material from the ,google ,print project47 ,,barometer ,,and ,,weather ,,guide4 ,,board ,,of ,,trade4 #ahei4 ,,compiled ,,by ,,rear-,,admiral ,,fitzroy1 ,f4,r4,s4 ,,third ,,edition4 7,,with ,,additions47 ,,london3 ,,printed ,,by ,,george ,e4 ,,eyre ,,and ,,william ,,spottiswoode1 ,,printers ,,to ,,the ,,queen',s ,,most ,,excellent ,,majesty4 ,,for ,,her ,,majesty',s ,,stationery ,,office4 ,,and ,,sold ,,by ,j4 ,d4 ,,potter1 ,agent for the ,admiralty ,charts1 #ca1 ,,poultry1 ,,and #aa1 ,,king ,,street1 ,,tower ,,hill4 #ahei4 ,price ,one ,shilling4 ,transcriber's ,note3 ,minor typographical errors have been corrected without note4 ,however1 due to an omission in the original text1 the anchor for footnote #d has been placed in an assumed position4 ,a brief table of contents1 though not present in the original publication1 has been provided below3 ,,preface ,,how ,,to ,,foretell ,,weather ,,marine ,,barometer 444 ,a contraction of rules for foretelling weather--in accordance with the following pages--is submitted1 for scales of common barometers4 ,,rise ,,fall ,,for ,,for ,n4 ,,ely4 ,s4 ,,wly4 ,,nw4-,n4-,e4 ,,se4-,s4-,w4 ,,dry ,,wet ,,or ,,or ,,less ,,more ,,wind4 ,,wind4 ------ ------ ,,except ,,except ,,wet ,,from ,,wet ,,from ,n4 ,,ed4 ,n4 ,,ed4 ,add one tenth for each hundred feet above the ,sea4 99 99 99 ,,long ,,foretold--,,long ,,last1 ,,short ,,notice--,,soon ,,past4 99 99 99 ,,first ,,rise ,,after ,,low1 ,,foretells ,,stronger ,,blow4 ,,preface4 ,many persons have advocated placing barometers at exposed fishing villages2 and the ,board of ,trade has sanctioned the principle of some assistance by ,government to a limited extent1 depending on the necessity of each case1 and other contingencies1 such as the care1 publicity1 and setting of the barometers4 ,it was thought advisable to substitute a few words on the scales of these instruments in place of those usually engraved 7which are not the most suitable71 and to compile brief and plain information respecting the use of weather-glasses4 ,the following pages were prepared2 but only the first few were intended particularly for this purpose4 ,after writing these1 it was suggested that some remarks might be added for the benefit of many persons1 especially young officers at sea1 and the suggestion was complied with2 yet not so as to diminish the portability of this compilation1 or increase its price4 ,these remarks1 derived from the combined observation1 study1 and personal experience of various individuals1 are in accordance1 generally1 with the results obtained by eminent philosophers4 ,the works of ,humboldt1 ,herschel1 ,dov1 ,sabine1 ,reid1 ,redfield1 ,espy1 and others1 are appealed to in confirmation of this statement4 ,to obviate any charge of undue haste1 or an insufficiently considered plan--which may be fairly brought against many novelties--the following testimony to the first published suggestion of such a measure is submitted4 ,in the ,first ,report of the ,committee on ,shipwrecks 7#ahdc71 at pages #a1 #b1 #c1 the following evidence was printed by order of the ,house of ,commons4 ,i think that the neglect of the use of the barometer has led to the loss of many ships4 ,from a want of attention to the barometer1 they have either closed the land 7if at sea71 or have put to sea 7being in harbour in safety7 at improper times2 and in consequence of such want of precaution the ships have been lost1 owing to bad weather coming on suddenly1 which might have been avoided had proper attention been paid to that very simple instrument4 ,while alluding to the use of barometers1 ,i may remark1 that if such weather-glasses were put in charge of the ,coast-guard1 at the principal stations round the coast1 so placed as to allow any one passing by to look at them1 they might be the means1 not only of preventing ships from going to sea just before bad weather was coming on1 but of preventing the great losses of life which take place every year on our coasts 7particularly in the ,orkney ,islands and on the coasts of ,scotland and ,ireland71 owing to fishing vessels and boats going to sea when bad weather is impending4 ,no bad weather ever comes on our coasts without timely warning being given by the barometer4 ,the oldest seaman are often deceived by the look of the weather1 but there is no instance on record of very bad weather1 such as would have involved loss of life to the extent we have heard of in several years1 having come on without the barometer having given timely warning4 ,by the very small expense of an establishment of barometers1 so placed as to be accessible to any fishermen1 boatmen1 or others on the coasts1 much loss of life1 as well as loss of boats1 and even shipping1 might be prevented4 ,what state of the barometer indicates danger8--,it varies in different climates according to the range4 ,the range is small between the tropics1 but very large in the higher latitudes4 ,in our climate the range is usually about two inches4 ,the barometer falling considerably below its average height is at once an indication that some considerable change is going to take place1 and when it falls low1 as for instance 7in our climate7 to near #bi inches1 or below #bi inches1 a gale is certain to follow4 ,are the ,committee to understand that you are of opinion that every ship ought to have a barometer on board8--,i think that every ship ought to have either a barometer or sympiesometer1 which is an efficient substitute for a barometer4 ,does the barometer show a sudden change of wind as well as the coming on of bad weather8 ,supposing a gale of wind is blowing1 and you are sailing with a fair wind1 does the barometer show any change of wind8--,decidedly4 ,supposing the wind was at ,west-north-west and it shifted suddenly to ,west-south-west1 would the barometer indicate that8--,it requires some practice to be able to say exactly what is likely to take place after a change in the barometer2 but the principal point for a seaman is1 that no violent wind will blow without the barometer giving warning4 ,he may not know exactly from what quarter the wind will come1 but no strong wind will come on without warning being given4 ,you recommend that at the ,coast-guard stations there should be a barometer1 by means of which people would know when a violent wind was coming on2 but as it would not indicate the quarter from which it was coming1 would you have the merchant ship always remain in port till the barometer showed fine weather8--,being accustomed to the barometer on our coast1 one could tell from what quarter the wind would probably come by the height of the barometer1 taken in connexion with its previous height1 and the state of the weather1 and the strength of winds that had prevailed before4 ,taking the state of the barometer in connexion with the appearance of the weather one could make a satisfactory conclusion as to the quarter from which any violent wind would come4 ,and the barometer1 after very little practice1 can be used by any man4 ,there is no difficulty in using it sufficiently to know that danger is coming on2 and if danger is coming on1 a man refrains1 of course1 from exposing himself to it2 the quarter from which the wind comes being of minor consequence4 ,with a ,north-easterly wind1 in this part of the world1 the barometer stands1 on an average1 about half an inch higher than with the same strength of wind from the ,south-westward4 ,all over the world there is a similar difference proportionate to the range of the mercury for which allowance should always be made in considering the height of the barometer4#a ,in the first ,number of ,meteorological ,papers1 published by the ,board of ,trade1 #aheg1 is the following passage respecting the use of weather-glasses3-- ,the variety of interesting and useful1 if not always important1 subjects included within the range of meteorology1 is not perhaps sufficiently realized in the minds of active participators in the world's stirring work4 ,irrespective of any scientific object1 how much utility is there to all classes in what is commonly called 'weather wisdom'8 ,in our variable climate1 with a maritime population1 numbers of small vessels1 and especially fishing boats1 how much life and property is risked unnecessarily by every unforeseen storm8 ,even animals1 birds1 and insects have a presaging instinct1 perhaps a bodily feeling1 that warns them2 but man often neglects his perceptive and reasoning powers2 neither himself observes1 nor attends to the observations of others1 unless special inclination or circumstances