement of celestial objects1 #aib-aif ,apparent size of celestial objects deceptive1 #aif1 #bid ,apparent sizes of sun and moon1 variations in1 #fg1 #hj1 #agh ,aquila 7constellation71 #bie ,arabian astronomers1 #ajg1 #cjg ,arago1 #ib1 #beg ,arc1 degrees minutes and seconds of1 #fj ,arcturus1 #bhj1 #bhb1 #bij1 #bie ,argelander1 #bij ,argo 7constellation71 #bih ,aristarchus of ,samos1 #aga ,aristarchus 7lunar crater71 #bje ,aristophanes1 #aja ,aristotle1 #afa1 #agc1 #ahe ,arrhenius #bbb1 #bec-bed ,assyrian tablet1 #hd ,asteroidal zone1 analogy of1 to ,saturn's rings1 #bch ,asteroids 7or minor planets71 #cj-ca1 #bbe-bbh1 #ccf2 discovery of the1 #bc1 #bdd2 ,wolf's method of discovering1 #bbf-bbg ,astrology1 #ef ,astronomical ,essays1 #fc1 #ccg ,astronomical ,society1 ,royal1 #add ,astronomy1 ,manual of1 #aff ,atlantic ,ocean1 parallelism of opposite shores1 #cdj-cda ,atlas1 the ,titan1 #ah ,atmosphere1 absorption by earth's1 #abi-acj2 ascertainment of1 by spectroscope1 #abd-abe1 #bab2 height of earth's1 #afg1 #bfg2 of asteroids1 #bbf2 of earth1 #abi1 #acj1 #aff-afi1 #bah1 #bbb1 #bfg1 #cdf2 of ,mars1 #aef1 #bab1 #baf2 of ,mercury1 #aef2 of moon1 #gj-ga1 #aef1 #bja-bjc2 of ,jupiter1 #bca2 of planets1 #abe2 of ,saturn's rings1 #bci ,atmosphere of the stars1 #cca ,atmospheric layer and glass-house compared1 #afg1 #bjc ,august ,meteors 7,perseids71 #bgj ,auriga 7constellation71 #bid-bif1 #cjf1 #caa2 ,new ,star in1 #caa ,aurig1 b 7,beta71 #bid1 #big1 #cjd ,aurora ,borealis1 #ada1 #adc1 #bei ,australia1 suggested origin of1 #cdj ,axis1 #bi-cj2 of earth1 #afc1 #ahj2 small movement of earth's1 #ahj-aha ,babylonian tablet1 #hd ,babylonian idea of the moon1 #ahe ,bacon1 ,roger1 #ajh ,bacubirito meteorite1 #bgg ,bagdad1 #ajg ,baily1 ,francis1 #ib ,baily's ,beads1 #fi1 #gj1 #ia-ib1 #aed ,bailly 7lunar crater71 #aii ,ball1 ,sir ,robert1 #bga ,barnard1 ,e4,e41 #ca1 #bbd1 #bcb-bcd1 #bcg1 #beh ,bay of ,rainbows1 #aig ,bayer's classification of stars1 #bhi1 #bia-bib ,bayeux ,tapestry1 #bfc ,bear1 ,great 7constellation74 ,see ,ursa ,major2 ,little1 see ,ursa ,minor ,beehive 7,prsepe71 #cjg ,beer1 #bjf ,belopolsky1 #cjd ,belt of ,orion1 #big ,belt theory of ,milky ,way1 #cba ,belts of ,jupiter1 #bcj ,bergstrand1 #cad ,berlin star chart1 #bdd ,bessel1 #agc1 #bhj1 #cje ,beta 7b7 ,lyr1 #cjg ,beta 7b7 ,persei4 ,see ,algol ,betelgeux1 #big ,bible1 eclipses in1 #he ,biela's ,comet1 #bef-beg1 #bgb-bgc1 #cde ,bielids1 #bgj1 #bgb-bgc ,billion1 #ea-eb ,binary stars1 spectroscopic1 #cja-cjf1 #cji2 visual1 #cjj1 #cjc-cjf ,black ,drop1 #aeb-aed ,black ,hour1 #hi ,black ,saturday1 #hi ,blood1 moon in eclipse like1 #ajb ,blue 7rays of light71 #aba1 #acj ,bode's ,law1 #bb-bc1 #bdd-bde ,bolometer1 #abg ,bond1 ,g4,p41 #bcf1 #beg ,bonpland1 #bgj ,botes 7constellation71 #bie1 #cad ,bradley1 #aaa ,brahe1 ,tycho1 #bij1 #caa ,brdikhine's theory of comets' tails1 #bec-bed1 #bef ,bright eclipses of moon1 #fe1 #ajb ,british ,association for the ,advancement of ,science1 #cah ,british ,astronomical ,association1 ,journal of1 #aid ,british ,museum1 #hd ,bull 7constellation74 ,see ,taurus2 ,eye of the1 #big2 ,head of the1 #big ,burgos1 #ih ,busch1 #ic ,csar1 ,julius1 #he1 #aaj1 #ahj1 #bei1 #bfb1 #bia1 #bic ,calcium1 #ach1 #ade ,callisto1 #bcc-bcd ,cambridge1 #bd1 #ia1 #aai1 #bdc ,campbell1 #cje ,canali1 #bad ,canals of ,mars1 #bad-bbb1 #bbd-bbe ,cancer 7constellation71 #cjg ,canes ,venatici 7constellation71 #cjf1 #cad ,canis ,major 7constellation71 #bhi1 #bif-big2 ,minor1 #bif-big ,canopus1 #bhe1 #bih-bii1 #cbj ,capella1 #bhj1 #bhb1 #bij1 #bid1 #big1 #cjc1 #cac ,carbon1 #ade ,carbon dioxide4 ,see ,carbonic acid gas ,carbonic acid gas1 #aff1 #bac1 #bba-bbb ,carnegie ,institution1 ,solar ,observatory of1 #aah ,cassegrainian telescope1 #aad1 #aah ,cassini1 ,j4,d41 #bcf1 #bdj ,cassini's ,division in ,saturn's ring1 #bcf1 #bch ,cassiopeia 7constellation71 #bgi1 #bid1 #caa1 #cad ,cassiopei1 7,eta71 #cjc ,cassiopeia's ,chair1 #bid ,cassius1 ,dion1 #hf ,castor1 #bhb1 #big1 #cjd ,catalogues of stars1 #ajf1 #bij-bia1 #caa ,centaur4 ,see ,centaurus ,centaurus 7constellation71 #bih1 #cjf ,centre of gravity1 #db1 #bhc-bhd1 #cbd ,ceres1 diameter of1 #cj1 #bbe ,ceti1 ,omicron 7or ,mira71 #cjg-cjh ,cetus1 or the ,whale 7constellation71 #cjg ,chaldean astronomers1 #gd1 #gf ,challis1 #bdc-bdd ,chamberlin1 #ccg ,chambers of the ,south1 #bii ,chandler1 #cjh ,charles ,v41 #bfa ,charles' ,wain1 #bia ,chemical rays1 #abg ,chinese and eclipses1 #hc ,chloride of sodium1 #abb ,chlorine1 #abb1 #ade ,christ1 ,birth of1 #ajb ,christian ,era1 first recorded solar eclipse in1 #he ,chromatic aberration1 #aaj ,chromosphere1 #ga-gb1 #ic-id1 #acj-acb1 #ach-aci ,circle1 #aga-agc ,clark1 ,alvan1 ,sons1 #aag-aah1 #cjc ,claudius1 ,emperor1 #hf ,clavius 7lunar crater71 #aii ,clerk ,maxwell1 #bcg ,clouds 7of ,aristophanes71 #aja ,clustering power1 #cbe ,clusters of stars1 #cjj1 #cjf1 #cad1 #cbh ,coal ,sacks4 ,see ,holes in ,milky ,way ,coelostat1 #aai ,coggia's ,comet1 #bed ,colour1 production of1 in telescopes1 #aji-aaa1 #aae1 #aba ,collision of comet with earth1 #cde-cdf2 of dark star with sun1 #cdf-cdh2 of stars1 #bhe1 #cab ,columbus1 #ajc ,coma ,berenices 7constellation71 #cjg1 #caf ,comet1 first discovery of by photography1 #beh2 first orbit calculated1 #bee2 first photograph of1 #beg-beh2 furthest distance seen1 #beh2 passage of among satellites of ,jupiter1 #bej2 passage of earth and moon through tail of1 #beg1 #cdf ,comet of #ajjj ,a4,d41 #bfb2 #ajff1 #bfb-bfd2 #afhj1 #bee1 #bfe2 #ahaa1 #bed-bee2 #ahfa1 #bed1 #beg1 #cdf2 #ahha1 #beg-beh2 #ahhb1 #bea1 #beh1 #bia2 #ahhi1 #beh2 #aijg1 #beh ,comets1 #bg-bh1 #eh1 ,chaps4 ,,xix4 and ,,xx41 #cde-cdf2 ancient view of1 #bei-bfa2 captured1 #bea-bec2 ,chinese records of1 #hc-hd2 composition of1 #beb2 contrasted with planets1 #bdg2 families of1 #bea-beb1 #bef2 meteor swarms and1 #bgd2 revealed by solar eclipses1 #ie-if2 tails of1 #ada1 #ahb1 #bdh1 #beb-bed ,common1 telescopes of ,dr4 ,a4,a41 #aah ,conjunction1 #bji ,constellations1 #aje1 #bgh-bgi1 #bhe1 #bhi ,contraction theory of sun's heat1 #abh-abi1 #cce ,cook1 ,captain1 #aed ,cooke1 #aah ,copernican system1 #bj1 #ajg1 #adi1 #agj-agc1 #bgi1 #bhj ,copernicus1 #bj1 #ajh1 #adi1 #aeh1 #agj-agb1 #bcf ,copernicus 7lunar crater71 #bjj1 #bjd ,copper1 #ade ,corder1 ,h41 #add ,corona1 #gj-gb1 #ij1 #ib-ig1 #acb1 #adj-ada1 #bgj2 earliest drawing of1 #ia2 earliest employment of term1 #ij2 earliest mention of1 #hf2 earliest photograph of1 #ic2 illumination given by1 #ga2 possible change in shape of during eclipse1 #if-ih2 structure of1 #adb-adc2 variations in shape of1 #ada ,corona ,borealis 7constellation71 #bie ,coronal matter1 #adb2 streamers1 #ie-if1 #ada-adc ,coronium1 #acc1 #adb1 #cag ,cotes1 #ia ,coud1 equatorial1 #aai ,cowell1 ,p4,h41 #bee1 #bfd ,crabtree1 #aeb ,crape ring of ,saturn1 #bcf-bcg ,craterlets on ,mars1 #bbj ,craters 7ring-mountains7 on moon1 #aig-bje1 #bad1 #cdj2 suggested origin of1 #bjc-bjd1 #bad ,crawford1 ,earl of1 #id ,crecy1 supposed eclipse at battle of1 #hh-hi ,crescent moon1 #ahc1 #ahe ,crommelin1 ,a4,c4,d41 #bee1 #bfd ,crossley ,reflector1 #aah1 #cae-caf ,crown glass1 #aae ,crucifixion1 darkness of1 #hf ,crucis1 a 7,alpha71 #bih ,crux1 or ,southern ,cross 7constellation71 #bih-bii1 #cbc ,cycle1 sunspot1 #acf-acg1 #ada1 #adc-add ,cygni1 #fa1 #agc1 #bhj ,cygnus1 or the ,swan 7constellation71 #bie1 #cbe ,daniel's ,comet of #ahig1 #beh ,danzig1 #aaa ,dark ,ages1 #ajb1 #ajg1 #bfj ,dark eclipses of moon1 #fe1 #ajb-ajc ,dark matter in space1 #cbc ,dark meteors1 #bge-bgf ,dark stars1 #cji-caj1 #cab1 #cbc1 #cdf-cdg ,darkness behind the stars1 #cbe ,darwin1 ,sir ,g4,h41 #cci ,davis1 #id ,dawes1 #bcf ,dearborn ,observatory1 #cjc ,death from fright at eclipse1 #gc ,debonnaire1 ,louis le1 #hh1 #bfa ,deimos1 #bbc ,deity1 symbol of the1 #hg ,demon star4 ,see ,algol ,denebola1 #bif ,denning1 ,w4,f41 #bfi ,densities of sun and planets1 #ci ,density1 #ch ,deslandres1 #adj ,diameters of sun and planets1 #ca ,disappearance of moon in lunar eclipse1 #fe1 #ajb-ajc ,disc1 #fj ,disc theory4 ,see ,grindstone theory ,discoveries1 independent1 #bcf ,discovery1 anticipation in1 #bcf-bcg2 indirect methods of1 #abj ,dipper1 the1 #bia2 the ,little1 #bid ,distance of a celestial body1 how ascertained1 #ef-eh2 of sun from earth1 how determined1 #aea1 #baa ,distances of planets from sun1 #dg ,distances of sun and moon1 relative1 #fh ,dog1 the ,greater4 ,see ,canis ,major2 the ,lesser1 see ,canis ,minor ,dog ,star1 #bhi1 #big ,dollond1 ,john1 #aae-aaf ,donati's ,comet1 #bed1 #beg ,doppler's method1 #abe1 #acf1 #bhb1 #cja-cjb ,dorpat1 #aag ,double canals of ,mars1 #bad-bae1 #bah-bbj ,double planet1 earth and moon a1 #ahi ,double stars1 #cjj ,douglass1 #bcc ,dreams1 ,lake of1 #aig ,dumb-bell ,nebula1 #caf ,earth1 #bj1 #bb1 #ca1 #ci1 #dh1 #fd1 ,chap4 ,,xv41 #bfg2 cooling of1 #cdc2 diameter of1 #ca2 interior of1 #aff2 mean distance of from sun1 #dg2 rigidity of1 #aha2 rotation of1 #cj1 #cc1 #afa-afe1 #agj2 shape of1 #afe2 