VS-Y! 
 
 VINHOJilVO JO A1ISH3AINI) 3H1 JO AUVU8M 
 
 man VINUOJIIVO jo AUSTIN!) am jo Ayvuaii VINUOJIIVO 
 
RSI1Y OF CALIFORKU LIBRARY OF THE UNIVERSITY OF CALIFORNIA 
 
 VXD 
 
 RSITY OF CALIFORNIA LIBRARY OF THE UNIVERSITY OF CALIFORNIA 
 
 9| 
 
 I I 
 
 
 
 3 
 
TREATISE ON METEOROLOGY. 
 
TREATISE ON METEOROLOGY: 
 
 BAROMETER, THERMOMETER, HYGROMETER, 
 RAIN-GAUGE, AND OZONOMETER: 
 
 RULES AND REGULATIONS TO BE OBSERVED 
 FOR THEIR CORRECT USE. 
 
 TO WHICH ARE APPENDED SOME OF THE LATEST DISCOVERIES AND THEORIES 
 
 OF SCIENTIFIC MEN RESPECTING VARIOUS SOLAR AND 
 
 TERRESTRIAL PHENOMENA. 
 
 DEDICATED TO THE METEOROLOGISTS OF STRATHEARN. 
 
 BY 
 
 ALBERT J. T. MORRIS, 
 
 (QUEEN'S COLLEGE, OXFORD), 
 
 INCUMBENT OF ST JAME.S' CHCRCH. MCTHI1.L. PERTHSHIRE. 
 
 EDINBURGH : 
 
 R. GRANT AND SON, PRINCES STREET. 
 
 MDCCCLXVI. 
 
PREFACE. 
 
 THE following Meteorological data are mainly derived 
 from such well-known sources as Messrs SCOFFERN 
 and LOWE on Practical Meteorology ; Mr GLAISHER'S 
 Hygrometrical Tables ; Sir W. ARMSTRONG'S Presi- 
 dential Address to the British. Association, 1863 ; 
 together with certain discoveries and uncertain 
 theories, propounded by Professor Tyndall, Mr Nas- 
 myth, Sir John Leslie, and others ; all of which we 
 would gladly accept with implicit faith, if only their 
 authors would always agree not to differ. 
 
 A very valuable treatise, on this same subject, was 
 published a few years ago by Messrs Scoffern and 
 Lowe ; but, in many respects, it is far deeper than 
 the ordinary meteorologist will require, embracing 
 optics, acoustics, electricity, and other scientifically 
 treated matters, for the full understanding of which 
 the reader should have dipped into " the Mathe- 
 matics," more deeply than the amateur meteorologist 
 will generally be found to have done. 
 
 I therefore presume to offer this more familiar 
 style of composition for the convenience of those 
 
VI PREFACE. 
 
 who may wish for an easy Hand-book to the right 
 employment of the few meteorological instruments 
 commonly in use. 
 
 It will probably be thought that the facts supplied 
 are of the greater value, in that I do not pretend to 
 offer them as the original fruits of my own mind, 
 but merely attempt to exhibit them in such a form 
 as may commend itself by its brief simplicity. 
 
 A. J. T. MORRIS. 
 
 BALWHAKRIE, NEAK, CRIEFF, 
 SIM March 1865. 
 
 After recording the long sad list of ships and 
 human lives lost in the terrible storm which reached 
 its height on the 10th of January 1866, when the 
 noble steam-ship " London," with 220 passengers, 
 foundered in the open sea, the " Edinburgh Evening 
 Courant" makes the following appeal : 
 
 " We trust that this sad narrative will not be 
 thrown away on the shipping enterprise of this 
 country ; or, above all, on the votaries of meteoro- 
 logical science. If that science were in the state of 
 advancement in which it ought to be, and to which 
 it is certainly destined to attain, the hurricane which 
 sweeps the ocean, and overwhelms our most sea- 
 worthy ships, could be, if not averted, at least fore- 
 seen and shunned. 
 
 " There is no science which is so abundant in 
 facilities for its prosecution ; none which enlists in 
 
PREFACE. VI 1 
 
 its service so manifold and so various a body of 
 auxiliaries. Were all the ships which cover our seas 
 and coasts to be adequately supplied with meteoro- 
 logical observers, were landsmen in every sea-port 
 town, and in every convenient inland situation, to 
 teach themselves how to make and to register 
 meteorological observations, an induction of facts 
 would soon be accumulated, which would enable us, 
 not only to predict the coming of a storm, but even 
 the force with which it would be charged. 
 
 " Governments have done much for the advance- 
 ment of the sciences on which the security of our 
 maritime enterprise depends ; but governments may 
 easily do more. They have contributed to protect 
 the ship of the mariner from the lighting bolt, they 
 have planted beacons and light-houses on the head- 
 lands, to ensure his safe entrance into harbour, 
 and they have established the life-boat apparatus at 
 every point menaced by the storm. 
 
 " Is it too much to ask that an equal impetus be 
 given to that meteorological science, which is des- 
 tined, in a great measure, to supersede the necessity 
 of relying on such uncertain aids in the hour of 
 extreme peril ? Through the voice of the departing 
 storm, let humanity and wisdom reply." 
 
 It may very well be, that the "Evening Courant" 
 will fail to rouse government into anything like 
 action in this matter, but its appeal to the humanity 
 of our countrymen will not be thrown away, even 
 though to respond to that appeal, by devoting them- 
 
Vlll PREFACE. 
 
 selves to the science of the winds, will demand of 
 them a long patience. For the meteorologist cannot 
 measure his progress in science by. the results of 
 weeks or months, but is content to know, that the 
 carefully recorded phenomena of five or ten or fifteen 
 successive years, may help to point out to some more 
 gifted genius than himself the certain laws which 
 govern the apparently uncertain elements. It is 
 with such a hope that I venture to commend this 
 little work to the favourable notice of both friends 
 and strangers. 
 
 Happily, we are not, one and all, so slavishly 
 bound down to the never-ending task- work of an 
 iron age, but that we can call some of Time's hours 
 our own, and may devote them to a study which, 
 whilst it aims at the public good, also reveals new 
 and unsuspected charms to the student, in propor- 
 tion as the passing years remind him that he himself 
 is growing old. 
 
 I cannot close these introductory remarks without 
 thanking Stewart Hepburn, Esq., of Colquhalzie, for 
 various suggestions and explanatory notes, and for 
 the -hearty way in which, after perusing the MS., 
 he signified his approval of my small labours. 
 
 A. J. T. M. 
 
 January 22, 1866. 
 
TREATISE OX METEOROLOGY, 
 
 ATMOSPHERE, 
 
 THE atmosphere is the subject with which the- meteor- 
 ologist has to deal, with all the ever-changing phenomena of 
 pressure, temperature, drought, and moisture, which it is 
 constantly bringing before his notice. 
 
 In the widest sense of the word, the atmosphere is that 
 mass of thin, elastic fluid by which any body is entirely sur- 
 rounded ; as when we speak of the atmosphere of the sun, 
 moon, or planets, the existence of which may not be abso- 
 lutely certain, though it is highly probable. Our earth 
 may be said to swim through space, in company with an 
 all-surrounding atmosphere of air and watery vapour, in- 
 separably attached to the revolving body by the attractive 
 principle which, as it were, draws all outer things together 
 by some invisible central force. When speaking of this 
 general tendency of all bodies to draw towards each other, 
 with greater or less force, according to their density, we 
 commonly merge cause and effect in one, by the use of the 
 terms " heavy" and " weight." 
 
 By means of its weight, then, the air is inseparably con- 
 nected with the earth, and presses on it in accordance with 
 the laws of heavy elastic fluids, its pressure being equally 
 exerted on all sides, and in every possible direction. If 
 
 A 
 
2 ATMOSPHERE. 
 
 now, from any cause, a stronger pressure is exerted in one 
 direction, certain resulting phenomena arise in some other 
 direction, and continue to act until the equilibrium is 
 restored. Thus, for instance, water ascends in the bore of 
 a pump, above its general level, as soon as a vacuum is 
 created between it and the ascending piston. The cause 
 of this is the disturbance of the equilibrium, since the air 
 outside the bore presses on the water outside, whilst no 
 air is present within the bore to counterbalance the outer 
 pressure. By means of this pressure if the tube be long 
 enough the water may be raised to the height of thirty- 
 two and a-half feet. 
 
 This column of water in the tube represents the weight 
 with which the atmosphere presses on the earth ; or we 
 may speak of the whole atmospheric pressure as being 
 equal to an ocean of water thirty-two and a-half feet deep, 
 spread over the entire surface of the earth. Hence it is 
 calculated that with the barometric column standing at about 
 twenty-eight inches, the atmosphere presses with a weight of 
 32,400 Ibs. on the human body, reckoning the body's surface 
 at fifteen square feet. The man, however, is unconscious of 
 this enormous pressure, because the air surrounds him, and 
 is, besides, within him. On account of its elasticity, it 
 presses in every direction, even from within a man out- 
 wards, and in this way counterbalances the air spread ex- 
 ternally over the body. 
 
 The atmosphere is not everywhere of uniform density ; 
 for the lower strata of the air, having to support the weight 
 of the upper ones, become more compressed and dense. 
 According to the law of Mariotte, the density of the 
 atmosphere diminishes in geometrical, as the height in- 
 creases in arithmetical, progression ; or we may state the 
 law thus, viz., that " the compression of the air is inversely 
 to the pressure applied," that is to say, if the pressure be 
 
BAROMETER. 3 
 
 doubled, the volume of the air is reduced to one-half; if 
 tripled, it is reduced to one-third ; if quadrupled, to one- 
 fourth, and so on. This law will not, probably, hold true 
 at the extreme limits of our upper air, because, at that 
 height the air being more free from superincumbent pressure 
 must be more completely in its natural state. 
 
 The height of the atmosphere has been variously esti- 
 mated at from thirty to fifty miles, calculating partly from 
 the pressure which it exerts, and partly from the duration 
 of twilight. For it may be supposed that the very loftiest 
 stratum of air which reflects light upon us, before sunrise 
 or after sunset, belongs to our planet. It is not of equal 
 height, however, over all parts of the earth, but may be 
 regarded as a spheroid, being most elevated at the equator, 
 both on account of the centrifugal effects of our earth's 
 diurnal motion, and on account of the expansive action of 
 the sun's vertical rays, which is at its maximum between 
 the tropics. 
 
 Nor is the atmosphere by any means the simple element 
 which the ancients believed it to be, but is made up of 
 several gases, invariably found in the same proportions 
 everywhere, together with foreign ingredients unequally 
 distributed, and floating about until again deposited on the 
 earth, from whence they at first arose. 
 
 Mention will be made of these constituent and accidental 
 parts of the air later on. Enough has now been said to 
 prepare the way for the consideration of our first instru- 
 ment, the barometer. 
 
 BAEOMETER 
 
 The barometer is the instrument by which changes in 
 the weight of the air are ascertained. 
 
 The pressure of the superincumbent air, at one and the 
 
4 BAROMETER. 
 
 same place, would always be alike, or nearly so, were it 
 not that lateral disturbances remove a portion of the pres- 
 sure at one point and add to it elsewhere. Thus, supposing 
 the average pressure to be 29'70 in inches of a mercurial 
 column, then, if the barometer rises to 30*20 inches, or 
 upwards, it is because a corresponding fall has taken place 
 in some other part of the earth. 
 
 Hence it is that a very sudden rise of the barometric 
 column is nearly always followed by a speedy fall, and vice 
 versa, backwards and forwards, each time less and less, 
 until, by these oft-repeated undulations, the equilibrium of 
 the whole air, over an area of some thousands of square 
 miles, is at last attained, when a steady barometer and 
 calm weather, more or less continuous, are the result. 
 
 Effect vf Elevation on the Barometric Column. The 
 greater the perpendicular height above sea-level, the less will 
 be the pressure of the air, simply, or rather chiefly, because 
 there is less air above to exert this downward pressure. 
 
 By the application of this principle, with corrections 
 and reductions for temperature and elevation above sea- 
 level, we are able to judge, pretty correctly, as to the 
 height Of a mountain ; and if mines could be sunk thou- 
 sands instead of hundreds of feet, below the surface of the 
 earth, the same principle, applied the contrary way, would 
 give us a tolerably accurate idea of their depth. Indeed, 
 if all the neeessary precautions and allowances are observed, 
 and the instrument be a good one, the height of a mountain 
 may be learnt, within five or six feet, by barometric 
 measurement, as certainly as by a trigonometric survey. 
 
 At an elevation of about thirty-six miles, the pressure of 
 the atmosphere is probably not more than O'OOl, or the 
 one-thousandth part of an inch of the barometric column ; 
 in other words, the mercury, at such an elevation, would 
 sink down and leave the barometer-tube empty, because 
 
BAROMETER. O 
 
 the air would be of such a rarity as to be nearly a vacuum 
 exerting no pressure. Conversely, at the depth of about 
 sixty-six miles below the earth's surface (supposing a mine 
 sunk to that depth, and left open for the ingress of the air !) 
 the density of the air would be about 100,000 times greater 
 than at the sea-level, or six times more than the density of 
 gold, so that a lump of gold would actually float very 
 buoyantly in such an atmosphere. 
 
 Elevation of Observers' Stations. On the sea-coast it is 
 probable that an observer's house may not be many feet 
 (say thirty or forty feet) above sea-level ; more inland he 
 may be, as at Crieff, 250 feet above the sea ; whilst at the 
 Glasgow Waterworks' station, between Glenfinlas and Ben 
 Ledi, he may be as much as 1800 feet above the sea. 
 
 Supposing, then, that three good standard barometers, 
 all alike as to their " reading " at sea-level, were placed at 
 these different elevations, their mercurial columns would 
 stand at very different points : 
 
 The one at the sea-coast might stand, say, at 30-00 inches. 
 
 That at the elevation of 250 feet would 
 
 be at 2975 
 
 That at the elevation of 1800 feet would 
 
 be at 28-20 
 
 And yet, at all these places, the weather, as we popularly 
 term it, might be equally good and steady ; and the only 
 reason for the very low barometer at Glenfinlas is, that 
 its elevation is 1800 feet above the sea. 
 
 Rules for Allowances. Now, it is obvious that if ob- 
 servers, so differently situated, are to take observations, 
 capable of being compared with each other, and with such 
 head-quarters as Greenwich, Liverpool, Edinburgh, and 
 Glasgow, they must, one and all, adopt the same rules of 
 allowances. 
 
 Two such rules are now recognised, as sufficiently ao 
 
6 BAROMETER. 
 
 curate for all the practical objects of the meteorologist, 
 viz. 
 
 1st, The allowance for elevation above sea-level. 
 
 2d, The allowance for temperature. 
 
 In the meteorological statement which Admiral Fitzroy 
 first published daily in the " Times " (and which is still 
 reported there by the authority of his successor), he thus 
 expresses it : 
 
 " Barometer Corrected and Reduced. 
 
 " Each ten feet of vertical elevation, above half-tide level, 
 causes about one-hundredth of an inch diminution ; and 
 each 10 above 32 causes nearly three-hundredths of an 
 inch increase/' (See any copy of the " Times.") 
 
 If we wished to find the height of a lofty mountain (say, 
 15,000 feet high) the above rules of allowance would not be 
 sufficiently precise for our purpose, but would leave us, 
 perhaps, some hundreds of feet wide of the mark. But 
 they are accurate enough for the stations of observers in 
 this country, which are rarely 1000 feet above sea-level ; 
 and being now recognised as the rules for allowance, it is 
 clear that any little inaccuracy is at least counterbalanced 
 by the advantages of uniformity. 
 
 Of course, 32 (Fahr.) as the starting-point is partly 
 arbitrary ; any other temperature might have been chosen 
 as the standard. A rule is often made more clear by some 
 familiar example. We will therefore suppose a case which 
 shall take in both allowances requisite, viz., for elevation 
 and for temperature. 
 
 Required to know the true altitude of the mercury at 
 the level of the sea, and at the temperature of 32 (Fahr.) : 
 
 Let the observation be made at Crieff, 250 feet above 
 the sea ; 
 
 Let the temperature of the barometer-room be 55 (Fahr.); 
 
BAROMETER. 7 
 
 Let the apparent height of the mercurial column be 
 
 29-565 inches ; 
 
 Then the apparent reading is . . . 29'565 
 
 250 x 0-001 = 0-250, and gives . { p + 8 } -250 j ( For . eleva " 
 
 29-815 
 But 55 -32 = 23; and 23 X "003 gives {"} 0'069 | ( F 
 
 or 
 / 
 
 And so (" Barometer corrected and reduced ") = 29746 
 
 Let us now suppose that any person having an hour to 
 spare every morning, and living at one fixed spot, wishes 
 to take part in the meteorological observations so much in 
 vogue ; we may suppose, also, that he has provided himself 
 with the best instruments that can be obtained for the 
 moderate sum of L.10. His first inquiry, for the sake of 
 securing barometrical accuracy, must be, " How many feet 
 is my house above the level of the sea ?" This he will 
 learn either from the published Ordnance Survey of the 
 district in which he lives, or by writing to one of the chief 
 officials of this department. 
 
 This altitude once correctly ascertained, he will have no 
 further trouble than to multiply it by O001, and add the 
 product to every apparent reading of his barometer ; thus* 
 if 35 feet above the sea, then 35 x 0-001 = 0-035 ;- 
 or if 365 feet 365 x 0*001 =,0-365 ;- 
 and the like. 
 
 If the observer's house is (say) 245 feet above the sea, 
 and his memory very treacherous, he may write " + 0-245" 
 on a slip of paper, and paste it on the wall, close to his 
 barometer, for constant reference. 
 
 Thus much as to " Collection for Altitude," which never 
 varies, so long as an observer does not change his place of 
 abode. 
 
 But the " Reduction for Temperature" does vary con- 
 
8 
 
 BAEOMETER. 
 
 tinually ; and therefore it is advisable to keep a full table 
 of degrees, and their reductions, always at hand, from 32 
 up to 90, never forgetting that, whilst the " Correction for 
 Altitude" is added to the apparent reading, the " Eeduction 
 for Temperature" is subtracted from it. 
 
 In saying that the " Eeduction for Temperature" is to be 
 subtracted from the barometer's apparent reading, it shoiild, 
 however, be stated that this is supposing the temperature 
 of the barometer-room to be above 32 (Fahr.), as it almost 
 always will be. 
 
 Eeduction for Temperature. 
 
 .,, ' ' ' o ( requires + 0*000 
 
 63 requires 
 64 . 
 
 . - 0-093 
 0-096 
 
 33 requires 
 
 
 -0-003 
 
 65 . 
 
 0-099 
 
 34 
 
 
 
 0-006 
 
 66 . 
 
 0-102 
 
 35 
 
 
 
 0-009 
 
 67 . 
 
 0-105 
 
 36 
 
 
 
 0-012 
 
 68 . 
 
 0-108 
 
 37 
 
 
 
 0-015 
 
 69 . 
 
 0-111 
 
 38 
 
 
 
 0-018 
 
 70 . 
 
 0-114 
 
 39 
 
 
 
 0-021 
 
 71 . 
 
 0-117 
 
 40 
 
 
 
 0-024 
 
 72 . 
 
 0-120 
 
 41 
 
 
 
 0-027 
 
 73 . 
 
 0-123 
 
 42 
 
 
 
 0-030 
 
 74 . 
 
 0-126 
 
 43 
 
 
 
 0-033 
 
 75 . 
 
 0-129 
 
 44 
 
 
 
 0-036 
 
 76 . 
 
 0-132 
 
 45 
 
 
 
 0-039 
 
 77 . 
 
 0-135 
 
 46 
 
 
 
 0-042 
 
 78 . 
 
 0-138 
 
 47 
 
 
 
 0-045 
 
 79 . 
 
 0-141 
 
 48 
 
 
 
 0-048 
 
 80 . 
 
 0-144 
 
 49 
 
 
 
 0-051 
 
 81 . 
 
 0-147 
 
 50 
 
 
 
 0-054 
 
 82 . 
 
 0-150 
 
 51 
 
 
 
 0-057 
 
 83 . 
 
 0-153 
 
 52 
 
 
 
 0-060 
 
 84 . 
 
 0-156 
 
 53 
 
 
 
 0-063 
 
 85 . 
 
 0-159 
 
 54 
 
 . 
 
 
 0-066 
 
 86 . 
 
 0-162 
 
 55 
 
 
 * 
 
 0-069 
 
 87 . 
 
 0-165 
 
 56 
 
 
 
 0-072 
 
 88 . 
 
 0-168 
 
 57 
 
 
 
 0-075 
 
 89 . 
 
 0-171 
 
 58 
 
 
 
 0-078 
 
 90 . 
 
 0-174 
 
 59 
 
 
 
 0-081 
 
 91 . 
 
 0-177 
 
 60 
 
 
 
 0-084 
 
 92 . 
 
 0-180 
 
 61 
 
 
 
 0-087 
 
 93 . 
 
 0-183 
 
 62 
 
 
 
 0-090 
 
 
BAROMETER. 9 
 
 But supposing that the temperature should ever be below 
 28, the opposite process must be adopted, i.e., 0*003 must 
 be added to the apparent reading of the barometer, for every 
 degree below 28 (Fahr.) 
 
 It may perhaps be as well to repeat that the temperature 
 referred to, as requiring allowance to be made, is not that of 
 the air outside the house, but of the air in the room, where 
 the barometer is hung. 
 
 A good thermometer should either be attached to the 
 barometer, or hung close to it, so that the temperature may 
 be carefully noted at the moment of reading off the barome- 
 trical column, and due allowance made, in accordance with 
 the foregoing table. The necessity for making this allowance 
 may be shown by taking an extreme case : Suppose a per- 
 son has two barometers, exactly equal when in the same 
 room, and that he places one in a room artificially heated, 
 and the other in a very cold room (when the hot room may 
 represent an unusually hot summer's day, and the cold 
 room may stand for the temperature of a winter's day) 
 the one at 90, and the other at 35, 
 
 Then, apparent reading in the room at 90 is 30-200 
 (Eeduction for temperature) 0*174 
 
 (True reading is) 30-026 
 
 And, apparent reading in the room at 35 is 30*035 
 (Eeduction for temperature) 0-009 
 
 (True reading is) 30-026 
 
 So that between the two rooms (30-200 and 30-035) there 
 is a difference of 0165, or about one-sixth of an inch, due 
 entirely to the expansive action of the heated air. 
 
 But it may be that the observer does not care particularly 
 for such precise accuracy in his readings of the barometer, as 
 
 A2 
 
10 BAROMETER. 
 
 is implied in the corrections and reductions which have been 
 described, and yet he would like to know how much he 
 should allow for elevation and temperature, upon an aver- 
 age, throughout the year. Then let us say that he is living 
 250 feet above sea-level, and that 9 A.M. is his favourite 
 hour for examining the barometer, or just immediately 
 before breakfast. To be at all nearly approaching the true 
 reading, he must always add to the apparent height of the 
 column 
 
 In the summer months, . . . 016 
 
 In the winter months, .... 0'24 
 In spring and autumn months . . 0'20 
 
 or, more roughly still, 0'20 all the year round. 
 
 The Standard Barometer. For trustworthy observations 
 the barometer should be a standard instrument, and not 
 one of the dial-faced kind, which works a long arm by 
 the revolution of a small wheel, thus multiplying every 
 error. Even if the wheel-barometer (dial-faced) be a very 
 superior one, still its minimum of error will amount to as 
 much as 0*25, or a quarter of an inch both ways, that is, when 
 very high and when very low. For example, when its true 
 reading would be 28-50, it will stand at 28-25 (0-25 too low) ; 
 or, when it ought to rest at 30-50, it will have mounted to 
 30*75 (0-25 too high). And this is a small amount of error 
 compared with what many of the supposed good wheel 
 barometers will exhibit. Therefore, always use a standard 
 barometer. 
 