stimulate attention to the subject4 ,agriculturists1 it is true1 use weather-glasses3 the sportsman knows their value for indicating a good or bad scenting day2 but the coasting vessel puts to sea1 the ,shetland fisherman casts his nets1 without the benefit of such a monitor1 and perhaps without the weather wisdom which only a few possess1 and cannot transfer to others4 ,difficult as it is to foretell weather accurately1 much useful foresight may be acquired by combining the indications of instruments 7such as the barometer1 thermometer1 and hygrometer7 with atmospheric appearances4 ,what is more varying than the aspect of the sky8 ,colour1 tint of clouds1 their soft or hard look1 their outline1 size1 height1 direction1 all vary rapidly1 yet each is significant4 ,there is a peculiar aspect of the clouds before and during westerly winds which differs from that which they have previous to and during easterly winds1 which is one only of the many curious facts connected with the differing natures of easterly and westerly currents of air throughout the world1 which remain unchanged1 whether they blow from sea to land1 or the reverse4#b ,perhaps some of those who make much use of instruments rather undervalue popular knowledge1 and are reluctant to admit that a 'wise saw' may be valuable as well as a 'modern instance2' while less informed persons who use weather-glasses unskilfully too often draw from them erroneous conclusions1 and then blame the barometer4 ,not only are reliable weather-glasses required at the smaller outlying ports and fishing places1 but plain1 easily intelligible directions for using them should be accessible to the seafaring population1 so that the masters of small vessels1 and fishermen1 might be forewarned of coming changes in time to prepare for them1 and thus become instrumental in saving much property and many lives4 ,june #aheh4 ,,how ,,to ,,foretell ,,weather4 ,familiar as the practical use of weather-glasses is1 at sea as well as on land1 only those who have long watched their indications1 and compared them carefully1 are really able to conclude more than that the rising glass#c ,,usually foretells less wind or rain1 a falling barometer more rain or wind1 or both2 a high one fine weather1 and a low1 the contrary4 ,but useful as these general conclusions are in most cases1 they are sometimes erroneous1 and then remarks may be rather hastily made1 tending to discourage the inexperienced4 ,by attention to the following observations 7the results of many years' practice and many persons' experience7 any one not accustomed to use a barometer may do so without difficulty4 ,the barometer shows whether the air#d is getting lighter or heavier1 or is remaining in the same state4 ,the quicksilver falls as the air becomes lighter1 rises as it becomes heavier1 and remains at rest in the glass tube while the air is unchanged in weight4 ,air presses on everything within about forty miles of the world's surface1 like a much lighter ocean1 at the bottom of which we live--not feeling its weight1 because our bodies are full of air1 but feeling its currents1 the winds4 ,towards any place from which the air has been drawn by suction1#e air presses with a force or weight of nearly fifteen pounds on a square inch of surface4 ,such a pressure holds the limpet to the rock when1 by contracting itself1 the fish has made a place without air#f under its shell4 ,another familiar instance is that of the fly which walks on the ceiling with feet that stick4 ,the barometer tube1 emptied of air1 and filled with pure mercury1 is turned down into a cup or cistern containing the same fluid1 which1 feeling the weight of air1 is so pressed by it as to balance a column of about thirty inches 7more or less7 in the tube1 where no air presses on the top of the column4 ,if a long pipe1 closed at one end only1 were emptied of air1 filled with water1 the open end kept in water and the pipe held upright1 the water would rise in it more than thirty feet4 ,in this way water barometers have been made4 ,a proof of this effect is shown by any well with a sucking pump--up which1 as is commonly known1 the water will rise nearly thirty feet1 by what is called suction1 which is1 in fact1 the pressure of air towards an empty place4 ,the words on scales of barometers should not be so much regarded for weather indications1 as the rising or falling of the mercury2 for1 if it stand at ,changeable1 and then rise towards ,fair1 it presages a change of wind or weather1 though not so great1 as if the mercury had risen higher2 and1 on the contrary1 if the mercury stand above fair and then fall1 it presages a change1 though not to so great a degree as if it had stood lower3 besides which1 the direction1 and force of wind1 are not in any way noticed4 ,it is not from the point at which the mercury may stand that we are alone to form a judgment of the state of the weather1 but from its rising or falling2 and from the movements of immediately preceding days as well as hours1 keeping in mind effects of change of direction1 and dryness1 or moisture1 as well as alteration of force or strength of wind4 99 99 99 ,in this part of the world1 towards the higher latitudes1 the quicksilver ranges1 or rises and falls1 nearly three inches--namely1 between about thirty inches and nine-tenths 7#cji71 and less than twenty-eight inches 7#bhj7 on extraordinary occasions2 but the usual range is from about thirty inches and a half 7#cje71 to about twenty-nine inches4 ,near the ,line1 or in equatorial places1 the range is but a few tenths1 except in storms1 when it sometimes falls to twenty-seven inches4 ,the sliding-scale 7vernier7 divides the tenths into ten parts each1 or hundredths of an inch4 ,the number of divisions on the vernier exceeds that in an equal space of the fixed scale by one4#g 99 99 99 ,by a thermometer the weight of air is not shown4 ,no air is within the tube4 ,none can get in4 ,but the bulb of the tube is full of mercury1 which contracts by cold1 and swells by heat--according to which effect the thread of metal in the small tube is drawn down or pushed up so many degrees3 and thus shows the temperature4#h ,if a thermometer have a piece of linen tied round the bulb1 wetted enough to keep it damp by a thread or wick dipping into a cup of water1 it will show less heat than a dry one1 in proportion to the dryness of the air1 and quickness of drying4#i ,in very damp weather1 with or before rain1 fog1 or dew1 two such thermometers will be nearly alike4 ,for ascertaining the dryness or moisture of air1 the readiest1 and surest method is the comparison of two thermometers2 one dry1 the other just moistened1 and kept so4 ,cooled by evaporation as much as the state of the air admits--the moist 7or wet7 bulb thermometer shows a temperature nearly equal to that of the other one1 when the atmosphere is extremely damp1 or moist2 but lower at other times1--in proportion to the dryness of air1 and consequent evaporation1--as far as twelve or fifteen degrees in this climate2 twenty or even more elsewhere4 ,from four to eight degrees of difference is usual in ,england2 and about seven is considered healthy for living rooms4 ,the thermometer fixed to a barometer intended to be used only as a weather-glass shows the temperature of air about it nearly--but does not show the temperature of mercury within exactly4 ,it does so however near enough for ordinary practical purposes--provided that no sun1 nor fire1 nor lamp heat is allowed to act on the instrument partially4 ,the mercury in the cistern and tube being affected by cold or heat1 makes it advisable to consider this when endeavouring to foretell coming weather by the length of the column4 99 99 99 ,briefly1 the barometer shows weight or pressure of the air2 the thermometer--heat and cold1 or temperature2 and the wet thermometer1 compared with a dry one1 the degree of moisture or dampness4#aj ,it should be remembered that the state of the air foretells1 rather than shows present weather 7an invaluable fact too often overlooked72 that the longer the time between the signs and the change foretold by them1 the longer such altered weather will last2 and1 on the contrary1 the less the time between a warning and a change1 the shorter will be the continuance of such foretold weather4 99 99 99 ,if the barometer has been about its ordinary height1 say near thirty inches1 at the sea level1#aa and is steady1 or rising--while the thermometer falls1 and dampness becomes less--,north-westerly1 ,northerly1 or ,north-easterly