tail to1 #ahb ,earthlight1 or ,earthshine1 #ahf ,earth's axis1 ,precessional movement of1 #age-agg1 #bie1 #bih-bii ,earth's shadow1 circular shape of1 #fd1 #afj ,eclipse1 #fa ,eclipse knowledge1 delay of1 #gd ,eclipse party1 work of1 #gc ,eclipse of sun1 advance of shadow in total1 #fi2 animal and plant life during1 #ga2 earliest record of total1 #hd2 description of total1 #fi-gc2 duration of total1 #fi1 #gb2 importance of total1 #fh ,eclipses1 ascertainment of dates of past1 #gd2 experience a necessity in solar1 #gc-gd2 of moon1 #fc-fe1 ,chap4 ,,ix41 #bjc2 photography in1 #ic2 prediction of future1 #gd2 recurrence of1 #gd-hj ,eclipses of sun1 #be1 #fe-gd1 ,chap4 ,,viii41 #bja-bjb1 #bcd2 #afab ,a4,d41 #ij2 #agae1 #hh1 #ia2 #agbd1 #hh1 #ia2 #ahcf1 #ib2 #ahdb1 #ib-ic2 #ahea1 #ha1 #ic2 #ahfh1 #ic2 #ahgj1 #id2 #ahga1 #id2 #ahgh1 #ie2 #ahhb1 #ie2 #ahhc1 #ie-if2 #ahic1 #ie-if2 #ahif1 #if1 #ii2 #ahih1 #if1 #ih2 #aijj1 #ig2 #aije1 #ge-gf1 #hj-ha1 #ig-ih2 #aijg1 #ih2 #aijh1 #ih2 #aiad1 #ii2 #aibg1 #ib1 #ii-ajj ,eclipses1 ,past and ,future1 #cdj ,egenitis1 #bgb ,electric furnace1 #abh ,electric light1 spectrum of1 #abb ,elements composing sun1 #add-ade ,ellipses1 #cb1 #ff1 #agb-agc1 #agg-agh ,elliptic orbit1 #ff1 #agg ,ellipticity1 #cb ,elongation1 ,eastern1 #adg1 #adi2 ,western1 #adg1 #adi ,encke's ,comet1 #bec1 #bef ,end of the ,world1 #cdb ,england1 solar eclipses visible in1 #hg-hh1 #ia-ib ,epsilon1 7e7 ,lyr1 #cjb ,equator1 #dh ,equatorial telescope1 #bbf ,equinoxes4 ,see ,precession of ,eros1 #baj-baa1 #bbc1 #bbf-bbg2 discovery of1 #bd1 #baj1 #bbg2 importance of1 #baa2 orbit of1 #cb1 #cg1 #baj1 #ccf ,eruptive prominences1 #aci ,esclistre1 #hi ,ether1 #cbb-cbc1 #cca-ccb ,europa1 #bcc1 #bce ,evans1 ,j4,e41 #bai ,evening star1 #adi-aej1 #bda ,everest1 ,mount1 #bjj ,evershed1 #ahb ,eye-piece1 #aaj ,fabricius1 #cjg ,facul1 #acf1 #adc ,fauth1 #bje ,faye1 #cce ,fin du ,monde1 #cdf ,first quarter1 #ahc ,fixed stars1 #bhj ,flagstaff1 #bae-baf1 #bbj ,flammarion1 ,camille1 #cdf ,flamsteed1 #ij ,flash spectrum1 #acg ,flat1 #aab ,flint glass1 #aae ,focus1 #ff1 #agg ,forty-foot ,telescope1 #aae ,foster1 #ajb ,fraunhofer1 #aag ,french ,academy of ,sciences1 #aae ,froissart1 #hi ,full moon of ,laplace1 #aij ,galaxy4 ,see ,milky ,way4 ,galilean telescope1 #aji ,galileo1 #ee1 #aji1 #agb1 #aig1 #bjf1 #bcb-bce1 #bdb ,galle1 #bd1 #baa1 #bdd ,ganymede1 #bcc-bcd ,gas light1 spectrum of1 #abb ,gegenschein1 #aha-ahb ,gem of meteor ring1 #bga ,gemini1 or the ,twins 7constellation71 #bb1 #bif-big ,geminorum1 z 7,zeta71 #cjd ,geometrical groupings of stars1 #bib ,giant planet1 #bcj1 #bch-bci ,gibbous1 #ahc1 #ahe ,gill1 ,sir ,david1 #baa1 #beh1 #bia1 #cag-cah ,gold1 #ade ,goodricke1 #cjg ,gore1 ,j4,e41 #fc1 #bhe1 #cjc1 #cjg-cjh1 #caj1 #cbc-cbd1 #cca1 #ccg1 #cdg ,granulated structure of photosphere1 #acd ,gravitation 7or gravity71 #ci1 #da-de1 #abh1 #cjf ,greek ideas1 #ah1 #aeh1 #afa-afb1 #aga1 #ahf1 #aig ,green 7rays of light71 #aba ,greenwich ,observatory1 #adc-add1 #bcb1 #bee1 #cjc ,gregorian telescope1 #aac-aad ,grimaldi 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sun and planets compared1 #ch-ci ,vulcan1 #be ,wallace1 ,a4,r41 on ,mars1 #bbj-bbc ,water1 lack of1 on moon1 #bja-bjb ,water vapour1 #bjb1 #bac1 #bbb ,wargentin1 #ajc ,warner and ,swasey ,co41 #aag ,weather1 moon and1 #bjf-bjg ,weathering1 #bjb ,webb1 ,rev4 ,t4,w41 #bjd ,weight1 #dc1 #afe-aff ,wells1 ,h4,g41 #cdd ,whale 7constellation74 ,see ,cetus ,whewell1 #aij ,willamette meteorite1 #bgg ,wilson1 ,mount1 #aah ,wilson1 ,w4,e41 #cac ,winged circle 7or disc71 #hg ,winter1 #age1 #agh ,witt1 #bbg ,wolf1 ,max1 #bbf-bbg1 #bcb ,wright1 ,thomas1 #cai1 #ccd ,wybord1 #hi ,xenophon1 #aja ,year1 #ce ,year in ,uranus and ,neptune1 #ce-cf ,year1 number of eclipses in a1 #fh ,year of the ,stars1 #bgj ,yellow 7rays of light71 #aba-abb1 #abd ,yerkes ,telescope ,great1 #aag1 #cjc ,young1 #id1 #acg1 #aff ,zenith1 #agd ,zinc1 #ade ,zodiacal light1 #aha ,zone of asteroids1 #cj-ca1 #bbg ,,the ,,end ,printed by ,,ballantyne1 ,,hanson ,,co4 ,edinburgh ,london ,,the ,,science ,,of ,,to-,,day ,,series ,with many illustrations4 ,extra ,crown #hvo4 #es4 net4 ,,botany ,,of ,,to-,,day4 ,a ,popular ,account of the ,evolution of ,modern ,botany4 ,by ,prof4 ,g4,f4 ,,scott ,,elliot1 ,m4,a41 ,b4,sc41 ,author of ,the ,romance of ,plant ,life1 c4 c4 ,one of the books that turn botany from a dryasdust into a fascinating study4--,evening ,standard4 ,,aerial ,,navigation ,,of ,,to-,,day4 ,a ,popular ,account of the ,evolution of ,aeronautics4 ,by ,,charles ,c4 ,,turner4 ,mr4 ,turner is well qualified to write with authority on the subject4 ,the book sets forth the principles of flight in plain non-technical language4 ,one is impressed by the complete thoroughness with which the subject is treated4--,daily ,graphic4 ,,scientific ,,ideas ,,of ,,to-,,day4 ,a ,popular ,account1 in ,non-technical ,language1 of the ,nature of ,matter1 ,electricity1 ,light1 ,heat1 ,electrons1 c4 c4 ,by ,,charles ,r4 ,,gibson1 ,a4,i4,e4,e41 ,author of ,electricity of ,to-,day1 c4 ,supplies a real need4444 ,mr4 ,gibson has a fine gift of exposition4--,birmingham ,post4 ,,astronomy ,,of ,,to-,,day4 ,a ,popular ,introduction in ,non-technical ,language4 ,by ,,cecil ,g4 ,,dolmage1 ,,ll4,d41 ,f4,r4,a4,s4 ,with frontispiece in colours1 #de other illustrations4 ,dr4 ,dolmage has absolutely kept to his promise to introduce the reader to an acquaintance with the astronomy of to-day in non-technical language4--,saturday ,review4 ,,electricity ,,of ,,to-,,day4 ,its ,work and ,mysteries ,explained4 ,by ,,charles ,r4 ,,gibson1 ,a4,i4,e4,e4 ,mr4 ,gibson has given us one of the best examples of popular scientific exposition that we remember seeing4 ,his book may be strongly commended to all who wish to realise what electricity means and does in our daily life4--,the ,tribune4 ,,seeley ,,co41 ,,limited ,,the ,,science ,,of ,,to-,,day ,,series ,with many ,illustrations4 ,extra ,crown #hvo4 #es4 net4 ,,aerial ,,navigation ,,of ,,to-,,day4 ,a ,popular ,account of the ,evolution of ,aeronautics4 ,by ,,charles ,c4 ,,turner4 ,if ever the publication of a book was well timed1 surely it is the case with this book on aviation4444 ,of the technical chapters we need only say that they are so simply written as to present no grave difficulties to the beginner who is equipped with an average education4--,globe4 ,,botany ,,of ,,to-,,day4 ,a ,popular ,account of the ,evolution of ,modern ,botany4 ,by ,prof4 ,g4,f4 ,,scott-,,elliot1 ,m4,a41 ,b4,sc41 ,author of ,the ,romance of ,plant ,life1 c4 c4 ,this most entertaining and instructive book4 ,it is the fruit of wide reading and much patient industry4--,globe4 ,,scientific ,,ideas ,,of ,,to-,,day4 ,a ,popular ,account1 in ,non-technical ,language1 of the ,nature of ,matter1 ,electricity1 ,light1 ,heat1 ,electrons1 c4 c4 ,by ,,charles ,r4 ,,gibson1 ,a4,i4,e4,e41 ,author of ,electricity of ,to-,day1 c4 ,as a knowledgeable writer1 gifted with the power of imparting what he knows in a manner intelligible to all1 ,mr4 ,c4,r4 ,gibson has established a well-deserved reputation4--,field4 ,,astronomy ,,of ,,to-,,day4 ,a ,popular ,introduction in ,non-technical ,language4 ,by ,,cecil ,g4 ,,dolmage1 ,,ll4,d41 ,f4,r4,a4,s4 ,with frontispiece in colours1 #de other illustrations4 ,a lucid exposition much helped by abundant illustrations4--,the ,times4 ,from cover to cover the book is readable1 and every word is intelligible to the layman4 ,dr4 ,dolmage displays literary powers of a very high order4 ,those who read it without any previous knowledge of astronomy will find that a new interest has been added to their lives1 and that in a matter of #cej pages they have gained a true conception of the meaning of astronomy4--,the ,standard4 ,,electricity ,,of ,,to-,,day4 ,its ,work and ,mysteries ,explained4 ,by ,,charles ,r4 ,,gibson1 ,a4,i4,e4,e4 ,mr4 ,gibson has given us one of the best examples of popular scientific exposition that we remember seeing4 ,his aim has been to produce an account of the chief modern applications of electricity without using technical language or making any statements which are beyond the comprehension of any reader of ordinary intelligence4 ,in this he has succeeded to admiration1 and his book may be strongly commended to all who wish to realise what electricity means and does in our daily life4--,the ,tribune4 ,,seeley ,,co41 ,,ltd41 #ch ,,great ,,russell ,,street4 ,,the ,,romance ,,of ,,modern ,,electricity ,,describing ,,in ,,non-,,technical ,,language ,,what ,,is ,,known ,,about ,,electricity ,,many ,,of ,,its ,,interesting ,,applications ,,by ,,charles ,r4 ,,gibson1 ,a4,i4,e4,e4 ,,author or ,,electricity of ,,to-,,day1 ,,etc4 ,extra ,crown #hvo4 ,with #cd ,illustrations and #aa ,diagrams4 #es4 ,everywhere ,mr4 ,charles ,r4 ,gibson makes admirable use of simple analogies which bespeak the practised lecturer1 and bring the matter home without technical detail4 ,the attention is further sustained by a