 It may not be amiss to return, for a moment, to the idea 
 that was hinted at in the first pages on Atmosphere, viz., 
 that the reason the mercurial column rises in the tube to the 
 mean height of about thirty inches is that the whole weight 
 of a column of air, reaching from the ground perpendicu- 
 larly to the utmost limits of the air, amounts to the same 
 
BAROMETER. 11 
 
 as the weight of the mercury suspended in the barometric 
 tube. Thus, imagine the tube to be square instead of ro.und 
 say an inch square the thirty inches of mercury would 
 then be thirty cubic inches, and would be exactly balanced 
 by the column of air, whose dimensions were cubic inches, 
 but of unknown number, because the height of the aerial 
 column is unknown. Well, then, as thirty cubic inches of 
 mercury weigh fifteen pounds, so the atmosphere is said to 
 press with fifteen pounds weight on every square inch at 
 the surface of the earth. In the case of a column of water, 
 you may consider the height to be feet instead of inches, 
 the diameter of the column being still an inch; so that the 
 atmospheric column, an inch square at the base, will support 
 a water column, in a vacuum tube, an inch square and thirty 
 feet in height. This is not the exact amount (it should be 
 thirty-two and a-half feet), but it is near enough to the mark 
 to show the principle on which the pump-maker works* 
 who knows that he can raise the water from the well by a 
 common pump, only just sucli a height, as that the weight 
 of water, between the well's surface and the pump bucket, 
 will be balanced by the pressure of the atmosphere. 
 
 Diameter of the Barometer Tube. This should not be less 
 than three-tenths of an inch, internal measurement ; but 
 four, or even five-tenths, or half an-inch, will be still better ; 
 for the wider the tube, the less will be the friction of the 
 mercury against the sides of the glass. 
 
 For such a very nice observation as that for taking a 
 mountain height, correction is made for this friction, and is 
 called " correction for capillarity ; " it requires a small addi- 
 tion to the apparent height of the barometric column ; but 
 we need not take it into account for climatic observations. 
 
 Testing the Barometer. Before fixing the barometer to 
 the wall, hold it securely with both hands, and gently and 
 slowly move it sideways into a partially horizontal position. 
 
12 BAROMETER. 
 
 In this way the mercurial column will run quickly to the 
 top of the tube, and should give a clearly-heard sharp tap 
 against the head of the tube, provided the vacuum be quite 
 perfect. If this clear tapping sound is not produced, there 
 must be air in the glass tube above the mercury, and this, if 
 not removed, will prevent the instrument from acting truly. 
 
 To remove the air, the observer must slowly and carefully 
 turn the barometer upside down ; and whilst holding it thus 
 inverted, he must continue, for three or four minutes, to 
 tap the tube and framework with his fingers, so as to dis- 
 lodge the air, and make it pass out of the tube into the 
 cistern. Then turn it round again slowly as before, and see 
 if the sharp tap can be heard against the top of the tube. 
 If it still sounds dull, or not at all, it will be wise to make 
 no more experiments, but to put it into the hands of the 
 maker, or of an optician who understands the details of the 
 barometer professionally. The whole operation of turning 
 and tapping must be done very carefully ; because, if the 
 glass tube be a wide bore, as in a good barometer, any 
 sudden change of position may cause the weight of the mov- 
 ing mercury to shatter the glass. 
 
 How and where to hang the Barometer. See that it 
 hangs perpendicularly, by applying a plumbline, and at 
 such a height that the 30 inches on the scale may be level 
 with the eye. Let the room be a cool one as little subject 
 as possible to any rapid changes of temperature. Never let 
 the sun shine upon the instrument ; and therefore, where it 
 can be done, it will be well to choose a room with the win- 
 dow looking towards the north. If it can be avoided, do 
 not hang the barometer on the outer main wall of the room, 
 on account of .the vibration likely to accompany windy 
 weather. 
 
 The Vernier and its use. The standard barometer is 
 furnished with a permanent vertical scale, divided into 
 
BAROMETER. 13 
 
 inches and tenths of an inch ; whilst the further subdivi- 
 sion into hundredths of an inch being scarcely possible, the 
 vernier is made to obviate the difficulty. It is an ingenious 
 instrument, intended to give the value of fractions which 
 fall between two of the smallest linear divisions already 
 supplied. The vernier is sometimes one inch and one-tenth 
 of an inch in length, making eleven-tenths; and it is divided 
 into ten equal parts, each being a tenth and a hundredth 
 ( or T i_\ o ) of an inch. It is made to slide easily up and down 
 the permanent scale at the side of the barometer tube ; but 
 by means of a spring it is kept from slipping down from any 
 point to which it is brought. 
 
 In taking an observation, we can, of course, read off hand 
 the number of inches and tenths of an inch at which the 
 mercury stands, for they are legibly marked on the perma- 
 nent scale ; and to find the number of hundredths of an 
 inch, if there be any, we raise or depress the vernier, until 
 its uppermost line, or projecting point, is exactly on a level 
 with the surface of the mercurial column. We then count 
 downwards the number of lines, or parts, on the vernier, 
 which occur before we reach a line on the said vernier co- 
 incident with a line on the permanent scale ; and that num- 
 ber of pails on the vernier represents the additional hun- 
 dredths of an inch about which we were at first in doubt. 
 It is not, however, essential that the vernier should be H^hs 
 of an inch in length, and divided into ten equal parts ; for 
 it would serve equally well if it were i^ths of an inch in 
 length, and divided into ten equal parts. In either case, 
 the subdivision into hundredths of an inch is equally well 
 attained. But the rule generally followed in the construc- 
 tion of a vernier whether for a barometer or for circles 
 and quadrants is this, that the number of parts on the 
 vernier should be equal to the denominator of the fraction, 
 which expresses the required subdivision, whilst the value 
 
14 BAROMETER. 
 
 of each of its standard divisions of measure should be one 
 more or one less. This will no doubt sound hopelessly un- 
 intelligible to any one who has never examined and worked 
 the vernier ; but a very little practice with it will explain 
 its principle better than any amount of words. 
 
 Manner of taking an Observation. Give the barometer a 
 few gentle taps with the fingers, so as to help the mercury 
 to run freely up or down the tube to its true level ; but do 
 not shake it roughly, nor be continually tapping it at short 
 intervals. 
 
 This is not meant by way of deprecating hourly observa- 
 tions, under some such special circumstances as a rapid and 
 continuous fall, forewarning the observer of the approach of 
 a severe tempest. 
 
 For more precise information as to atmospheric pressure, 
 and the precautions necessary in taking a delicate baro- 
 metric measurement at great elevations, Mr Glaisher's 
 " Tables of Barometrical Corrections," and other works 
 published under the sanction of the British Meteorological 
 Society, may be referred to with advantage. 
 
 The Indications of the Barometer. The barometer does 
 not tell us, at all certainly, whether rainy or dry weather 
 may be expected, but, primarily, whether wind or calm is 
 approaching. With a very high barometer we may have 
 rain or fog ; and with an exceedingly low barometer, the sky 
 may be dry and clear. If the barometer be already high 
 and steady, and a further rise takes place, it is often followed 
 quickly by rain or snow. When the barometer is very low 
 indeed, we know that a severe gale is at work somewhere, 
 though it may not touch us. It is generally after the baro- 
 meter has risen considerably from a very low point that the 
 heavy rains take place. The greatest pressure of wind to 
 the square inch, in a storm, is almost always recorded by 
 the anemometer or " force of wind measurer," after the baro- 
 
BAROMETER. 15 
 
 meter has begun to rise. In winter, severe though not con- 
 tinuous frost, with or without snow, often follows close after 
 a very low barometer. 
 
 Hourly Fluctuations of the Barometer. It should be re- 
 membered that the barometer has, in all places, regular 
 hourly fluctuations. From mid-day, it falls until between 
 three and five in the afternoon ; it then rises till about ten 
 in the evening. It falls again to a second minimum about 
 four in the morning, and attains a second maximum about 
 ten in the morning. The hours vary a little in different 
 countries. But in this country we may assign ten as the 
 morning and evening maximum, and four as the morning 
 and evening minimum height of the mercurial column. 
 
 At the equator this fluctuation averages a tenth of an 
 inch per day throughout the year. But in this latitude it 
 may be said to be not much more than O01 of an inch per 
 day. Still it is very perceptible ; and the fact is worth 
 bearing in mind, for this reason, that when the movement 
 of the mercurial column is contrary to the regular course 
 of its fluctuation, it is more expressive of change than when 
 it agrees with the regular diurnal course. For instance, if 
 the mercury fall ever so little, between 8 A.M. and mid-day, 
 it indicates decreasing pressure far more surely than even 
 a greater fall would, which occurred between mid-day and 
 4 P.M. These hourly fluctuations are, doubtless, connected 
 with the variations of temperature and amount of vapour, 
 arising from the sun's daily course, causing inequalities 
 in the height of the atmosphere. For it has been found 
 that these hours of maximum and minimum, in the daily 
 fluctuation of the mercurial column, farther north than 
 latitude 65, are exactly the reverse of what they are between 
 the tropics. 
 
16 TEMPERATURE. 
 
 TEMPERATURE. 
 
 If we dig deep into the ground at any place, we shall 
 find, by the insertion of a thermometer, that as we succes- 
 sively descend we approach constantly to some limiting 
 temperature, which, under a certain depth, will continue 
 unchanged. The point of this equilibrium in temperature 
 varies in different soils ; but it very rarely exceeds fifty feet. 
 If the excavation be made about the end of November, 
 the temperature will increase gradually as we descend in 
 the lower strata to the limiting point ; but, on the contrary, 
 if the pit be formed in May, the ground will be found to 
 grow colder as w r e descend. 
 
 In the severe climate of that region to the north of 
 Canada, known as the Hudson's Bay Territory, it is stated 
 by the residents there, that even in the summer months, 
 when digging through the ground to make a grave, they 
 always come, at the depth of a few feet, to a stratum of 
 frozen earth. Hence it is manifest that the mass of the 
 earth transmits very slowly indeed the impressions of heat 
 or cold received at its surface. The external temperature 
 of any given day will ^probably take nearly a month to 
 penetrate one foot into the ground, where it is not abso- 
 lutely saturated with water. By digging downwards in 
 summer, therefore, we soon reach the impressions of the 
 preceding spring and winter ; but a farther progress down- 
 wards into the ground brings us to the temperature of the 
 previous autumn and summer ; and still lower down, we 
 find all the various fluctuations of heat, belonging to the 
 different seasons, intermingled and confounded in one com- 
 mon mean. We may therefore conclude that the tempera- 
 ture of the ground, at a depth of thirty, or forty, or fifty 
 feet, is always the mean result of the impressions made at 
 the surface during a long series of years ; in other words, 
 
TEMPERATURE. 17 
 
 that whatever be the temperature of the ground at that 
 depth, the same will be the mean temperature of the air at 
 the surface over a number of years. 
 
 The celebrated fountain of Vaucluse, situated in the lati- 
 tude of 43 55', and 360 feet above the level of the Medi- 
 terranean Sea, has been observed to reach its highest tem- 
 perature in September, and its lowest some time in April 
 the former being 56-3, and the latter 54-l, by Fahrenheit's 
 scale, which gives 55'2 for its mean heat ; and this corres- 
 ponds very nearly indeed with the mean temperature of the 
 place. Hence we may conclude, that however the weather 
 may have varied from year to year, or changed its character 
 at intervals of short periods of years, it has yet undergone 
 no material alteration during the lapse of many ages. 
 
 This slow conducting quality of the ground, if not 
 regulated by extraneous influence, would, doubtless, fix the 
 heat where it was received from the solar rays, and cause 
 such an accumulation of heat there as would gradually 
 become insupportable. It is here that the mobility of the 
 atmosphere plays such.a very conspicuous part, as the great 
 regulator of the system, dispensing moderate warmth, and 
 attempering the extremities of heat and cold over the sur- 
 face of the globe. As the heat accumulates within the tropics, 
 it draws in currents of cooler air from the Northern and 
 Southern Poles. And the activity of the winds thus pro- 
 duced, being proportional to their exciting cause, must pre- 
 vent the heat from ever surpassing certain limits. A per- 
 petual commerce of heat between the poles and the equator 
 is thus maintained by the continuous agency of opposite 
 atmospheric currents. These currents often have their direc- 
 tion modified ; but they will still produce the same effects, 
 only a little more slowly, by pursuing an oblique or devious 
 course. For the actual phenomena of climate only require 
 the various winds throughout the year to advance south- 
 
18 TEMPERATURE. 
 
 wards or northwards, at the mean rate of about two miles 
 an hour, and they will, in effect, perform three journeys of 
 transfer annually from the equator to either pole. 
 
 Not, observe, that these currents carry the impressions 
 of heat or cold directly from one extremity of the globe to 
 another, but by their incessant play they contribute, in the 
 succession of ages, to spread them gradually over the inter- 
 vening space. 
 
 These deductions are confirmed by the results of the 
 nicest astronomical observations. Any change in the tem- 
 perature of our globe would occasion a corresponding 
 change of volume, and consequently an alteration in the 
 momentum of the revolving mass. Thus, if from the ac- 
 cession of heat the earth had gained only the millionth part 
 of linear expansion, it would have required an increase of 
 five times proportionally more momentum to maintain the 
 same rate of rotation. And, on this supposition, the diur- 
 nal revolution would have been retarded at the rate of three 
 seconds in a week. But the length of the day has certainly 
 not experienced a variation of even two seconds in a year, 
 since the age of Hipparchus (B.C. 140) ; for we cannot imagine 
 that the ancient observations of eclipses could ever deviate 
 an hour from the truth ; and this would be about the 
 amount of deviation in 2000 years, supposing two seconds 
 to be the amount of deviation in each year. So that we 
 may well believe that, at the end of 2000 years, the mass of 
 our globe has not acquired even the ten-millionth part of 
 expansion, an effect which would have been brought 
 about by the smallest fraction of a degree of extra heat. 
 And conversely, by the same argument, we cannot suppose 
 that the earth has experienced any, the slightest, decrease of 
 its mean temperature. 
 
 But though there be this general uniformity of tempera- 
 ture at any one place, when we take the mean of centuries, 
 
THERMOMETER. 19 
 
 yet the difference is very great between two days in different 
 parts of the same year. Even in the mild climate of Great 
 Britain, the thermometer will range frorh 92, or even 95, 
 down to 12, or 44 below freezing, making a difference of 
 more than 100 (Fahr.) And as it is upon this excess or defect, 
 above or below the mean temperature, that the violence of 
 our gales mainly depends, the subject is a study possessing 
 more than a curious interest, affecting, as it does, the com- 
 merce of a great nation, and the safety of so many precious 
 lives, occupied in traversing the treacherous deep ; and to 
 the farmer and amateur gardener the wisdom taught by 
 thermometer, as well as barometer, is surely worth the pains 
 of acquiring, when the outlay is little more than an outlay 
 of patience, to record the changes, as they occur from clay 
 to day, and the mode in which dame Nature always con- 
 trives to recover her lost ground, sometimes creeping up 
 like the tortoise, sometimes bounding forward like the hare. 
 
 THERMOMETER, 
 
 Mr Lowe tells us that " the first object of an observer 
 should be to procure good instruments, and then to place 
 them so that they may not be affected by any local circum- 
 stances, such as heat from a fire, draughts in a passage, 
 dripping of rain, or radiation and reflection from walls 
 adjacent, &c." 
 
 " Much time is often lost by the discovery that we have been 
 using imperfect instruments, or good ones badly placed." 
 
 "In most cases the common cheap thermometers are 
 utterly valueless and unreliable as meteorological instru- 
 ments. Mr Hartnup, of the Liverpool Observatory, men- 
 tions that among the thermometers used by the captains 
 of the merchant service, an error of 4 or 5 is quite 
 common ; even a thermometer fitted up for taking the 
 
20 THERMOMETER. 
 
 temperature of water at different depths, and professing to 
 have been made with care, was found to be more than 8 
 in error at one part of its scale." Mercurial thermometers 
 are by far the best. 
 
 The smaller the bulb the more delicate will be the re- 
 sults ; and the finer the bore of the tube, within certain 
 limits, the wider will be the degree marks. 
 
 A large tube for the barometer, a small tube for the 
 thermometer, are standing rules. 
 
 Equally in both instruments, it is essential for accuracy 
 that the tube be equal in bore throughout, or the column 
 will expand unequally in some parts of the scale. 
 
 The fitness of a tube for a thermometer is tested (before 
 filling the instrument) by putting a little mercury into the 
 empty tube, and ascertaining, with the compasses, whether 
 this quantity of mercury occupies the same space when 
 shifted into various parts of the tube. 
 
 If we lived in arctic regions, where the mercury is often 
 frozen solid, we should be compelled to resort to the use of 
 thermometers filled with alcohol, which never freezes. 
 But where the cold seldom reaches even 10, and never 30 
 or 40 below zero, it is on many accounts better to use the 
 substance most to be relied on, and that substance is 
 mercury. 
 
 . We can form scarcely any adequate notion of the intense 
 severity of the frost in an arctic winter, a severity which 
 lasts, not for a few hours only, but for weeks together. Dr 
 Kane, who was one of a relieving expedition in search of 
 Sir John Franklin, says " that on the 5th of February 1854, 
 the alcoholic thermometers indicated the terrible tempera- 
 ture of 75 below zero, or 107 below the freezing-point of 
 water ! At such temperatures chloric ether became solid, 
 and carefully prepared chloroform exhibited a granular 
 pellicle on its surface. Spirit of naptha froze at 54, and 
 
THERMOMETER. 21 
 
 oil of sassafras at 49, below zero. The exhalations of 
 insensible perspiration, from the surface of the body; in- 
 vested the exposed or partially clad parts with a wreath of 
 vapour. The air had a perceptible pungency upon inspira- 
 tion, and, when breathed for any length of time, it imparted 
 a sensation of dryness to the air-passages, inducing the men 
 to breathe guardedly and with lips compressed." In such 
 temperatures alcohol is the proper fluid for a thermometer, 
 as it will not freeze, even when subjected by chemical pro- 
 cess to a temperature of 166 below zero, or nearly 200 
 below the freezing-point of water. 
 
 The objections to the ordinary spirit thermometer, when 
 it can be dispensed with, are that the spirit is apt to vola- 
 tilise or float in vapour towards the vacuum end of the 
 tube, so lessening the quantity of spirit in the bulb ; this 
 especially takes place when the temperature is high. The 
 spirit is also less quickly affected by rapid changes of the 
 temperature, so that it often fails to record the true maxi- 
 mum or minimum of the twenty-four hours. And it does 
 not expand quite equally, for equal increments of heat at 
 different temperatures ; this, however, is only a minor 
 objection, as its expansive action does not differ materially 
 from that of mercury, except under a greater heat than 
 ever occurs in climatic observations. 
 
 Supposing, then, that we determine to employ a mercurial 
 set of thermometers, as we cannot be continually on 
 the watch to note the maximum and minimum of each 
 day, we must have two instruments, at least, which will 
 register, the one the maximum and the other the minimum. 
 Such registering instruments, if really good ones, will cost 
 about L.I each, or three times the price of the common 
 registering thermometers. This extra expense will not be 
 grudged by any one who really takes an interest in meteor- 
 ology, the chief element in which is accuracy. If such 
 
22 THERMOMETER. 
 
 registering thermometers are obtained direct from Negretti, 
 or from Casella, in London, or from Adie, in Princes Street, 
 Edinburgh, and if they warrant them as tested and approved, 
 they may be fully relied on. 
 
 Solar and Terrestrial Radiation Thermometers. These, 
 again, should also register, the solar as a maximum, and the 
 terrestrial as a minimum, the former to be placed with 
 a due south aspect, full in the sun's rays, the latter in any 
 open spot, on the grass. Botli these instruments should 
 be made, scale, frame, and all, of glass or porcelain, 
 which will not swell with damp, nor lose their scale-marks, 
 as those do which have their scales engraved on wood. 
 
 Wet and Dry Bulb Thermometers. These belong to the 
 hygrometer, and will be explained later on, under the head 
 of " Hygrometer Dew-point." 
 
 Eules and examples may now be given for finding 
 
 (I.) The Mean of the Day's Temperature. 
 (II.) The Amount of Solar Eadiation. 
 (III.) The Amount of Terrestrial Eadiation. 
 
 To find the Day's Mean Temperature. Add together the 
 shaded maximum and shaded minimum, and divide the sum 
 by 2, thus 
 
 Max. 45 + min. 31 = ^ = 38 (Day's mean) ; 
 2 
 
 93 
 or, Max. 58 + min. 35 ^ = 46-5 (Day's mean). 
 
 To find the Amount of Solar Radiation. Subtract the 
 maximum in the shade from the maximum in the sun ; 
 then the amount of difference will be the amount of solar 
 radiation, thus 
 
 Solar max. 85 - shaded max. 47 = 38; 
 . . 38 is the amount of solar radiation. 
 
THERMOMETER. 23 
 
 To find the A mount of Terrestrial Radiation. Let there 
 be one minimum on the grass not shaded, and another 
 about 4 or 5 feet above the ground, and in the shade ; sub- 
 tract the minimum on the grass from the minimum in the 
 shade, thus, 
 
 Shaded min., 28-grass inin., 21=7 (terrest. radiation) 
 or, 31- 30=1 
 
 or, 27- 27- 
 
 If the night be very cloudy, the terrestrial radiation will be 
 little and sometimes nothing. 
 
 We must, therefore, have seven thermometers for all the 
 observations, viz., for the barometer-room for the maxi- 
 mum in the sun for the maximum in the shade for the 
 minimum in the shade for the minimum on the grass 
 and two combined, as dry and wet bulbs, for the hygrometer. 
 All but the two last-named should be self-registering. 
 
 The only thermometers that ought ever to be exposed, 
 either to the sun or the rain, are those for finding the maxi- 
 mum in the sun, and the minimum on the grass ; this 
 brings us to consider 
 
 The lest Position for the Thermometers. The shaded 
 maximum and minimum thermometers, for finding the daily 
 mean temperature, and the wet and dry bulbs (hygrometer), 
 should occupy the same spot, about four or five feet above 
 the ground, and facing due north. The north side of a high 
 strong wall, running east and west, will be a good position. 
 First of all, a broad wooden board should be firmly secured 
 to the stone or brick wall, as a kind of lining to the wall, 
 and having small projecting screws, on which to hang 
 the instruments. Next, to keep off rain, a kind of roof 
 should be placed a foot or more above the instruments, slant- 
 ing outwards and downwards from the wall. Then, again, 
 projecting sides of wood should be placed, east and west, 
 
24 THERMOMETER. 
 
 to keep oft' the rising and setting summer's sun, and they 
 should be bored with a dozen holes or more, of half an inch 
 diameter, for the passage of air. 
 
 The whole of this wooden enclosure should be very firm, 
 so as to prevent vibration in stormy weather ; arid, at the 
 same time, so contrived that there may be free ventilation. 
 It will preserve the wood, and be less unsightly, if the 
 whole is painted white. A small button of wood is also 
 desirable, to press the lower part of each instrument to the 
 wooden frame at its back ; this will prevent any shifting of 
 the maximum and minimum in windy weather. 
 
 The Solar-radiation thermometer should be blackened, 
 as to its bulb, with lamp black, so as to absorb the sun's 
 rays. It may be hung just outside a south window, with 
 its face turned to the full action of the mid-day and 2 P.M. 
 sun. It should be mercurial and self-registering ; but the 
 ordinary maximum will not do, unless its scale reaches 
 higher than 130, as the intense heat of a July sun may 
 burst the glass, in the effort of the mercury to expand above 
 130. The observation of this solar glass, for each day, 
 may be taken any time towards evening, so as to be entered 
 in the Meteorological Day-Book, in a column close beside 
 the column for the minimum on the grass, which latter 
 should be noted at 9 A.M, of that same day. 
 
 Never change the Position of the Instruments. When 
 once satisfied that the position is a tolerably good one, 
 make no change. It is astonishing what a difference may be 
 produced by this shifting from one set of local circum- 
 stances to another enough to upset entirely any exact 
 comparison between one day, or even one week, and an- 
 other. 
 
 Daily Hour of Observation. Excepting the solar maxi- 
 mum, every instrument should be examined and recorded 
 at 9 A.M., viz., the barometer, thermometer, hygrometer, 
 
THERMOMETER. 25 
 
 and rain-gauge. A second observation of the barometer, 
 at 10 P.M., will give the day's true mean more nearly ; but 
 It is not essential. The observer should be very punctual 
 to the hour of 9 A.M., and not indifferently half an-hour 
 earlier or later. This hour (may we call it breakfast-time ?) 
 is the one least likely 'to be interfered with by the avoca- 
 tions of the day or absence from home ; it is the hour by 
 which, at the latest, every well-behaved member of society, 
 of every rank, will be (health permitting) awake and 
 visible. Those who think it too early to be out of their 
 bedroom at 9 A.M. all the year round, had better give up 
 meteorology as a study, or even as a pastime. 
 