wind--or less wind--may be expected4 ,on the contrary--if a fall takes place1 with a rising thermometer and increased dampness1 wind and rain may be expected from the ,south-eastward1 ,southward1 or ,south-westward4 ,a fall1 with a low thermometer1 foretells snow4 ,exceptions to these rules occur when a ,north-easterly wind1 with wet 7rain or snow7 is impending1 before which the barometer often rises 7on account of the direction of the coming wind alone71 and deceives persons who1 from that sign only1 expect fair weather4 ,when the barometer is rather below its ordinary height1 say1 below twenty-nine inches and nine-tenths 7at the sea level only71 a rise foretells less wind1 or a change in its direction towards the ,northward1--or less wet2 but when the mercury#ab has been low1 say near #bi inches--the first rising usually precedes1 and foretells1 strong wind--7at times heavy squalls7--from the ,north-westward--,northward--or ,north-eastward--after which violence a rising glass foretells improving weather--if the thermometer falls4 ,but1 if the warmth continue1 probably the wind will back 7shift against the sun's course71 and more ,southerly1 or ,south-westerly wind will follow4 ,backing is a bad sign1 with any wind4 ,the most dangerous shifts of wind1 and the heaviest ,northerly#ac gales happen after the mercury first rises from a very low point4 ,indications of approaching changes of weather1 and the direction and force of winds are shown less by the height of mercury in the tube1 than by its falling or rising4 ,nevertheless1 a height of about #cj inches 7at the level of the sea7 with a continuance of it1 is indicative of fine weather and moderate winds4 ,the barometer is said to be falling when the mercury in the tube is sinking1 at which time its upper surface is sometimes concave or hollow4 ,the barometer is rising when the mercurial column is lengthening2 its upper surface being then1 as in general1 convex or rounded4#ad ,a rapid rise of the barometer indicates unsettled weather4 ,a slow rise1 or steadiness1 with dryness1 shows fair weather4 ,a considerable and rapid fall is a sign of stormy weather and rain4 ,alternate rising and sinking show very unsettled weather4 ,the greatest depressions of the barometer are with gales from the ,s4,e41 ,southward1 or ,s4,w42 the greatest elevations1 with winds from the ,n4,w41 ,northward1 or ,n4,e41 or when calm4 ,although the barometer generally falls with a ,southerly1 and rises with a ,northerly wind1 the contrary sometimes occurs2 in which cases the ,southerly wind is dry and the weather fine2 or the ,northerly wind is wet and violent4#ae ,when the barometer sinks considerably1 high wind1 rain1 or snow will follow3 the wind will be from the ,northward if the thermometer is low 7for the season7--from the ,southward if the thermometer is high4 ,sudden falls of the barometer1 with a ,westerly wind1 are sometimes followed by violent storms from ,n4,w4 or ,north4 ,if a gale sets in from the ,eastward or ,s4,e41 and the wind veers by the ,south1 the barometer will continue falling until the wind becomes ,s4,w41 when a comparative lull may occur2 after which the gale will be renewed2 and the shifting of the wind towards the ,n4,w4 will be indicated by a fall of the thermometer as well as a rise of the barometer4 ,three things appear to affect the mercury in a barometer3-- #a4 ,the direction of the wind--the ,north-east wind tending to raise it most--the ,south-west to lower it the most1 and wind from points of the compass between them proportionally as they are nearer one or the other extreme point4 ,n4,e4 and ,s4,w4 may therefore be called the wind's extreme bearings 7rather than poles87 ,the range1 or difference of height1 of the mercury1 due to change of direction only1 from one of these bearings to the other 7supposing strength or force1 and moisture1 to remain the same7 amounts in these latitudes to about half an inch 7shown by the barometer as read off74 #b4 ,the amount1 taken by itself1 of vapour1 moisture1 wet1 rain1 hail1 or snow1 in the wind or current of air 7direction and strength remaining the same7 seems to cause a change amounting1 in an extreme case1 to about half an inch4 #c4 ,the strength or force alone of wind from any quarter 7moisture and direction being unchanged7 is preceded1 or foretold1 by a fall or rise1 according as the strength will be greater or less1 ranging1 in an extreme case1 to more than two inches4 ,hence1 supposing the three causes to act together--in extreme cases--the mercury might range from about #ca 7#cji7 inches to near #bg inches1 which has happened occasionally4 ,generally1 however1 as the three act much less strongly1 and are less in accord--ordinary varieties of weather 7the wind varying as usual--with more or less cloudiness1 or rain7 occur much more frequently than extreme changes4 ,another general rule requires attention2 which is1 that the wind usually veers1 shifts1 or goes round1 with the sun1 7right-handed in northern places1 left-handed in the southern parts of the world17 and that1 when it does not do so1 or backs1 more wind or bad weather may be expected instead of improvement4 ,in a barometer the mercury begins to rise occasionally before the conclusion of gale1 sometimes even at its commencement1 as the equilibrium of the atmosphere begins to be restored4 ,although the mercury falls lowest before high winds1 it frequently sinks considerably before heavy rain only4 ,the barometer falls1 but not always1 on the approach of thunder and lightning1 or when the atmosphere is highly charged with electricity4#af ,before and during the earlier part of serene and settled weather1 the mercury commonly stands high1 and is stationary4#ag ,instances of fine weather1 with a low glass1 occur exceptionally1 but they are always preludes to a duration of wind or rain1 if not both4 ,after very warm and calm weather1 rain or a storm is likely to occur2 or at any time when the atmosphere has been heated much above the usual temperature of the season4 ,allowance should invariably be made for the previous state of the instrument during some days as well as hours1 because its indications may be affected by remote causes1 or by changes close at hand4 ,some of these changes may occur at a greater or less distance1 influencing neighbouring regions1 but not visible to each observer whose barometer1 nevertheless1 feels their effect4 ,there may be heavy rains or violent winds beyond the horizon1 out of view of an observer1 by which his instruments may be affected considerably1 though no particular change of weather occurs in his immediate locality4 ,it may be repeated1 that the longer a change of wind or weather is foretold by the barometer before it takes place1 the longer the presaged weather will last2 and1 conversely1 the shorter the warning1 the less time whatever causes the warning2 whether wind or a fall of rain1 hail1 or snow1 will continue4 ,sometimes severe weather from an equatorial#ah direction1 not lasting long1 may cause no great fall of the barometer1 because followed by a duration of wind from polar regions3--and at times it may fall considerably with polar winds and fine weather1 apparently against these rules1 because a continuance of equatorial wind is about to follow4 ,by such changes as these one may be misled1 and calamity may be the consequence if not thus forewarned4 ,the veering of the winds is a direct consequence of the earth's rotation1 while currents of air from the polar regions are alternating or contending with others from the equator4 ,the polar currents are cold1 dry1 and heavy4 ,those from the equatorial parts of the world are warm1 moist1 and comparatively light4 ,their alternate or combined action1 with the agencies of solar heat and electricity1 cause the varieties of weather that we experience4 ,it is not intended to discourage attention to what is usually called weather wisdom4 ,on the contrary1 every prudent person will combine observation of the elements with such indications as he may obtain from instruments4 ,the more carefully and accurately these two sources of foreknowledge are compared and combined1 the more satisfactory will the results prove4 ,a few of the more marked signs of weather--useful alike to seaman1 farmer1 and gardener1 are the following3 ,whether clear or cloudy1 a rosy sky at sunset presages fine weather2 a red sky in the morning1 bad weather1 or much wind 7if not rain73--a grey sky in the morning fine weather2 a high dawn1 wind2 a low dawn2 fair weather4#ai ,soft-looking or delicate