series of surprises4 ,the description of electric units1 the volt1 the ohm1 and especially the ampere1 is better than we have found in more pretentious works4--,academy4 ,mr4 ,gibson's style is very unlike the ordinary text-book4 ,it is fresh1 and is non-technical4 ,its facts are strictly scientific1 however1 and thoroughly up to date4 ,if we wish to gain a thorough knowledge of electricity pleasantly and without too much trouble on our own part1 we will read ,mr4 ,gibson's ',romance4'--,expository ,times4 ,a book which the merest tyro totally unacquainted with elementary electrical principles can understand1 and should therefore especially appeal to the lay reader4 ,especial interest attaches to the chapter on wireless telegraphy1 a subject which is apt to 'floor' the uninitiated4 ,the author reduces the subject to its simplest aspect1 and describes the fundamental principles underlying the action of the coherer in language so simple that anyone can grasp them4--,electricity4 ,contains a clear and concise account of the various forms in which electricity is used at the present day1 and the working of the telephone1 wireless telegraphy1 tramcars1 and dynamos is explained with the greatest possible lucidity1 while the marvels of the ,x-rays and of radium receive their due notice4 ,now that electricity plays such an all-important part in our daily life1 such a book as this should be in the hands of every boy4 ,indeed1 older people would learn much from its pages4 ,for instance1 how few people could explain the principles of wireless telegraphy in a few words if suddenly questioned on the subject4 ,the book is well and appropriately illustrated4--,graphic4 ,mr4 ,gibson sets out to describe in non-technical language the marvellous discoveries and adaptation of this pervasive and powerful essence1 and being a most thorough master of the subject1 he leads the reader through its mazes with a sure hand4 ,throughout he preserves a clear and authoritative style of exposition which will be understood by any intelligent reader4--,yorkshire ,observer4 ,a popular and eminently readable manual for those interested in electrical appliances4 ,it describes in simple and non-technical language what is known about electricity and many of its interesting applications4 ,there are a number of capital illustrations and diagrams which will help the reader greatly in the study of the book4--,record4 ,,seeley ,,co41 ,,ltd41 #ch ,,great ,,russell ,,street4 ,,the ,,romance ,,of ,,savage ,,life ,,describing ,,the ,,habits1 ,,customs1 ,,everyday ,,life1 c41 ,,of ,,primitive ,,man ,,by ,,prof4 ,g4,f4 ,,scott ,,elliot1 ,m4,a41 ,b4,,sc41 ,c4 ,with ,thirty ,illustrations4 ,extra ,crown #hvo4 #es4 ,mr4 ,scott ,elliot has hit upon a good idea in this attempt to set forth the life of the primitive savage4 ,on the whole1 too1 he has carried it out well and faithfully4444 ,we can recommend the book as filling a gap4--,athenum4 ,a readable contribution to the excellent series of which it forms a part4 ,mr4 ,scott ,elliot writes pleasantly 444 he possesses a sufficiently vivid imagination to grasp the relation of a savage to his environment4--,nature4 ,there are things of remarkable interest in this volume1 and it makes excellent reading and represents much research4--,spectator4 ,,the ,,romance ,,of ,,plant ,,life ,,describing ,,the ,,curious ,,and ,,interesting ,,in ,,the ,,plant ,,world ,,by ,,prof4 ,g4,f4 ,,scott ,,elliot1 ,m4,a41 ,b4,,sc41 ,c4 ,with ,thirty-four ,illustrations4 ,extra ,crown #hvo4 #es4 ,the author has worked skilfully into his book details of the facts and inferences which form the groundwork of modern ,botany4 ,the illustrations are striking1 and cover a wide field of interest1 and the style is lively4--,athenum4 ,in twenty-nine fascinating1 well-printed1 and well-illustrated chapters1 ,prof4 ,scott ,elliot describes a few of the wonders of plant life4 ,a very charming and interesting volume4--,daily ,telegraph4 ,mr4 ,scott ,elliot is of course a well-known authority on all that concerns plants1 and the number of facts he has brought together will not only surprise but fascinate all his readers4--,westminster ,gazette4 ,,seeley ,,co41 ,,ltd41 #ch ,,great ,,russell ,,street4 ,,the ,,romance ,,of ,,insect ,,life ,,describing ,,the ,,curious ,,interesting ,,in ,,the ,,insect ,,world ,,by ,,edmund ,,selous ,,author ,,of ,,the ,,romance ,,of ,,the ,,animal ,,world1 ,,etc4 ,with ,sixteen ,illustrations4 ,extra ,crown #hvo4 #es4 ,an entertaining volume1 one more of a series which seeks with much success to describe the wonders of nature and science in simple1 attractive form4--,graphic4 ,offers most interesting descriptions of the strange and curious inhabitants of the insect world1 sure to excite inquiry and to foster observation4 ,there are ants white and yellow1 locusts and cicadas1 bees and butterflies1 spiders and beetles1 scorpions and cockroaches--and especially ants--with a really scientific investigation of their wonderful habits not in dry detail1 but in free and charming exposition and narrative4 ,an admirable book to put in the hands of a boy or girl with a turn for natural science--and whether or not4--,educational ,times4 ,both interesting and instructive4 ,such a work as this is genuinely educative4 ,there are numerous illustrations4--,liverpool ,courier4 ,with beautiful original drawings by ,carton ,moore ,park and ,lancelot ,speed1 and effectively bound in dark blue cloth1 blazoned with scarlet and gold4--,lady4 ,admirably written and handsomely produced4 ,mr4 ,selous's volume shows careful research1 and the illustrations of insects and the results of their powers are well done4--,world4 ,,the ,,romance ,,of ,,modern ,,mechanism ,,interesting ,,descriptions ,,in ,,non-,,technical ,,language ,,of ,,wonderful ,,machinery1 ,,mechanical4 ,,devices1 ,,marvellously ,,delicate ,,scientific ,,instruments ,,by ,,archibald ,,williams1 ,b4,a41 ,f4,r4,g4,s4 ,,author ,,of ,,the ,,romance ,,of ,,modern ,,exploration1 ,,etc4 ,with ,twenty-six ,illustrations4 ,extra ,crown #hvo4 #es4 ,no boy will be able to resist the delights of this book1 full to the brim of instructive and wonderful matter4--,british ,weekly4 ,this book has kept your reviewer awake when he reasonably expected to be otherwise engaged4 ,we do not remember coming across a more fascinating volume1 even to a somewhat blas reader whose business it is to read all that comes in his way4 ,the marvels miracles they should be called1 of the modern workshop are here exploited by ,mr4 ,williams for the benefit of readers who have not the opportunity of seeing these wonders or the necessary mathematical knowledge to understand a scientific treatise on their working4 ,only the simplest language is used and every effort is made1 by illustration or by analogy1 to make sufficiently clear to the non-scientific reader how the particular bit of machinery works and what its work really is4 ,delicate instruments1 calculating machines1 workshop machinery1 portable tools1 the pedrail1 motors ashore and afloat1 fire engines1 automatic machines1 sculpturing machines--these are a few of the chapters which crowd this splendid volume4--,educational ,news4 ,it is difficult to make descriptions of machinery and mechanism interesting1 but ,mr4 ,williams has the enviable knack of doing so1 and it is hardly possible to open this book at any page without turning up something which you feel you must read2 and then you cannot stop till you come to the end of the chapter4--,electricity4 ,this book is full of interest and instruction1 and is a welcome addition to ,messrs4 ,seeley and ,company's ,romance ,series4--,leeds ,mercury4 ,a book of absorbing interest for the boy with a mechanical turn1 and indeed for the general reader4--,educational ,times4 ,an instructive and well-written volume4--,hobbies4 ,,seeley ,,co41 ,,ltd41 #hh ,,great ,,russell ,,street4 ,a ,catalogue of ,books on ,art1 ,history1 and ,general ,literature ,published by ,seeley1 ,service ,co ,ltd4 #ch ,great ,russell ,st4 ,london ,some of the ,contents ,crown ,library1 ,the #d ,elzevir ,library1 ,the #e ,events of ,our ,own ,times ,series #f ,illuminated ,series1 ,the #h ,miniature ,library of ,devotion1 ,the #i ,miniature ,portfolio ,monographs1 ,the #i ,missions1 ,the ,library of #aj ,new ,art ,library1 ,the #aa ,portfolio ,monographs #aa ,science of ,to-,day ,series1 ,the #ad ,seeley's ,illustrated ,pocket ,library #ad ,seeley's ,standard ,library #ae ,story ,series1 ,the #ae ,things ,seen ,series1 ,the #af ,the ,publishers will be pleased to post their complete ,catalogue or their ,illustrated ,miniature ,catalogue on receipt of a post-card ,,catalogue ,,of ,,books ,arranged alphabetically under the names of ,authors and ,series ,,abbott1 ,rev4 ,e4,a41 ,d4,d4 ,how to ,parse4 ,an ,english ,grammar4 ,fcap4 #hvo1 #cs4 #f;d4 ,how to ,tell the ,parts of ,speech4 ,an ,introduction to ,english ,grammar4 ,fcap4 #hvo1 #bs4 ,how to ,write ,clearly4 ,rules and ,exercises on ,english ,composition4 #as4 #f;d4 ,latin ,gate1 ,the4 ,a ,first ,latin ,translation ,book4 ,crown #hvo1 #cs4 #f;d4 ,via ,latina4 ,a ,first ,latin ,grammar4 ,crown #hvo1 #cs4 #f;d4 ,,abbott1 ,rev4 ,e4,a41 and ,sir ,j4,r4 ,,seeley4 ,english ,lessons for ,english ,people4 ,crown #hvo1 #ds4 #f;d4 ,,ady1 ,mrs4 ,see ,,cartwright1 ,,julia4 ,,kempis1 ,,thomas4 ,of the ,imitation of ,christ4 ,with ,illuminated ,frontispiece and ,title ,page1 and ,illuminated ,sub-,titles to each book4 ,in white or blue cloth1 with inset miniatures4 ,gilt top2 crown #hvo1 #fs4 nett2 also bound in same manner in real classic vellum4 ,each copy in a box1 #ajs4 #f;d4 nett2 ,antique leather with clasps1 #ajs4 #f;d4 nett4 ,it may well be questioned whether the great work of ,thomas ,kempis has ever been presented to better advantage4--,the ,guardian4 ,,anderson1 ,prof4 ,w4 ,japanese ,wood ,engravings4 ,coloured ,illustrations4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett2 also small #dto1 cloth1 #bs4 nett2 lambskin1 #cs4 nett4 ,,armstrong1 ,sir ,,walter4 ,the ,art of ,velazquez4 ,illustrated4 ,super-royal #hvo1 #cs4 #f;d4 nett4 ,the ,life of ,velazquez4 ,illustrated4 ,super-royal #hvo1 #cs4 #f;d4 nett4 ,velazquez4 ,a ,study of his ,life and ,art4 ,with ,eight ,copper ,plates and many minor ,illustrations4 ,super-royal #hvo1 cloth1 #is4 nett4 ,thomas ,gainsborough4 ,illustrated4 ,super-royal #hvo1 half-linen1 #cs4 #f;d4 nett4 ,also new edition small #dto1 cloth1 #bs4 nett2 leather1 #cs4 nett and #es4 nett4 ,the ,peel ,collection and the ,dutch ,school of ,painting4 ,with ,illustrations in ,photogravure and ,half-tone4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 #gs4 nett4 ,w4,q4 ,orchardson4 ,super-royal #hvo1 sewed1 #bs4 #f;d42 half-linen1 #cs4 #f;d4 nett4 ,,augustine1 ,s4 ,confessions of ,s4 ,augustine4 ,with ,illuminated pages4 ,in white or blue cloth1 gilt top1 crown #hvo1 #fs4 nett2 also in vellum1 #ajs4 #f;d4 nett4 ,,baker1 ,captain ,b4 ,,granville ,the ,passing of the ,turkish ,empire in ,europe4 ,with ,thirty-two ,illustrations4 ,demy #hvo1 #afs4 nett4 ,,baring-,,gould1 ,rev4 ,s4 ,family ,names and their ,story4 ,demy #hvo1 #gs4 #f;d4 nett4 #es4 nett4 ,,bedford1 ,rev4 ,w4,k4,r4 ,malta and the ,knights ,hospitallers4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 ,,benham1 ,rev4 ,canon ,d4,d41 ,f4,s4,a4 ,the ,tower of ,london4 ,with ,four ,plates in ,colours and many other ,illustrations4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 #gs4 nett4 ,medival ,london4 ,with a ,frontispiece in ,photogravure1 ,four ,plates in ,colour1 and many other ,illustrations4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 gilt top1 #gs4 nett4 ,also extra crown #hvo1 #cs4 #f;d4 nett4 ,old ,st4 ,paul's ,cathedral4 ,with a ,frontispiece in ,photogravure1 ,four ,plates printed in ,colour1 and many other ,illustrations4 ,super-royal #hvo1 sewed1 #es4 nett1 or cloth1 gilt top1 #gs4 nett4 ,,bennett1 ,,edward4 ,the ,post ,office and its ,story4 ,an interesting account of the activities of a great ,government department4 ,with ,twenty-five ,illustrations4 ,ex4 crn4 #hvo1 #es4 nett4 ,,bickersteth1 ,rev4 ,e4 ,family ,prayers for ,six ,weeks4 ,crown #hvo1 #cs4 #f;d4 ,a ,companion to the ,holy ,communion4 #cbmo1 cloth1 #as4 ,,binyon1 ,,laurence4 ,dutch ,etchers of the ,seventeenth ,century4 ,illustrated4 ,super-royal #hvo1 sewed1 #bs4 #f;d42 half-linen1 #cs4 #f;d4 nett4 ,john ,crome and ,john ,sell ,cotman4 ,illustrated4 ,super-royal #hvo sewed1 #cs4 #f;d4 nett4 ,,birch1 ,g4,h4 ,london on ,thames in ,bygone ,days4 ,with ,four ,plates printed in ,colour and many other ,illustrations4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 #gs4 nett4 ,,bridges1 ,rev4 ,c4 ,an ,exposition of ,psalm ,,cxix4 ,crown #hvo1 #es4 ,,butcher1 ,e4,l4 ,things ,seen in ,egypt4 ,with ,fifty ,illustrations4 ,small #dto1 cloth1 #bs4 nett2 lambskin1 #cs4 nett2 velvet leather1 in box1 #es4 nett4 ,poems1 #as4 #f;d4 nett4 ,,cachemaille1 ,rev4 ,e4,p41 ,m4,a4 ,,xxvi ,present-,day ,papers on ,prophecy4 ,an explanation of the visions of ,daniel and of the ,revelation1 on the continuous historic system4 ,with ,maps and ,diagrams4 #gjj pp4 #fs4 nett4 ,,cartwright1 ,,julia4 ,jules ,bastien-,lepage4 ,super-royal #hvo1 sewed1 #bs4 #f;d42 cloth1 #cs4 #f;d4 nett4 ,sacharissa4 ,some ,account of ,dorothy ,sidney1 ,countess of ,sunderland1 her ,family and ,friends4 ,with ,five ,portraits4 ,demy #hvo1 #gs4 #f;d4 ,raphael in ,rome4 ,illustrated4 ,super-royal #hvo1 sewed1 #bs4 #f;d42 half-linen1 #cs4 #f;d4 nett2 also in small #dto1 cloth1 #bs4 nett2 leather1 #cs4 nett and #es4 nett4 ,the ,early ,work of ,raphael4 ,illustrated4 ,super-royal #hvo1 sewed #bs4 #f;d42 half-linen1 #cs4 #f;d4 ,also new edition1 revised1 in small #dto1 in cloth1 #bs4 nett2 leather1 #cs4 nett4 ,raphael3 ,a ,study of his ,life and ,work4 ,with ,eight ,copper ,plates and many other ,illustrations4 ,super-royal #hvo1 #gs4 #f;d4 nett4 ,,cesaresco1 ,the ,countess ,,martinengo ,the ,liberation of ,italy4 ,with ,portraits on ,copper4 ,crown #hvo1 #es4 ,,chatterton1 ,e4 ,,keble4 ,fore and ,aft4 ,the ,story of the ,fore and ,aft ,rig from the ,earliest ,times to the ,present ,day4 ,sq4 ex4 royal #hvo4 ,with #aej ,illustrations and ,coloured ,frontispiece by ,c4 ,dixon1 ,r4,i4 #afs4 nett4 ,through ,holland in the ,vivette4 ,the ,cruise of a #d-,tonner from the ,solent to the ,zuyder ,zee1 through the ,dutch ,waterways4 ,with ,sixty ,illustrations and ,charts1 #fs4 nett4 ,,chitty1 ,j4,r4 ,things ,seen in ,china4 ,with ,fifty ,illustrations4 ,small #dto2 cloth1 #bs42 leather1 #cs42 velvet leather in a box1 #es4 nett4 ,,choral ,,service-,,book ,,for ,,parish ,,churches1 ,,the4 ,compiled and ,edited by ,j4,w4 ,,elliott1 ,organist and ,choirmaster of ,st4 ,mark's1 ,hamilton ,terrace1 ,london4 ,with some ,practical ,counsels taken by permission from ,notes on the ,church ,service1 by ,bishop ,,walsham ,,how4 ,a4 ,royal #hvo1 sewed1 #as42 cloth1 #as4 #f;d4 ,b4 #afmo1 sewed1 #f;d42 cloth1 #h;d4 ,the following portions may be had separately3-- ,the ,ferial and ,festal ,responses and the ,litany4 ,arranged by ,j4,w4 ,,elliott4 ,sewed1 #d;d4 ,the ,communion ,service1 ,kyrie1 ,credo1 ,sanctus1 and ,gloria in ,excelsis4 ,set to ,music by ,dr4 ,j4 ,,naylor1 ,organist of ,york ,minster4 ,sewed1 #d;d4 ,,church1 ,sir ,,arthur ,h41 ,f4,r4,s4 ,josiah ,wedgwood1 ,master ,potter4 ,with many ,illustrations4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 #gs4 nett2 also small #dto1 cloth1 #bs4 nett2 leather1 #cs4 and #es4 nett4 ,the ,chemistry of ,paints and ,painting4 ,third ,edition4 ,crown #hvo1 #fs4 ,,church1 ,rev4 ,a4,j4 ,nicias1 and the ,sicilian ,expedition4 ,crown #hvo1 #as4 #f;d4 ,for other books by ,professor ,,church see ,complete ,catalogue4 ,,clark1 ,j4,w41 ,m4,a4 ,cambridge4 ,with a coloured ,frontispiece and many other ,illustrations by ,a4 ,,brunet-,,debaines and ,h4 ,,toussaint c4 ,extra crown #hvo1 #fs42 also crown #hvo1 cloth1 #bs4 nett2 leather1 #cs42 special leather1 in box1 #es4 nett4 ,,cody1 ,rev4 ,h4,a4 ,an ,apostle of the ,north4 ,the ,biography of the late ,bishop ,,bompas1 ,first ,bishop of ,athabasca1 and with an ,introduction by the ,,archbishop of ,,ruperts-,,land4 ,with #db ,illustrations4 ,demy #hvo1 #gs4 #f;d4 nett4 #es4 nett4 ,,corbin1 ,t4,w4 ,engineering of ,to-day4 ,with ,seventy-three ,illustrations and ,diagrams4 ,extra crown #hvo1 #es4 nett4 ,mechanical ,inventions of ,to-,day4 ,ex4 ,crown #hvo2 with ,ninety-four ,illustrations1 #es4 nett4 ,,cornish1 ,c4,j4 ,animals of ,to-day3 ,their ,life and ,conversation4 ,with ,illustrations from ,photographs by ,c4 ,,reid of ,wishaw4 ,crown #hvo1 #fs4 ,the ,isle of ,wight4 ,illustrated4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett2 also a new edition1 small #dto1 cloth1 #bs42 leather1 #cs4 and #es4 ,life at the ,zoo4 ,notes and ,traditions of the ,regent's ,park ,gardens4 ,illustrated from ,photographs by ,,gambier ,,bolton4 ,fifth ,edition4 ,crown #hvo1 #fs4 ,the ,naturalist on the ,thames4 ,many ,illustrations4 ,demy #hvo1 #gs4 #f;d4 ,the ,new ,forest4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett2 also new edition1 small #dto1 cloth1 #bs42 leather1 #cs4 nett2 and special velvet leather1 each copy in a box1 #es4 ,the ,new ,forest and the ,isle of ,wight4 ,with ,eight ,plates and many other ,illustrations4 ,super-royal #hvo1 #gs4 #f;d4 nett4 ,nights with an ,old ,gunner1 and other ,studies of ,wild ,life4 ,with ,sixteen ,illustrations by ,,lancelot ,,speed1 ,,charles ,,whymper1 and from ,photographs4 ,crown #hvo1 #fs4 99 99 99 99 99 ,,the ,,crown ,,library ,a series of notable copyright books issued in uniform binding4 ,extra crown #hvo4 ,with many illustrations1 #es4 nett4 ,,just ,,issued4 ,,second ,,and ,,cheaper ,,edition4 ,,swann1 ,a4,j4 ,fighting the ,slave ,hunters in ,central ,africa4 ,a ,record of ,twenty-six ,years of ,travel and ,adventure round the ,great ,lakes1 and of the