 Manner of Observing. In reading off the thermometers 
 be speedy, so that the human body may not warm them ; 
 and be careful not to breathe on them. The observer will 
 find it convenient to make up a small manuscript book of 
 twenty pages, and rule them for the entries belonging to 
 each instrument. This will serve to take down the observa- 
 tions of ten days or more, on each page, roughly, but accu- 
 rately and quickly ; and they can, at the observer's leisure, 
 be copied neatly into the general day-book of larger size, 
 which he keeps for the daily, weekly, and monthly means 
 of many years, and which should be a large quarto, strongly 
 bound.* 
 
 Above and below Zero. The thermometer sinks below 
 zero very rarely in Great Britain, perhaps once or twice in 
 seven or eight years. Above zero may be written down as 
 + (plus), or the sign may be omitted, as it generally is : 
 thus + 7, or 7 means seven degrees above 0, or zero. 
 But if you wish to record a point below zero, the sign 
 
 * Forms for recording the various observations, each sheet to serve 
 for a whole month, may be obtained for a few shillings from Casella, 
 and after the observer has had a year's practice with them, he will be able 
 to rule his own after the same manner. 
 
 B 
 
26 THERMOMETER. 
 
 (minus) must be prefixed, or it will be mistaken for a point 
 above zero. 
 
 Decimal notation. In all calculations, give the fractional 
 parts in decimals, thus : Never write 29J, or 29f for the 
 barometer, but 29'50, or 29*75 ; and similarly for the ther- 
 mometer, 44 0> 5, and not 44|. Yet, as a rule, it will be 
 simpler to omit the decimal, in recording the thermometric 
 maximum or minimum, and simply record the last whole 
 degree, which the mercury has just passed or reached, at the 
 feame time giving the decimal for the mean of the two, 
 which will thus be invariably half a degree, when any. 
 This plan will be found sufficiently accurate for the mean 
 of a whole week, though it may be a little above that of 
 one day and below that of another. For example, say that 
 the real maximum and minimum of the day are 47'4 and 
 36-3, we may state them as 47 and 37, whose mean is 42. 
 Or, again, 49'6 and 37'2 we may call 49 and 38, whose 
 mean is 43 0> 5. So that there will never be any fraction 
 in the stating of the maximum and minimum ; and the 
 fraction, in the statement of the mean, will always be '5, 
 if any at all. It will keep the book-columns of maximum 
 arid minimum more clear, and there will be less chance of 
 error in striking the mean of the two ; whilst any number 
 of fives, in the column of the day's mean, can be run up 
 very quickly. This, however, is all a matter of fancy, if 
 the observer feels that he is in no danger of making mis- 
 takes ! 
 
 Occasional testing of the thermometers. " From time to 
 time thermometers should be compared with a standard 
 instrument of acknowledged accuracy, in order to see if the 
 scale mark of freezing is correct ; because it is well known 
 that the zero point moves forward after high summer tempe- 
 rature." Mr Lowe and others assign a different cause for 
 this shifting of the zero point, and, therefore, of all the 
 
THERMOMETER. 27 
 
 marks on the scale. They suspect 'that it is not due to 
 thermal expansion of the mercury, but to a slight contrac- 
 tion of the tube and bulb, under continuous atmospheric 
 pressure, and they recommend that the thermometers 
 should remain for a few months (or years ?) filled, but not 
 graduated. Whatever be the cause, the remedy may be 
 found by taking off the tube and adjusting it afresh, a de- 
 gree or so below its former position. But it is not worth 
 while to do this, unless the instrument be, in other respects, 
 a particularly good one. It would be less trouble to pur- 
 chase another, and discard the offender. 
 
 Care to be taken for accuracy's sake. Before adding up a 
 week's or a month's column of figures, look it -through very 
 carefully, to see that the figures are in no case transposed, 
 that is, the maximum item put into the minimum column, 
 or vice versa, a blunder by no means uncommon, and 
 which the eye will detect afterwards without difficulty. In 
 the same way, the barometer's mean of each day should be 
 examined, before adding up to strike the week's mean ; 
 for it not unfrequently happens that, in an absent mood, 
 the observer writes, say, 2947 for 2847, or for 3047, per- 
 haps because 29 is the number of inches he is most in the 
 habit of recording. This last warning is given under the 
 supposition that the observer records the barometer twice 
 a-day (at 9 A.M. and at 10 P.M.), when a daily mean has to 
 be struck. If he only records once a-day (at 9 A.M.), he 
 will have no such power of correcting an oversight. 
 
 INVENTORS, MAKERS, AND DESCRIPTIONS. 
 
 Rutherford's Mercurial Maximum Thermometer. In this 
 instrument a small steel pin is pushed forward by the mer- 
 cury to its highest point, and left there. It is not neces- 
 sary to say much about this instrument, which is now quite 
 superseded by others on a better principle. Its great draw- 
 
28 THERMOMETER. 
 
 back is that the pin is very liable to be entangled in the 
 mercury by a slight oxidizing of the fluid, when it becomes 
 utterly useless. 
 
 Negrettis Mercurial Patent Maximum. This has no re- 
 gistering pin. A small piece of enamel is pushed into the 
 tube, and secured a little distance from the bulb ; if the 
 thermometer act at once, it will always act correctly. As 
 the temperature rises, the mercury flows over this partial 
 obstruction of the enamel to its highest point ; but it cannot 
 return, the enamel cutting off the return passage ; and so it 
 remains to record the maximum, until the observer has 
 seen it. By turning the bulb end of the instrument down- 
 wards, and giving it a gentle shake, all the obstructed mer- 
 cury will flow over the obstruction into the bulb, or towards 
 the bulb, ready for a future observation. 
 
 Improvement on the above. Negretti has further improved 
 on this idea by dispensing with the enamel and flattening 
 the tube, at the bend near the bulb, until it is so contracted 
 that, though the mercury will flow forward with the pres- 
 sure of expansion, the mere cohesion of the mercury is in- 
 sufficient to cause it to flow backwards ; and so it stands 
 at th highest point reached. As in the former instrument 
 by Negretti, to invert it and give it a slight shake is enough 
 to set it again for another time. It may be regarded as per- 
 fection. 
 
 Phillips' Mercurial Maximum. A small bubble of air 
 detaches a portion of the mercurial column, leaving the de- 
 tached portion to mark the maximum. It is a valuable in- 
 strument, but scarcely equal to Negretti's last invention. 
 
 Casella's Mercurial Maximum. This instrument is con- 
 structed on Phillips' principle, with the air-bubble to de- 
 tach a portion of the mercury. It is sometimes found that 
 these air-bubble thermometers get deranged in travelling, 
 the constant jolting, no doubt, moving the bubble out of 
 
THERMOMETER. 29 
 
 its position. But supposing no such accident has hap- 
 pened in the transfer of the instrument from the maker 
 to the observer, it is still constantly liable to an error of 
 small amount from the following cause : The air-bubble 
 itself will expand and contract at high and low temperatures ; 
 and therefore, though it may be absolutely correct at one 
 given temperature (say at 32) it will read too high and 
 too low at 70, and at zero, respectively. Happily the 
 error will scarcely ever amount to more than a single de- 
 gree either way. All Casella's thermometers have this ad- 
 vantage, that they are mounted on small porcelain slabs, 
 which preserves them from swelling like wood, or expand- 
 ing and contracting like metal. This is a most important 
 consideration, in the case of the minimum to be placed on 
 the grass, and the solar maximum. But the most remark- 
 able instrument for thermal purposes is Casella's Mercurial 
 Minimum, which will be noticed presently at some length. 
 
 For a long time, it seemed quite impossible to construct 
 a thoroughly good mercurial minimum; and, consequently, 
 the alcoholic minimum has hitherto been in most general 
 use, the chief objections to which have been alluded to 
 already. But very lately Xegretti and Casella have each 
 of them offered a mercurial minimum which professes to 
 act perfectly. 
 
 Ncfjrettis New Mercurial Minimum retains the old steel 
 pin, but, being pointed, it penetrates a short distance into 
 the mercury, and, adhering to the mercury, falls with it to 
 the lowest point to be indicated. AVhen the temperature 
 rises, the mercury flows past the steel pin, pressing it firmly 
 to the side of the tube, so that the minimum record remains. 
 It is said that this invention is a valuable one ; but I have 
 not seen it, and therefore cannot say by what means the 
 observer is able to bring the steel pin to the surface of the 
 mercury again, to be ready for a future observation ; possibly 
 
30 THERMOMETER. 
 
 it is effected, as formerly, by a magnet, though the fact that 
 the pin must often be covered by the mercurial fluid seems 
 opposed to this idea. The old objection of entanglement 
 of the pin, through the oxidising of the mercury, seems to 
 have been guarded against by some process, perhaps that of 
 enamelling. 
 
 Casellas Mercurial Patent Minimum. The difficulty 
 has always been to discover some means by which the 
 mercury itself might be detained at the minimum point, 
 until observed. 
 
 In various experiments conducted by Mr Casella, it 
 occurred to him that the adhesive property of mercury for 
 glass in vacuo, together with the fact, that where a large 
 and a small tube are united in one bulb, the fluid will rise 
 by expansion in the larger tube, and recede by contraction 
 in the smaller tube, might enable him to attain the end 
 in view. The result is the invention of probably the first 
 instrument known to register past indications of a low tem- 
 perature, without having or forming any separate index, or 
 in which the adhesive property of mercury for glass, as a 
 fixed point, has ever been employed. The general form 
 and arrangements are seen in the whole sketch, and more 
 clearly in the enlarged section of the bend and chamber 
 which accompany this description, d ... d is a tube with 
 large bore, at the end of which a flat glass diaphragm is 
 formed by the abrupt junction of the small chamber a &, 
 the inlet to which at b is larger than the bore of the indi- 
 cating tube c. The result is, that on setting the thermo- 
 meter for the next observation, in the manner to be de- 
 scribed presently, the contracting force of the mercury, in 
 cooling, withdraws the fluid down the small indicating 
 stem c only ; whilst, on its expanding with heat, the long 
 slender column c does not move, because the increased 
 bulk of mercury finds for itself an easier passage, namely, 
 
THERMOMETER. 
 
 31 
 
 through the larger bore, and into the small pear-shaped 
 chamber a, I. 
 
 To set the instrument, place it in a horizontal position, 
 suspended to a nail by the back plate E, and with the lower 
 part resting on a pin or hook at F. The bulb end may 
 now be gently raised or lowered, causing the mercury to 
 flow slowly, until the chamber a b is quite empty, and the 
 bent part d . . . d is full. At this point the flow of mercury 
 
 in the long slender stem c is arrested by adhesion to the 
 diaphragm (b), and indicates the exact temperature of the 
 bulb, or air, at the time the observer is setting the instru- 
 ment. On an increase of temperature, the mercury will 
 expand, as before explained, into the small chamber a b ; 
 and a return of cold will cause its recession from tlie chamber 
 only, until it reaches the diaphragm b, at which point it 
 was set. Any further diminution of heat withdraws the 
 mercury down the slender graduated stem c, to whatever 
 degree of cold it may attain, where it remains until further 
 withdrawn by increased cold, or until the observer re-sets 
 it. There is no separation of the mercury, in any of its 
 indications, nor in the operation of setting ; and the maker 
 declares that no changes of climate or transit can derange it. 
 
32 HYGROMETER DEW-POINT. 
 
 This mercurial minimum thermometer may be considered 
 the most valuable addition to our already admirable set of 
 meteorological instruments that could have been desired. 
 
 HYGROMETER DEW-POINT. 
 
 Atmospheric Moisture. The atmosphere, in the very 
 driest weather, is never really dry, nor at all near being 
 quite dry. Even when the air seems to be very parching, 
 drying the skin, and withering vegetables, it can be 
 shown, by chemical agents, that aqueous moisture is 
 present. Indeed, without it, we know that neither vege- 
 table nor animal life could be supported. Even when the 
 air approaches dryness very remotely, as in a close room 
 heated by a stove and pipes, breathing becomes painfully 
 oppressed, and there is a sensation of nervous restlessness. 
 Whilst, if an open dish filled with water be placed on the 
 stove, the rapid evaporation, visible or invisible, will quickly 
 remove many of the unpleasant sensations. 
 
 Various instruments have been invented to indicate any 
 lack or excess of the atmospheric moisture. It is on this 
 hygrometric principle that the German toy acts, in which a 
 miniature man comes out in wet weather, and a woman in 
 dry. The two toys (male and female) are made to swing 
 easily on a pivot, and the expansion or contraction of a fine 
 piece of catgut, attached to them, regulates their move- 
 ments. Thus the catgut is a kind of hygrometer, or rather 
 hygroscope, indicating the presence of moisture, though not 
 the amount. The human hair is also an indicator of mois- 
 ture, as when a lady's curls droop, lank and untidy, in very 
 damp weather. 
 
 Invisible Aqueous Vapour. Now this moisture in the 
 air will remain suspended as invisible vapour, so long as it 
 does not exceed a certain quantity for a certain tempera- 
 
HYGROMETER DEW-POINT. 33 
 
 ture. Raise the temperature, and the air will sustain more 
 moisture ; lower the temperature, and the air will sustain 
 less moisture. Consequently, a hot summer day will often 
 give absolutely more moisture than a cold winter's day ; 
 though, judging by our mere sensations, we may think the 
 opposite to be the case. 
 
 When the air is so filled with moisture that it can sustain 
 no more *at that temperature, it is said to be " saturated" 
 When in this condition, let the temperature fall a few 
 degrees (say) from 57 to 51, then the air being unable to 
 sustain its now superabundant moisture, some must fall to 
 the ground, in the shape of rain or heavy dews. And if it- 
 be winter time, and the change of temperature has been 
 (say) from 36 to 28, then the deposit will take the form 
 of hail, snow, or hoar-frost. 
 
 Conversely, if the air be saturated at 50, and the tempe- 
 rature rises a few degrees, the air will no longer be satu- 
 rated. Hence complete saturation depends on temperature 
 as well as on the absolute amount of moisture in the air. 
 Thus it is that a damp morning is often succeeded by a 
 fine and comparatively dry day, the temperature rising ; 
 and a damp afternoon is followed by rain or snow in the 
 early part of the night, the temperature falling. 
 
 Now the mere appearance of the sky, even with a know- 
 ledge of the temperature and direction of the wind, will not 
 tell us for certain whether rain is probable or not. What 
 we want, to convert our guesses into something like cer- 
 tainty, is some instrument, or combination of instruments, 
 which shall tell us how near the air is to a state of com- 
 plete saturation at a given temperature. We shall then 
 know, at once, what will be result of any change in the 
 temperature. 
 
 The Hygrometer-ly-Dew-point is the instrument required. 
 This is sometimes called a psychrometer, or "cold-measurer," 
 
 B2 
 
34 HYGROMETER DEW-POINT. 
 
 the fitness of which title we shall presently discover, in de- 
 scribing the instrument and its mode of action. 
 
 The Dew-point Hygrometer of Daniell. If a wine bottle 
 be brought from its cellar, it will often be found to be 
 covered with moisture; and in proportion as the air is 
 more or less saturated, so will the depression of the tempe- 
 rature (at which this moisture begins to be deposited on 
 the cold bottle), be less or more ; that is, more moisture, 
 then less depression of temperature, at the deposit-point ; 
 and vice versa. The degree of temperature at which mois- 
 ture begins to be deposited in this way, is called the " Dew- 
 point, "and hence the name of Hygrometer Dew-point given 
 to the instrument invented by Daniell. 
 
 It consists of a doubly-bent exhausted glass tube, each 
 end terminating in a bulb. One bulb is covered with a 
 thin coating of gold or platinum-foil, the other with a thin 
 linen rag. The foil-coated bulb is partly filled with ether, 
 and holds a small thermometer, the graduated stem of 
 which passes up the hygrometer tube, and can be read 
 through it. If now, good ether be dropped on the rag- 
 covered bulb, speedy evaporation ensues, and the bulb is 
 cooled, thereby condensing the vapour of ether, which had 
 floated into it from the ether-filled bulb, and permitting a 
 new evolution of vapour from the ether in the bulb. This 
 evolution of ether cools the bulb, and causes dew to be de- 
 posited on its outer foil-coated surface. 
 
 Explanation of the above experiment. In proportion as 
 the temperature of the air is elevated will it be capable of 
 sustaining more moisture ; and on the contrary, by cooling 
 the air, its power of carrying its moisture is diminished, and 
 a portion of the moisture is condensed, on any cold body 
 near in the form of dew-vesicles. If the air be very moist, 
 condensation will take place quickly and largely, without any 
 great lowering of the temperature of the foil-coated bulb. 
 
HYGROMETER DEW-POINT. 35 
 
 This dew-point hygrometer of Daniell, though a great 
 advance beyond the earlier rude experiments, is not quite 
 satisfactory. Its construction has been improved upon by 
 Doberemer, and by Kegnault ; but it still leaves much to 
 be desired. It demands a plentiful use of good ether, which 
 is expensive ; and in very dry weather it is difficult to ob- 
 tain the dew-deposit, the alternate processes of evapora- 
 tion and condensation not taking place rapidly enough to 
 lower the temperature of the foil-coated bulb to the point 
 of dew deposit. 
 
 PsycJirometric Hygrometer. This compound term, though 
 slightly pedantic, expresses the mode of action and results 
 obtained by it, as the " Cold-measuring moisture-measurer!' 
 It consists of two good equal thermometers, mounted on the 
 same frame of wood, six inches wide by twelve inches 
 long, or thereabouts, the bulb of one thermometer being 
 naked, whilst the bulb of the other is wrapt in some thin 
 absorbent covering, such as a little muslin bag, with a kind 
 of wick reaching from it into a small cistern of water, such 
 as a small preserve-pot, or a short-necked bottle. 
 
 For the instrument to act truly, great care should be 
 taken to choose two thermometers, which correspond 
 exactly, degree for degree, from about 15 up to 90. This 
 is not at all an easy matter, for thermometers vary in 
 the most tiresome manner, even when both are superior 
 instruments. Both the bulbs (naked and covered, or 
 " dry " and " wet,") should project an inch or two, clear all 
 round, below their frame, for the action of the air to be 
 exerted on them more perfectly. The little cistern of water 
 should be suspended, so that the surface of the water may 
 be from one to three inches away from the bulb, to which it 
 is connected by the wick, and it should be placed on the 
 side farthest from the dry bulb, so that its evaporation may 
 not affect the dry bulb, as well as the wet bulb. 
 
36 HYGROMETER -DEW-POINT. 
 
 Mr Glaisher's remarks. " The water-vessel, or cistern, 
 should always be supplied with rain water. If the tempe- 
 rature of the air (i. e., the dry bulb) should have descended 
 below 32, it will often happen that the wet-bulb thermo- 
 meter will for a time read higher than the dry bulb. Such 
 observations must not be recorded ;. but when the water sur- 
 rounding the wet bulb has begun to freeze, the proper read- 
 ings will take place. 
 
 " In frosty weather, the water in the reservoir will be 
 frozen ; but this is no reason for ceasing the observations, 
 for if the water on the muslin be frozen too, the readings 
 are perfectly available. 
 
 " If the muslin be found dry, it should be wetted with a 
 brush or small sponge, and then be left a little time for the 
 water on the muslin to be frozen ; and when satisfied that 
 such is the case, the observer may proceed to take the 
 readings in the usual way. 
 
 " Unless this caution be attended to, the wet bulb will 
 read as high, or higher than the dry bulb. When the 
 weather is frosty, the muslin should be thoroughly wetted 
 some time (say an hour) before the usual and chief hour of 
 observation ; and, as a rule, it is desirable, in frosty weather, 
 to immerse the wet bulb and its conducting wick in water, 
 so as to secure their having a good soaking, after every ob- 
 servation, ready for the next time. 
 
 " If the temperature should have ascended above 32 
 (in frosty weather) immerse the wet-bulb thermometer in 
 warm water for a minute or so, that any ice remaining on 
 the muslin may be melted. Unless this be attended to, 
 the wet-bulb thermometer will continue to read 32, so 
 long as any ice remains iii contact with it. 
 
 " The cotton lamp-wick should first be washed in a solu- 
 tion of carbonate of soda, and well pressed, whilst under 
 water, throughout its length. 
 
HYGROMETER DEW-POINT. 37 
 
 " The amount of water supplied to the muslin can be 
 regulated, according as the wick is of greater or less length, 
 from the bulb to the water ; about three inches is a good 
 medium interval between the bulb and the water surface. 
 
 " The observer must carefully abstain from breathing 
 on the thermometers, at the moment of recording their 
 respective readings." 
 
 The muslin and wick should so act as, by capillarity, to 
 keep the wet bulb always wet, but not actually dripping, so 
 that rapid evaporation may be constantly going on.* 
 
 The more the dry bulb is elevated in temperature above 
 that of the wet bulb, the less is the amount of moisture 
 in the air, in proportion to the temperature of the air, 
 and vice versa. The process of evaporation lowers the 
 temperature of the wet bulb, beneath that of the dry bulb, 
 either by some whole degrees, or some decimal parts of 
 a degree. 
 
 If the two thermometers correspond exactly, when both 
 of them are dry, they can never stand alike, when one 
 of them is wetted, except when the atmosphere is so com- 
 pletely saturated, that it can take up no more moisture. 
 In this condition of the air, the dry bulb is really as much 
 wetted by the surrounding air, as the wet bulb is wetted 
 by the surrounding moistened muslin. The thermo- 
 metric variation of the hygrometer is therefore said 
 to be in an inverse ratio to the amount of atmospheric 
 moisture. 
 
 But now, supposing we find the dry bulb standing at 
 41, and the wet bulb at 38, we see that there is a differ- 
 ence of 3 degrees, but we cannot tell yet what is the true 
 point of dew deposit. To know this, we must discover some 
 formulas or tables, which will show us that 
 
 * The little muslin bag and its cotton \vick, should be changed about 
 once a month. 
 
38 HYGROMETER DEW-POINT. 
 
 When the dry bulb is at 41, 
 And the wet bulb is at 38, 
 The true point of dew deposit is 34 0< 2. 
 Such tables have been constructed for us by men who have 
 spent years in experimenting, for the purpose of devising 
 such a set of factors for the dry bulb, as, when multiplied 
 by the difference between the dry and wet bulbs, will give, 
 as their results, the same dew-point, as that which can be 
 found (so expensively and wearisomely) by direct observa- 
 tion, with Daniell's Ethereal Hygrometer. 
 
 Speaking of the Table of Factors, which will be given 
 presently, Mr Glaisher says : " The numbers in this table 
 have been found from the combination of all the simulta- 
 neous observations of the dry and wet bulb thermometers, 
 with Daniell's hygrometer, taken at the Eoyal Observatory, 
 Greenwich, from the year 1841 to 1854, with some obser- 
 vations, taken at high temperatures in India, and others 
 taken at low and medium temperatures at Toronto. The 
 results at the same temperatures were found to be alike at 
 these different places ; and, therefore, the factors may be 
 considered as of general application." 
 
 This method, by the use of factors, is called " Finding 
 the dew-point by calculation" The other method, with 
 ether, is called, " Finding the dew-point by observation" 
 
 The results obtained from the one are almost always 
 identical with those found by the other. Let us take a 
 specimen, such as Mr Lowe gives in his " Practical Me- 
 teorology." 
 
 By Observation. (Daniell's Hygrometer.) 
 
 Let the temperature of the air be at . 56-0 
 
 temperature of the dew-point when } ,g 
 the ring of dew was deposited . J 
 
 Dew-point (lower than the air) 7'8 
 
HYGKOMETER DEW-POINT. 39 
 
 By Calculation (with Dry-bulb Factors). 
 
 Let the temperature of the air be as before 56 0- 
 
 of the wet bulb be . 52 -0 
 
 Then the calculated dew-point is .48 '2 
 
 Subtract 48-2 from 56'0, and the difference is 7'8 
 
 Thus, there is the same result by both methods. 
 
 The expression " Calculated dew-point," will not be 
 understood by any unlearned reader, until he has mastered 
 the whole plan of factors, which he will find given at 
 length after a few more sentences, when he may return to 
 this point, and see that all is clear. 
 
 The credit of this idea of factors for the dry bulb 
 belongs to Mr Belville, and was first made known to the 
 meteorological world in the " Greenwich Observations for 
 1844." The table which follows is abridged from Mr 
 Glaisher's only in so far as I have given his tenth parts of 
 a degree, and omitted his hundredths. 
 
 Rule for using the Table of Factors. " Multiply the differ- 
 ence between the dry and wet bulbs, by the factor assigned 
 in the table to the dry bulb ; subtract this product from 
 the dry-bulb temperature ; the remainder will be the tem- 
 perature of the dew-point." 
 