clouds foretell fine weather1 with moderate or light breezes2--hard edged oily-looking clouds1 wind4 ,a dark1 gloomy1 blue sky is windy2--but a light1 bright blue sky indicates fine weather4 ,generally1 the softer clouds look1 the less wind 7but perhaps more rain7 may be expected2--and the harder1 more greasy1 rolled1 tufted1 or ragged1 the stronger the coming wind will prove4 ,also1 a bright yellow sky at sunset presages wind2 a pale yellow1 wet3--and thus by the prevalence of red1 yellow1 or grey tints1 the coming weather may be foretold very nearly3 indeed1 if aided by instruments1 almost exactly4#bj ,small inky-looking clouds foretell rain2 a light scud1 driving across heavy clouds1 wind and rain2 but if alone1 wind only4 ,high upper clouds crossing the sun1 moon1 or stars1 in a direction different from that of the lower clouds1 or wind then blowing1 foretell a change of wind 7beyond tropical latitudes74#ba ,after fine clear weather the first signs 7in the sky7 of change are usually small1 curled1 streaked1 or spotty clouds1 followed by an overcasting of vapour1 that grows into cloudiness4 ,this murky appearance1 more or less oily or watery1 as wind or rain will prevail1 is a sure sign4 ,the higher and more distant the clouds seem to be1 the more gradual1 but extensive1 the coming change of weather will prove4 ,generally speaking1 natural1 quiet1 delicate tints or colours1 with soft undefined forms of clouds1 foretell fine weather3 but gaudy or unusual hues1 with hard1 definite outlines1 presage rain and wind4 ,misty clouds forming1 or hanging on heights1 show wind and rain coming--if they remain1 or descend4 ,if they rise1 or disperse1 the weather will improve1 or become fine4 ,when sea birds fly out early1 and far to seaward1 moderate wind and fair weather may be expected4 ,when they hang about the land1 or over it1 sometimes flying inland1 expect a strong wind1 with stormy weather4 ,as many creatures1 besides birds1 are affected by the approach of rain or wind1 such indications should not be slighted by the observer of weather4 ,there are other signs of a coming change in the weather known less generally than may be desirable2 and1 therefore worth notice here4 ,when birds of long flight1 such as swallows and others1 hang about home and fly low--rain or wind may be expected4 ,also when animals seek sheltered places1 instead of spreading over their usual range3 when pigs carry straw to their sties2 and when smoke from chimneys does not ascend readily1 7straight upwards during a calm17 an unfavourable change may be looked for4 ,dew is an indication of fine weather4 ,so is fog4 ,neither of these two formations occurs under an overcast sky1 or when there is much wind4 ,one sees the fog occasionally rolled away1 as it were1 by wind--but not formed while it is blowing4 ,remarkable clearness of atmosphere1 near the horizon2 distant objects1 such as hills1 unusually visible2 or raised 7by refraction72 and what is called a good hearing day may be mentioned among signs of wet1 if not wind1 to be expected4#bb ,more than usual twinkling of the stars2 indistinctness or apparent multiplication of the moon's horns2 haloes2 wind-dogs2 and the rainbow2 are more or less significant of increasing wind1 if not approaching rain4#bc ,near land1 in sheltered harbours1 in valleys1 or over low ground1 there is usually a marked diminution of wind during part of the night--and a dispersion of clouds4 ,at such times an eye on an overlooking height may see an extended body of vapour below2 which the cooling of night has rendered visible4 99 99 99 ,although the preceding remarks are probably sufficient for their principal purpose--these pages may fall into the hands of persons familiar with the subject1 to whom the following observations may be addressed1 as some of the reasons for what has been so briefly1 if not too positively outlined4 ,as the mercurial column rises with increase of pressure by the atmosphere1 and descends when the pressure diminishes1 it indicates a greater or less accumulation of air1 which1 like other fluid1 such as water 7when heaped above its average level or reduced below it1 from whatever cause71--will have a tendency to fall or rise till the general equilibrium is restored4 ,an observer may be under the centre of such accumulation or depression1 he may be more or less distant from it1 though within the influence of whatever horizontal movement of air may be caused by such temporary increase or diminution of pressure4 ,hence the barometer shows1 and generally foretells1 changes of wind2 but as complications always occur1 and as changes are of greater or less extent1 affecting or extending through a wider or more limited area1 accompanied by hygrometric and electrical alterations1 it is extremely difficult at times to say beforehand what particular change of weather is to be expected1 and at what interval of time2 although after the event the correspondence of barometric changes with those of the weather can be readily traced4 ,however1 notwithstanding occasional perplexity1 the general character of weather during the next few days may be predicted by an observer who understands the nature and use of this instrument and the thermometer1 and has watched them in the few immediately preceding days4 ,in endeavouring to foretell weather1 the general peculiarity should always be remembered1 that the barometric column usually stands higher with easterly than it does with westerly winds2 and with winds from the polar regions higher than with those from the direction of the equator4 ,hence the highest columns are observed with north-east winds in northern latitudes1 and with south-east in the southern hemisphere4 ,in middle latitudes there is an average difference 7unreduced or observed height as read off7 of about half an inch1 other things being similar1 between the heights of the mercury with ,north-easterly1 and with ,south-westerly winds4 ,the steadier the column1 or the more gradually it moves1 the more settled in character will the weather be1 and conversely3 because it shows a quiet settled state of the atmosphere2 or1 if otherwise1 the reverse4 ,in the tropics1 when the barometric column moves contrary to its usual daily motion1 inferior weather may be expected 7temporarily71 because the usual air currents are disturbed4 ,this regular movement1 whether tidal1 or otherwise connected with the sun's influence--sensible in tropical latitudes1 but more or less masked elsewhere--amounts to nearly two-tenths of an inch near the equator1 the highest being at about nine1 and the lowest near three o'clock4 99 99 99 ,some movements of the atmosphere may be illustrated by reference to the motion of water drawn off from a reservoir by a small opening below2 or by similar upward draught through a syphon2 or by a gradual pouring in at the upper surface4 ,from a slight motion at the commencement1 affecting only that portion of the fluid adjoining either of those places of diminution or repletion1 gradually all the water becomes influenced and acquires more or less rapid movement4 ,but suppose a long reservoir or canal of fluid which has two such points of exhaustion or two of such repletion 7as imagined above71 and that one of either is near each end of the vessel4 ,if each aperture be opened at the same moment1 equal effects will be caused in each half of the fluid towards either end of the vessel1 but in the middle there must be a neutral point at which the water falls1 yet has no horizontal motion4 ,the converse takes place in raising the level4 ,and in the case of fluid drawn off or diminished in weight at one end while increased by repletion at the other1 the whole body of water will move similarly to that in the former vessel1 but unequally4 ,hence it is evident1 that before horizontal motion occurs1 an augmentation or a diminution of pressure must take place somewhere more or less remote2 and so it is with the lighter fluid atmosphere1--which has centres1 lines1 or areas of depression towards which currents flow4 ,such considerations show in some degree why the barometric changes usually precede1 but sometimes only accompany1 changes of weather3 and1 though very rarely1 occur without any sensible alteration in the wind current of the atmosphere4 ,an observer may be near a central point towards which the surrounding fluid tends1--or from which it diverges4 ,he may be at the very farthest limit of the portion of fluid that is so influenced4 ,he may be at an intermediate point--or he may be between bodies of atmosphere