overthrow of ,tip-pu-,tib1 ,rumaliza1 and other great ,slave ,traders4 ,with #de ,illustrations and a ,map1 #es4 nett4 ,,recently ,,issued4 ,,grubb1 ,w4 ,,barbrooke4 ,an ,unknown ,people in an ,unknown ,land4 ,an ,account of the ,life and ,customs of the ,lengua ,indians of the ,paraguayan ,chaco1 with ,adventures and ,experiences met with during ,twenty ,years' ,pioneering and ,exploration amongst them4 ,with ,twenty-four ,illustrations and a ,map4 ,extra crown #hvo1 #es4 nett4 ,,fraser1 ,sir ,a4,h4,l41 ,k4,c4,s4,i41 ,m4,a41 ,,ll4,d41 ,litt4,d41 ex-,lieutenant-,governor of ,bengal4 ,among ,indian ,rajahs and ,ryots4 ,a ,civil ,servants' ,recollections and ,impressions of ,thirty-seven ,years of ,work and ,sport in the ,central ,provinces and ,bengal4 ,third ,edition1 #es4 nett4 ,,cody1 ,rev4 ,h4,a4 ,an ,apostle of the ,north4 ,the ,story of ,bishop ,bompas's ,life amongst the ,red ,indians ,eskimo4 ,third ,edition1 #es4 nett4 ,,pennell1 ,t4,l41 ,m4,d41 ,b4,sc4 ,among the ,wild ,tribes of the ,afghan ,frontier4 ,a ,record of ,sixteen ,years' close intercourse with the natives of ,afghanistan and the ,north-,west ,frontier4 ,introduction by ,,earl ,,roberts4 ,extra crown #hvo4 ,twenty-six ,illustrations and ,map4 ,fifth ,edition1 #es4 net4 99 99 99 99 99 ,,cust1 ,,lionel4 ,the ,engravings of ,albert ,drer4 ,illustrated4 ,super-royal #hvo1 half-linen1 #cs4 #f;d4 nett4 ,paintings and ,drawings of ,albert ,drer4 ,illustrated4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett4 ,albrecht ,drer4 ,a ,study of his ,life and ,work4 ,with ,eight ,copper ,plates and many other ,illustrations4 ,super-royal #hvo1 #gs4 #f;d4 ,,davenport1 ,,cyril4 ,cameos4 ,with examples in ,colour and many other ,illustrations4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 #gs4 nett4 ,royal ,english ,bookbindings4 ,with ,coloured ,plates and many other ,illustrations4 ,super-royal #hvo1 sewed1 #cs4 #f;d42 cloth1 #ds4 #f;d4 ,,davies1 ,,randall1 ,f4,s4,a4 ,english ,society of the ,eighteenth ,century in ,contemporary ,art4 ,with ,four ,coloured and many other ,illustrations4 ,super royal #hvo1 sewed1 #es4 nett2 cloth1 #gs4 nett4 ,,dawson1 ,rev4 ,e4,c4 ,the ,life of ,bishop ,hannington4 ,crown #hvo1 paper boards1 #bs4 #f;d42 or with ,map and ,illustrations1 cloth1 #cs4 #f;d4 ,,destr,e1 ,o4,g4 ,the ,renaissance of ,sculpture in ,belgium4 ,illustrated4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 ,,dolmage1 ,,cecil ,g41 ,m4,a41 ,d4,c4,l41 ,,ll4,d41 ,f4,r4,a4,s4 ,astronomy of ,to-,day4 ,a popular account in non-technical language4 ,with ,forty-six ,illustrations and ,diagrams4 ,extra crown #hvo1 #es4 nett4 ,,domville-,,fife1 ,,charles ,w4 ,submarine ,engineering of ,to-,day4 ,extra crown #hvo1 #es4 nett4 ,,elzevir ,,library1 ,,the4 ,selections from the choicest ,english ,writers4 ,exquisitely ,illustrated1 with ,frontispiece and ,title-page in ,colours by ,h4,m4 ,,brock1 and many other ,illustrations4 ,half bound in cloth1 coloured top1 #as4 nett2 full leather1 #as4 #f;d4 nett2 velvet leather1 gilt edges1 in a box1 #bs4 #f;d4 nett4 ,volume ,i4 ,fancy ,humour of ,lamb4 ,,ii4 ,wit ,imagination of ,disraeli4 ,,iii4 ,vignettes from ,oliver ,goldsmith4 ,,iv4 ,wit ,sagacity of ,dr4 ,johnson4 ,v4 ,insight ,imagination of ,john ,ruskin4 ,,vi4 ,vignettes of ,london ,life from ,dickens4 ,,vii4 ,x,v,i,i,ith ,century ,vignettes from ,thackeray4 ,,viii4 ,vignettes of ,country ,life from ,dickens4 ,,ix4 ,wisdom ,humour of ,carlyle4 ,decidedly natty and original in get-up4--,the ,saturday ,review4 ,,evans1 ,,willmott1 ,m4,d4 ,medical ,science of ,to-,day4 ,ex4 crn4 #hvo2 #bd ,illustrations1 #es4 nett4 ,,wilmot1 ,,eardley1 ,rear-,admiral ,s4 ,our ,fleet ,to-day and its ,development during the last ,half ,century4 ,with many ,illustrations4 ,crown #hvo1 #es4 ,,events ,,of ,,our ,,own ,,times ,crown #hvo4 ,with ,illustrations1 #es4 each4 ,the ,war in the ,crimea4 ,by ,general ,sir ,e4 ,,hamley1 ,k4,c4,b4 ,the ,indian ,mutiny4 ,by ,colonel ,,malleson1 ,c4,s4,i4 ,the ,afghan ,wars1 #ahci-db1 and #ahgh-hj4 ,by ,,archibald ,,forbes4 ,our ,fleet ,to-,day and its ,development during the last ,half-,century4 ,by ,rear-,admiral ,s4 ,,eardley ,,wilmot4 ,the ,refounding of the ,german ,empire4 ,by ,colonel ,,malleson1 ,c4,s4,i4 ,the ,liberation of ,italy4 ,by the ,countess ,,martinengo ,,cesaresco4 ,great ,britain in ,modern ,africa4 ,by ,,edgar ,,sanderson1 ,m4,a4 ,the ,war in the ,peninsula4 ,by ,a4 ,,innes ,,shand4 ,,fletcher1 ,w4,y4 ,bookbinding in ,france4 ,coloured ,plates4 ,super-royal1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 ,,forbes1 ,,archibald4 ,the ,afghan ,wars of #ahci-ahdb and #ahgh-ahhj4 ,with ,four ,portraits on ,copper1 and ,maps and ,plans4 ,crown #hvo1 #es4 ,,fraser1 ,sir ,,andrew ,h4,l4 ,among ,indian ,rajahs and ,ryots4 ,with #cd ,illustrations and a ,map4 ,demy #hvo1 #ahs4 nett4 ,third and ,cheaper ,edition1 #es4 nett4 ,,fraser1 ,,donald4 ,winning a ,primitive ,people4 ,illustrated4 ,extra crown #hvo1 #es4 nett4 ,,fripp1 ,sir ,,alfred ,d41 ,k4,c4,v4,o41 ,r4 ,,thompson1 ,f4,r4,c4,s4 ,human ,anatomy for ,art ,students4 ,profusely ,illustrated with ,photographs and ,drawings by ,,innes ,,fripp1 ,a4,r4,c4,a4 ,square extra crown #hvo1 #gs4 #f;d4 nett4 ,,frobenius1 ,,leo4 ,the ,childhood of ,man4 ,a ,popular ,account of the ,lives and ,thoughts of ,primitive ,races4 ,translated by ,prof4 ,a4,h4 ,,keane1 ,,ll4,d4 ,with #daf ,illustrations4 ,demy #hvo1 #afs4 nett4 ,,fry1 ,,roger4 ,discourses ,delivered to the ,students of the ,royal ,academy by ,sir ,joshua ,reynolds4 ,with an ,introduction and ,notes by ,,roger ,,fry4 ,with ,thirty-three ,illustrations4 ,square ,crown #hvo1 #gs4 #f;d4 nett4 ,,gardner1 ,j4 ,,starkie4 ,armour in ,england4 ,with ,eight ,coloured ,plates and many other ,illustrations4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett4 ,foreign ,armour in ,england4 ,with ,eight ,coloured ,plates and many other ,illustrations4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett4 ,armour in ,england4 ,with ,sixteen ,coloured ,plates and many other ,illustrations4 ,the two parts in one volume4 ,super-royal #hvo1 cloth1 gilt top1 #is4 nett4 ,,garnett1 ,r41 ,,ll4,d4 ,richmond on ,thames4 ,illustrated4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett4 ,,giberne1 ,,agnes4 ,beside the ,waters of ,comfort4 ,crown #hvo1 #cs4 #f;d4 ,,gibson1 ,,charles ,r41 ,f4,r4,s4,e4 ,electricity of ,to-,day4 ,its ,works and ,mysteries described in non-technical language4 ,with #cj ,illustrations4 ,extra crown #hvo1 #es4 nett4 ,scientific ,ideas of ,to-day4 ,a ,popular ,account in non-technical language of the ,nature of ,matter1 ,electricity1 ,light1 ,heat1 c41 c4 ,with #be ,illustrations4 ,extra crown #hvo1 #es4 nett4 ,how ,telegraphs and ,telephones ,work4 ,with many ,illustrations4 ,crown #hvo1 #as4 #f;d4 nett4 ,the ,autobiography of an ,electron4 ,with #h ,illustrations4 ,long #hvo1 #cs4 #f;d4 nett4 ,wireless ,telegraphy4 ,with many ,illustrations4 ,ex4 crn4 #hvo1 #bs4 nett4 ,,godley1 ,a4,d4 ,socrates and ,athenian ,society in his ,day4 ,crown #hvo1 #ds4 #f;d4 ,aspects of ,modern ,oxford4 ,with many ,illustrations4 ,crown #hvo1 cloth1 #bs4 nett2 lambskin1 #cs4 nett2 velvet leather1 in box1 #es4 nett4 ,,golden ,,reciter 7,see ,,james1 ,prof4 ,,cairns47 ,,gomes1 ,,edwin ,h41 ,m4,a4 ,seventeen ,years among the ,sea ,dyaks of ,borneo4 ,with #dj ,illustrations and a ,map4 ,demy #hvo1 #afs4 nett4 ,,grahame1 ,,george4 ,claude ,lorrain4 ,illustrated4 ,super-royal #hvo1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 ,,griffith1 ,m4,e4 ,,hume4 ,behind the ,veil in ,persia and ,turkish ,arabia4 ,an ,account of an ,englishwoman's ,eight ,years' ,residence amongst the ,women of the ,east4 ,with #cg ,illustrations and a ,map4 ,demy #hvo1 #afs4 nett4 ,,grindon1 ,,leo4 ,lancashire4 ,brief ,historical and ,descriptive ,notes4 ,with many ,illustrations4 ,crown #hvo1 #fs4 ,,grubb1 ,w4 ,,barbrooke 7,pioneer and ,explorer of the ,chaco74 ,an ,unknown ,people in an ,unknown ,land4 ,with ,sixty ,illustrations and a ,map4 ,demy #hvo1 #afs4 nett4 ,third and ,cheaper ,edition1 #es4 ,a ,church in the ,wilds4 ,illustrated4 ,extra crown #hvo1 #es4 nett4 ,,hadow1 ,w4,h4 ,a ,croatian ,composer4 ,notes toward the ,study of ,joseph ,haydn4 ,crown #hvo1 #bs4 #f;d4 nett4 ,studies in ,modern ,music4 ,first ,series4 ,berlioz1 ,schumann1 ,wagner4 ,with an ,essay on ,music and ,musical ,criticism4 ,with ,five ,portraits4 ,crown #hvo1 #gs4 #f;d4 ,studies in ,modern ,music4 ,second ,series4 ,chopin1 ,dvork1 ,brahms4 ,with an ,essay on ,musical ,form4 ,with ,four ,portraits4 ,crown #hvo1 #gs4 #f;d4 ,,hamerton1 ,p4,g4 ,the ,etchings of ,rembrandt1 and ,dutch ,etchers of the ,seventeenth ,century4 ,by ,p4,g4 ,,hamerton and ,,laurence ,,binton4 ,with ,eight ,copper ,plates and many other ,illustrations4 ,super-royal #hvo1 #gs4 #f;d4 nett4 ,the ,mount4 ,narrative of a ,visit to the ,site of a ,gaulish ,city on ,mount ,beuvray4 ,with a ,description of the