 For example, when the dry bulb stands at 51, and the 
 wet at 44, their difference is 7 ; and the factor for 51 be- 
 ing 20; then 7 x 2-0=14-0 ; now, subtract 14-Q from 
 51, there remains 37. 
 
 Therefore, 
 
 When the dry bulb is at . . . 51 
 
 And the wet bulb .... 44 
 
 The temperature of dew-point is . 37 
 
40 
 
 HYGROMETER DEW-POINT. 
 
 TABLE OF FACTORS FOR THE DRY BULB. 
 
 " Factors by which it is necessarg to Multiply the Excess of the Reading 
 of the Dry Thermometer over that of the Moist, in order to find 
 the Excess of the Temperature of the Air above that of the Dew- 
 point -from 10 (Fahr.) upwards" 
 
 Dry 
 
 Bulb. 
 
 Factors. 
 
 Dry 
 Bulb. 
 
 Factors. 
 
 Dry 
 Bulb. 
 
 Factors. 
 
 Diy 
 Bulb. 
 
 | 
 
 
 Dry 
 Bulb. 
 
 Factors. 
 
 Dry 
 Bulb. 
 
 1 
 
 10 
 
 8-8 
 
 
 
 25 
 
 6-5 
 
 
 
 40 
 
 2-3 
 
 
 
 55 
 
 1-9 
 
 o 
 
 70 
 
 17 
 
 85 
 
 1-6 
 
 11 
 
 8-8 
 
 26 
 
 6-1 
 
 41 
 
 2-2 
 
 56 
 
 1-9 
 
 71 
 
 17 
 
 86 
 
 1-6 
 
 12 
 
 8-8 
 
 27 
 
 5-6 
 
 42 
 
 2-2 
 
 57 
 
 1-9 
 
 72 
 
 17 
 
 87 
 
 1-6 
 
 13 
 
 8'8 
 
 28 
 
 5-1 
 
 43 
 
 2-2 
 
 58 
 
 1-9 
 
 73 
 
 17 
 
 88 
 
 1-6 
 
 14 
 
 87 
 
 29 
 
 4-6 
 
 44 
 
 2-2 
 
 59 
 
 1-9 
 
 74 
 
 17 
 
 89 
 
 1-6 
 
 15 
 
 87 
 
 30 
 
 4-1 
 
 45 
 
 2-1 
 
 60 
 
 1-9 
 
 75 
 
 17 
 
 90 
 
 1-6 
 
 16 
 
 87 
 
 31 
 
 37 
 
 46 
 
 2-1 
 
 61 
 
 1-8 
 
 76 
 
 17 
 
 91 
 
 1-6 
 
 17 
 
 8-6 
 
 32 
 
 3'3 
 
 47 
 
 21 
 
 62 
 
 1-8 
 
 77 
 
 17 
 
 92 
 
 1-6 
 
 18 
 
 8-5 
 
 33 
 
 3-0 
 
 48 
 
 2-1 
 
 63 
 
 1-8 
 
 78 
 
 17 
 
 93 
 
 1-6 
 
 19 
 
 8-3 
 
 34 
 
 27 
 
 49 
 
 2-1 
 
 64 
 
 1-8 
 
 79 
 
 17 
 
 94 
 
 1-6 
 
 20 
 
 8-1 
 
 35 
 
 2-6 
 
 50 
 
 2-1 
 
 65 
 
 1-8 
 
 80 
 
 17 
 
 95 
 
 1-5 
 
 21 
 
 7'9 
 
 36 
 
 2-5 
 
 51 
 
 2-0 
 
 66 
 
 1-8 
 
 81 
 
 17 
 
 96 
 
 1-5 
 
 22 
 
 7-6 
 
 37 
 
 2-4 
 
 52 
 
 2-0 
 
 67 
 
 1-8 
 
 82 
 
 1-6 
 
 97 
 
 1-5 
 
 23 
 
 7'3 
 
 38 
 
 2-3 
 
 53 
 
 2-0 
 
 68 
 
 1-8 
 
 83 
 
 1-6 
 
 98 
 
 1-5 
 
 24 
 
 6-9 
 
 39 
 
 2-3 
 
 54 
 
 2-0 
 
 69 
 
 1-8 
 
 84 
 
 1-6 
 
 99 
 
 1-5 
 
 This method of finding the dew-point, by calculation, is 
 speedy and inexpensive (for what can be cheaper than 
 wicks and water ?) ; and, if the instrument is broken, the 
 observer's own ingenuity can quickly supply him with 
 another, at least as a temporary substitute, until he can 
 replace it by one entirely to his taste. 
 
 Diurnal Variation of A tmospheric Moisture. The amount 
 of moisture, present in the air, varies at different times in 
 the day. It attains a maximum twice, and a minimum 
 twice, in the 24 hours, taking one day with another. The 
 first maximum occurs about 9 A.M., the second about 9 P.M. 
 The first minimum is shortly before sunset, the second 
 about 4 A.M. Popularly, the air is said to be most damp 
 
HYGROMETER DEW-POINT. 41 
 
 about sunrise ; and in the sense of dew, or palpable moisture, 
 the idea is correct, because, the temperature being very low 
 at that hour, there is rapid condensation. But at a much 
 hotter period of the day there may be absolutely more 
 moisture than at sunrise ; for the higher temperature causes 
 it to be retained invisibly, and without imparting any sen- 
 sation of moisture. 
 
 Mr Glaisher says, of the hygrometer bulbs, that " the 
 simple inspection of the two thermometers will often afford 
 a better criterion of the weather, and of the probability of 
 rain, than the barometer itself ; regard, however, being had 
 to the time of the day, and of the year, when the observa- 
 tion is made. 
 
 " In summer, when the diurnal range of temperature is 
 great, if in the early morning the difference between the 
 air temperature and dew-point temperature be small, and 
 the rise of temperature during the day be considerable, 
 it is probable that the difference will increase ; and if the 
 temperature of the dew-point at the same time decrease, it 
 is an indication of very fine weather. 
 
 " If, on the contrary, the temperature of both should 
 increase, as the day advances, in nearly equal proportion, 
 rain will almost certainly follow, as the air cools with the 
 declining sun. 
 
 " In winter, when the diurnal range of temperature is 
 small, the indication of the weather is shown by the increase 
 or decrease in the temperature of the dew-point, rather 
 than by the difference between the temperatures of the air 
 and of the dew-point. 
 
 " In showery weather, the indications vary rapidly ; and 
 a person making observations, at short intervals, may pre- 
 dict the approach of a storm, particularly if he take simul- 
 taneous observations with the barometer." 
 
 Monthly Variation of Atmospheric Moisture. "All months 
 
42 HYGROMETER DEW-POINT. 
 
 in the year are not equally moist. In London, at Paris, 
 Geneva, and Great St Bernard, the absolute amount of 
 aqueous vapour is at its maximum in January, and its 
 minimum in July; but the relative maximum, in those 
 places, is in December, and the relative minimum in May." 
 This dictum of the philosophers seems to need some expla- 
 nation, as it implies that the temperature of December is 
 lower than that of January, and of July lower than that of 
 May(?). 
 
 Fluctuations of Aqueous Vapour. It is found that the 
 evaporation of a single day can only raise the dew-point 
 temperature a very little way, so that it is nearly the same 
 at noon as it was the previous night. And as its tempera- 
 ture at night was determined by the lowest temperature of 
 the night air, we have the means of learning pretty nearly 
 the dew-point for any day, by finding the lowest tempera- 
 ture of the previous night. Thus, if the shaded minimum 
 gave the previous night at 36, the mean dew-point tem- 
 perature, for the whole of the next day, will be a little 
 above 36. 
 
 Similarly, the dryness of a day depends on the difference 
 between that day's maximum and the previous night's 
 minimum temperature : Thus, if to-day's maximum be 60, 
 and last night's minimum were 40, the day's mean dryness 
 is very considerable. But if the night's minimum and the 
 next day's maximum temperature be nearly equal, the air 
 of the whole day will approach nearly to complete satura- 
 tion. And so it appears that dryness depends on cold 
 nights being followed by warm days ; and, therefore, one of 
 the most important of the thermometrical observations is 
 the range of the day's temperature. It is often noticed 
 that a warm night is followed by heavy rains ; but an 
 extremely cold night can hardly ever be succeeded by a 
 rainy day. 
 
HYGROMETER DEW-POINT. 43 
 
 Again, if we take the night's shaded minimum and the 
 next day's mean temperature, the difference in amount of 
 vapour sustainable at each will give the average dryness of 
 the day. Suppose, for example, that the night's minimum 
 had been 35, and the following day's mean were 42, 
 then 
 
 
 
 Vapour sustainable at 42 = . . 0-283 (inches), 
 35 = . . 0-222 ( ), 
 
 Therefore, dryness or capacity for more 
 
 moisture =O061 ( ). 
 
 And now let us compare the dryness of a summer's day 
 with that of a day in winter. We will suppose the same 
 range of 20 in each case. Let the summer's day maximum 
 have been 70, and its minimum 50, then 
 
 Vapour sustainable at 70 = . . 0727 (inches), 
 
 50= . . 0-373 ( ), 
 
 (N.B.) Therefore, the extreme dryness of 
 
 the air, = 0-354 ( ). 
 
 Next, let the winter's day maximum have been 50, and 
 its minimum 30, then 
 
 Vapour sustainable at 50 = . . 0'373 (inches), 
 
 30 = . . 0-192 ( ), 
 
 (X.B.) Therefore, the extreme dryness of 
 
 ' the air, =0181 ( ). 
 
 Thus, the extreme dryness of a winter's day is only half 
 that of a summer's day, though the range be 20 in both ; 
 and when we remember that this range of 20 is not un- 
 frequent in summer, and is very rare, indeed, in winter, we 
 may judge what an immense difference there is in the dry- 
 ness of the two seasons. These fluctuations in the amount 
 
44 HYGROMETER DEW-POINT. 
 
 of aqueous vapour are therefore directly dependent on the 
 course of the temperature. As a rule the air is drier at the 
 increase than at the fall of the day and of the year, the 
 morning is drier than the evening, and the spring is drier 
 than the autumn. -In the one case, the temperature is 
 hourly or daily increasing, and leaving the dew-point, as it 
 were, at a greater distance behind it ; in the other case, the 
 temperature is hourly or daily falling, and coming gradually 
 nearer and nearer to the point at which some precipitation 
 of superabundant moisture must take place. 
 
 In his preface to the hygrometrical tables, Mr Glaisher 
 says : " The two thermometers should be delicate and 
 sensitive in the extreme, such as have been made for several 
 years by Messrs ISTegretti and Zambra. These opticians 
 have enabled me, up to the present time, to carry out my 
 idea of the requirements of good thermometers. The in- 
 struments supplied by them are graduated, with the utmost 
 nicety, upon their own stems ; and their bulbs are small, 
 so as to insure sensitiveness. 
 
 " In my recent balloon ascents, I took a series of simul- 
 taneous readings with the dry and wet bulb thermometers 
 and Daniell's hygrometer, for the purpose of determining 
 to what elevation above the sea the dry and wet bulb ther- 
 mometers could be used with confidence. The following 
 are some of the results : The temperature of the dew- 
 point, by dry and wet bulbs, at heights less than 5000 
 feet, was the same as by Daniell's hygrometer, from 73 
 experiments ; at heights between 5000 and 10,000 feet, 
 was 0-1 higher than by Daniell's hygrometer, from 29 
 experiments.; at heights between 10,000 and 15,000 feet, 
 was 2-0 higher than by Daniell's hygrometer, from 3 expe- 
 riments ; at heights between 15,000 and 20,000 feet, was 
 0-5 higher than by Daniell's hygrometer, from 9 experi- 
 ments. The results, therefore, by Daniell's hygrometer, are 
 
HYGROMETER DEW-POINT. 45 
 
 identical with those by the dry and wet bulb thermometers, 
 up to about 10,000 feet. At heights exceeding 10,000" feet, 
 the dew-point was somewhat lower by Daniell's hygrometer 
 than by the dry and wet bulb thermometers, but at those 
 heights the temperature was very low. 
 
 " The general result, from all these experiments, is that 
 the dry and wet bulb thermometers may be used with con- 
 fidence up to great heights above the sea-level." 
 
 " Its use in the sick-room. The value of this instrument 
 in a sick-room will be at once obvious to those who know 
 that the comfort of the patient often depends quite as 
 much on the hygrornetric state of the air in the room, as 
 on its temperature. If the air in an apartment be too dry 
 (that is to say, if the difference between the readings of 
 the dry and wet bulbs be as much as 12, or even more, 
 it may be remedied by placing on a table in the room 
 some broad, shallow vessel, such as a small tea tray, partly 
 filled with water, when evaporation will gradually give the 
 air a pleasant and healthy degree of moisture ; or a pan of 
 boiling water, open and steaming, will produce the same 
 effect far more speedily. If, on the contrary, the room's 
 atmosphere be too damp, it may be corrected either by 
 raising the temperature considerably with a larger fire, 
 or (if this appear to the medical men not advisable) by 
 placing a small open vessel, partly filled with sulphuric 
 acid, or any other medium capable of rapidly absorbing 
 moisture. 
 
 " The dry and wet bulbs will serve as a guide either way. 
 The bulbs should be so placed that neither the fire nor 
 draughts may produce partial or local effects upon them. 
 A difference of 7 or 8 between the two bulbs will be 
 found to give a very pleasant sensation of healthy 
 moisture. 
 
 "Its use in greenhouses and hot-houses. It does not follow, 
 
46 THE RAIN-GAUGE. 
 
 because the temperature is kept at the proper height, that 
 the air will be conducive to healthy growth ; for it may be 
 far too dry. A large shallow tank, with a sliding lid, to 
 uncover more or less surface of water, as required, will re- 
 medy this dry ness ; and the dry and wet bulb thermo- 
 meters will enable the gardener to regulate the moisture 
 with a very little practice." 
 
 THE BAIN-GAUGE. 
 
 There are several constructions of this instrument ; but 
 little need be said about any of them, as they are all good 
 in their way. If the instrument be effective, it is the better 
 for being as cheap, and, therefore, as simple as possible. 
 To be effective, the gauge should be an equal cylinder., 
 whose diameter is always the same from top to bottom. It 
 should therefore have no enlarged rim. at the top, but a 
 sharp edge all round ; or otherwise the diameter, at its 
 uppermost point, will be less than lower down, and so 
 admit less than the true quantity of water. In theory, the 
 edge should be as sharp as a razor, so as to cut in two any 
 drops of rain that fall upon it, in order that no minute 
 splashings from without the area of the gauge may find 
 their way into it. And further, it should be covered in, 
 (funnel fashion) a few inches below the top, a very small 
 hole being left in the centre of the funnel-cover, enough to 
 permit the rain to fall through. A float, with a very 
 slender stem graduated in inches and tenths of an inch, 
 and passing up the aperture, will both record the rain-fall, 
 and partially close the passage against loss by evaporation. 
 Indeed, this arrangement will so reduce the loss by evapo- 
 ration in hot weather, that we may reckon it as "Nil." 
 
 The more complex gauges, of the kind provided with a 
 graduated glass tube at their side, are handsome instru- 
 
THE RAIN-GAUGE. 47 
 
 ments, but far better suited to tropical climates, where frost 
 is unknown. In this country, the frequent frosts of winter 
 will render *the tube very liable to breakage, through an 
 occasional oversight in not emptying the gauge of its con- 
 tents immediately after rain. 
 
 Mr Adie of Edinburgh supplies the Meteorological 
 Society, and the public generally, with a very good gauge 
 at about L.l. 
 
 Complaints are sometimes made that evaporation takes 
 place in hot dry weather through the small funnel aperture. 
 This need not be a serious objection, if observers would 
 only examine their rain-gauge every morning at 9 A.M., and, 
 if rain has fallen, empty it down to zero ; and if they find, 
 in very dry weather, that it is a little below zero at the end 
 of a few days, they may raise the indicating stem to its 
 proper place, at 0, by pouring in a dozen drops from a small 
 watering-can. Of course, if they leave the gauge to take 
 care of itself from week to week, perhaps even for a whole 
 month, evaporation in summer will certainly rob it of a c 
 portion of its proper contents. 
 
 A small brass tap below allows the gauge to be emptied, 
 after the observer has recorded it. The tap is secured from 
 accidents by the protection of the larger cylinder, into 
 which the whole gauge is sunk. This outer cylinder should 
 be sunk in the grass, in any open spot, free from trees or 
 buildings for fifteen or twenty yards clear all round, to such 
 a depth that the rim of the gauge may be about one foot 
 above the ground. 
 
 Those who are interested in the subject of the " British 
 Eainfall," may receive a monthly abstract, and a full annual 
 report, with much varied information, in return for a yearly 
 subscription of ten shillings, by applying to F. Syrnons, 
 Esq., M.D., Camden Eoad Villas, London. 
 
 Snow Measurement. When a wet, sleety kind of snow 
 
48 THE RAIN-GAUGE. 
 
 falls, melting almost as fast as it reaches the ground, the 
 rain-gauge will give the depth of melted snow, just as if it 
 were rain. But if the snow be of a more frosty kind, and 
 lies to any depth, it may happen that the rain-gauge retains 
 only a small part of it, especially if there be any wind ; and, 
 obviously, if the snow amount to six or eight inches, the 
 ordinary rain-gauge, covered in with a funnel, as it should 
 be, is quite useless for purposes of measurement. 
 
 The depth in inches of water may be found in two ways, 
 first, by measuring the depth of fallen snow, in any open 
 spot, with a common foot-rule, and dividing the number of 
 inches by 8, 14, or 20, according as the snow is wet and 
 close dry and frosty or very light and feathery; and, 
 secondly, by lifting a portion of the snow, and measuring 
 after melting it. 
 
 This method is as follows : Take a well-made cylinder, 
 exactly eight inches in diameter, and eighteen inches deep, 
 though the depth is immaterial, provided it be deep enough. 
 Invert it on the snow, in some level place free from drifts ; 
 press it down through the snow to the ground ; if its edge 
 be very sharp, it will not displace the snow much. Then 
 clear away the snow all round, and pass under the cylinder 
 a very thin broad piece of metal. You may now lift the 
 cylinder, " snow and all," and carry it in doors, and melt 
 the snow in the cylinder. Next, pour the water into another 
 smaller cylinder, which is to be exactly four inches diameter, 
 and four inches deep. (The diameter and depth must loth 
 be exact.) 
 
 This four-inch measure, when quite full, will contain 
 exactly one inch of water, as collected in an eight-inch 
 gauge or cylinder. If the melted snow does not quite fill 
 the four-inch measure or, having filled it once, will partly 
 fill it again you may obtain the number of decimal parts of 
 an inch, by plunging to the bottom of the four-inch measure 
 
THE RAIN-GAUGE. 
 
 49 
 
 a little rule, exactly four inches long, and divided into 
 
 one hundred equal parts, as in the accompanying sketch. 
 
 For, as the whole depth of four inches in the little measure 
 
 represents one inch of water, as rain-fall, 
 
 in the larger measure, so each of these 
 
 divisions on the rule represents 0*01 
 
 of an inch. If the 8-inch and 4-inch 
 
 cylinders are accurately made, this 
 
 method of computing the depth of fallen 
 
 snow, in the form of water, may be re- 700( 
 
 garded as the best. 
 
 In melting the snow in the 8-inch 
 cylinder, it will be a good plan to place 
 the cylinder in front of the fire, with the 
 flat piece of metal lying over the mouth 
 of the cylinder, so as to prevent evapo- 
 ration as much as possible. 
 
 If you wish to be quite satisfied that 
 the two cylinders are accurately made, 
 you may do so in the following manner : 
 Pour water into the larger cylinder 
 to the depth of six inches exactly. If 
 the cylinders correspond in their pro- 
 portional sizes, this depth of water in 4o 
 the 8-inch cylinder will fill the 4-inch 
 cylinder six times. 
 
 Variation of Rain-fall. Of all the 25 
 instruments in general use by meteor- 20 
 ologists, there is not one in which lo- 
 cality produces such very different re- 
 sults, even in the same district, as in the 
 rain-gauge. The vicinity of a mountain 
 range adds enormously to the amount of 
 rain-fall. For, though the mountain may occasionally 
 
 
 
 00 
 
 ="" 
 
 80 
 
 E 
 
 u ou in 
 _ 
 
 f- 
 
 0.70 
 60 
 
 E 
 
 in 
 
 f) Kf\ 2 
 
 i 
 
 StO 
 
 = 
 
 
 '""" t at 
 
 = 
 
 20 
 
 E 
 
 0.15 
 n.jn 
 
 = 0. OS 
 
50 THE RAIN-GAUGE. 
 
 divert a passing storm, so that some particular fall of rain 
 or snow may be less at the mountain's foot than at a place 
 some miles distant from it, yet the total rain-fall of a month, 
 and still more of a whole year, will be found to decrease 
 regularly the farther we advance from the lofty range. 
 
 Thus, in some of the rain-gauges stationed near Loch 
 Katrine, more than a hundred inches of rain are recorded as 
 the year's total fall. In the district of Callander, the annual 
 amount of rain is between sixty and seventy inches. At 
 Muthill, near Crieff, the fall averages about forty-three 
 inches. At Colquhalzie, at Auchterarder House, and at 
 Trinity-Cask, it is a few inches less than at Muthill. And 
 when we arrive at Perth, we find that the year's rain-fall 
 there is often not much above twenty inches. 
 
 A glance at the map of Perthshire will show that this 
 decrease of rain-fall, at the places I have named, follows, 
 in regular steps, the increase of distance from the great 
 centres of rain, or the lofty south-western ranges of the 
 county. 
 
 Now, in view of such an unequal distribution of rain, 
 the first thought that naturally occurs to the mind is, that if 
 the land near the hills receives no more rain than is neces- 
 sary for its productiveness, the lands farther away must 
 receive too little ; or, vice versa. And yet it is not so 
 certainly not in these islands because, by the wear and 
 tear of ages, the richest soil, and the soil least requiring 
 frequent showers, is farthest from the mountain side. There 
 are some exceptions, of course, to this wide statement ; but 
 the law is a general one over the whole of those portions 
 of our earth, known as the Temperate Zones. 
 
 On examining the soil of a mountain farm, we find it to 
 be little else than disintegrated rock, reduced to an almost 
 impalpable powder by the action of wind and water, aided 
 by the constant alternations of heat and frost. And what- 
 
FACTS AND THEORIES. 51 
 
 ever of producing power may be imparted to a soil -thus 
 situated, either by the art of man, or by the natural decay 
 of the scanty vegetation around, it is quickly carried through, 
 downwards and forwards, to the lowest level, by the filter- 
 ing of water through the porous stratum, and in obedience 
 to the universal law of gravitation. 
 
 The result is, that the lower lands of the strath, by the 
 alluvial depositions of many ages, have obtained by far the 
 larger share of what we may be allowed to call nature's 
 producing elements. To this must be added the mechanical 
 effects of a low level, in that the water supplied there by 
 rain lies in store, in a kind of subterranean basin, ready to 
 be drawn up again by the evaporating power of the sun, for 
 the support of the vegetable life above ; whereas, in the case 
 of the higher grounds, the frequent fresh supply of water 
 passes rapidly away, by invisible underground channels, to 
 the lower levels. And thus it is that our lowland farms 
 and gardens are rich with healthy verdure, under a con- 
 tinuance of heat and drought which would destroy all high- 
 land vegetation to the very roots. 
 
 FACTS AND THEORIES. 
 
 Classes of Cloud. The clouds were first classified and 
 named descriptively by Luke Howard, the meteorologist. 
 The names were afterwards abbreviated by Mr Glaisher 
 thus 
 
 Ci = cirrus, .... feathery looking, most lofty cloud. 
 Cu = cumulus, . . . mountainous looking. 
 
 , f the ground cloud, forming at sun- 
 
 ot = stratus, . . < i T 
 
 ( set, and disappearing at sun-rise. 
 
 Ci-cu= cirro-cumulus, rounded masses, or woolly tufts. 
 Ci-st= cirro-stratus, . horizontal masses, rather lofty. 
 
52 FACTS AND THEORIES. 
 
 Cu-st cumulo- stratus, layer of cumuli, also lofty. 
 
 xr _ . -, [ the rain-cloud, often seen with the 
 
 ' I stratus. 
 _ i fa broken portion of the nimbus, 
 
 ' ( smoke like, and nearly vertical. 
 