tending towards opposite directions4 ,it has been said1 that a whirlwind which sets an extended portion of the atmosphere into a state of rapid revolution diminishes the pressure of the atmosphere over that portion of the earth's surface1 and most of all at the centre of the whirl4 ,the depth of the compressing column of air will1 at the centre1 be least1 and its weight will be diminished in proportion to the violence of the wind4 ,yet this has been controverted with respect to the general effect of air in horizontal motion1 and the depth of the column in question4 ,certainly there are two kinds of whirlwinds--one caused by rarefaction1 tending to lighten vertical pressure under the vortex1 though not1 perhaps1 under all the current drawn towards it2 and the other1 a consequence of opposing winds1 which occasion huge eddies or whirlwinds of compression4 ,some whirlwinds are accompanied by rushes from the upper atmosphere1 from the colder regions1 which1 mingling with warmer and moister air near the sea1 cause dense clouds4 ,about their centre it sometimes happens that the barometer falls as much as two or three inches1 showing a diminution of atmospheric pressure by nearly a tenth part2 when it should be expected1 from physical considerations alone1 that very dense clouds would be formed4#bd 99 99 99 ,the column of mercury falls about one tenth of an inch for each of the first few hundred feet above the sea level1 but varying when it becomes much more elevated4#be ,due allowance1 therefore1 should be made in observing1 when on high land4 ,the tides are affected by atmospheric pressure1 so much that a rise of one inch in the barometer will have a corresponding fall in the tides of nine to sixteen inches1 or about one foot for each inch4#bf 99 99 99 ,vessels sometimes enter docks1 or even harbours1 where they have scarcely a foot of water more than their draught2 and as docking1 as well as launching large ships1 requires a close calculation of height of water1 the state of the barometer becomes of additional importance on such occasions4 99 99 99 99 99 ,to render these pages rather more useful at sea1 in any part of the world1 a few words about squalls and hurricanes are here offered to the young seaman4 ,generally1 squalls are preceded1 or accompanied1 or followed by clouds2 but the very dangerous white squall 7of the ,west ,indies and other regions71 is indicated only by a rushing sound1 and by white wave crests4 ,descending squalls come slanting downwards1 off high land1#bg or from upper regions of atmosphere4 ,they are dangerous1 being sometimes violently strong4 ,a squall cloud that can be seen through or under is not likely to bring1 or be accompanied by1 so much wind as a dark continued cloud extending beyond the horizon4 ,how the comparative hardness or softness of clouds foretells more or less wind or rain1 was stated in pages #ac and #ad4 ,the expressions hardening up1 softening1 or looking greasy1 are familiar to seamen3 and such very sure indications are the appearances so designated1 that they can hardly be mistaken4 ,the rapid or slow rise of a squall cloud--its more or less disturbed look--that is1 whether its body is much agitated1 and changing form continually1 with broken clouds1 or scud1 flying about--or whether the mass of cloud is shapeless and nearly quiet1 though floating onwards across the sky--foretells more or less wind accordingly4 ,an officer of a watch1 with a good eye for clouds and signs of changing weather1 may save his men a great deal of unnecessary exposure1 as well as work1 besides economising sails1 spars1 and rigging4 ,in some of the saws about wind and weather1 there is so much truth that1 though trite and simple1 their insertion here can do no harm4 ,adverting to the barometer3-- ,when rise begins1 after low1 ,squalls expect and clear blow4 ,or3--,first rise1 after very low1 ,indicates a stronger blow4 ,also3--,long foretold1 long last3 ,short notice1 soon past4 ,to which may be added3--,in squalls-- ,when rain comes before wind1 ,halyards1 sheets1 and braces mind4 ,and3--,when wind comes before rain1 ,soon you may make sail again4 99 99 99 ,also1 generally speaking3-- ,when the glass falls low1 ,prepare for a blow2 ,when it rises high1 ,let all your kites fly4#bh 99 99 99 ,to these short expressions--well known1 in practice1 to the experienced2 a very concise but sure rule may be added1 for avoiding the central or strongest part of a hurricane1 cyclone1 typhoon1 tornado1 or circling storm4 ,with your face towards the wind1 in ,north latitude1 the centre of the circling1 or rotatory storm1 will be square to your right4 ,in ,south latitude1 square to your left4 ,the apparent veering of the wind1 and the approach or retreat of the dangerous central circle1 depend on your position in the curvilinear whirl or sweep4 ,draw a circle2--mark the direction of the rotation or circulation1 by an arrow with the head towards the left hand 7against the movement of a watch's hands7 in ,north latitude2 but towards the right 7or with the hands of a watch7 if in ,south latitude4 ,the direction of the wind1 and the bearing of the centre1 show your position in the meteor1 for such it is1 though perhaps hundreds of miles in diameter2 and the veering of the wind1 or the contrary1 and its change in strength1 will show how the meteor is moving bodily--over an extensive region1 revolving horizontally--or inclined at a certain angle to the horizontal plane4 ,if the observer be stationary1 in ,north latitude1 and the centre pass on his polar side1 he will experience a change of wind from ,southward by the ,west towards ,north2 but if it pass between him and the ,equator1 the change will be from ,southward by the ,east towards ,north2 but otherwise in ,south latitude1 as his place in circles sketched will show more clearly than words4 ,the roughest sketch or diagram1 indicating the various directions of wind1 and the course of the meteor's centre1 will show more plainly than descriptions--which must necessarily vary with each case1 and are tedious4 ,cyclonology1 or really meteorology1 is simple enough in these great characteristic effects2 but their causes must be the philosopher's study1 rather than that of the young practical seaman4 ,were it not for this reflection1 one might endeavour to show how all the great ,easterly trade winds--the no less important anti-trades1#bi or nearly constant ,westerly winds1--and their complicated eddying offsets1 are all 7on greater or smaller scales7 breadths1 or zones of atmosphere1 alternating1 or circulating1 or crossing 7superposed or laterally7--between which1 at distant intervals1 occur those strong eddies1 or storms1 called hurricanes--typhoons--tornadoes--or cyclones4 ,the great easterly and westerly movements--so clearly shown by philosophers to be the consequences of cold polar currents of air--warm equatorial currents--and diurnal rotation of the earth2#cj are grand ruling phenomena of meteorology--to which storms1 and all local changes1 occurring but occasionally1 are subordinate and exceptional4 ,further investigations into electrical and chemical peculiarities will probably throw additional light1 perhaps the strongest1 on meteorological science4 99 99 99 99 99 ,in the previous observations1 general reference has been made to mercurial barometers of the ordinary kind2 but1 excepting the construction of the instruments themselves1 those observations apply to all barometers1 wheel--aneroid--or metallic--and likewise1 of course1 to the sympiesometer1 which is a modified barometer4 ,but as these four last-mentioned instruments are scarcely so familiar as the simplest form of barometer1 it may be useful to add a few words about each of them4 99 99 99 ,the ,,wheel barometer has a syphon tube1 partly filled with mercury1 on which1 at the short or open end of the tube1 a float moves1 to which a line is attached that moves a wheel1 carrying an index4#ca 99 99 99 ,,aneroid barometers1 if often compared with good mercurial columns1 are similar in their indications1 and valuable2 but it must be remembered that they are not independent instruments2 that they are set originally by a barometer1#cb require adjustment occasionally1 and may deteriorate in time1 though slowly4 ,the aneroid is quick in showing the variation of atmospheric pressure1 and to the navigator who knows the difficulty1 at times1 of using barometers1 this instrument is a great boon1 for it can be placed anywhere1 quite out of harm's way1 and is not affected by the ship's motion1 although faithfully