neighbouring ,city of ,autun4 ,crown #hvo1 #cs4 #f;d4 ,round my ,house4 ,notes on ,rural ,life in ,peace and ,war4 ,crown #hvo1 with ,illustrations1 #bs4 #f;d4 nett4 ,cheaper edition1 #bs4 nett4 ,paris4 ,illustrated4 ,new edition4 ,cloth1 #bs4 nett2 leather1 #cs4 nett in special leather1 full gilt1 in box1 #es4 nett4 ,,hamley1 ,gen4 ,sir ,e4 ,the ,war in the ,crimea4 ,with ,copper ,plates and other ,illustrations4 ,crown #hvo1 #es4 ,,hanoum ,,zeyneb 7,heroine of ,pierre ,loti's ,novel ,les ,dsenchantes47 ,a ,turkish ,woman's ,european ,impressions4 ,edited by ,,grace ,,ellison4 ,with a portrait by ,,auguste ,,rodin and #bc other ,illustrations from photographs4 ,crown #hvo1 #fs4 nett4 ,,hartley1 ,c4 ,,gasquoine4 ,things ,seen in ,spain4 ,with ,fifty ,illustrations4 ,small #dto1 cloth1 #bs42 leather1 #cs42 velvet leather in a box1 #es4 nett4 ,,haywood1 ,capt4 ,a4,h4,w4 ,through ,timbuctu ,across the ,great ,sahara4 ,demy #hvo1 with #da ,illustrations and a ,map4 #afs4 nett4 ,,henderson1 ,major ,,percy ,e4 ,a ,british ,officer in the ,balkans4 ,through ,dalmatia1 ,montenegro1 ,turkey in ,austria1 ,magyarland1 ,bosnia and ,herzegovina4 ,with #ej ,illustrations and a ,map4 ,gilt top4 ,demy #hvo1 #afs4 nett4 ,,herbert1 ,,george4 ,the ,temple4 ,sacred ,poems and ,ejaculations4 ,the ,text reprinted from the ,first ,edition4 ,with ,seventy-six ,illustrations after ,,albert ,d,,rer1 ,,holbrin1 and other ,masters4 ,crown #hvo1 cloth1 #bs4 nett2 leather1 #cs4 nett42 velvet leather in box1 #es4 nett4 ,,holland1 ,,clive4 ,things ,seen in ,japan4 ,with ,fifty beautiful illustrations of ,japanese life in ,town and ,country4 ,small #dto1 cloth1 #bs4 nett2 leather1 #cs4 nett2 velvet leather1 in box1 #es4 nett4 ,,hutchinson1 ,rev4 ,h4,n4 ,the ,story of the ,hills4 ,a ,popular ,account of ,mountains and ,how ,they were ,made4 ,with many ,illustrations4 ,crown #hvo1 #es4 ,,hutton1 ,c4,a4 ,greek ,terracotta ,statuettes4 ,with a ,preface by ,a4,s4 ,,murray1 ,,ll4,d4 ,with ,seventeen ,examples printed in ,colour and ,thirty-six printed in ,monochrome4 #es4 nett2 or cloth1 #gs4 nett4 ,,hutton1 ,,samuel ,,king1 ,m4,b4 ,among the ,eskimos of ,labrador4 ,demy #hvo2 with ,forty-seven ,illustrations and a ,map4 #afs4 nett4 ,,james1 ,,cairns4 ,the ,golden ,reciter4 ,with an ,introduction by ,,cairns ,,james1 ,professor of ,elocution at the ,royal ,academy of ,music1 c4 ,with ,selections from ,rudyard ,kipling1 ,thomas ,hardy1 ,r4,l4 ,stevenson1 ,seton ,merriman1 ,h4,g4 ,wells1 ,christina ,rossetti1 ,anthony ,hope1 ,austin ,dobson1 ,maurice ,hewlett1 ,conan ,doyle1 c4 c4 ,extra crown #hvo1 #gjd pp4 ,cloth1 #cs4 #f;d41 and thin paper edition in cloth with gilt edges1 #es4 ,a more admirable book of its kind could not well be desired4--,liverpool ,courier4 ,the ,golden ,humorous ,reciter4 ,edited1 and with a ,practical ,introduction1 by ,,cairns ,,james1 ,professor of ,elocution at the ,royal ,college of ,music and the ,guildhall ,school of ,music4 ,a volume of ,recitations and ,readings selected from the writings of ,f4 ,anstey1 ,j4,m4 ,barrie1 ,s4,r4 ,crockett1 ,jerome ,k4 ,jerome1 ,barry ,pain1 ,a4,w4 ,pinero1 ,owen ,seaman1 ,g4,b4 ,shaw1 c4 c4 ,extra crown #hvo1 over #gjj pages1 cloth1 #cs4 #f;d42 also a thin paper edition1 with gilt edges1 #es4 99 99 99 99 99 ,,the ,,illuminated ,,series ,,new ,,binding4 ,bound in antique leather with metal clasps4 ,with illuminated frontispiece and title-page1 and other illuminated pages4 ,finely printed at the ,ballantyne ,press1 ,edinburgh4 ,crown #hvo4 ,each copy in a box1 #ajs4 #f;d4 nett4 ,also in real classic vellum4 ,each copy in a box4 #ajs4 #f;d4 nett4 ,the ,confessions of ,s4 ,augustine4 ,of the ,imitation of ,christ4 ,by ,,thomas ,,kempis4 ,the ,sacred ,seasons4 ,by the ,,bishop ,,of ,,durham4 ,also cloth1 #fs4 and #gs4 #f;d4 nett4 ,,joy1 ,,bedford4 ,a ,synopsis of ,roman ,history4 ,crown #hvo1 #bs4 ,,keane1 ,prof4 ,a4,h4 7,see ,,frobenius47 ,,lang1 ,,andrew4 ,oxford4 ,new ,edition4 ,with #ej ,illustrations by ,j4,h4 ,,lorimer1 ,r4,s4,a41 ,t4 ,,hamilton ,,crawford1 ,r4,s4,w41 ,j4 ,,pennell1 ,a4 ,,brunet-,,debaines1 ,a4 ,,toussaint1 and ,r4 ,,kent ,,thomas4 ,extra crown #hvo1 #fs4 ,also ,pocket ,edition1 #bs4 nett2 leather1 #cs4 nett4 ,special yapp leather1 full gilt1 in box1 #es4 nett4 ,,lee1 ,sir ,,sidney4 ,stratford-on-,avon4 ,from the ,earliest ,times to the ,death of ,shakespeare4 ,new revised edition1 with additional ,illustrations4 ,extra crown #hvo1 #fs4 ,pocket ,edition1 #bs4 nett2 leather1 #cs4 nett2 and in special yapp leather1 full gilt1 in box1 #es4 nett4 ,,lefroy1 ,w4 ,,chambers4 ,the ,ruined ,abbeys of ,yorkshire4 ,with many ,illustrations by ,a4 ,,brunet-,,debaines and ,h4 ,,toussaint4 ,cr4 #hvo1 ,cloth1 #bs4 nett2 leather1 #cs4 #es4 nett4 ,,leyland1 ,,john4 ,the ,peak of ,derbyshire4 ,with ,map1 ,etchings1 and other ,illustrations by ,,herbert ,,railton and ,,alfred ,,dawson4 ,new ,edition1 ,crown #hvo1 ,cloth1 #bs42 leather1 #cs42 velvet leather1 in a box1 #es4 nett4 ,,loftie1 ,rev4 ,w4,j4 ,the ,inns of ,court and ,chancery4 ,with many ,illustrations1 chiefly by ,,herbert ,,railton4 ,crown #hvo1 cloth1 #bs4 nett2 leather1 #cs4 nett and #es4 nett4 ,westminster ,abbey4 ,with ,seventy-four ,illustrations1 chiefly by ,,herbert ,,railton4 ,crown #hvo1 #bs4 #f;d4 ,extra crown #hvo1 #fs4 ,whitehall4 ,with many ,illustrations4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 ,,mackenzie1 ,rev4 ,w4,b4 ,married ,life and the ,dwellings of the ,righteous4 #cs4 #f;d4 ,,malleson1 ,colonel ,g4,b41 ,c4,s4,i4 ,the ,indian ,mutiny4 ,with ,copper ,plates and other ,illustrations4 ,crown #hvo1 #es4 ,the ,refounding of the ,german ,empire4 ,with ,portrait and ,plans4 ,crown #hvo1 #es4 99 99 99 99 99 ,,miniature ,,library ,,of ,,devotion ,little ,volumes of ,short ,extracts from the ,christian ,fathers4 ,with ,decorative ,title-page and ,photogravure ,frontispiece4 #cbmo1 cloth extra1 each #as4 nett2 leather1 each #as4 #f;d4 nett4 ,also ,three ,volumes in leather in case1 #ds4 #f;d4 nett4 ,white vellum with gilt edges1 each volume in a box1 #bs4 nett4 #a4 ,saint ,augustine4 #b4 ,jeremy ,taylor4 #c4 ,saint ,chrysostom4 #d4 ,bishop ,andrewes4 #e4 ,john ,keble4 #f4 ,thomas ,kempis4 #g4 ,canon ,liddon4 #h4 ,fnelon4 #i4 ,william ,law4 99 99 99 99 99 ,,miniature ,,portfolio ,,monographs ,a ,new ,edition in #afmo4 ,most of the ,volumes have been carefully revised by the ,authors4 ,each ,volume profusely ,illustrated4 ,cloth1 #bs4 nett2 leather1 #cs4 nett2 velvet leather1 in box1 #es4 nett4 ,peter ,paul ,rubens4 ,by ,r4,a4,m4 ,,stevenson4 ,japanese ,wood ,engravings4 ,by ,professor ,w4 ,,anderson4 ,josiah ,wedgwood4 ,by ,sir ,a4,h4 ,,church1 ,f4,r4,s41 ,professor of ,chemistry1 ,royal ,academy of ,arts4 ,new ,revised ,edition4 ,d4,g4 ,rossetti4 ,by ,f4,g4 ,,stephens1 ,one of the ,seven ,members of the ,pre-,raphaelite ,brotherhood4 ,the ,early ,work of ,raphael4 ,by ,,julia ,,cartwright 7,mrs4 ,ady74 ,fair ,women in ,painting and ,poetry4 ,by ,,william ,,sharp 7,fiona ,macleod74 ,antoine ,watteau4 ,by ,,claude ,,phillips1 ,keeper of the ,wallace ,collection4 ,raphael in ,rome4 ,by ,,julia ,,cartwright 7,mrs4 ,ady74 ,the ,new ,forest4 ,by ,c4,j4 ,,cornish1 ,author of ,life of the ,zoo1 c4 ,the ,isle of ,wight4 ,by ,c4,j4 ,,cornish4 ,gainsborough4 ,by ,sir ,,walter ,,armstrong1 ,keeper of the ,national ,gallery of ,ireland4 ,,the ,,library ,,of ,,missions ,illustrated4 ,extra ,crown1 #es4 #hvo1 nett4 ,a ,church in the ,wilds4 ,the ,remarkable ,story of the ,establishment of the ,south ,american ,mission amongst the hitherto ,savage and ,intractable ,natives of the ,paraguayan ,chaco4 ,by ,w4 ,,barbrooke ,,grubb4 ,winning a ,primitive ,people4 ,sixteen ,years' ,work among the ,warlike ,tribe of the ,ngoni and the ,senga and ,tumbuka ,peoples of ,central ,africa4 ,by the ,rev4 ,,donald ,,fraser4 99 99 99 99 99 ,,mitford1 ,,mary ,,russell4 ,country ,stories4 ,with #fh ,illustrations by ,,george ,,morrow4 ,crown #hvo1 cloth1 gilt top1 #bs4 nett2 also in leather1 #cs4 nett2 and leather yapp1 full gilt in box1 #es4 nett4 ,,moule1 ,archdeacon ,a4,e4 ,new ,china and ,old4 ,notes on the ,country and ,people made during a ,residence of ,thirty ,years4 ,with ,thirty ,illustrations4 ,new ,edition1 ,revised4 ,crown #hvo1 #es4 ,,moule1 ,right ,rev4 ,h4,c4,g41 ,d4,d4 7,bishop of ,durham74 ,the ,sacred ,seasons4 ,readings for the ,sundays and ,holy ,days of the ,christian ,year4 ,printed in red and black throughout1 and illuminated with specially drawn initial letters and ornaments1 and with #ab illuminated pages printed in three colours and gold after illuminations in manuscripts at the ,british ,museum4 ,extra crown #hvo1 #fs4 nett2 also white cloth1 in box1 #gs4 #f;d4 nett2 antique leather with clasps1 #ajs4 #f;d4 nett4 ,at the ,holy ,communion4 ,helps for ,preparation and ,reception4 ,cloth1 #as42 leather1 #bs4 nett2 calf1 #ds4 #f;d4 ,christ's ,witness to the ,life to ,come4 ,crown #hvo1 #cs4 #f;d4 ,grace and ,godliness4 ,studies in the ,epistle to the ,ephesians4 ,crown #hvo1 #bs4 #f;d4 ,in the ,house of the ,pilgrimage4 ,hymns and ,sacred ,songs4 #bs4 #f;d4 ,imitations and ,translations4 ,crown #hvo1 #bs4 #f;d4 nett4 ,jesus and the ,resurrection4 ,expository ,studies on ,st4 ,john xx4 and xxi4 ,third ,edition1 #bs4 #f;d4 ,lord's ,supper1 ,the4 ,by ,,bishop ,,ridley4 ,edited with ,notes and a ,life by the ,,bishop ,,of ,,durham4 ,crown #hvo1 #es4 ,our ,prayer ,book4 ,short ,chapters on the ,book of ,common ,prayer4 #afmo1 #as42 leather1 #bs4 nett4 ,pledges of ,his ,love1 ,the4 ,thoughts on the ,holy ,communion4 #afmo1 #as42 leather1 #bs4 nett4 ,prayers for the ,home4 ,a ,month's ,cycle of ,morning and ,evening ,family ,worship1 with some ,occasional ,prayers4 ,crown #hvo1 #cs4 #f;d4 ,prayers and ,promises4 ,messages from the ,holy ,scriptures4 #afmo1 #as42 leather1 #bs4 nett2 calf1 #ds4 #f;d4 ,the ,secret of the ,presence1 and other ,sermons4 ,crown #hvo1 #cs4 #f;d4 ,temptation and ,escape4 ,short ,chapters for ,beginners in the ,christian ,life4 #afmo1 #as42 leather1 #bs4 nett4 ,thoughts on ,christian ,sanctity4 #afmo1 cloth1 #as42 leather1 #bs4 nett4 ,thoughts on ,secret ,prayer4 #afmo1 cloth1 #as42 leather1 #bs4 nett2 calf1 #ds4 #f;d4 ,thoughts on the ,spiritual ,life4 #afmo1 cloth1 #as42 leather1 #bs4 nett4 ,thoughts on ,union with ,christ4 #afmo1 cloth1 #as42 leather1 #bs4 nett4 ,,murray1 ,a4,s41 ,,ll4,d4 ,greek ,bronzes4 ,with ,four ,copper ,plates and many other ,illustrations4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett2 cloth1 #ds4 #f;d4 nett4 ,greek ,bronzes1 by ,dr4 ,,murray1 and ,greek ,terracotta ,statuettes1 by ,c4,a4 ,,hutton4 ,with ,four ,photogravures1 ,eight ,coloured ,plates1 and ,seventy-seven other ,illustrations4 ,in one ,volume4 ,super-royal #hvo1 cloth1 #ajs4 #f;d4 nett4 ,,nettleship1 ,j4,t4 ,morland1 ,george4 ,with ,six ,copper ,plates and ,thirty other ,illustrations4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 #fs4 nett4 ,,the ,,new ,,art ,,library ,,edited ,,by ,m4,h4 ,,spielmann1 ,f4,s4,a41 ,p4,g4 ,,konody4 ,the admirable ,new ,art ,library4444 ,thoroughly practical4--,the ,connoisseur4 ,,the ,,practice ,,and ,,science ,,of ,,drawing4 ,by ,,harold ,,speed1 ,associ de la ,socit ,nationale des ,beaux-,arts2 ,member of the ,society of ,portrait ,painters2 ,professor of ,drawing at the ,goldsmiths' ,college1 c4 ,with ,ninety-six ,illustrations and ,diagrams4 ,square ex4 crn4 #hvo1 #fs4 nett4 ,,the ,,practice ,,of ,,oil ,,painting ,,and ,,drawing4 ,by ,,solomon ,j4 ,,solomon1 ,r4,a4 ,with ,eighty ,illustrations4 #fs4 nett4 ,,human ,,anatomy ,,for ,,art ,,students4 ,by ,sir ,,alfred ,,downing ,,fripp1 ,k4,c4,v4,o41 ,lecturer upon ,anatomy at ,guy's ,hospital1 ,london1 and ,,ralph ,,thompson1 ,ch4,m41 ,f4,r4,c4,s41 with a chapter on ,comparative ,anatomy1 and ,drawings by ,,harry ,,dixon4 ,with ,one hundred and fifty-nine ,photographs and ,drawings4 ,square extra crown #hvo1 #gs4 #f;d4 nett4 ,,modelling ,,and ,,sculpture4 ,by ,,albert ,,toft1 ,a4,r4,c4,a41 ,m4,s4,b4,s4 ,with #aai ,photographs and ,drawings4 ,square extra crown #hvo1 #fs4 nett4 99 99 99 99 99 ,,page1 ,j4 ,ll4 ,,warden4 ,exmoor1 ,an ,exploration of4 ,with ,maps1 ,etchings1 and other ,illustrations4 ,cheap ,edition1 #cs4 #f;d4 ,,pennell1 ,t4,l41 ,m4,d41 ,b4,sc41 ,f4,r4,c4,s4 ,among the ,wild ,tribes of the ,afghan ,frontier4 ,a ,record of ,sixteen ,years' ,close ,intercourse with the ,natives of the ,indian ,marches4 ,with an ,introduction by ,field-,marshal ,,lord ,,roberts1 ,v4,c4 ,extra ,crown #hvo4 ,with #bf ,illustrations and a ,map4 #es4 nett4 ,fourth and ,cheaper ,edition4 ,things ,seen in ,northern ,india4 ,with #ej ,illustrations4 #bs41 #cs41 #es4 nett4 ,,phillips1 ,,claude4 ,the ,earlier ,work of ,titian4 ,with many ,illustrations4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett2 cloth1 #ds4 #f;d4 nett4 ,the ,later ,work of ,titian4 ,with many ,illustrations4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett2 cloth1 #ds4 #f;d4 nett4 ,titian1 a ,study of his ,life and ,work4 ,with ,eight ,copper ,plates and many other ,illustrations4 ,super-royal #hvo1 #is4 nett4 ,the ,picture ,gallery of ,charles ,i4 ,with many ,illustrations4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett2 cloth1 #ds4 #f;d4 nett4 ,frederick ,walker4 ,sup4-roy4 #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 ,antoine ,watteau4 ,sup4-roy4 #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett2 also small #dto1 cloth1 #bs4 nett2 and #cs4 and #es4 nett in leather4 ,,pollard1 ,a4,w4 ,italian ,book ,illustrations4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 99 99 99 99 99 ,,portfolio ,,monographs ,,on ,,artistic ,,subjects ,a triumph of magnificent illustration and masterly editing4--,the ,times4 ,many of the ,volumes are issued in two forms and at various nett prices4 ,where two prices are given1 the first is that of the paper cover edition2 the second that of the cloth4 ,when only one price is given1 the ,volume is bound in paper only4 ,,anderson1 ,prof4 ,w4 ,japanese ,wood ,engravings4 #bs4 #f;d4 and #cs4 #f;d4 ,,armstrong1 ,sir ,,walter4 ,the ,art of ,velazquez4 #cs4 #f;d4 ,the ,life of ,velazquez4 #cs4 #f;d4 ,the ,peel ,collection and the ,dutch ,school of ,painting4 #es4 and #gs4 ,thomas ,gainsborough4 ,half-linen1 #cs4 #f;d4 ,w4,q4 ,orchardson4 #bs4 #f;d4 and #cs4 #f;d4 ,,bedford1 ,w4,k4,r4 ,malta4 #bs4 #f;d4 ,,benham1 ,canon1 and ,,charles ,,welch1 ,f4,s4,a4 ,medival ,london4 #cs4 #f;d41 #es41 and #gs4 ,the ,tower of ,london4 #es4 and #gs4 ,,benham1 ,canon4 ,old ,st4 ,paul's ,cathedral4 #es4 and #gs4 ,,binyon1 ,,laurence4 ,dutch ,etchers of ,x,v,i,ith ,century4 #bs4 #f;d4 and #cs4 #f;d4 ,john ,crome and ,j4,s4 ,cotman4 #cs4 #f;d4 ,,birch1 ,g4,h41 ,f4,s4,a4 ,london on ,thames4 #es4 and #gs4 ,,cartwright1 ,,julia 7,mrs4 ,,ady74 ,jules ,bastien-,lepage4 #bs4 #f;d4 and #cs4 #f;d4 ,the ,early ,work of ,raphael4 #bs4 #f;d4 and #cs4 #f;d4 ,raphael in ,rome4 #bs4 #f;d4 and #cs4 #f;d4 ,,church1 ,a4,h41 ,f4,r4,s4 ,josiah ,wedgwood4 #es4 and #gs4 ,,cornish1 ,c4,j4 ,the ,isle of ,wight4 #bs4 #f;d4 #cs4 #f;d4 ,the ,new ,forest4 #bs4 #f;d4 #cs4 #f;d4 ,,cust1 ,,lionel1 ,f4,s4,a4 ,the ,engravings of ,albert ,drer4 #bs4 #f;d4 and #cs4 #f;d4 ,the ,paintings and ,drawings of ,albert ,drer4 #cs4 #f;d4 ,,davenport1 ,,cyril1 ,f4,s4,a4 ,royal ,english ,bookbindings4 #cs4 #f;d4 #ds4 #f;d4 ,cameos4 #es4 #gs4 ,,davies1 ,,randall1 ,f4,s4,a4 ,english ,society of the ,eighteenth ,century in ,contemporary ,art4 ,,destr,e1 ,o4,g4 ,the ,renaissance of ,sculpture in ,belgium4 #bs4 #f;d4 and #cs4 #f;d4 ,,fletcher1 ,w4,y4 ,bookbinding in ,france4 #bs4 #f;d4 and #cs4 #f;d4 ,,gardner1 ,j4 ,,starkie4 ,armour in ,england4 #cs4 #f;d4 ,foreign ,armour in ,england4 #cs4 #f;d4 ,,garnett1 ,,richard1 ,c4,b41 ,,ll4,d4 ,richmond on ,thames4 #cs4 #f;d4 and #ds4 #f;d4 ,,grahame1 ,,george4 ,claude ,lorrain4 #bs4 #f;d4 and #cs4 #f;d4 ,,hamerton1 ,p4,g4 ,the ,etchings of ,rembrandt4 #bs4 #f;d4 and #cs4 #f;d4 ,,hutton1 ,c4,a4 ,greek ,terracotta ,statuettes4 #es4 and #gs4 ,,loftie1 ,w4,j4 ,whitehall4 #bs4 #f;d4 and #cs4 #f;d4 ,,murray1 ,a4,s41 ,,ll4,d4 ,greek ,bronzes4 #cs4 #f;d4 and #ds4 #f;d4 ,,nettleship1 ,j4,t4 ,george ,morland4 #es4 and #fs4 ,,phillips1 ,,claude4 ,frederick ,walker4 #bs4 #f;d4 and #cs4 #f;d4 ,antoine ,watteau4 #bs4 #f;d4 and #cs4 #f;d4 ,the ,picture ,gallery of ,charles ,i4 #cs4 #f;d4 ,the ,earlier ,work of ,titian4 #cs4 #f;d4 ,the ,later ,work of ,titian4 #cs4 #f;d4 ,,pollard1 ,,alfred ,w4 ,italian ,book ,illustrations4 #bs4 #f;d4 and #cs4 #f;d4 ,,prior1 ,e4,s41 ,f4,s4,a4 ,the ,cathedral ,builders in ,england4 #es4 and #gs4 ,,sharp1 ,,william4 ,fair ,women4 #bs4 #f;d4 and #cs4 #f;d4 ,,stephens1 ,f4,g4 ,dante ,gabriel ,rossetti4 #bs4 #f;d4 ,,stevenson1 ,r4,a4,m4 ,peter ,paul ,rubens4 #cs4 #f;d4 ,,waern1 ,,cecilia4 ,john ,la ,farge4 #cs4 #f;d4 ,,weale1 ,w4,h4 ,,james4 ,gerard ,david1 ,painter and ,illuminator4 #bs4 #f;d4 and #cs4 #f;d4 ,,prior1 ,canon ,e4,s41 ,f4,s4,a4 ,the ,cathedral ,builders of ,england4 ,illustrated4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 extra gilt top1 #gs4 nett4 99 99 99 99 99 ,,quiller ,,couch1 ,,sir ,a4,t4 ,the ,pilgrims' ,way4 ,a ,little ,scrip for ,travellers4 ,in ,prose and ,verse4 ,with end papers in colour1 and gilt top4 ,fcap4 #hvo1 cloth1 #cs4 #f;d4 nett2 on thin paper1 leather1 #es4 nett4 ,,ragg1 ,,lonsdale1 ,b4,d4 7,oxon471 and ,l4,m4 ,,ragg4 ,things ,seen in ,venice4 ,with ,fifty ,illustrations4 #bs41 #cs41 #es4 nett4 ,,rannie1 ,,douglas 7late ,government ,agent for ,queensland47 ,my ,adventures ,among ,south ,sea ,cannibals4 ,demy #hvo4 ,with ,thirty-nine ,illustrations and a ,map1 #afs4 nett4 ,,rawling1 ,captain ,c4,g4 ,the ,land of the ,new ,guinea ,pygmies4 ,demy #hvo4 ,with ,forty-eight ,illustrations and a ,map1 #afs4 nett4 ,,reynolds1 ,sir ,,joshua4 ,discourses ,delivered to the ,students of the ,royal ,academy4 ,with an ,introduction and ,notes by ,,roger ,,fry4 ,with ,thirty-,three ,illustrations4 ,square extra ,crown #hvo1 #gs4 #f;d4 nett4 ,,roche1 ,c4,e4 ,things ,seen in ,holland4 ,with ,fifty ,illustrations4 ,small #dto1 cloth1 #bs4 nett2 lambskin1 #cs4 nett2 velvet leather1 #es4 nett4 ,,ropes1 ,a4,r4 ,lady ,mary ,wortley ,montagu4 ,with #h ,illustrations4 ,crown #hvo1 cloth1 #bs4 #f;d4 nett4 ,,russell1 ,w4 ,,clark4 ,the ,british ,seas4 ,with upwards of ,fifty ,illustrations4 ,crown #hvo1 cloth1 #bs42 leather1 #cs42 special yapp leather in box1 #es4 nett4 ,,sandby1 ,w4 ,thomas and ,paul ,sandby1 ,royal ,academicians4 ,their ,lives and ,works4 ,with many ,illustrations4 ,crown #hvo1 #gs4 #f;d4 ,,sanderson1 ,e4 ,great ,britain in ,modern ,africa4 ,with ,four ,portraits on ,copper and a ,map4 ,crown #hvo1 #es4 ,,scott-,,elliot1 ,professor ,g4,f41 ,m4,a41 ,b4,sc4 ,botany of ,to-day4 ,with ,twenty-seven ,illustrations4 ,ex4 cr4 #hvo1 #es4 nett4 99 99 99 99 99 ,,science ,,of ,,to-,,day ,,series ,the volumes of this series give an attractive1 lucid1 yet at the same time scientifically accurate account of various subjects in non-technical language4 ,large crown #hvo1 #es4 nett4 ,submarine ,engineering of ,to-day4 ,by ,,charles ,w4 ,,domville-,,fife4 ,photography of ,to-day4 ,by ,h4 ,,chapman ,,jones1 ,f4,i4,c41 ,f4,c4,s41 ,f4,r4,p4,s4 ,aerial ,navigation of ,to-day4 ,by ,,charles ,c4 ,,turner4 ,astronomy of ,to-,day4 ,by ,c4,g4 ,,dolmage1 ,m4,a41 ,,ll4,d41 ,d4,c4,l41 ,f4,r4,a4,s4 ,botany of ,to-day4 ,by ,prof4 ,g4,f4 ,,scott-,,elliot1 ,m4,a41 ,b4,sc4 ,electricity of ,to-,day4 ,by ,,charles ,r4 ,,gibson1 ,f4,r4,s4,e4 ,engineering of ,to-day4 ,by ,,thomas ,w4 ,,corbin4 ,mechanical ,inventions of ,to-,day4 ,by ,t4,w4 ,,corbin4 ,medical ,science of ,to-,day4 ,by ,,willmott ,,evans1 ,m4,d4 ,scientific ,ideas of ,to-,day4 ,by ,,charles ,r4 ,,gibson1 ,f4,r4,s4,e4 99 99 99 99 99 ,,seeley',s ,,illustrated ,,pocket ,,library ,crown #hvo1 cloth1 gilt edge1 #bs4 nett2 also in leather1 #cs4 nett2 and yapp leather in box at #es4 ,,addison and ,,steele4 ,the ,spectator in ,london4 ,with ,fifty-six ,illustrations by ,,ralph ,,cleaver1 and ,headpieces by ,w4,a4 ,,atkin ,,berry1 ,,clough ,,bromley1 c4 ,,clark1 ,j4,w41 ,registrary of the ,university of ,cambridge4 ,cambridge4 ,with many ,illustrations4 ,,godley1 ,a4,d4 ,aspects of ,modern ,oxford4 ,with many ,illustrations4 ,,hamerton1 ,p4,g4 ,paris4 ,with many ,illustrations4 ,,lee1 ,sir ,,sidney4 ,stratford-on-,avon4 ,from the ,earliest ,times to the ,death of ,shakespeare4 ,with #eb ,illustrations by ,,herbert ,,railton and ,e4 ,,hull4 ,,mitford1 ,,mary ,,russell4 ,country ,stories4 ,with #fh ,illustrations by ,,george ,,morrow4 ,,herbert1 ,,george4 ,the ,temple4 ,sacred ,poems and ,ejaculations4 ,the ,text reprinted from the first edition4 ,with #gf ,illustrations after ,d,,rer1 ,,holbein1 and other ,masters4 ,,lang1 ,,andrew4 ,oxford4 ,with #dj ,illustrations by various artists4 ,,lefroy1 ,w4 ,,chambers4 ,the ,ruined ,abbeys of ,yorkshire4 ,with many ,illustrations4 ,,leyland1 ,,john4 ,the ,peak of ,derbyshire3 its ,scenery and ,antiquities4 ,,loftie1 ,w4,j4 ,the ,inns of ,court4 ,with #fj ,illustrations4 ,,russell1 ,w4 ,,clark4 ,british ,seas4 ,with #ej ,illustrations by ,j4,c4 ,,hook1 ,r4,a41 ,,hamilton ,,maccallum1 ,,colin ,,hunter1 c4 ,,stevenson1 ,r4,l4 ,edinburgh4 ,with many ,illustrations by ,t4 ,,hamilton ,,crawford1 ,r4,s4,a4 7,this volume is only to be had in this series in leather1 #es4 nett4 ,for other editions of this book1 see below47 99 99 99 99 99 ,,solomon1 ,,solomon ,j41 ,r4,a4 ,the ,practice of ,oil ,painting and ,drawing4 ,with #hj ,illustrations4 #fs4 nett4 ,,speed1 ,,harold4 ,the ,practice and ,science of ,drawing4 ,with ,ninety-six ,illustrations and ,diagrams4 ,square extra crown #hvo1 #fs4 99 99 99 99 99 ,,the ,,standard ,,library ,extra ,crown #hvo1 ,with many ,illustrations4 ,price #bs4 #f;d4 nett4 ,lady ,mary ,wortley ,montagu4 ,by ,a4,r4 ,,ropes4 ,mrs4 ,thrale4 ,by ,l4,b4 ,,seeley4 ,round ,my ,house4 ,by ,p4,g4 ,,hamerton4 ,fanny ,burney ,her ,friends4 ,by ,l4,b4 ,,seeley4 ,,story ,,series1 ,,the4 ,extra crown #hvo1 #es4 nett4 ,the ,post ,office and its ,story4 ,by ,,edward ,,bennett4 ,with #ca ,illus4 ,family ,names and their ,story4 ,by the ,rev4 ,s4 ,,baring ,,gould4 ,the ,press and its ,story4 ,by ,,james ,d4 ,,symon4 ,,seeley1 ,sir ,j4,r4 ,goethe ,reviewed after ,sixty ,years4 ,with ,portrait4 ,crown #hvo1 #cs4 #f;d4 ,a ,short ,history of ,napoleon the ,first4 ,with ,portrait4 ,crown #hvo1 #es4 ,,seeley1 ,sir ,j4,r41 and ,dr4 ,,abbott4 ,english ,lessons for ,english ,people4 ,crown #hvo1 #ds4 #f;d4 ,,seeley1 ,l4,b4 ,mrs4 ,thrale1 afterwards ,mrs4 ,piozzi4 ,with ,eight ,illustrations4 ,crown #hvo1 #bs4 #f;d nett4 ,fanny ,burney and her ,friends4 ,with ,eight ,illustrations4 ,crown #hvo1 #bs4 #f;d nett4 ,,shand1 ,a4 ,,innes4 ,the ,war in the ,peninsula4 ,with ,portraits and ,plans4 #es4 ,,sharp1 ,,william4 ,fair ,women4 ,illustrated4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 ,also new edition1 small #dto1 cloth1 #bs4 nett2 leather1 #cs4 and #es4 nett4 ,,shipley1 ,m4,e4 ,daily ,help for ,daily ,need4 ,a ,selection of ,scripture ,verses and ,poetry for ,every ,day in the ,year4 ,crown #hvo1 #ds4 #f;d4 ,,stephens1 ,f4,g4 ,rossetti1 ,d4,g4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 also small #dto1 cloth1 #bs4 nett2 leather1 #cs4 nett2 velvet leather1 in a box1 #es4 nett4 ,,stevenson1 ,r4,l4 ,edinburgh4 ,fcap4 #hvo1 with ,frontispiece1 gilt top1 cloth1 #bs4 nett2 leather1 #cs4 nett4 ,crown #hvo1 ,illustrated1 cloth1 #cs4 #f;d4 ,roxburgh1 gilt top1 #es4 ,library ,edition4 ,crown #hvo1 buckram1 dark blue1 gilt top1 ,sixteen ,full-page ,illustrations1 #fs4 ,presentation ,edition4 ,extra crown #hvo1 with ,sixty-four ,illustrations1 #fs4 nett2 also ,people's ,edition1 demy #hvo1 #f;d4 nett4 ,with ,twenty-four ,illustrations in colour1 by ,,james ,,heron4 ,crown #dto4 ,printed by ,messrs4 ,t4 ,a4 ,constable1 of ,edinburgh4 ,ordinary ,edition1 #abs4 #f;d4 nett4 ,,edition ,,de ,,luxe1 limited to #che copies1 of which only #cge are for sale1 printed on unbleached ,arnold handmade paper1 and bound in buckram1 with paper label1 each copy numbered1 #bes4 nett4 ,,stevenson1 ,r4,a4,m4 ,rubens1 ,peter ,paul4 ,illustrated4 ,super-royal #hvo1 #cs4 #f;d4 nett1 sewed4 ,also small #dto1 cloth1 #bs4 nett2 leather1 #cs4 nett and #es4 nett4 ,,stigand1 ,captain ,c4,h41 ,f4,r4,g4,s41 ,f4,z4,s4 ,to ,abyssinia ,through an ,unknown ,land4 ,with ,thirty-six ,illustrations and ,two ,maps4 ,demy #hvo1 #afs4 nett4 ,,swann1 ,,alfred ,j4 ,fighting the ,slave ,hunters in ,central ,africa4 ,with ,forty-five ,illustrations and a ,map4 ,demy #hvo1 #afs4 nett4 ,extra crown #hvo4 #es4 nett4 ,,talbot1 ,f4,a4 ,the ,makings of a ,great ,canadian ,railway4 ,demy #hvo4 ,with ,forty-one ,illustrations and a ,map4 #afs4 nett4 99 99 99 99 99 ,,the ,,things ,,seen ,,series ,each volume with #ej ,illustrations4 ,small #dto1 cloth1 #bs42 leather1 #cs42 and velvet leather1 in a box1 #es4 nett4 ,things ,seen in ,oxford4 ,by ,n4,j4 ,,davidson1 ,b4,a4 7,oxon47 ,things ,seen in ,russia4 ,by ,w4 ,,barnes ,,steveni4 ,things ,seen in ,palestine4 ,by ,a4 ,,goodrich ,,freer4 ,things ,seen in ,japan4 ,by ,,clive ,,holland4 ,things ,seen in ,china4 ,by ,j4,r4 ,,chitty4 ,things ,seen in ,egypt4 ,by ,e4,l4 ,,butcher4 ,things ,seen in ,holland4 ,by ,c4,e4 ,,roche4 ,things ,seen in ,spain4 ,by ,c4 ,,gasquoine ,,hartley4 ,things ,seen in ,northern ,india4 ,by ,t4,l4 ,,pennell1 ,m4,d41 ,b4,sc4 ,things ,seen in ,venice4 ,by ,,lonsdale ,,ragg1 ,b4,d4 7,oxon47 ,,toft1 ,,albert1 ,hon41 ,a4,r4,c4,a41 ,m4,s4,b4,s4 ,modelling and ,sculpture4 ,profusely ,illustrated with #aai ,photographs and ,drawings4 ,square extra crown #hvo1 #fs4 nett4 ,,torday1 ,e4 ,camp and ,tramp in ,african ,wilds4 ,demy #hvo4 ,with ,forty-five ,illustrations and a ,map1 #afs4 nett4 ,,townshend1 ,captain ,a4,t4 ,a ,military ,consul in ,turkey4 ,with #bi ,illustrations4 ,demy #hvo1 #afs4 nett4 ,,tremearne1 ,major ,a4,j4,n4 ,the ,tailed ,head-,hunters of ,nigeria4 ,demy #hvo1 with #ch ,illustrations and a ,map4 #afs4 nett4 ,,turner1 ,,charles ,c4 ,aerial ,navigation of ,to-day4 ,with ,seventy ,illustrations and ,diagrams4 ,extra crown #hvo1 #es4 nett4 ,,waern1 ,c4 ,john ,la ,farge4 ,illustrated4 ,super-royal #hvo1 sewed1 #cs4 #f;d4 nett4 ,,weale1 ,w4,h4 ,,james4 ,gerard ,david1 ,painter and ,illuminator4 ,illustrated4 ,super-royal #hvo1 sewed1 #bs4 #f;d4 nett2 half-linen1 #cs4 #f;d4 nett4 ,,weeks1 ,,john ,h4 ,among ,congo ,cannibals4 ,demy #hvo4 ,with ,fifty-four ,illustrations and a ,map1 #afs4 nett4 ,,welch1 ,c41 and ,canon ,,benham4 ,medival ,london4 ,with a ,frontispiece in ,photogravure1 ,four ,plates in ,colour1 and many other ,illustrations4 ,super-royal #hvo1 sewed1 #es4 nett2 cloth1 gilt top1 #gs4 nett4 ,also extra crown #hvo1 #cs4 #f;d4 nett4 ,,wicks1 ,,mark4 ,to ,mars via the ,moon4 ,an ,astronomical ,story4 ,with ,sixteen ,illustrations and ,diagrams4 ,extra crown #hvo1 #es4