 The stratus of the night often rises into detached cumuli, 
 in fair and warm weather ; and if these (cumuli) go on in- 
 creasing in number and density towards mid-day, thunder 
 may be expected before night. 
 
 The cirrus is seen mostly in fine steady weather. 
 
 The cumulus is for the most part a summer cloud. 
 
 The cirro-cumulus betokens a dry, calm atmosphere. 
 
 The cirro-stratus is often the first visible token of the 
 breaking up of a long continuance of settled fine weather ; 
 it then rises in the eye of the coming wind, and gradually 
 overspreads the heavens with a pall, which grows denser 
 and denser, till rain or snow falls. 
 
 The scud is very partial, often pouring its contents of 
 rain, hail, or snow, on one field, and scarcely even sprink- 
 ling another field, within a distance of a few hundred yards. 
 
 Dark patchy masses, horizontal and detached, a little be- 
 low a curtain of paler cloud, generally betoken heavy rains. 
 
 An entire absence of clouds, with distant objects stand- 
 ing out very sharply against the clear sky, is often the pre- 
 cursor of an easterly fog or drizzle. 
 
 A combination of many of the above classes of clouds is 
 seen occasionally, at one and the same time ; but in general, 
 the day is very plainly characterised by the presence of one 
 class of clouds, to the exclusion of all the other classes. 
 
 Thunder and Gales at the Equinox. It often happens 
 that, in spring and autumn, the character of the coming two 
 or three months is determined, pretty closely, by the equi- 
 noctial disturbances, which precede them. Thus, in April 
 a thunder storm will sometimes change the weather most 
 
FACTS AXD THEORIES. 53 
 
 materially ; if coming up from a westerly or southerly 
 quarter, by introducing moist nights and warm days ; and 
 if coming from the east, by leading the way to a long dreary 
 succession of dry, keen, easterly winds. 
 
 As a rule, the prevailing winds of autumn are from the 
 west, and those of spring from the east ; and when this rule 
 of the seasons is departed from to any great extent, the 
 balance is equalised in the succeeding months. 
 
 Sometimes the weeks, immediately before and after the 
 equinox, pass by almost entirely free from any great atmo- 
 spheric disturbance. When this is the case with the 
 autumnal equinox, the temperature continues higher than 
 usual, until far into the winter months ; and, on the con- 
 trary, a calm spring equinox maintains a very low tempera- 
 ture for many succeeding weeks. The reasons for this are 
 easily perceived, when it is remembered that the one chief 
 cause of high winds is the difference of temperature in vast 
 masses of adjacent air. If this difference be less than 
 usual, the result will be calm, at both the equinoxes, with 
 higher than average temperature in the autumn or early 
 winter months, and with lower than average temperature, 
 in the spring and early summer months. 
 
 The Velocity of Light It was accepted until very lately, 
 as an established fact, that light travels at the rate of about 
 192,000 miles in a second of time. But doubts are now 
 entertained as to whether our earth's mean distance from 
 the sun be, as was formerly thought, 95,000,000 of miles. 
 When the true mean distance between the sun and the 
 earth is determined, we shall, perhaps, be compelled to 
 alter our axiom as to the velocity of light. The difference 
 will not probably be very great a twentieth, perhaps, more 
 or less than we have reckoned it hitherto, or from 184,000 
 to 200,000 miles in a second. 
 
 The Velocity of sound. It has been calculated that, when 
 
54 FACTS AND THEORIES. 
 
 the temperature (?) and pressure of the atmosphere are about 
 at their mean, Sound travels, in an open space, with a speed 
 of about 1120 feet in a second, or about a mile in five 
 seconds. We may thus determine the distance at which a 
 flash of lightning is from us, by counting the number of 
 seconds between the flash and the sound of the thunder. 
 Suppose twenty-five seconds have elapsed, before the thun- 
 der is heard, we may reckon that the focus of that particu- 
 lar flash was distant about five miles from us. 
 
 The Velocity of wind. A light pleasant breeze moves 
 forward at the rate of about 4 or 5 miles an hour ; a fresh 
 breeze at from 10 to 20 miles an hour; a high wind at from 
 30 to 40 miles an hour ; an ordinary storm at about 50 or 
 60 miles an hour ; a raging hurricane at from 80 to 120 
 miles in an hour. 
 
 Hurricanes are chiefly confined to tropical regions, and 
 above all are peculiar to the West Indies. 
 
 Tornado is the term generally applied in speaking of 
 African hurricanes. 
 
 Typhoon is the name given to the hurricanes in the seas 
 around China and Japan. 
 
 The Symoom is the hot desert wind of Africa, Egypt, 
 and Syria. 
 
 The Sirocco is the hot wind of Italy. 
 
 The Mistral is a cold north-eastern wind, which prevails 
 at times in Southern France, and is said to be the most 
 tempestuous wind with which Europe is ever visited. 
 
 The earth's rotary motion from west to east has no doubt 
 some effect in directing the gradual, and apparently circu- 
 lar changes in the direction of all the winds ; but thermal 
 expansion must be considered as the chief cause of any very 
 great aerial commotion. 
 
 TJie Aurora Borealis. We often see near the northern 
 horizon, and usually a short time after sunset, a dark seg- 
 
FACTS AND THEORIES. 55 
 
 ment of a circle, surrounded by a brilliant arch of white or 
 fiery light ; and this arch is again often separated into several 
 concentric arches, leaving the dark segment visible between 
 them. From these arches, and from the dark segment it- 
 self, in northern latitudes, columns of light, of the most 
 beautifully variegated colours, shoot up towards the zenith ; 
 whilst irregular masses, like sheaves of light, are scattered 
 in all directions. The appearance is then surpassingly 
 grand, as the whole heavens seem to move, in measured 
 cadence, to the general undulation of the masses of light. 
 
 It has been asserted that in the arctic regions, these bril- 
 liant appearances are attended with loud noises, resembling 
 the hissing and crackling of fireworks. If this statement 
 could be relied on, there would be no further doubt as to 
 the distance from our earth at which these magnetic cur- 
 rents play to and fro, because the transmission of sound 
 would at once show that they were in contact with our 
 atmosphere, which acts as a medium to convey the sound 
 to our ears. But Captain Lyon, who accompanied Parry in 
 his arctic expedition of 1819, denies that any sound was 
 ever heard by him during some of the most brilliant 
 auroras that man, perhaps, ever beheld. He tells us that 
 the sudden glare and rapid bursts of those wondrous 
 showers of fire make it difficult to persuade oneself that 
 their movements are wholly without sound. He declares 
 that he stood on the ice for hours listening, and at a dis- 
 tance from his men and the ship, so as to secure stillness of 
 all things around him, and he was thoroughly satisfied that- 
 Hot the very faintest sound came from the Aurora. 
 
 It is now generally believed that these streams of light 
 are magnetic currents, periodically evolved by the earth it- 
 self intensified occasionally by magnetic sympathy with 
 certain changes taking place in the sun ; and that particu- 
 lar conditions of the higher stratum of our atmosphere tend 
 
56 FACTS AND THEORIES. 
 
 to make their passage through it visible to us. It is pro- 
 bable that though, at a vast height above the earth, far 
 beyond the clouds, the line of their passage is within fifty 
 miles of us ; or, in other words, that the outer and most 
 attenuated of our atmospheric layers is the one in which 
 they play their merry gambols. 
 
 A similar appearance has been observed by travellers in 
 the southern hemisphere, and proceeding from the South 
 Pole, and therefore called " Aurora Australis." Hence it 
 would be more appropriate to speak of these phenomena as 
 " Polar Lights." 
 
 Thermal Expansion of Water. The general law that 
 bodies expand when heated, and contract when cooled, 
 only applies to water within certain well-defined limits. 
 Thus, down to 39, water contracts in bulk ; from 39 to 32, 
 it rather increases in bulk : whilst in the act of becomm** 1 
 
 o 
 
 ice, at or below 32, it undergoes a vast expansion. By this 
 Providential departure from a general law in nature, the ice 
 is kept at the surface of the water. 
 
 If the general law of contraction in bulk, at decreasing 
 temperatures, had prevailed in the case of water, without 
 the marvellous exception just named, the ice would have 
 sunk to the bottom of our rivers and lochs, one layer 
 after another, and the ocean itself, except perhaps just 
 under the equatorial line, would have become, ages ago, a 
 solid impassable mass. Even in summer, the sun's rays 
 would have had but little warming power over the air, in 
 these now temperate regions, on account of the immense 
 cooling influence which would have been exerted over all 
 the land, by the surrounding ocean of ice. 
 
 Atmospheric Aqueous Vapour. Professor Tyndall's re- 
 cent discoveries respecting the absorption and radiation of 
 heat by aqueous vapour, are an important addition to our 
 previous knowledge. They are of great value as illustrat- 
 
FACTS AND THEORIES. 57 
 
 ing the vibratory actions in matter, which constitute heat. 
 But it is in connection with meteorology that they chiefly 
 command our attention. From his experiments we learn 
 that the minute quantity of water, suspended as invisible 
 vapour in our atmosphere, acts as a warm clothing to the 
 earth. The efficacy of this watery vapour in arresting and 
 preserving radiant heat is, in comparison with that of air, 
 perfectly astounding. Although the atmosphere contains 
 on an average, only one particle of aqueous vapour to 200 
 of air, yet that single particle absorbs eighty times more 
 heat than the collective 200 particles of air, or 16,000 times 
 more heat than that absorbed by one similar particle of air. 
 
 Professor Tyndall says that " if you were to remove, for 
 a single summer night, the aqueous vapour from the air 
 which overspreads these islands, you would assuredly de- 
 stroy every plant which is not capable of bearing extreme 
 cold. The warmth of our fields and gardens would pour it- 
 self unrequited into space ; and the summer's sun would 
 rise in the morning with scorching 'power, on an island fast 
 bound with frost." 
 
 Mr Glaisher has settled the question, previously conjec- 
 tured, that rain falls only when cloud exists in double layer > 
 and that rain-drops diminish in size with elevation, merg- 
 ing into wet mist, and above that into an apparently dry 
 impalpable fog. In his balloon excursions he has met with 
 snow falling for a mile in thickness, below rain, contrary 
 to our preconceived notions, showing that the decrease of 
 temperature with elevation does not follow (so steadily and 
 regularly as had been assumed) the law of about 3 dimin- 
 ution of heat for every thousand feet of elevation. 
 
 TJic Gulf Stream. Whatever may be the urging cause of 
 the Gulf Stream, the direction of its current and its influ- 
 ence upon the British Isles are plainly to be traced. Set- 
 ting out from the hot regions of the Gulf of Mexico and the 
 
 c2 
 
j58 FACTS AND THEORIES. 
 
 Caribbean Sea, it proceeds northward to the great fishing 
 banks of Newfoundland, and thence to the shores of 
 Europe, yielding up its heat to the westerly winds, and thus 
 transferring a portion of the superfluous warmth of the 
 tropics to our colder shores. 
 
 The greatest heat of the oceanic water, in the Mexican 
 Gulf, is about 87, or about 9 above the ocean temperature 
 that would be due to latitude alone ; and when it has 
 reached 10 of north latitude, the Gulf Stream is found to 
 have lost only about two or three degrees of its original 
 heat, and after ascending northwards a distance of three 
 thousand miles from its starting-point, this mighty oceanic 
 river still maintains a summer heat, when all outside of it is 
 cold as winter. It thence crosses in a westerly direction, and 
 spreading itself more widely, imparts to Western Europe a 
 degree of mildness which is much greater than would be 
 due only to latitude. Ireland and the British Isles split 
 the stream into two directions, one tending to the North- 
 North-East, the other passing down the west coast of 
 France. 
 
 Every westerly and south-westerly breeze that blows 
 towards us crosses this wonderful body of warm water, and 
 comes floating over the lands laden with warmth and 
 moisture, to mitigate the wintry blasts and the summer's 
 burning sun. 
 
 If we wish to realise in imagination the full benefit of 
 the Gulf Stream to these islands, we have only to compare 
 our condition in winter and spring with the state of the 
 harbours of Labrador and Newfoundland, in the same lati- 
 tude. Whilst they are rigid with ice as late as May and 
 even June, we are robed in green, and our harbours at the 
 coast have scarcely ever known what it is to be locked 
 with ice, even in our severest winters. 
 
 Magnetic Sympathy between the Earth and the Sun. Mr 
 
FACTS AND THEORIES. 59 
 
 Xasmyth's theory (shall we say discovery .?) is that the 
 bright surface of the sun is composed of an aggregation of 
 apparently solid forms, shaped like willow leaves, or some 
 well-known forms of diatomacese, and interlacing one an- 
 other in every direction. These forms are so regular in 
 size and shape, that one of our profoundest philosophers 
 suggests their being organisms, perhaps even partaking of 
 the nature of life, but at all events closely connected with 
 the heating and vivifying powers of the sun. These 
 mysterious objects are computed to be not less than a 
 thousand miles each in length, and one hundred miles in 
 breadth ! The enormous chasms in the sun's photosphere, 
 to which we apply the diminutive term " spots," exhibit the 
 extremities of these leaf-like bodies pointing inwards and 
 downwards, fringing the sides of the cavern, far down 
 into the abyss, sometimes forming a kind of rope or bridge 
 across the chasm, and seeming to adhere to each other by 
 lateral attraction. 
 
 It now appears certain that sympathy exists between 
 forces operating in the sun, and magnetic forces belonging 
 to the earth. A most remarkable phenomenon, tending to 
 prove this sympathy, was seen by different and indepen- 
 dent observers, at two distant places, on the 1st of Septem- 
 ber 1859. A sudden outburst of light, far exceeding the 
 brightness of the sun's surface, was seen to take place, and 
 sweep, like a drifting cloud, across the solar disc. This 
 was attended by terrestrial magnetic disturbances of very 
 unusual intensity, and with most extraordinarily brilliant 
 auroras. The identical instant at which the solar effusion 
 of light took place, was recorded by an abrupt and strongly 
 marked deflection in the self-registering instruments at 
 Kew. 
 
 If conjecture may be hazarded, we may suppose that this 
 remarkable event had some connection with the means bv 
 
60 FACTS AND THEOKIES. 
 
 which the sun's heat is renovated. It is a reasonable 
 supposition that the sun, at this time, was in the act of 
 receiving a more than usual accession of new energy. And 
 the theory which assigns the maintenance of the sun's 
 power to the plunging of cosmical matter into it, with 
 that prodigious velocity which gravitation would impart, as 
 the foreign body approached to actual contact with the 
 solar orb, would explain this sudden exhibition of intensi- 
 fied light, in accordance with our previous knowledge, 
 viz., that " suddenly arrested motion results in equivalent 
 heat." (?) 
 
 Component Parts of the Atmosphere. The atmosphere 
 may be treated of in various ways, according to the nature 
 of the subject to which it bears reference. Thus we may 
 regard it statically, that is, at rest ; or dynamically, that is 
 to say, in motion. Its relation to the imponderable agencies 
 of heat, light, electricity, magnetism, and actinism, is another 
 way in which to view the atmosphere. Or again, as in the 
 present instance, we may wish to speak of its chemical con- 
 ditions, and to enumerate its component parts. 
 
 The air is composed of four different bodies, which are 
 mixed, but generally believed to be not chemically combined 
 each existing as an independent atmosphere, penetrating 
 through the others to the greatest height, from which speci- 
 mens for analysis have been brought, and being found in 
 these specimens always in about the same proportions as in 
 the air at the level of the sea. 
 
 One hundred parts of air consist mainly of 78 or 79 parts 
 of nitrogen gas, called also azote, and about 21 parts of 
 oxygen gas. The other two chief ingredients are in very 
 small proportions, as carbonic acid gas, about the T 2\-o tn 
 part, varying to a little more or less ; and watery vapour, also 
 very variable in quantity, but rarely exceeding 1 part in 
 100 parts of common air. 
 
FACTS AND THEORIES. 61 
 
 The atmosphere contains also minute portions of am- 
 monia and nitric acid, and occasionally of hydrogen, said to 
 be most manifested during thunder-storms. It also contains 
 in the form of vapour a multitude of adventitious substances, 
 in those injurious mixtures known as miasmata, the nature 
 of which can hardly be investigated. And in the near 
 neighbourhood of large towns there will, doubtless, be other 
 temporary ingredients floating about, of serious conse- 
 quence to the health and comfort of the inhabitants, but 
 of infinitesimally small amount when compared with the 
 whole mass of the atmosphere at places distant from those 
 crowded quarters of humanity. 
 
 Atmospheric Electricity. The great constant fact respect- 
 ing atmospheric electricity is, that the earth is always 
 becoming negatively charged, while the air, or all conduct- 
 ing substances contained in it, is at the same time positively 
 charged. In fine weather this goes on without interrup- 
 tion, but it is different for different hours of the day. When 
 the state of the air is steadily observed by an insulated 
 conducting rod, we find that it is least charged at eight in 
 the morning, ancT most charged between eight and ten in 
 the evening. In foggy weather the states are reversed, and 
 the air is generally negative. During an actual shower the 
 air is commonly positive, but the rain-drops themselves, 
 when examined, are found to be in an opposite state. But 
 during showers, and especially during thunder-storms, the 
 state is constantly changing from one kind of electricity to 
 the other. The dense fogs which sometimes settle over a 
 place, and last for hours, have usually a strong negative 
 character ; and their being thus highly charged with elec- 
 tricity, seems to prevent them from being dissolved by heat 
 so readily as vapours generally are, for it has been observed 
 that a cold fog entering a warm room will remain a con- 
 siderable time in the visible form. The ordinary action 
 
62 FACTS AND THEOKIES. 
 
 taking place upon the air will, therefore, render all floating 
 clouds liable to become negatively electric, especially in 
 the lower regions, if we suppose that it is at the surface of 
 the earth that the electricity is generated. If other clouds 
 float above, with a stratum of dry air between, these may 
 become positive by induction, and thus there will be an 
 opposition of states among the clouds themselves, as well 
 as the opposition between the lower strata and the earth. 
 When the accumulation has reached a certain pitch, it will 
 be discharged in some one of the three following ways : 
 If there is a communication of moist air between the two 
 charged clouds, or between a cloud and the earth, it will 
 pass off quietly by conduction, with or without the deposi- 
 tion of moisture in the visible form of rain, hail, or snow, 
 &c. Or, if there is a great movement among the clouds 
 themselves, it may be neutralised by convection. But if 
 two contiguous masses are highly charged, and a dielectric 
 of very dry air lie between them, it will be discharged by 
 disruption in the form of thunder and lightning. When 
 two clouds are mutually discharged in this way, the whole 
 commotion takes place in the upper air, the lightning being 
 faint and diffused, and the thunder always distant. But 
 when a large mass of positive cloud hangs over the nega- 
 tive earth, and when the intervening air is dry, and the 
 electric accumulation great, the discharge bursts forth 
 between the sky and the ground, and is then the most 
 terrific and dangerous. The light has then the zig-zag 
 known by the name of forked lightning, and it is apt to be 
 concentrated in some one spot, which is torn and scorched by 
 the stroke. The thunderbolts which throw down or set fire 
 to houses, shiver trees, and destroy life, are of this character. 
 All the effects capable of being produced on a small scale by 
 electrical jars and batteries are caused on a grand scale by 
 these thundery discharges between the clouds and the earth. 
 
FACTS AND THEORIES. 63 
 
 What is Ozone ? A summary of our knowledge relative 
 to ozone may be thus briefly stated : Oxygen gas is sus- 
 ceptible of undergoing a change, the nature of which is 
 almost wholly wrapt in mystery. It is capable of becoming 
 odorous, corrosive, and irritating when breathed. Its 
 chemical action is capable of being so modified and in- 
 creased, as that, whilst ordinary oxygen gas neither bleaches 
 nor corrodes silver, nor decomposes iodide of potassium, the 
 allotropic or second form of oxygen gas will accomplish 
 all these, and many other results peculiar to itself. It 
 will be found capable of removing the colour of sulphate 
 of indigo, and other vegetable and animal colourings. All 
 this is due to the modification which ordinary oxygen gas 
 has undergone, and which is known as its conversion into 
 ozone, 
 
 Electricity in the air is believed to be one of the chief 
 agencies in the production of ozone. 
 
 Ozone is inconceivably beneficial in rapidly removing the 
 bad odours which arise from the decomposition of animal 
 and vegetable bodies. If the temperature be high, and very 
 little ozone be present in the air, decomposition will take 
 place on every side, charging the air with disease and 
 death. But ozone, though so very useful an agent, may 
 become injurious when present in the air to any great 
 excess, by its irritating effects on the sensitive air passages 
 of the throat and lungs. 
 
 As an ozonometer, the observer may obtain test papers 
 from several makers, which may be hung in the open 
 air; but sheltered from the sun and rain. According as 
 ozone is present in the air, in greater or less abundance, the 
 test-papers will be coloured with varying shades of blue. 
 The intensity of these shades of blue may be measured by 
 comparing them with a graduated scale of twelve tints, 
 which may be obtained, together with a packet of the pre- 
 
64 FACTS AND THEORIES. 
 
 pared slips of paper, from Messrs Casella, 23 Hatton Gar- 
 den, London (E. C.), at a cost of 6s. 6d. 
 
 If the observer wishes to try the experiment of preparing 
 his own test-papers, they may be made thus : 
 
 200 parts of distilled water, 
 10 starch, 
 1 iodide of potassium, 
 
 which should be boiled together for a few seconds, and thin 
 strips of bibulous paper should be dipped into the solution ; 
 and when dry, they will be ready for use. If there be any 
 ozone present in the air, it seizes on the potassium the 
 blue colour left being iodide of farina. It will be as well 
 to keep the strips of prepared paper (until wanted for use) 
 in a box or drawer, dark and dry. 
 
 Meteoric Stones, or Aerolites. These are solid semi- 
 metallic substances, which fall from the atmosphere. The 
 larger stones have been seen as luminous bodies, moving 
 with great velocity, descending in oblique directions, and 
 frequently with a loud, hissing noise, resembling that of a 
 inortar-shell when projected from a piece of ordnance ; they 
 are sometimes surrounded with a flame, tapering off to a 
 narrow stream at the hinder part, and are heard to explode, 
 and seen to fly in pieces. Of course these appearances have 
 been observed most frequently in the night ; but when the 
 stones have fallen in the day-time, only the report and 
 shower of stones have been noticed. 
 
 The same meteoric mass has often been seen over a great 
 extent of country in some instances, 100 miles in breadth, 
 and 500 in length, which implies that they must have 
 had a great elevation. Indeed, from various calculations, it 
 appears that during the time that they are visible, their per- 
 pendicular altitude is generally from 20 to 100 miles ; and 
 their diameter has, in some instances, been estimated to be 
 
FACTS AND THEORIES. 65 
 
 at least half a mile. Though rarely visible for a whole 
 minute, they are seen to traverse many degrees in the 
 heavens. Their rate of motion cannot be, generally, less 
 than 300 miles a minute. Probably the stones which come 
 to us from them form but a very small portion of their 
 bulk, while the main body holds on its way through the 
 heavens. 
 
 Such falls have happened in cloudy as well as in clear 
 weather, which leads to the belief that they are wholly 
 unconnected with the state of the atmosphere. 
 
 The most remarkable circumstance respecting them is, 
 that they invariably resemble each other in certain marked 
 respects, of external properties and chemical composition, 
 so as to render it possible for a mineralogist or a chemist to 
 recognise them with certainty, even though he has not been 
 informed of their origin and fall. They invariably contain, 
 disseminated throughout their substance, an alloy of iron and 
 nickel, which, it is believed, has never yet been discovered 
 among the productions of our earth. This alloy varies in 
 the proportion it bears to the earthy matters, being some- 
 times scarcely to be recognised without the aid of a micro- 
 scope, and at other times forming more than one-half of 
 the stone. They are generally coated on the outside with a 
 thin black incrustation ; and indentations may often be 
 noticed, as though the mass had been impressed with the 
 fingers. 
 
 These constant characters, as respects both their fall and 
 their chemical and mechanical composition, indicate a 
 common origin, and have given rise to numberless theories to 
 account for their phenomena. Some have attributed them to 
 terrestrial, and others to lunar volcanoes. But if our earth's 
 volcanoes had anything to do with them, we could not 
 have avoided noticing the coincidence of the one with the 
 other ; and there is, besides, a want of similarity between 
 
66 FACTS AND THEORIES. 
 
 meteoric stones and ordinary volcanic exuviae. And as to 
 their coming from lunar volcanoes, the theory might be 
 tenable if we had only to account for the showers of 
 stones which come to our earth's surface, but these are, pro- 
 bably, only a very small part of the masses from which they 
 descend ; and since we experience a shower of these stones 
 every few months in some part of the world, it is obvious 
 that, at this rate, the whole mass of the moon would soon 
 be shot away. 
 