giving indication of increased or diminished pressure of air4#cc ,in ascending or descending elevations1 the hand of the aneroid may be seen to move 7like the hand of a watch71 showing the height above the level of the sea1 or the difference of level between places of comparison4#cd ,the principle on which it is constructed may be explained in a few words1 without going into a scientific or too minute detail of its various parts4 ,the weight of a column of air1 which in a common barometer acts on the mercury1 in the aneroid presses on a small circular metal box1 from which nearly all air is extracted2 and to this box is connected1 by nice mechanical arrangement1 the hand visible over the face of the instrument4 ,when the atmospheric pressure is lessened on the vacuum box1 a spring acting on levers1 turns the hand to the left1 and when the pressure increases1 the spring is affected differently1 the hand being turned to the right4 ,it acts in any position1 but as it often varies several hundredths with such a change1 it should be held uniformly1 while read off4 ,the known expansion and contraction of metals under varying temperatures1 caused doubts as to the accuracy of the aneroid under such changes2 but they were partly removed by introducing into the vacuum box a small portion of gas1 as a compensation for the effects of heat or cold4 ,the gas in the box1 changing it bulk on a change of temperature1 was intended to compensate for the effect on the metals of which the aneroid is made4 ,besides which1 a further and more1 reliable compensation has lately been effected by a combination of brass and steel bars4#ce ,,metallic barometers 7in outer shape and size like aneroids7 have not yet been tested adequately in very moist1 hot1 or cold air for a sufficient time4 ,they1 as well as sympiesometers1 are likewise dependent or secondary instruments1 and liable to deterioration4 ,for limited employment1 when sufficiently compared1 they may be very useful1 especially in a few cases of electrical changes not foretold or shown by mercury4 ,the ,,sympiesometer is considered to be more sensitive than the marine barometer1 falling sooner1 and rising earlier3 but this is partly in consequence of the marine barometer tube being contracted1 to prevent oscillation or pumping4 ,in the sympiesometer a gas is used1 which presses on the confined surface of the liquid with an uniform pressure at an equal state of temperature4 ,the liquid is raised or depressed by an increase or diminution in the density of the atmosphere1 and change of temperature is allowed for1 by the sliding scale of the instrument being always set to agree with the height of the mercury in the attached thermometer1 bringing the pointer on the sliding scale of the sympiesometer to the same degree on the inverted scale 7over which it slides7 as is indicated by the thermometer4 ,the height of the fluid1 as then shown by the sliding scale1 indicates the pressure of the atmosphere4 ,as the instrument is delicate1 great care should be taken1 in carrying or handling1 to keep the top always upwards1 and to exclude casual rays of the sun1 or a fire1 or lamp4 ,oil sympiesometers seem to be affected more than mercurial1 or others1 and much more than the barometer1 by lightning or electricity4 ,that they1 and the hermetically sealed ,,storm ,,glasses1 are influenced by causes besides pressure and temperature1 appears now to be certain4 99 99 99 ,the daily movement of the barometer may be noted 7in a form or table of double entry7 at the time of each observation1 by a dot at the place corresponding to its altitude1 and the time of observing2 which dot should be connected with the previous one by a line4 ,the resulting free curve 7or zig-zag7 will show at a glance what have been the movements during the days immediately previous1 by which1 and not merely by the last observation1 a judgment may be formed of the weather to be expected4 ,such a diagram may be filled up by uncorrected observations1 its object being to serve as a weather guide for immediate use1 rather than for future investigation4 ,if closely kept up1 it will prove to be of utility1 and will in some degree reward the trouble of keeping a regular record4 ,for purely scientific objects much more nicety and detail are required4 99 99 99 99 99 ,,hesitation is sometimes felt by young seamen1 at first using the vernier of a barometer1 for want of some such familiar explanation as the following3-- ,the general principle of this moveable dividing scale is1 that the total number of the smallest spaces or subdivisions of the vernier are made equal1 taken altogether1 to one less than that number of the smallest spaces in an equal length of the fixed scale4 ,for example3 ten spaces on the vernier being made equal to nine on the scale1 each vernier space is one tenth less than a scale space2 and if the first line or division of the vernier agree exactly with any line of the scale1 the next line of the vernier must be one tenth of a tenth 7or one hundredth7 of an inch from agreement with the next scale division2 the following vernier line must be two hundredths out1 and so on3 therefore1 the number of such differences 7from the next tenth on the scale7 at which a vernier line agrees with a scale line1 when set1 is the number of hundredths to be added to the said tenth2 7in a common barometer1 reading only to hundredths of an inch74 ,the vernier of a barometer reading to thousandths of an inch1 is on a similar principle1 though differently divided4 ,in this application of it1 generally1 twenty-five vernier spaces equal twenty-four of the scale spaces1 which are each half a tenth1 or five hundredths of an inch2 therefore1 the difference between one of the vernier and one of the scale is two-tenths of a hundredth1 or two thousandths of an inch #be7jej7jjb4 ,this is the usual graduation of scientific barometers2 but for ordinary purposes1 as weather-glasses1 a division1 or reading1 to the hundredth of an inch is sufficient4 ,when set properly1 the vernier straight edge1 the top of the mercury1 and the observer's eye1 should be on the same level2 the edge 7or pointer7 just touching#cf the middle and uppermost point of the column4 ,great care should be taken to look thus square1 or at right angles to the scale4 ,light1 or something white1 at the back of the tube1 assists in accurately setting the vernier1 and may be shifted about to aid in reading off4 99 99 99 ,,the ,,aneroid has been recommended1 in these pages1 as a weather-glass2 but it may increase its usefulness to append a table for measuring heights 7approximately7 by this1 or any barometer1 which can be compared with another1 or itself1 at a higher or lower station4 ,if the measure of a height rather greater than the aneroid will commonly show1 be required1 it may be re-set thus--,when at the upper station 7within its range71 and having noted the reading carefully1 touch the screw behind so as to bring back the hand a few inches 7if the instrument will admit71 then read off and start again4 ,reverse the operation when descending4 ,this may add some inches of measure approximately4 99 99 99 99 99 ,in the following ,table1 the difference between the number of feet opposite the height of a barometer1 at one station1 and that at another station1 is their approximate difference of height4 ,,table4 ---------------------------------------- -------------------------- ,barometer ,height in ,barometer ,height in ,barometer ,height in ,inches4 feet4 ,inches4 feet4 ,inches4 feet4 ---------------------------------------- -------------------------- #caj #j #bfh #chbi #bbg #hbja #cji #he #bfg #cibg #bbf #hcag #cjh #agj #bff #djbe #bbe #hdcd #cjg #bee #bfe #dabd #bbd #heea #cjf #cda #bfd #dbbc #bbc #hffi #cje #dbg #bfc #dcbc #bbb #hghg #cjd #eac #bfb #ddbc #bba #hijf #cjc #fjj #bfa #debd #bbj #ijbe #cjb #fhg #bfj #dfbe #bai #iade #cja #ggd #bei #dgbf #bah #ibff #cjj #hfb #beh #dhbh #bag #ichh #bii #iej #beg #dicj #baf #ieaj #bih #ajch #bef #ejcc #bae #ifcb #big #aabf #bee #eacf #bad #igee #bif #abae #bed #ebdj #bac #ihgh #bie #acjd #bec #ecdd #bab #ajjjb #bid #acic #beb #eddh #baa #ajabg #bic #adhb #bea #eeec #baj #ajbec #bib #aegb #bej #efeh #bji #ajcgi #bia #affb #bdi #egfc #bjh #ajejf #bij #agec #bdh #ehfi #bjg #ajfcc #bhi #ahdd #bdg #eigf #bjf #ajgfj #bhh #aice #bdf #fjhc #bje #ajhhi #bhg #bjbg #bde #faij #bjd #aajah #bhf #baai #bdd #fbig #bjc #aaadh #bhe #bbaa #bdc #fdje #bjb #aabgh #bhd #bcjc #bdb #fead #bja #aadji #bhc #bcif #bda #ffbc #bjj #aaeda #bhb #bdhi #bdj #fgcc #aii #aafgc #bha #behb #bci #fhdc #aih #aahje #bhj #bfge #bch #fiec #aig #aaici #bgi #bgfi #bcg #gjfd #aif #abjgd #bgh #bhfd #bcf #gage #aie #abbaj #bgg #biei #bce #gbhg #aid #abcdf #bgf #cjed #bcd #gcii #aic #abdhc #bge #cadi #bcc #geab #aib #abfbj #bgd #cbde #bcb #gfbe #aia #abgeg #bgc #ccda #bca #ggbi #aij #abhid #bgb #cdch #bcj #ghed #ahi #abidb #bga #cece #bbi #gifi #ahh #acjhj #bgj #cfcc #bbh #hjhe #ahg #acbai #bfi #cgca ---------------------------------------- -------------------------- ,,marine ,,barometer1 ,,adopted ,,by ,,her ,,majesty',s ,,government1 ,on the recommendation of the ,kew ,observatory ,committee of the ,british ,association for the ,advancement of ,science4 ,this instrument should be suspended in a good light for reading1 but out of the reach of sunshine or the heat of a fire or lamp4 ,it should be as nearly amidships1 and exposed as little to sudden changes of temperature1 gusts of wind1 or injuries1 as possible4 ,in a ship of war it should be below the lowest battery or gun-deck4 ,light should have access to the back of the tube1 to admit of setting the index so as to have its lower edge a tangent to the surface of the mercury--the eye being on the same level1 which is known by the back and front edges of the index being in one line with the mercury surface4 ,white paper or card will reflect light for setting the vernier correctly4 ,the height of the cistern above or below the ship's water-line should be ascertained1 and entered on the register4 ,it is desirable to place the barometer in such a position as not to be in danger of a side blow1 and also sufficiently far from the deck above to allow for the spring of the metal arm in cases of sudden movements of the ship4 ,if there is risk of the instrument striking anywhere when the vessel is much inclined1 it will be desirable either to put some soft padding on that place1 or to check movement in that direction by a light elastic cord2 in fixing which1 attention must be paid to have it acting only where risk of a blow begins1 not interfering otherwise with the free swing of the instrument3 a very light cord attached above1 when possible1 will be least likely to interfere injuriously4 ,the vernier1 as usual in standard barometers1 reads to the two thousandth 7#jjb7 part of an inch4 ,every long line cut on the vernier corresponds to #ja part2 each small division on the scale is #je2 the hundredth parts on the vernier being added to the five when its lower edge is next above one of the short lines2 or written down as shown by the figures on the vernier only1 when next above one of the divisions marking tenths4 ,in placing this barometer1 it is only necessary to fix the instrument carefully1 as indicated in the above directions1 and give a few gentle taps with the fingers on the bottom1 to move the mercury4 ,without further operation it will usually be ready for observation in less than an hour4 ,when moving the barometer1 or replacing it in its case1 the mercury should be allowed to run gently up to the top of the tube1 by holding the instrument for a few minutes inclined at an angle4 ,the vernier should be brought down to the bottom of the scale4 ,no other adjustment for portability is required4 ,during carriage1 it ought to be kept with the cistern end uppermost1 or lying flat1 the former position being preferable4 ,if the mercury should not descend at first by a few gentle taps1 use sharper 7but of course without violence71 by which1 and two or three taps1 with the finger ends1 on the tube--between the scale and the tangent screw--the mercury will be made to begin to descend4 ,in reading off from a barometer1 it should hang freely1 not inclined by holding1 or even by touch4 ,sometimes1 though rarely1 at sea the mercury seems stopped4 ,if so1 take down the instrument 7after sloping71 reverse it1 tap the tube gently while the cistern end is upwards1 and then replace as before4 99 99 99 99 99 ,,testing ,,barometers1 ,,hydrometers1 ,,and ,,thermometers4 ,in the year #ahec a conference of maritime nations was held at ,brussels1 on the subject of meteorology at sea4 ,the report of this conference was laid before ,parliament1 and the result was a vote of money for the purchase of instruments and the discussion of observations1 under the superintendence of the ,board of ,trade4 ,arrangements were then made1 in accordance with the views of the ,royal ,society and the ,british ,association for the ,advancement of ,science1 for the supply of instruments properly tested4 ,in the barometers now in general use by meteorologists on land1 the diameters of the tubes are nearly equal throughout their whole length1 and a provision is made for adjusting the mercury in the cistern to the zero point1 previous to reading the height of the top of the column4 ,the object of the latter arrangement1 it is well known1 is to avoid the necessity of applying a correction to the readings for the difference of capacity between the cistern and the tube4 ,at sea1 barometers of this construction cannot be used4 ,part of the tube of the marine barometer must be very much contracted to prevent pumping1 and the motion of the ship would render it impracticable to adjust the mercury in the cistern to the zero point4 ,in the barometer usually employed on shore1 the index error is the same throughout the whole range of scale readings1 if the instrument be properly made2 but in nearly all the barometers which have till recently been employed at sea1 the index correction varies through the range of scale readings1 in proportion to the difference of capacity between the cistern and the tube4 ,to find the index correction for a land barometer1 comparison with a ,standard at any part of the scale at which the mercury may happen to be1 is generally considered sufficient4 ,to test the marine barometer is a work of much more time1 since it is necessary to find the correction for scale readings at about each half inch throughout the range of atmospheric pressure to which it may be exposed2 and it becomes necessary to have recourse to artificial means of changing the pressure of the atmosphere on the surface of the mercury in the cistern4 ,the barometers intended to be tested are placed1 together with a ,standard1 in an air-tight chamber1 to which an air pump is applied1 so that1 by partially exhausting the air1 the ,standard can be made to read much lower than the lowest pressure to which marine barometers are likely to be exposed2 and by compressing the air it can be made to read higher than the mercury ever stands at the level of the sea4 ,the tube of the ,standard is contracted similarly to that of the marine barometer1 but a provision is made for adjusting the mercury in its cistern to the zero point4 ,glass windows are inserted in the upper part of the iron air-chamber1 through which the scales of the barometers may be seen2 but as the verniers cannot be moved in the usual way from outside the chamber1 a provision is made for reading the height of the mercury independent of the verniers attached to the scales of the respective barometers4 ,at a distance of some five or six feet from the air-tight chamber a vertical scale is fixed4 ,the divisions on this scale correspond exactly with those on the tube of the ,standard barometer4 ,a vernier and telescope are made to slide on the scale by means of a rack and pinion4 ,the telescope has two horizontal wires1 one fixed1 and the other moveable by a micrometer1 screw so that the difference between the height of the column of mercury and the nearest division on the scale of the ,standard1 and also of all the other barometers placed by the side of it for comparison1 can be measured either with the vertical scale and vernier or the micrometer wire4 ,the means are thus possessed of testing barometers for index error in any part of the scale1 through the whole range of atmospheric pressure to which they are likely to be exposed1 and the usual practice is to test them at every half inch from #bge to #ca inches4 ,in this way barometers of various other descriptions have been tested1 and their errors found to be so large that some barometers read half an inch and upwards too high1 while others read as much too low4 ,in some cases those which were correct in one part of the scale were found to be from half an inch to an inch wrong in other parts4 ,these barometers were of the old and ordinary construction4 ,in some the mercury would not descend lower than about #bi inches1 owing to a fault very common in the construction of the marine barometer till lately