 With regard to the theory of these bodies having formed 
 in our own atmosphere, there is one principal objection, viz., 
 that the velocity with which they strike the earth, as shown 
 by the depth to which they have sometimes penetrated, 
 indicates their having fallen from heights far exceeding the 
 limits of the terrestrial atmosphere. 
 
 The remaining theory is the one now generally accepted, 
 viz., that they are terrestrial comets, or detached portions 
 of solar comets. And the periodicity of their occurrence 
 favours this idea. The second week in August, and the 
 beginning of November, are the periods in each year when 
 these meteoric falls seem to be most frequent, plainly indi- 
 cating by their regular recurrence, that our earth is then 
 passing near the line of the annual orbit of a large com- 
 pany of these comets or miniature planets. 
 
 They all appear, on examination, to have undergone the 
 action of fire, through violent collision with our atmosphere. 
 
 It is recorded that a meteoric mass fell at Agram in 
 Hungary in 1751, weighing 71 pounds. But the largest 
 and heaviest ever known fell in Mexico, and was computed 
 to weigh about 15 tons ! 
 
 Our Earth's Internal Heat. " The Monkwearmouth col- 
 liery reaches a depth of 1800 feet below the surface of the 
 ground, and nearly as much below the level of the sea." 
 
 " The observed temperature of the strata at this depth 
 
FACTS AND THEORIES. 67 
 
 agrees closely with what has been ascertained at other 
 places, showing that the increase of heat takes place at 
 the rate of about 10 (Fahr.)for every 600 feet downwards 
 vertically from the surface. Assuming, then, the tempera- 
 ture of subterranean fusion to be equal to 3000 (Fahr.) and 
 that the heat goes on increasing uniformly (which, however, 
 is not quite certain), then the thickness of tlizfilm separating 
 us from the fiery ocean beneath, will be about 35 miles, a 
 thickness which may fairly be represented by the skin of a 
 peach, as compared with the body of the fruit which it en- 
 closes." (!) 
 
 The above statement was addressed, in 1863, to the 
 British Association, by their President, Sir \V. Armstrong. 
 
 But this theory of increasing heat at greater depths be- 
 low the earth's surface is altogether scouted by Sir John 
 Leslie (a Scotchman of scientific eminence), in a work pub- 
 lished as late as 1860. Sir John accounts for the increase 
 of heat in deep coal-pits solely by the number of lamps 
 used by the miners, and by the difficulty of introducing 
 fresh cool air from the surface. He even goes so far as to 
 assert that the contrary is the case maintaining that if one 
 of these very deep shafts were left open and not used for a 
 considerable time, and then examined, greater cold would 
 be found at the bottom of the shaft, than the mean annual 
 temperature of the air at the surface of the ground 
 above. (!) 
 
 It was also urged by the supporters of Sir John Leslie's 
 theory, that the running water at the bottom of deep mines 
 was always colder than the air at the same place. This 
 would have been a powerful argument indeed, if it could 
 have been shown that the water at the bottom of a deep 
 coal-pit found its way thither from a still lower point, well- 
 ing up from the bowels of the earth. As, however, there 
 can be no doubt that the water had flowed downwards, from 
 
68 FACTS AND THEORIES. 
 
 points nearer the surface of the ground, its colder tempe- 
 rature (if it is to prove anything) rather militates against 
 Sir John Leslie's idea than in favour of it. But who shall 
 decide when these two doctors disagree ? 
 
 Relation of Climate to Organic Development. (From Scof- 
 fern and Lowe's Practical . Meteorology.) " Even in the 
 narrow region of European travel the intelligent observer 
 will not fail to see distinctive physiognomies. Passing 
 from the cold green sward and modest vegetation of our own 
 isles to the Mediterranean shore, a striking change in the 
 aspect of nature meets the eye. The sturdy oaks and elms 
 of our own forests disappear ;- the absence of smaller grasses 
 removes the green carpet of our meadows ; tall graminacese 
 spring up ; the aloe and the prickly pear bespeak a mixed 
 condition of heat and drought ; and the date palm, barely 
 acclimatised there, gives some faint notion of what the 
 characteristics of a tropical forest must be. It would be 
 an enterprise worthy of a great artist, says Humboldt, to 
 study the aspect and character of all these vegetable 
 groups, not merely in hot-houses or in the descriptions of 
 botanists, but in their native grandeur in the tropical zone. 
 How interesting and instructive to the landscape painter 
 would be a work which should present to the eye, first, 
 separately, and then in combination and contrast, their 
 leading forms ! How picturesque is the aspect of tree- 
 ferns spreading their delicate fronds above the laurel-oaks 
 of Mexico, or the groups of plaintains overshadowed by 
 arborescent grasses ! It is the artist's privilege, having 
 studied these groups, to analyse them ; and thus, in his 
 hands, the grand and beautiful forms of nature resolve 
 themselves into a few simple elements. But when the 
 meteorologist has exhausted his knowledge in laying out 
 climatic groups ; when he has placed in correlation condi- 
 tions identical in every respect, as he may think the 
 
FACTS AXD THEORIES. 69 
 
 growth of vegetable forms demonstrates his inability to 
 comprehend many hidden secrets in nature which their 
 delicate organisation reveals. Thus, European olive trees 
 grow luxuriantly at Quito, but they bear neither fruit 
 nor flowers ; and a similar remark applies to walnut trees 
 and the hazel in the island of Mauritius. In India the 
 bamboo flowers luxuriantly ; but in South America, where 
 it grows equally well, so far as general vigour can be 
 judged by its appearance, so rare an event is the flower- 
 ing of the bamboo, that, during a four years' residence 
 in South America, Humboldt was only able to obtain blos- 
 soms once. But, perhaps, the most remarkable example 
 of luxuriant growth, without inflorescence, is furnished by 
 the sugar-cane. The West Indies have come to be considered 
 the region, par excellence, of the sugar-cane ; yet it seldom 
 bears flowers there, nor, indeed, does it on any part of the 
 American continent, thus affording a strong presumptive 
 argument in favour of the theory which asserts that no 
 variety of the sugar-cane is indigenous to the New World." 
 In all these so-called freaks of nature, there are subtle 
 influences at work which baffle our most curious research, 
 for the present time at least, and must for ever commend to 
 our admiration the wisdom and power of Him "which 
 doeth great things past finding out ; yea, and wonders with- 
 out number." 
 
 The A tornic Theory. Heat, Light, Electricity, &c. Much 
 as we have yet to learn respecting these agencies, we know 
 enough already to infer that they cannot be transmitted 
 from the sun to the earth, except by communication from 
 particle to particle. Not that the term " particles" need be 
 understood in the sense of the atomist. Whatever our views 
 as to the nature of particles, we must conceive them to be 
 centres invested with surrounding forces. But we have no 
 reason to believe that these centres are occupied by solid 
 
?0 FACTS AND THEORIES. 
 
 cores of indivisible, incompressible matter, essentially dis- 
 tinct from force. 
 
 And why encumber our conceptions of material forces 
 with this needless imagining of a central molecule ? If we 
 retain the forces and reject the molecule, we have still 
 every property that we can recognise in matter, by the use 
 of our senses or by the aid of our reason. Viewed in this 
 light, matter is not only a thing subject to force, but is 
 itself composed and constituted of force. 
 
 The Dynamical theory of heat is, perhaps, the most im- 
 portant discovery of the present century. We now know 
 that each Fahrenheit degree of temperature, in a pound of 
 water, is equivalent to a weight of 772 pounds lifted one 
 foot high, and that these amounts of heat and power are 
 reciprocally convertible into one another. This discovery 
 may be assigned to the present century, because it is only of 
 late that it has been indisputably settled. But if we search 
 back for an earlier conception of the identity of heat and 
 motion, we shall find that similar ideas have been held be- 
 fore, though only in a clouded and un demonstrated form. 
 In the writings of Lord Bacon, we find it stated that heat 
 is to be regarded as motion, and nothing else. In dilating 
 upon this subject, that extraordinary man shows that he had 
 grasped the true theory of heat, to the fullest extent that was 
 compatible with the state of knowledge existing in his day. 
 Even Aristotle (B.C. 350) seems to have entertained the idea, 
 that motion was to be considered as the foundation and 
 cause, not only of heat, but of all other manifestations in 
 matter. And for aught we know, still earlier thinkers may 
 have held the same views. In this age of practical experi- 
 ment, superadded to close reasoning, we have proved that 
 many of their guesses on the subject of heat, light, motion, 
 &c., were actually flashes of truth. 
 
 Imponderable A gents or Forces. These expressions are now 
 
FACTS AND THEORIES. 71 
 
 applied generally to indicate the causes, whatever they may 
 be, which give rise to the phenomena of heat, light, electri- 
 city, and magnetism ; and we must now include actinism, 
 or the radiant influence of the sun, to the operation of which 
 photographic pictures are due, and which is believed to be 
 the chemical agency of a portion of the sun's rays. 
 
 The imponderable agents have always presented a field of 
 great interest to the student ; and more especially is it so 
 at this present time, seeing that it is the tendency of modern - 
 philosophy to refer all these agencies or forces to various 
 modifications of one grand cause. 
 
 The correlations between light and heat, electricity and 
 magnetism, are so intimate and so well marked, that it is im- 
 possible to avoid the conclusion that they must all be due to 
 a modification of one common agent. We may say that this 
 grand cause is motion ; and it may be that we shall never 
 reach a higher step in our search after nature's " causa 
 causarum" than that we have now attained. Must we ; then, 
 at one step, pass thence from the regions of the material to 
 those of the spiritual from matter to mind and will ? At 
 our present stage of knowledge we show the humility of 
 true wisdom by allowing this question to be answered 
 affirmatively. 
 
 Theories respecting Light. There are two aspects under 
 which light is now regarded either as being an emission 
 of material particles from the luminous body, or as undula- 
 tions of a very subtle medium (ether) which fills all space, 
 and communicates vibrations from the solar disc to the 
 earth, or other planetary -bodies, by an uninterrupted series 
 of waves. Whichever theory is adopted, whether of particles 
 or waves, certain general truths will remain the same. 
 Every particle or wave of light is emitted in straight lines ; 
 and from every point of the luminous body these particles 
 or waves are thrown off in all directions. Under both 
 
72 FACTS AND THEORIES. 
 
 theories, light is subject to two great laws, viz., the law of 
 Refraction, and the law of Reflection. A ray of light is said 
 to be refracted, when its course is diverted from a straight 
 line by entering some denser medium ; and it is said to be 
 reflected, when it is thrown back by any body on which it 
 falls. In order that a ray may be refracted, it must enter 
 a more or less transparent body, such as air, water, or glass ; 
 and to be reflected, it must strike upon bodies through 
 which it cannot penetrate, such as bright metal, when, 
 instead of being transmitted, it is thrown back in whole or 
 in part. The beauty of the visible creation is almost 
 entirely the result of refraction and reflection. The refrac- 
 tion of the atmosphere diffuses the solar light throughout 
 the sky, renders the transition from day to night, and from 
 night to day, gradual and pleasing, and gives infinite variety 
 to every hue and tint. In like manner reflection, by its 
 more or less perfect character, gives tone and beauty to 
 what would otherwise be a dazzling multiplicity of images, 
 or a monotonous sameness in the diffusion of light and 
 colour. 
 
 Colour of the A tmospliere. On ascending to the top of a 
 very high mountain, we find that the sky, even in bright 
 daylight, has lost very much of the blue tint which we 
 generally observe when we gaze upwards from a lower level. 
 From this it appears, that were there no atmosphere sur- 
 rounding our planet, the heavens would be intensely black 
 at all times, whilst the heavenly bodies would be so many 
 brilliant points set in the deepest shadow. The air, how- 
 ever, diffuses and reflects the sun's rays of light, so that a 
 portion of them is received from every part of the sky, 
 causing a general illumination of the entire vault of heaven. 
 This reflected light ought, as we should at first suppose, to 
 be always of a whitish character, like the light of the sun 
 made very much fainter. But we find that the sky, when 
 
FACTS AND THEORIES. 73 
 
 very clear, has a strong blue tint, which deepens into black 
 the higher we ascend a lofty mountain side. This blueness 
 arises from the peculiar action of the atmosphere upon 
 light. If any solar beam pass through a great thickness of 
 air, the red will be transmitted the most readily, and lost 
 to our vision, whilst the blue is resisted and reflected ; and 
 from this cause it is that the reflected rays of the solar light 
 have a bluish tinge instead of being pure white. The red 
 tint that we sometimes see in the sky is caused by the 
 passage of the sun's rays through a more than usually dense 
 medium of air. This appearance, when seen at mid-day, 
 betokens much moisture in the air, and is generally the 
 precursor of wind and rain. But the same ruddy illumina- 
 tion at sunset or sunrise is caused by the multifold thick- 
 ness of atmospheric air through which the rays are obliquely 
 transmitted along the surface of the earth. 
 
 Gauge of Twilight. This is the effect of refraction, the 
 air causing a portion of the sun's light to reach the eartli 
 by an angular course, when the sun is below the observer's 
 horizon. It continues until the sun has descended 18, or 
 for about two hours after sunset in this country. 
 
 Cause of the Rainbow. This beautiful collection of 
 colours is owing to a complicated reflection and decom- 
 position of the sun's ray in passing through the drops of 
 rain. It appears when the sun is unclouded, and rain is 
 falling in the opposite quarter of the heavens, and requires 
 that the observer should be placed between the sun and 
 the shower to be acted upon. When a ray of light enters 
 a drop of rain, it is immediately decomposed into the pris- 
 matic colours ; and on reaching the other side of the drop, 
 they are partly transmitted and partly reflected, and thrown 
 out at the same side as that at which they entered, when 
 they emerge in the coloured state, and are visible, In the 
 brilliant or primary rainbow, the violet strip is the lowest 
 
 D 
 
74 FACTS AND THEORIES. 
 
 down, or on the inner side of the illuminated arch, and the 
 red is on its outermost edge. When a secondary rainbow 
 appears inclosing the primary one, it is the result of double 
 reflection, and therefore is less brilliant. In a very stormy 
 sea, with the sun shining on the broken waters, showers 
 of spray are sometimes tossed upwards by the action of the 
 wind, when the rays of the sun produce inverted rainbows, 
 of which more than twenty have often been seen at the 
 same moment. They cannot, however, be compared, for 
 brilliancy, with the ordinary rainbow, being very faint, 
 and but rarely consisting of more than two colours, viz., 
 yellow on the side towards the sea, and pale green on the 
 other side. 
 
 " Actinism" and the "Actinic Rays'' These expressions 
 are very much in use now-a-days ; but though photographers 
 and medical men may attach to them a correct and definite 
 meaning, it is probable that many persons have only a vague 
 idea of what it is they wish to express when they use these 
 terms. A few sentences may suffice to give an outline of 
 the Actinic theory. 
 
 It is well known that the solar light is made up of seve- 
 ral coloured rays, so blended as to appear white or colour- 
 less. Thus we speak of seven primary colours, meaning 
 that by the aid of a prism we can decompose the sun's 
 light, so as to produce seven differently coloured rays. It 
 appears, however, that it would be more correct to speak of 
 only three primary colours, viz., red, yellow, and blue ; and 
 to treat the others, viz., violet, indigo, green, and orange, 
 as compound colours, that is to say, as the result of the inter- 
 mingling of one or other pair of the three primary colours. 
 Red, yelloio, and Hue, then, are the three primary colours. 
 Each of these is proved to have a certain province, and to 
 produce certain effects, distinct from the other two ; thus : 
 
 The red is the heating ray : 
 
FACTS AND THEORIES. 75 
 
 The yellow is the luminous or visual ray : 
 
 The blue is the chemical or actinic ray. 
 
 These several effects will be more or less intensified or 
 blended together, according to the degree in which any one 
 ray prevails over the others. 
 
 AVe may sum up the chief points regarding the chemical 
 or actinic influence of solar light as follows : 
 
 I. " The rays having different illuminating and calorific 
 powers, they exhibit different degrees and kinds of chemi- 
 cal action." 
 
 II. " The most luminous rays exhibit the least chemical 
 action on all inorganic matter. The least luminous and 
 non-luminous rays manifest very powerful chemical action 
 on the same inorganic substances." 
 
 III. " The most luminous rays influence all substances 
 having an organic origin, particularly exciting vital power. 
 
 IV. " Thus, under modifications, chemical power is traced 
 to every part of the prismatic spectrum ; but in some cases 
 this action is positive, exciting; and in others negative, 
 depressing. 
 
 V. " The most luminous rays are proved to prevent all 
 chemical change upon inorganic bodies, though exposed at 
 the same time to the influence of the chemical rays." 
 
 VI. " Hence actinism, though regarded as only a phe- 
 nomenon different to light, really stands in direct antagon- 
 ism to light." 
 
 VII. " Heat radiations produce chemical change, in virtue 
 of some combined action, not yet understood." 
 
 VIII. "Actinism (i.e., the blue ray and its shades) is 
 necessary for the healthful germination of the seed. Light 
 (the yellow ray and its compounds) is required to excite 
 the plant to decompose carbonic acid. Caloric (the red 
 ray and its shades) is necessary for developing and carrying 
 out the reproductive functions of the plant." 
 
76 CONCLUSION. 
 
 IX. " Phosphorescence is due to actinism, and not to 
 light." 
 
 X. " Electrical phenomena are quickened by actinism, and 
 retarded by light." 
 
 The foregoing summary of actinism is taken from a 
 treatise on photography^by Professor Hunt. 
 
 CONCLUSION. 
 
 Use of Meteorology. It would be quite a mistake to 
 imagine, that the study of meteorology must necessarily be 
 a mere source of amusement for the rich and the idle. We 
 have seen how a knowledge of the hygrometer (dry and wet 
 bulbs) may be turned to good account, both in hot-houses 
 and in sick rooms ; and that the hygrometric condition of 
 the atmosphere is really a far surer guide than even the 
 barometer, in judging as to the near approach of rain. And so 
 of the rain-gauge, it is a valuable assistant in the manage- 
 ment of oiit-door plants and crops, as well as in the con- 
 struction of tanks -and reservoirs, for the regular supply of 
 water on a large scale. The observer may see how beneficial 
 is even a passing shower to growing plants, when he remem- 
 bers that one-tenth of an inch of rain, in his gauge, repre- 
 sents a deposit of about forty hogsheads per acre. 
 
 Or, to take the solar maximum and terrestrial minimum 
 thermometers, the one will show the necessity of screen- 
 ing delicate ripening fruits, in the hot-house, from the dry 
 glare of the mid-day sun ; the other will forewarn the 
 observer, to guard his tender plants from the chilling effect 
 of heavy dew and hoar frost. 
 
 All these instruments just named, differ from the baro- 
 meter in the mode of their indications, in that they warn us 
 of the present hour ; whereas, the barometer gives us notice 
 of general changes, which may require a week or more for 
 
CONCLUSION. 77 
 
 their full development. We might, therefore, call the 
 barometer the seaman's weather-gauge, rather than the 
 landsman's ; the more so, as its movements are indicative 
 not of moisture but of pressure; that is, not of rain, but of 
 wind. 
 
 Calendar of Nature. " Every meteorologist (Mr Lowe 
 says) should endeavour, as much as possible, to record the 
 arrival and departure of migratory birds, the dates on 
 which trees open and lose their leaves, the first appear- 
 ance of such insects as caterpillar-blight," &c. In regard to 
 trees, however, it may be necessary to remind the observer 
 that he should take one individual of a species, as the sub- 
 ject of his observations, say a Beech or a Lime, and not indif- 
 ferently one or another in successive years. For different 
 individuals of the same species will come into leaf at con- 
 siderable intervals. Thus, one beech will precede its neigh- 
 bour beech in the opening of its leaves by ten or even 
 fifteen days, though growing side by side. 
 
 This calendar of nature should be entered into the meteor- 
 ological book, in such a way that one page may serve as a 
 record for many years. It might be headed " Spring page," 
 and " Autumn page," and occur, the one between May and 
 June, and the other between November and December. 
 
 " Every observer who, for a series of years, pursues such 
 a course of observation, will find that he has done some 
 good to his kind. And if any method could be devised 
 for bringing together such a body of observations through- 
 out the kingdom, they would form a valuable mass of facts 
 for the naturalist and meteorologist to generalise upon." 
 Such a method has been contrived by Mr Symons, and is 
 being carried out by him, with the aid of a thousand 
 observers, distributed throughout the three kingdoms. 
 
 Law implies Mind (From the " Bridgewater Treatises"). 
 Though at present comparatively in an infant state, 
 
78 CONCLUSION. 
 
 the science of meteorology is no doubt as capable of 
 being accurately reduced to certain great, laws, as the 
 science of optics, acoustics, or astronomy, if only our obser- 
 vations could be as continuous and exact as the observations 
 which have led to the construction of the other sciences. 
 And the difficulties to be overcome in finding laws which 
 shall be of universal application, over so wide a field as that 
 embraced in meteorology, should rather tend to increase 
 our admiration at the infinite wisdom which could provide a 
 system so grandly complex, and yet so all-sufficient for the 
 minutest details. Now this connection between the laws 
 of the material world and an Intelligence which precon- 
 ceived and instituted the laws, is not only the belief of the 
 untutored mass of mankind, but has struck no less forcibly 
 those who have studied nature with the more systematic 
 attention, and with the peculiar views which belong to 
 science. The laws which such persons study seem, indeed, 
 most naturally to lead to the conviction of a Supreme Intel- 
 ligence, which originally gave each law its form. What 
 we call a law is, in truth, a form of expression, including a 
 number of facts of a like kind. The facts are separate ; 
 but the unity of view by which we associate them the 
 character of generality and of law resides in those rela- 
 tions which are the object of the intellect. The law when 
 once apprehended by us, takes in our mind the place of the 
 facts themselves, and is said to govern or determine them, 
 because it determines our anticipations of what they will 
 be. But we cannot, it would seem, receive a law founded 
 on such intelligible relations, as being itself able to govern 
 and determine the facts themselves any otherwise than by 
 supposing also an intelligence, by which these relations are 
 contemplated, and these consequences realised and provided 
 for. We cannot then represent to ourselves the universe 
 as governed by general laws, otherwise than by supposing 
 
CONCLUSION. 79 
 
 an intelligent and conscious Deity, by whom these laws 
 were originally contemplated, established, and applied. 
 This perhaps will appear more clear, when it is considered 
 that in every branch of physical science, be it astronomy 
 or meteorology, or the like, the laws of which we speak are 
 often of an abstruse and complex kind, depending upon 
 relations of time, space, number, and other properties. 
 These relations are often combined so variously and so 
 curiously, that the most subtle reasonings and calculations 
 which we can form are requisite in order to trace their 
 results. Can such laws be conceived to be instituted 
 without any exercise of knowledge and intelligence ? Can 
 material objects apply geometry and calculation to them- 
 selves ? Can the lenses of the eye, for instance, be formed 
 and adjusted with an exact suitableness to their refractive 
 powers, while there is in the agency which has formed 
 them no consciousness of the laws of light, of the course of 
 rays, of the visible properties of things ? This appears to be 
 altogether inconceivable. Every particle of matter possesses 
 an almost endless train of properties, each acting according 
 to its peculiar and fixed laws. For every atom of the same 
 kind of matter these laws are invariable and perpetually 
 the same. This constant and precise resemblance this 
 variation, equally constant and equally regular suggests 
 irresistibly the conception of some cause, independent of 
 the atoms themselves, by which their similarity and dis- 
 similarity, the agreement and difference of their deport- 
 ment, under the same circumstances, have been determined. 
 Such a view of the constitution of matter (as was remarked 
 by Herschel in his " Study of Natural Philosophy") effec- 
 tually destroys the idea of its eternal and self-existent 
 nature, " by giving to each of its atoms the essential char- 
 acter at once of a manufactured article and a subordinate 
 agent" Clarke, the friend and disciple of Newton, most 
 
80 CONCLUSION. 
 
 strenuously urges the same truth, that " all things which 
 we commonly say are the effects of the natural powers of 
 matter, and laws of motion, are indeed (if we will speak 
 strictly and properly) the effects of God's acting upon 
 matter continually and at every moment, either imme- 
 diately by Himself, or mediately by some created intelli- 
 gent being. Consequently, there is no such thing as the 
 cause of nature or the power of nature," independent, that 
 is, of the effects produced by the will and providence of 
 God. And Dugald Stewart has adopted and illustrated the 
 same opinion, quoting with admiration the well-known 
 passage of Pope concerning the divine agency, which 
 
 " Lives through all life, extends through all extent, 
 Spreads undivided, operates unspent." 
 
81 
 
 METEOKOLOGICAL TABLES. 
 
 TABLE I. PREVAILING WINDS IN STRATHEARN. 
 
 If we divide the, Winds into Three Classes, and call them " Moist Wester- 
 lies" "Dry Westerlies" and "Cold Easterlies" the accompanying 
 Table will show the Average Number of Days belonging to eadi 
 Class, in the several Months, during Six Tears (1860-1865). 
 
 Mean of Six Tears. 
 
 Muthill, near Crieff, 
 Perthshire, 
 245 feet above sea-level. 
 
 Moist Westerlies 
 (including) 
 S., S.S.W., 
 S.W., and 
 
 w.aw. 
 
 Dry Westerlies 
 (including) 
 \V.. W.N.W., 
 N.W., N.N.W., 
 and N. 
 
 Cold Easterlies 
 (including) 
 N.N'.E., N.E., 
 E.X.E., E., 
 E.S.E.,S.E., 
 and S S.E. 
 
 January, .... 
 February, .... 
 March, 
 
 9-1 
 6-8 
 6'8 
 
 9'8 
 
 9-0 
 11-3 
 
 12-0 
 12-5 
 12-8 
 
 M5f ' ' 
 
 8-1 
 12'0 
 
 87 
 61 
 
 131 
 
 12-8 
 
 June 
 
 9 '8 
 
 91 
 
 11-0 
 
 July, . 
 
 10'3 
 
 12-5 
 
 81 
 
 August, . 
 
 9-8 
 
 127 
 
 8-5 
 
 September, .... 
 October, .... 
 November, .... 
 December. .... 
 
 11-8 
 8-0 
 7-0 
 9-7 
 
 11-2 
 10-5 
 9-5 
 10-3 
 
 7-0 
 12-5 
 13-5 
 11-0 
 
 Mean total days in } 
 each class, during > 
 six years, . . ) 
 
 109 
 
 121 
 
 135 
 
 (STRATHEARN.) MUTHILL KAINFALL, IN INCHES. 
 Mean Monthly Fall of Six Tears (1860-1865). 
 
 Jan. 
 
 Feb. 
 
 March 
 
 April. 
 
 May. 
 
 June. 
 
 July. 
 
 Aug. 
 
 Sept. 
 
 OCL 
 
 Nov. Dec. 
 
 5-59 
 
 3-83 
 
 2-65 
 
 2-07 
 
 2-20 
 
 317 
 
 2-77 
 
 4'OS 
 
 3-69 
 
 4-43 1 3-95 ! 5-26 
 
 Mean Annual Total (43'69) Fall, in Inches. 
 
 D2 
 
82 
 
 METEOROLOGICAL TABLES. 
 
 3 
 
 8 
 
 So 
 
 33 
 
 33 
 
 3 
 
 Oi *O 
 
 33 
 
 3 
 
 <N 
 t^ 
 
 38 
 
 ooos | 
 
 3838 
 
 3 
 
 3 
 
 3 
 
 S3 
 38 
 
 OS 
 
 a 
 
 3 
 
 3 
 
 3 
 
 3 
 
 coco 
 
 ! 1 O 
 
 CO l> 
 
 TO C 
 
 rH CO CO 
 
 -xa 
 
 38 
 
 33 
 
 33 
 
 33 
 
 38 
 
 co8 cooi 
 
 3 
 
 s^ 
 
 38 
 
 SOUI9JJ 
 
 -xa 
 
 3 
 
 O100 
 
 33 
 
 3 
 
 3 
 
 ?S 
 
 
 33 
 
 38 
 
 38 
 
 33 
 
 3 
 
 iS 
 
 38 
 
 33 
 
 33 
 
 3 
 
 3 
 
 3 
 
 38 
 
 3 
 
 00 
 
 3 
 
 ^ CO 
 CO 10 
 
 o oo 
 
 CO 01 
 
 S9U19.I} 
 
 -xa 
 
 38 
 
 O O) 
 CO<M 
 
 CN O 
 
 ^(N 
 
 O1 CO 
 
 O O5 
 CO 01 
 
 3 
 
 33 
 
 3 
 
 33 
 
 3 
 
 33 
 
 3 
 
 8 
 33 
 
 3 
 
 33 
 
 3 
 
 33 
 
 33 
 
 o 
 
 CO 
 
 3 3 
 
 30 COOS 
 
 3838 
 
 38 
 
 3 
 
 3 
 
 rHOS 
 
 O OS 
 COOI ICO Ol 
 
 CO Ol 
 
 33 
 
 3 
 
 33 
 
 33 
 
 38 
 
 38 
 
 38 
 
 Mtithill, 
 Perthshirf, 
 245 ti-et abo 
 Sea-level. 
 
 1 1 1 t 
 
 S ! 
 
 * 1 
 
 1 1 1 1 
 
METEOROLOGICAL TABLES. 
 
 83 
 
 IS H 
 
84 
 
 METEOROLOGICAL TABLES. 
 
 The following Hygrometrical Tables are not intended so 
 much to help in finding the Dew-point, as to give the 
 amateur observer an approximate idea of the degree to 
 which the air is " saturated with moisture," taking 100 to 
 represent complete saturation. 
 
 For finding the dew-point, the observer had better take 
 the small amount of trouble ^required by the use of the 
 "Table of Factors," given on an earlier page. 
 
 But when the observer's dry and wet bulb thermometers 
 give, as their readings, some intermediate point between 
 the readings supplied in these columns, he will readily find 
 the amount of saturation by calculating the proportional 
 increase or decrease, in accordance with the column headed 
 " Less Saturation, for an increase of 1 in dry." 
 
 TABLE IV. HYGROMETER DEW-POINT AND DEGREE OF 
 SATURATION. 
 
 (Abridged from Mr Glaisher's Tables.) 
 
 Readings of 
 
 g 
 
 
 l-s 
 
 Readings of 
 
 "3 
 2 
 
 
 .2*3 
 
 Thermometers. 
 
 
 M S 
 
 2 S . 
 
 Thermometers. 
 
 
 M C 
 
 llA 
 
 
 || 
 
 O O 
 
 IK 
 
 
 II 
 
 II 
 
 . o E? 
 
 c3 '-> O 
 
 
 
 
 
 Dry. 
 
 Wet. 
 
 HO 
 
 ll 
 
 3,8*; 
 
 Dry. 
 
 Wet. 
 
 
 HO 
 
 II 
 
 1=; 
 
 
 
 o 
 
 
 
 
 
 
 
 
 
 o 
 
 
 
 15 
 
 15-0 
 
 15-0 
 
 100 
 
 -33 
 
 18 
 
 17-5 
 
 137 
 
 83 
 
 27 
 
 
 14-5 
 
 10-6 
 
 81 
 
 26 
 
 
 17-0 
 
 9-5 
 
 68 
 
 21 
 
 
 14-0 
 
 6-2 
 
 67 
 
 22 
 
 
 16-5 
 
 5-2 
 
 56 
 
 16 
 
 
 13'5 
 
 1-8 
 
 54 
 
 16 
 
 
 16-0 
 
 i-o 
 
 46 
 
 11 
 
 16 
 
 16-0 
 
 16-0 
 
 100 
 
 -32 
 
 19 
 
 19-0 
 
 19'0 
 
 100 
 
 -32 
 
 
 15-5 
 
 11-7 
 
 82 
 
 26 
 
 
 18-5 
 
 14-9 
 
 83 
 
 26 
 
 
 150 
 
 7-3 
 
 67 
 
 22 
 
 
 18-0 
 
 107 
 
 68 
 
 20 
 
 
 145 
 
 3-0 
 
 56 
 
 19 
 
 
 175 
 
 6-4 
 
 56 
 
 17 
 
 17 
 
 17-0 
 
 17-0 
 
 100 
 
 -32 
 
 
 17-0 
 
 2-3 
 
 47 
 
 13 
 
 
 16-5 
 
 127 
 
 83 
 
 27 
 
 20 
 
 20-0 
 
 20-0 
 
 100 
 
 -30 
 
 
 16-0 
 
 8-4 
 
 68 
 
 22 
 
 
 19'5 
 
 15-9 
 
 83 
 
 25 
 
 
 15-5 
 
 4-0 
 
 55 
 
 17 
 
 
 19-0 
 
 1T9 
 
 68 
 
 20 
 
 18 
 
 18-0 18-0 
 
 100 
 
 -32 
 
 
 18'5 
 
 7'8 
 
 57 
 
 16 
 
METEOROLOGICAL TABLES. 
 
 85 
 
 Readings of 
 Thermometers. 
 
 Temperature of 
 Dew-point. 
 
 Degree of 
 Saturation. 
 
 Less Saturation, 
 for increase of 
 1, in Dry. 
 
 Readings of 
 Thermometers. 
 
 s 
 
 if 
 ii 
 
 Decree of 
 Saturation. 
 
 Less Saluration, 
 for increase of 
 1*, in Dry. 
 
 Dry. 
 
 Wet. 
 
 Dry. 
 
 Wet. 
 
 o 
 
 o 
 
 o 
 
 
 
 o 
 
 o 
 
 o 
 
 
 
 20 
 
 18-0 
 
 37 
 
 48 
 
 13 
 
 27 
 
 26-0 
 
 21-4 
 
 79 
 
 15 
 
 
 17-5 
 
 o-o 
 
 40 
 
 10 
 
 
 25-5 
 
 18-6 
 
 70 
 
 13 
 
 21 
 
 21-0 
 
 21-0 
 
 100 
 
 -29 
 
 
 25-0 
 
 15-8 
 
 61 
 
 11 
 
 
 20-5 
 
 17-1 
 
 84 
 
 24 
 
 
 24-5 
 
 13'0 
 
 54 
 
 9 
 
 
 20-0 
 
 13-1 
 
 70 
 
 20 
 
 28 
 
 28-0 
 
 28-0 
 
 100 
 
 -18 
 
 
 19-5 
 
 9-2 
 
 58 
 
 16 
 
 
 275 
 
 25-5 
 
 89 
 
 14 
 
 
 19-0 
 
 5-2 
 
 49 
 
 13 
 
 
 27-0 
 
 22-9 
 
 80 
 
 13 
 
 
 18'5 
 
 1-3 
 
 42 
 
 11 
 
 
 26-5 
 
 20-3 
 
 72 
 
 11 
 
 22 
 
 22-0 
 
 22-0 
 
 100 
 
 -28 
 
 
 26-0 
 
 17-8 
 
 64 
 
 10 
 
 
 21-5 
 
 18-2 
 
 85 
 
 24 
 
 
 25-5 
 
 15-2 
 
 57 
 
 8 
 
 
 21-0 
 
 14-4 
 
 71 
 
 19 
 
 29 
 
 29-0 
 
 29-0 
 
 100 
 
 -17 
 
 
 20-5 
 
 10-6 
 
 60 
 
 16 
 
 
 28-5 
 
 267 
 
 91 
 
 14 
 
 
 20-0 
 
 6-8 
 
 50 
 
 14 
 
 
 28-0 
 
 24-4 
 
 82 
 
 13 
 
 
 19-5 
 
 3-0 
 
 40 
 
 12 
 
 
 27-5 
 
 22-1 
 
 75 
 
 12 
 
 23 
 
 23-0 
 
 23-0 
 
 100 
 
 -27 
 
 
 27-0 
 
 19-7 
 
 67 
 
 9 
 
 
 22-5 
 
 19-3 
 
 85 
 
 23 
 
 
 26-5 
 
 17-5 
 
 60 
 
 8 
 
 
 22-0 
 
 157 
 
 72 
 
 19 
 
 
 26-0 
 
 14-0 
 
 54 
 
 6 
 
 
 21-5 
 
 12-1 
 
 61 
 
 15 
 
 30 
 
 30-0 
 
 30-0 
 
 100 
 
 -15 
 
 
 21-0 
 
 8'4 
 
 52 
 
 13 
 
 
 29-5 
 
 27-9 
 
 91 
 
 13 
 
 
 20-5 
 
 4-8 
 
 44 
 
 11 
 
 
 29-0 
 
 25-9 
 
 83 
 
 11 
 
 24 
 
 24-0 
 
 24-0 
 
 100 
 
 -26 
 
 
 28-5 
 
 23-8 
 
 76 
 
 10 
 
 
 23-5 
 
 20-5 
 
 85 
 
 22 
 
 
 28-0 
 
 21-7 
 
 69 
 
 7 
 
 
 23-0 
 
 17-1 
 
 73 
 
 18 
 
 
 27-5 
 
 19.6 
 
 63 
 
 5 
 
 
 22-5 
 
 13-6 
 
 63 
 
 15 
 
 31 
 
 31-0 
 
 31-0 
 
 100 
 
 -13 
 
 
 22-0 
 
 10-2 
 
 53 
 
 12 
 
 
 30-5 
 
 291 
 
 92 
 
 12 
 
 
 21-5 
 
 67 
 
 46 
 
 11 
 
 
 30-0 
 
 27-3 
 
 85 
 
 9 
 
 - 
 
 21-0 
 
 3-2 
 
 39 
 
 9 
 
 
 29-5 
 
 25-5 
 
 78 
 
 8 
 
 25 
 
 25-0 
 
 25-0 
 
 100 
 
 -24 
 
 
 29-0 
 
 23-6 
 
 72 
 
 7 
 
 
 24-5 
 
 217 
 
 86 
 
 20 
 
 
 28-5 
 
 217 
 
 67 
 
 5 
 
 : 
 
 24-0 
 
 18-5 
 
 74 
 
 17 
 
 32 
 
 32-0 
 
 320 
 
 100 
 
 -11 
 
 
 23-5 
 
 15-2 
 
 64 
 
 14 
 
 
 31-5 
 
 30-3 
 
 93 
 
 10 
 
 
 23-0 
 
 11-9 
 
 55 
 
 11 
 
 
 31-0 
 
 287 
 
 87 
 
 8 
 
 
 22-5 
 
 87 
 
 48 
 
 9 
 
 
 30-5 
 
 27-0 
 
 80 
 
 7 
 
 26 
 
 26-0 
 
 26-0 
 
 100 
 
 -21 
 
 
 30-0 
 
 25-4 
 
 75 
 
 6 
 
 
 25-5 
 
 23-0 
 
 88 
 
 17 
 
 
 29-5 
 
 237 
 
 70 
 
 5 
 
 
 25-0 
 
 19-9 
 
 76 
 
 15 
 
 33 
 
 33-0 
 
 33-0 
 
 100 
 
 -11 
 
 
 24-5 
 
 16-9 
 
 66 
 
 12 
 
 
 32-5 
 
 31-5 
 
 94 
 
 10 
 
 
 240 
 
 13-8 
 
 58 
 
 11 
 
 
 32-0 
 
 30-0 
 
 89 
 
 9 
 
 
 23-5 
 
 10-8 
 
 51 
 
 10 
 
 
 31-5 
 
 28-5 
 
 83 
 
 8 
 
 27 
 
 27-0 
 
 27-0 
 
 100 
 
 -20 
 
 
 31-0 
 
 27-0 
 
 78 
 
 7 
 
 
 26-5 
 
 24-2 
 
 89 
 
 17 
 
 
 30-5 
 
 25-5 
 
 73 
 
 6 
 
 
 
 
 
 
 
 
 
 
86 
 
 METEOROLOGICAL TABLES. 
 
 
 "S 
 
 f 
 
 
 3 
 
 
 fa 
 
 Readings of 
 
 
 
 
 .*-f O 
 
 Readings of 
 
 S 
 
 
 11 
 
 Thermometers. 
 
 JN 
 
 
 
 J-. GG 
 
 Thermometers. 
 
 & -w 
 
 IM O 
 
 *"* W i>v 
 
 
 s 
 
 O f O 
 
 5 s e 
 $ Q 
 
 .S c 
 
 
 .s 
 
 || 
 
 0.0 
 
 "3 
 
 Is 
 
 III 
 
 
 
 
 
 Dry. 
 
 Wet. 
 
 II 
 
 ft! 
 
 Joo; 
 
 Dry. 
 
 Wet. 
 
 II 
 
 SI 
 
 Sss; 
 
 o 
 
 o 
 
 
 
 
 
 
 
 
 
 o 
 
 
 
 34 
 
 34-0 
 
 34-0 
 
 100 
 
 -10 
 
 40 
 
 30 
 
 17-1 
 
 38 
 
 3 
 
 
 33-5 
 
 32-6 
 
 94 
 
 9 
 
 
 28 
 
 12-5 
 
 31 
 
 2 
 
 
 33-0 
 
 31-2 
 
 89 
 
 9 
 
 41 
 
 41 
 
 41-0 
 
 100 
 
 -8 
 
 
 32-5 
 
 29-8 
 
 84 
 
 9 
 
 
 39 
 
 36-5 
 
 84 
 
 6 
 
 
 32-0 
 
 28-5 
 
 79 
 
 7 
 
 
 37 
 
 32-0 
 
 70 
 
 5 
 
 
 31-5 
 
 27-1 
 
 75 
 
 6 
 
 
 35 
 
 27-4 
 
 58 
 
 4 
 
 
 , 31-0 
 
 25-5 
 
 72 
 
 6 
 
 
 33 
 
 22-9 
 
 48 
 
 3 
 
 35 
 
 35-0 
 
 35-0 
 
 100 
 
 -10 
 
 
 31 
 
 18-4 
 
 39 
 
 3 
 
 
 31-5 
 
 337 
 
 95 
 
 9 
 
 
 29 
 
 13-9 
 
 31 
 
 2 
 
 
 34-0 
 
 324 
 
 90 
 
 8 
 
 42 
 
 42 
 
 42-0 
 
 100 
 
 -8 
 
 
 33-5 
 
 311 
 
 85 
 
 7 
 
 
 40 
 
 37-5 
 
 85 
 
 7 
 
 
 33-0 
 
 29-8 
 
 80 
 
 7 
 
 
 38 
 
 33-1 
 
 72 
 
 6 
 
 
 32-5 
 
 28-5 
 
 75 
 
 6 
 
 
 36 
 
 28-6 
 
 60 
 
 5 
 
 
 32-0 
 
 27-2 
 
 72 
 
 6 
 
 
 34 
 
 24-2 
 
 49 
 
 4 
 
 36 
 
 36 
 
 36-0 
 
 100 
 
 -9 
 
 
 32 
 
 19-7 
 
 40 
 
 3 
 
 
 34 
 
 31-0 
 
 82 
 
 7 
 
 
 30 
 
 15-2 
 
 33 
 
 2 
 
 
 32 
 
 26-0 
 
 66 
 
 5 
 
 
 28 
 
 10-8 
 
 27 
 
 2 
 
 
 30 
 
 21-0 
 
 53 
 
 4 
 
 43 
 
 43 
 
 43-0 
 
 100 
 
 -8 
 
 
 28 
 
 160 
 
 42 
 
 3 
 
 
 41 
 
 38-6 
 
 84 
 
 7 
 
 37 
 
 37 
 
 37-0 
 
 100 
 
 -9 
 
 
 39 
 
 34-2 
 
 71 
 
 6 
 
 
 35 
 
 32-2 
 
 83 
 
 7 
 
 
 37 
 
 29-8 
 
 59 
 
 5 
 
 
 33 
 
 27-3 
 
 68 
 
 6 
 
 
 35 
 
 25-4 
 
 49 
 
 4 
 
 
 31 
 
 22-5 
 
 55 
 
 5 
 
 
 33 
 
 21-0 
 
 41 
 
 4 
 
 
 29 
 
 17-6 
 
 44 
 
 3 
 
 
 31 
 
 16-6 
 
 34 
 
 3 
 
 38 
 
 38 
 
 380 
 
 100 
 
 -8 
 
 
 29 
 
 12-2 
 
 28 
 
 3 
 
 
 36 
 
 33-3 
 
 83 
 
 6 
 
 44 
 
 44 
 
 440 
 
 100 
 
 -8 
 
 
 34 
 
 28-6 
 
 68 
 
 5 
 
 
 42 
 
 39-6 
 
 84 
 
 6 
 
 
 32 
 
 23-8 
 
 56 
 
 4 
 
 
 40 
 
 35-3 
 
 71 
 
 5 
 
 
 30 
 
 19-1 
 
 45 
 
 3 
 
 
 38 
 
 30-9 
 
 59 
 
 4 
 
 
 28 
 
 14-4 
 
 37 
 
 3 
 
 
 36 
 
 26-6 
 
 49 
 
 4 
 
 39 
 
 39 
 
 39-0 
 
 100 
 
 -8 
 
 
 34 
 
 22-2 
 
 41 
 
 3 
 
 
 37 
 
 34-4 
 
 84 
 
 8 
 
 
 32 
 
 17-8 
 
 34 
 
 3 
 
 
 35 
 
 297 
 
 70 
 
 7 
 
 
 30 
 
 13-5 
 
 28 
 
 3 
 
 
 33 
 
 25-1 
 
 57 
 
 6 
 
 45 
 
 45 
 
 45-0 
 
 100 
 
 -7 
 
 
 31 
 
 20-4 
 
 47 
 
 5 
 
 
 43 
 
 407 
 
 85 
 
 6 
 
 
 29 
 
 15-8 
 
 38 
 
 4 
 
 
 41 
 
 36-4 
 
 72 
 
 5 
 
 40 
 
 40 
 
 40-0 
 
 100 
 
 -8 
 
 
 39 
 
 32-0 
 
 60 
 
 4 
 
 
 38 
 
 35'4 
 
 84 
 
 7 
 
 
 37 
 
 277 
 
 50 
 
 4 
 
 
 36 
 
 30-8 
 
 69 
 
 5 
 
 
 35 
 
 23-4 
 
 42 
 
 3 
 
 
 34 
 
 26-3 
 
 57 
 
 4 
 
 
 33 
 
 191 
 
 34 
 
 3 
 
 
 32 
 
 217 
 
 46 
 
 3 
 
 
 31 
 
 14-8 
 
 28 
 
 3 
 
METEOROLOGICAL TABLES. 
 
 87 
 
 Readings of 
 Thermometers. 
 
 Temperature of 
 Dew-point. 
 
 Degi-ee of 
 Sat uration. 
 
 Less Saturation, 
 for increase of 
 1, in Dry. 
 
 Readings of 
 fherinometers. 
 
 Temperature of 
 Dew-point. 
 
 Degree of 
 Saturation. 
 
 Less Saturation, 
 for increase of 
 1, in Dry. 
 
 Dry. 
 
 Wet. 
 