in general use1 that the cistern was not large enough to hold the mercury which descended from the tube in a low atmospheric pressure4 ,the practice which has long prevailed of mounting the marine barometer in wood is objectionable4 ,the instrument recently introduced agreeably to the recommendation of the ,kew ,committee1 is greatly superior to any other description of marine barometer which has yet been tested1 as regards the accuracy with which it indicates the pressure of the atmosphere4 ,the diameter of the cistern is about an inch and a quarter1 and that of the tube about a quarter of an inch4 ,the scale1 instead of being divided into inches in the usual way1 is shortened in the proportion of about #jjd of an inch for every inch4 ,the object of shortening the scale is to avoid the necessity of applying a correction for difference of capacity between the cistern and the tube4 ,the perfection with which this is done may be judged of from the fact1 that of the first twelve barometers tested at the ,liverpool ,observatory with an apparatus exactly similar to that used at ,kew 7whence these instruments were sent by railway1 after being tested and certified71 the index corrections in the two pressures of #bh and #ca inches in three of them were the same2 two differed #jjja of an inch2 and for the remainder the differences ranged from #jjjb to #jjjf of an inch4 ,the corrections for capacity were therefore considered perfect1 and1 with one unimportant exception1 agreed with those given at ,kew4 ,in order to check the pumping of the mercury at sea1 the tubes of these barometers are so contracted1 through a few inches1 that1 when first suspended1 the mercury is perhaps twenty minutes in falling from the top of the tube to its proper level4 ,when used on shore1 this contraction of the tube causes the marine barometer to be always a little behind an ordinary barometer1 the tube of which is not contracted4 ,the amount varies according to the rate at which the mercury is rising or falling1 and ranges from #jjj to #jjb of an inch4 ,as the motion of the ship at sea causes the mercury to pass more rapidly through the contracted tube1 the readings are almost the same there as they would be if the tube were not contracted1 and in no case do they differ enough to be of importance in maritime use4 ,the method of testing thermometers is so simple as scarcely to require explanation4 ,for the freezing point1 the bulbs and a considerable portion of the tubes of the thermometers1 are immersed in pounded ice4 ,for the higher temperatures1 the thermometers are placed in a cylindrical glass vessel containing water of the required heat2 and the scales of the thermometers intended to be tested1 together with the ,standard with which they are to be compared1 are read through the glass4 ,in this way the scale readings maybe tested at any required degree of temperature1 and the usual practice is to test them at every ten degrees from #cb to #ib of ,fahrenheit4 ,for this range of #fj the makers who supply ,government are limited to #jf of a degree as a maximum error of scale reading2 but so accurately are these thermometers made1 that it has not been found necessary to reject more than a very few of them4 99 99 99 99 99 ,hydrometers are tested by careful immersion in pure distilled water2 of which the specific gravity is taken as unity4 ,in water less pure1 more salt1 dense1 and buoyant1 the instrument floats higher1 carrying more of the graduated scale out of the fluid4 ,the zero of the scale should be level with the surface of distilled water1 and rise above it in proportion as increase of density causes less displacement4 ,the scale is graduated to thousandths--as far as #jdj only--because the sea water usually ranges between #ajad and about #ajcf4 ,only the last two figures need be marked4 ,,london3 ,printed by ,,george ,e4 ,,eyre and ,,william ,,spottiswoode1 ,printers to the ,queen's most ,excellent ,majesty4 ,for ,her ,majesty's ,stationery ,office4 ,,footnotes3 #a ,in ,south latitude the ,south wind corresponds to our ,north wind in its nature and effects4 ,the ,easterly and ,westerly winds retain their respective peculiarities in both hemispheres4 #b ,exclusive of local land and sea breezes of hot climates4 #c ,glass1 barometer1 column1 mercury1 quicksilver1 or hand4 #d ,or atmosphere1 or the atmospheric fluid which we breathe4 #e ,or exhaustion4 #f ,a vacuum4 #g ,see pages #bd and #be4 #h ,thirty-two degrees is the point at which water begins to freeze1 or ice to thaw4 #i ,evaporation4 #aj ,the two thus combined making a hygrometer3 for which some kinds of hair1 grass1 or seaweed may be a make-shift4 #aa ,it stands lower1 about a tenth of an inch for each hundred feet of height directly upwards1 or vertically1 above the sea2 where its average height1 in ,england1 is #biid inches 7at #cb74 #ab ,in an ,aneroid1 a metallic1 or a wheel barometer1 the hand's motion should correspond to that of mercury in an independent instrument4 #ac ,southerly in ,south latitude4 #ad ,in the best columns1 those of standards for example1 no concavity is seen1 at any time3 but it is otherwise with many barometers1 which do show a concavity4 #ae ,in these cases there is usually a combination or a contest of currents in the atmosphere1 horizontally1 or one above the other1 or diagonally4 #af ,thunder clouds sometimes rise and spread against the wind 7lower-current74 ,it is probable that there is a meeting1 if not a contest of air currents1 electrically different1 whenever lightning is seen4 ,their concurrence1 when the new one advances from polar regions1 does not depress the barometer1 except in oscillations of the mercury1 which are very remarkable at some such times4 #ag ,aneroids1 metallic barometers1 and oil sympiesometers1 seem to be much more affected than mercurial barometers by electrical changes4 #ah ,southerly1 in ,north latitude2 the reverse in the ,southern hemisphere4 #ai ,a high dawn is when the first indications of daylight are seen above a bank of clouds4 ,a low dawn is when the day breaks on or near the horizon4 ,the first streaks of light being very low4 #bj ,indications of weather1 afforded by colours1 seem to deserve more critical study than has been often given to the subject4 ,why a rosy hue at sunset1 or a grey neutral tint at that time1 should presage the reverse or their indications at sunrise2--why bright yellow should foretell wind at either time1 and pale yellow1 wet2--why clouds seem soft1 like water colour2 or hard edged1 like oil paint1 or ,indian ink on an oily plate2--and why such appearances are infallible signs--are yet to be shown satisfactorily to practical men4 #ba ,in the trade winds of the tropics there is usually a counter current of air1 with light clouds1--which does not indicate any approaching change4 ,in middle latitudes such upper currents are not so evident1 except before a change of weather4 #bb ,much refraction is a sign of ,easterly wind4 ,remarkable clearness is a bad sign4 #bc ,the young moon with the old moon in her arms 7,burns1 ,herschel1 and others7 is a sign of bad weather in the temperate zones or middle latitudes1 because 7probably7 the air is then exceedingly clear and transparent4 #bd ,even in ordinary changes of weather it is interesting1 as well as useful1 to mark the formation or disappearance of clouds1 caused by colder and warmer currents of air mixing3 or intermingling4 #be ,depending on pressure and temperature4 #bf ,sir ,james ,ross--,m4 ,daussy4 #bg ,williwaw 7,whirl-awa87 of the old sealers and whalers4 #bh ,seamen call the light sails1 used only in very fine weather1 flying kites4 #bi ,herschel4 #cj ,dov4 #ca ,for a barometer of this kind1 ,admiral ,milne has invented self-registering mechanism1 that answers well4 #cb ,a small turnscrew being applied gently to the screw head at the back4 ,this is often necessary1 on receiving or first using an aneroid that has long been lying by1 or that has been shaken by travelling4 #cc ,it is a good weather glass--to be suspended on or near the upper deck1 for easy reference2--and is unlikely to be injured by mere concussion of air1 or vibration of wood1 when guns are fired4 #cd ,allowing #j1jjaa of an inch for each foot4 #ce ,the manufacture of these useful auxiliary instruments 7all ,french originally7 has increased much latterly3 and now the patent has expired4 ,they might be so improved so to be worth more than double their present value4 #cf ,like the sun's edge or limb1 touching the sea horizon1 as seen inverted when using a sextant4