 Dry 
 
 Wet. 
 
 o 
 
 
 
 
 
 
 
 o 
 
 o 
 
 o 
 
 
 
 46 
 
 46 
 
 46-0 
 
 100 
 
 -7 
 
 51 
 
 49 
 
 46-9 
 
 86 
 
 6 
 
 
 44 
 
 41-7 
 
 86 
 
 7 
 
 
 47 
 
 42-8 
 
 74 
 
 5 
 
 
 42 
 
 37-4 
 
 73 
 
 6 
 
 
 45 
 
 38-8 
 
 63 
 
 4 
 
 
 40 
 
 33-2 
 
 61 
 
 5 
 
 
 43 
 
 347 
 
 54 
 
 4 
 
 
 38 
 
 28-9 
 
 51 
 
 4 
 
 
 41 
 
 30-6 
 
 46 
 
 3 
 
 
 36 
 
 24-6 
 
 43 
 
 3 
 
 
 39 
 
 26-5 
 
 38 
 
 3 
 
 
 34 
 
 203 
 
 35 
 
 3 
 
 
 37 
 
 22-4 
 
 32 
 
 2 
 
 
 32 
 
 16-0 
 
 29 
 
 3 
 
 52 
 
 52 
 
 52-0 
 
 100 
 
 _7 
 
 47 
 
 47 
 
 47-0 
 
 100 
 
 -7 
 
 
 50 
 
 48-0 
 
 86 
 
 6 
 
 
 45 
 
 42-8 
 
 86 
 
 6 
 
 
 48 
 
 43-9 
 
 74 
 
 5 
 
 
 43 
 
 38-5 
 
 73 
 
 5 
 
 
 46 
 
 39-9 
 
 64 
 
 4 
 
 
 41 
 
 34-3 
 
 61 
 
 5 
 
 
 44 
 
 359 
 
 54 
 
 4 
 
 
 39 
 
 30-0 
 
 51 
 
 4 
 
 
 42 
 
 31-8 
 
 46 
 
 3 
 
 
 37 
 
 25-8 
 
 43 
 
 3 
 
 
 40 
 
 27-8 
 
 39 
 
 3 
 
 
 35 
 
 21-6 
 
 36 
 
 3 
 
 
 38 
 
 237 
 
 33 
 
 2 
 
 
 33 
 
 17-3 
 
 30 
 
 2 
 
 53 
 
 53 
 
 53-0 
 
 100 
 
 -7 
 
 48 
 
 48 
 
 48-0 
 
 100 
 
 7 
 
 
 51 
 
 49-0 
 
 86 
 
 6 
 
 
 46 
 
 43-8 
 
 86 
 
 7 
 
 
 49 
 
 45-0 
 
 74 
 
 5 
 
 
 44 
 
 39-6 
 
 73 
 
 6 
 
 
 47 
 
 41-0 
 
 64 
 
 5 
 
 
 42 
 
 35-4 
 
 62 
 
 5 
 
 
 45 
 
 37-0 
 
 55 
 
 4 
 
 
 40 
 
 31-2 
 
 52 
 
 4 
 
 
 43 
 
 33-0 
 
 47 
 
 3 
 
 
 38 
 
 27-0 
 
 44 
 
 3 
 
 
 41 
 
 29-0 
 
 39 
 
 3 
 
 
 36 
 
 22-8 
 
 36 
 
 2 
 
 
 39 
 
 25-0 
 
 33 
 
 2 
 
 
 34 
 
 18-6 
 
 30 
 
 2 
 
 54 
 
 54 
 
 54-0 
 
 100 
 
 -7 
 
 49 
 
 49 
 
 49-0 
 
 100 
 
 -7 
 
 
 52 
 
 50-0 
 
 86 
 
 6 
 
 
 47 
 
 44-8 
 
 86 
 
 6 
 
 
 50 
 
 46-1 
 
 74 
 
 5 
 
 
 45 
 
 407 
 
 73 
 
 5 
 
 
 48 
 
 42-1 
 
 64 
 
 4 
 
 
 43 
 
 36-5 
 
 62 
 
 4 
 
 
 46 
 
 38-2 
 
 55 
 
 3 
 
 
 41 
 
 32-4 
 
 53 
 
 4 
 
 
 44 
 
 342 
 
 47 
 
 3 
 
 
 39 
 
 28-2 
 
 45 
 
 3 
 
 
 42 
 
 30-2 
 
 40 
 
 3 
 
 
 37 
 
 24-0 
 
 37 
 
 3 
 
 
 40 
 
 26-3 
 
 34 
 
 2 
 
 
 35 j 19-9 
 
 31 
 
 2 
 
 55 
 
 55 
 
 55-0 
 
 100 i -7 
 
 50 
 
 50 1 50'0 
 
 100 
 
 7 
 
 
 53 
 
 51-1 
 
 87 
 
 5 
 
 
 48 
 
 45-9 
 
 86 
 
 6 
 
 
 51 
 
 47-2 
 
 75 
 
 5 
 
 
 46 
 
 41-8 
 
 74 
 
 5 
 
 
 49 
 
 43-2 
 
 65 
 
 4 
 
 
 44 
 
 37-6 
 
 63 
 
 5 
 
 
 47 
 
 39-3 
 
 56 
 
 4 
 
 
 42 
 
 33-5 
 
 53 
 
 4 
 
 
 45 
 
 35-4 
 
 48 
 
 3 
 
 
 40 
 
 29-4 
 
 45 
 
 3 
 
 
 43 
 
 31-5 
 
 41 
 
 3 
 
 
 38 
 
 25-3 
 
 37 
 
 2 
 
 
 41 
 
 27-6 
 
 35 
 
 2 
 
 
 36 
 
 21-2 
 
 31 
 
 2 
 
 56 
 
 56 
 
 56-0 
 
 100 
 
 -7 
 
 51 
 
 51 
 
 511) 
 
 100 
 
 v 
 
 
 54 
 
 52-1 
 
 87 
 
 6 
 
88 
 
 METEOROLOGICAL TABLES. 
 
 Readings of 
 Thermometers 
 
 Temperature of 
 Dew-point. 
 
 Degree of 
 Saturation. 
 
 Less Saturation, 
 for increase of 
 1, in Diy. 
 
 Readings of 
 Thermometers 
 
 Temperature of 
 Dew-point. 
 
 Degree of 
 Saturation. 
 
 Less Saturation, 
 for increase of 
 !, in Diy. 
 
 Dry. 
 
 Wet. 
 
 Dry 
 
 Wet. 
 
 o 
 
 o 
 
 
 
 
 
 o 
 
 o 
 
 o 
 
 
 
 56 
 
 52 
 
 48-2 
 
 75 
 
 5 
 
 61 
 
 55 
 
 49-8 
 
 67 
 
 4 
 
 
 50 
 
 44-4 
 
 65 
 
 4 
 
 
 53 
 
 46-0 
 
 58 
 
 4 
 
 
 48 
 
 40-5 
 
 56 
 
 4 
 
 
 51 
 
 42-3 
 
 50 
 
 3 
 
 
 46 
 
 36'6 
 
 48 
 
 3 
 
 
 49 
 
 38-6 
 
 44 
 
 3 
 
 
 44 
 
 327 
 
 41 
 
 3 
 
 
 47 
 
 34-8 
 
 38 
 
 2 
 
 
 42 
 
 28-8 
 
 35 
 
 2 
 
 62 
 
 62 
 
 62-0 
 
 100 
 
 -6 
 
 57 
 
 57 
 
 57-0 
 
 100 
 
 -6 
 
 
 60 
 
 58-3 
 
 88 
 
 6 
 
 
 55 
 
 53-2 
 
 87 
 
 6 
 
 
 58 
 
 54-6 
 
 77 
 
 5 
 
 
 53 
 
 49-3 
 
 75 
 
 5 
 
 
 56 
 
 50-8 
 
 67 
 
 4 
 
 
 51 
 
 45-5 
 
 65 
 
 4 
 
 
 54 
 
 47-1 
 
 58 
 
 4 
 
 
 49 
 
 41-6 
 
 57 
 
 4 
 
 
 52 
 
 43-4 
 
 50 
 
 3 
 
 
 47 
 
 37-8 
 
 49 
 
 3 
 
 
 50 
 
 397 
 
 44 
 
 3 
 
 
 45 
 
 34-0 
 
 42 
 
 2 
 
 
 48 
 
 36-0 
 
 38 
 
 3 
 
 
 43 
 
 301 
 
 36 
 
 2 
 
 63 
 
 63 
 
 63-0 
 
 100 
 
 -6 
 
 58 
 
 58 
 
 58-0 
 
 100 
 
 -6 
 
 
 61 
 
 59-3 
 
 88 
 
 5 
 
 
 56 
 
 54-2 
 
 87 
 
 6 
 
 
 59 
 
 55-6 
 
 77 
 
 4 
 
 
 54 
 
 50-4 
 
 76 
 
 5 
 
 
 57 
 
 51-9 
 
 67 
 
 4 
 
 
 52 
 
 46-6 
 
 66 
 
 4 
 
 
 55 
 
 48-2 
 
 59 
 
 4 
 
 
 50 
 
 42-8 
 
 57 
 
 4 
 
 
 53 
 
 44-5 
 
 51 
 
 3 
 
 
 48 
 
 39-0 
 
 49 
 
 3 
 
 
 51 
 
 40-8 
 
 44 
 
 2 
 
 
 46 
 
 35-2 
 
 43 
 
 3 
 
 
 49 
 
 37-1 
 
 38 
 
 2 
 
 
 44 
 
 31-4 
 
 37 
 
 2 
 
 64 
 
 64 
 
 64-0 
 
 100 
 
 -6 
 
 59 
 
 59 
 
 59-0 
 
 100 
 
 r 
 
 
 62 
 
 60-3 
 
 88 
 
 5 
 
 
 57 
 
 55-2 
 
 88 
 
 6 
 
 
 60 
 
 567 
 
 77 
 
 5 
 
 
 55 
 
 51-4 
 
 76 
 
 5 
 
 
 58 
 
 53-0 
 
 67 
 
 4 
 
 
 53 
 
 47-7 
 
 66 
 
 4 
 
 
 56 
 
 49-4 
 
 59 
 
 4 
 
 
 51 
 
 43-9 
 
 57 
 
 4 
 
 
 54 
 
 457 
 
 51 
 
 3 
 
 
 49 
 
 40-1 
 
 49 
 
 3 
 
 
 52 
 
 42-0 
 
 45 
 
 3 
 
 
 47 
 
 36-3 
 
 43 
 
 3 
 
 
 50 
 
 38-4 
 
 39 
 
 2 
 
 
 45 
 
 32-5 
 
 37 
 
 2 
 
 65 
 
 65 
 
 65-0 
 
 100 
 
 -6 
 
 60 
 
 60 
 
 60-0 
 
 100 
 
 -6 
 
 
 63 
 
 61-4 
 
 88 
 
 6 
 
 
 58 
 
 56-2 
 
 88 
 
 6 
 
 
 61 
 
 577 
 
 78 
 
 5 
 
 
 56 
 
 52-5 
 
 76 
 
 5 
 
 
 59 
 
 541 
 
 68 
 
 4 
 
 
 54 
 
 487 
 
 66 
 
 4 
 
 
 57 
 
 50-4 
 
 59 
 
 4 
 
 
 52 
 
 45-0 
 
 58 
 
 4 
 
 
 55 
 
 46-8 
 
 51 
 
 3 
 
 
 50 
 
 41-2 
 
 50 
 
 3 
 
 
 53 
 
 43-2 
 
 45 
 
 3 
 
 
 48 
 
 37-4 
 
 43 
 
 3 
 
 
 51 
 
 39-5 
 
 39 
 
 2 
 
 
 46 
 
 337 
 
 37 
 
 2 
 
 66 
 
 66 
 
 66-0 
 
 100 
 
 -6 
 
 61 
 
 61 
 
 61-0 
 
 100 
 
 -6 
 
 
 64 
 
 62-4 
 
 88 
 
 5 
 
 
 59 
 
 57-3 
 
 88 
 
 6 
 
 
 62 
 
 58-8 
 
 78 
 
 5 
 
 
 57 
 
 53-5 
 
 77 
 
 5 
 
 
 60 
 
 55-1 
 
 68 
 
 4 
 
METEOROLOGICAL TABLES. 
 
 89 
 
 Readings of 
 Thermometers. 
 
 Temperature of 
 Dew-point. 
 
 Degree of 
 Saturation. 
 
 Less Saturation, 
 for increase of 
 1, in Dry. 
 
 Readings of 
 Thermometers. 
 
 Temperature of 
 DC: \v-point. 
 
 Degree of 
 
 Saturation. 
 
 Less Saturation, 
 for increase of 
 1, in Dry. 
 
 D '. 
 
 Wet. 
 
 Dry. 
 
 Wet. 
 
 o 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 66 
 
 58 
 
 51-5 
 
 60 
 
 3 
 
 71 
 
 61 
 
 53-4 
 
 53 
 
 3 
 
 
 56 
 
 47-9 
 
 52 
 
 3 
 
 
 59 
 
 46-9 
 
 47 
 
 2 
 
 
 54 
 
 44-3 
 
 45 
 
 3 
 
 
 57 
 
 46-4 
 
 41 
 
 2 
 
 
 52 
 
 407 
 
 40 
 
 2 
 
 72 
 
 72 
 
 72-0 
 
 100 
 
 -6 
 
 67 
 
 67 
 
 67-0 
 
 100 
 
 -6 
 
 
 70 
 
 68-5 
 
 89 
 
 5 
 
 
 65 
 
 63-4 
 
 88 
 
 ^6 
 
 
 68 
 
 65-0 
 
 79 
 
 4 
 
 
 63 
 
 59-8 
 
 78 
 
 5 
 
 
 66 
 
 61-5 
 
 69 
 
 4 
 
 
 61 
 
 56-2 
 
 68 
 
 5 
 
 
 64 
 
 58-0 
 
 61 
 
 4 
 
 
 59 
 
 52-6 
 
 60 
 
 4 
 
 
 62 
 
 54-5 
 
 54 
 
 3 
 
 
 57 
 
 49-0 
 
 52 
 
 4 
 
 
 60 
 
 51-0 
 
 48 
 
 3 
 
 
 55 
 
 45-4 
 
 46 
 
 3 
 
 
 58 
 
 47-5 
 
 42 
 
 2 
 
 
 53 
 
 41-8 
 
 40 
 
 ^ 
 
 73 
 
 73 
 
 73-0 
 
 100 
 
 -6 
 
 68 
 
 68 
 
 68-0 
 
 100 
 
 -6 
 
 
 71 
 
 69-5 
 
 89 
 
 5 
 
 
 66 
 
 64-4 
 
 88 
 
 6 
 
 
 69 
 
 66-0 
 
 79 
 
 4 
 
 
 64 
 
 60-8 
 
 78 
 
 5 
 
 
 67 
 
 62-6 
 
 70 
 
 4 
 
 
 62 
 
 57-3 
 
 68 
 
 5 
 
 
 65 
 
 59-1 
 
 62 
 
 3 
 
 
 60 
 
 537 
 
 60 
 
 4 
 
 
 63 
 
 55-6 
 
 54 
 
 3 
 
 
 58 
 
 50-1 
 
 52 
 
 4 
 
 
 61 
 
 52-1 
 
 48 
 
 3 
 
 
 56 
 
 46-5 
 
 46 
 
 3 
 
 
 59 
 
 48-6 
 
 42 
 
 2 
 
 
 54 
 
 42-9 
 
 40 
 
 3 
 
 74 
 
 74 
 
 74-0 
 
 100 
 
 -6 
 
 GO 
 
 69 
 
 69-0 
 
 100 
 
 -6 
 
 
 72 
 
 70-5 
 
 89 
 
 5 
 
 
 67 
 
 65-4 
 
 88 
 
 5 
 
 
 70 
 
 67-1 
 
 79 
 
 5 
 
 
 65 
 
 61-9 
 
 78 
 
 5 
 
 
 68 
 
 63-6 
 
 70 
 
 4 
 
 
 63 
 
 58-3 
 
 68 
 
 4 
 
 
 66 
 
 60-2 
 
 62 
 
 4 
 
 
 61 
 
 54-8 
 
 60 
 
 4 
 
 
 64 
 
 567 
 
 55 
 
 3 
 
 
 59 
 
 51-2 
 
 53 
 
 3 
 
 
 62 
 
 53-2 
 
 48 
 
 3 
 
 
 57 
 
 47-6 
 
 47 
 
 3 
 
 
 60 
 
 49-8 
 
 43 
 
 2 
 
 
 55 
 
 441 
 
 41 
 
 3 
 
 75 
 
 75 
 
 75-0 
 
 100 
 
 -6 
 
 70 
 
 70 
 
 70-0 
 
 100 
 
 -6 
 
 
 73 
 
 71-6 
 
 89 
 
 5 
 
 
 68 
 
 66-5 
 
 88 
 
 5 
 
 
 71 
 
 68-1 
 
 79 
 
 4 
 
 
 66 
 
 62-9 
 
 78 
 
 5 
 
 
 69 
 
 647 
 
 70 
 
 4 
 
 
 64 
 
 59-4 
 
 69 
 
 4 
 
 
 67 
 
 61-2 
 
 62 
 
 3 
 
 
 62 
 
 55-8 
 
 61 
 
 4 
 
 
 65 
 
 57-8 
 
 55 
 
 3 
 
 
 60 
 
 52-3 
 
 53 
 
 3 
 
 
 63 
 
 54-4 
 
 49 
 
 3 
 
 
 58 
 
 48-8 
 
 47 
 
 3 
 
 
 61 
 
 50-9 
 
 43 
 
 2 
 
 
 56 
 
 45-2 
 
 41 
 
 2 
 
 76 
 
 76 
 
 76-0 
 
 100 
 
 -5 
 
 71 
 
 71 
 
 71-0 
 
 100 
 
 -6 
 
 
 74 
 
 72-6 
 
 89 5 
 
 
 69 
 
 67-5 
 
 88 
 
 5 
 
 
 72 
 
 69-2 
 
 71) 
 
 4 
 
 
 67 
 
 64-0 
 
 78 
 
 5 
 
 
 70 
 
 65-7 
 
 71 
 
 4 
 
 
 65 
 
 60-4 
 
 69 
 
 4 
 
 
 68 
 
 62-3 
 
 63 
 
 3 
 
 63 
 
 56-9 
 
 61 
 
 3 
 
 
 66 
 
 58-9 
 
 55 
 
 3 
 
 
 
 
 
 
 
 ! ' 
 
90 
 
 METEOROLOGICAL TABLES. 
 
 
 *s 
 
 
 &* 
 
 
 'o 
 
 
 t* 
 
 Readings of 
 Thermometers. 
 
 2 
 
 S3 -tS 
 fl 
 
 SL' 
 
 S',2 
 
 if 
 
 .2 o 
 
 lit 
 
 l| 
 
 Readings of 
 Thermometers 
 
 EH 
 3 -ti 
 
 15 S 
 II 
 
 *J 
 
 2 
 
 X O 
 
 % . 
 *Sb 
 
 3&S 
 
 Dry. 
 
 Wet. 
 
 5 1 
 
 HQ 
 
 &| 
 & 
 
 J& 
 
 Dry. 
 
 Wet. 
 
 l| 
 
 E- 
 
 &* 
 
 a 
 
 CO .5 C 
 
 Ittf 
 
 o 
 
 o 
 
 I 
 o 
 
 
 
 
 
 
 
 
 
 
 
 76 
 
 64 
 
 55-5 
 
 49 
 
 3 
 
 81 
 
 67 
 
 57-5 
 
 44 
 
 2 
 
 
 62 
 
 521 
 
 43 
 
 2 
 
 82 
 
 82 
 
 82-0 
 
 100 
 
 -5 
 
 77 
 
 77 
 
 77-0 
 
 100 
 
 O 
 
 
 80 
 
 787 
 
 90 
 
 5 
 
 
 75 
 
 73-6 
 
 89 
 
 5 
 
 
 78 
 
 75-3 
 
 80 
 
 4 
 
 
 73 
 
 70-2 
 
 79 
 
 4 
 
 
 76 
 
 72-0 
 
 72 
 
 4 
 
 
 71 
 
 66-8 
 
 71 
 
 4 
 
 
 74 
 
 68-6 
 
 64 
 
 3 
 
 
 69 
 
 63-4 
 
 63 
 
 3 
 
 
 72 
 
 65-3 
 
 57 
 
 3 
 
 
 67 
 
 60-0 
 
 56 
 
 3 
 
 
 70 
 
 61-9 
 
 51 
 
 3 
 
 
 65 
 
 566 
 
 50 
 
 2 
 
 
 68 
 
 58-6 
 
 45 
 
 3 
 
 
 63 
 
 53-2 
 
 44 
 
 2 
 
 83 
 
 83 
 
 83-0 
 
 100 
 
 -5 
 
 78 
 
 78 
 
 78-0 
 
 100 
 
 -5 
 
 
 81 
 
 797 
 
 90 
 
 5 
 
 
 76 
 
 74-6 
 
 89 
 
 5 
 
 
 79 
 
 76-3 
 
 80 
 
 4 
 
 
 74 
 
 71-2 
 
 79 
 
 4 
 
 
 77 
 
 73-0 
 
 72 
 
 4 
 
 
 72 
 
 67-8 
 
 71 
 
 4 
 
 
 75 
 
 697 
 
 64 
 
 3 
 
 
 70 
 
 64-4 
 
 63 
 
 3 
 
 
 73 
 
 66-3 
 
 57 
 
 3 
 
 
 68 
 
 61-1 
 
 56 
 
 3 
 
 
 71 
 
 63-0 
 
 51 
 
 3 
 
 
 66 
 
 577 
 
 50 
 
 3 
 
 
 69 
 
 597 
 
 45 
 
 2 
 
 
 64 
 
 54-3 
 
 44 
 
 3 
 
 84 
 
 84 
 
 84-0 
 
 100 
 
 -5 
 
 79 
 
 79 
 
 79-0 
 
 100 
 
 -5 
 
 
 82 
 
 807 
 
 90 
 
 5 
 
 
 77 
 
 75-6 
 
 90 
 
 5 
 
 
 80 
 
 77-4 
 
 80 
 
 4 
 
 
 75 
 
 72-3 
 
 80 
 
 4 
 
 
 78 
 
 74-0 
 
 72 
 
 4 
 
 
 73 
 
 68-9 
 
 71 
 
 4 
 
 
 76 
 
 707 
 
 64 
 
 3 
 
 
 71 
 
 65-5 
 
 63 
 
 3 
 
 
 74 
 
 67-4 
 
 57 
 
 3 
 
 
 69 
 
 62-1 
 
 56 
 
 3 
 
 
 72 
 
 64-1 
 
 51 
 
 3 
 
 
 67 
 
 587 
 
 50 
 
 3 
 
 
 70 
 
 60-8 
 
 45 
 
 2 
 
 
 65 
 
 55-4 
 
 44 
 
 3 
 
 85 
 
 85 
 
 85-0 
 
 100 
 
 -5 
 
 80 
 
 80 
 
 80-0 
 
 100 
 
 -5 
 
 
 83 
 
 817 
 
 90 
 
 5 
 
 
 78 
 
 76-6 
 
 90 
 
 5 
 
 
 81 
 
 78-4 
 
 80 
 
 4 
 
 
 76 
 
 73-3 
 
 80 
 
 4 
 
 
 79 
 
 75-1 
 
 72 
 
 4 
 
 
 74 
 
 69-9 
 
 71 
 
 4 
 
 
 77 
 
 71-8 
 
 64 
 
 3 
 
 
 72 
 
 66-5 
 
 63 
 
 3 
 
 
 75 
 
 68-5 
 
 58 
 
 3 
 
 
 70 
 
 63-2 
 
 56 
 
 3 
 
 
 73 
 
 65-2 
 
 52 
 
 3 
 
 
 68 
 
 59'8 
 
 50 
 
 3 
 
 
 71 
 
 61-8 
 
 46 
 
 2 
 
 
 66 
 
 56-4 
 
 44 
 
 2 
 
 86 
 
 86 
 
 86-0 
 
 100 
 
 -5 
 
 81 
 
 81 
 
 81-0 
 
 100 
 
 -5 
 
 
 84 
 
 827 
 
 90 
 
 5 
 
 
 79 
 
 777 
 
 90 
 
 5 
 
 
 82 
 
 79-4 
 
 80 
 
 4 
 
 
 77 
 
 74-3 
 
 80 
 
 4 
 
 
 80 
 
 76-1 
 
 72 
 
 4 
 
 
 75 
 
 70-9 
 
 72 
 
 4 
 
 
 78 
 
 72-8 
 
 64 
 
 3 
 
 
 73 
 
 67-6 
 
 64 
 
 3 
 
 
 76 
 
 69-5 
 
 58 
 
 3 
 
 
 71 
 
 64-2 
 
 56 
 
 3 
 
 
 74 
 
 66-2 
 
 52 
 
 2 
 
 
 69 
 
 60-9 
 
 50 
 
 3 
 
 
 72 
 
 62-9 
 
 46 
 
 2 
 
METEOROLOGICAL TABLES. 
 
 91 
 
 Readings of 
 
 "3 
 
 V 
 
 
 l-o 
 
 Readings of 
 
 ^3 
 
 o 
 
 
 if 
 ."5 
 
 Thermometers. 
 
 h 
 
 si 
 
 o| 
 
 !i* 
 
 l* 
 
 Thermometers. 
 
 If 
 
 in 
 
 111 
 
 Dry. 
 
 Wet. 
 
 C.T* 
 
 11 
 
 IS 
 
 a- - 
 
 Dry. 
 
 Wet. 
 
 p. 1 
 
 tl 
 
 *: . 
 
 o 
 
 o 
 
 O 
 
 
 
 
 
 
 
 
 
 
 
 87 
 
 87 
 
 87-0 
 
 100 
 
 -5 
 
 92 
 
 92 
 
 92-0 
 
 100 
 
 -5 
 
 
 85 
 
 837 
 
 90 
 
 5 
 
 
 90 
 
 88-8 
 
 90 
 
 4 
 
 
 83 
 
 80-4 
 
 81 
 
 4 
 
 
 88 
 
 85-5 
 
 81 
 
 4 
 
 
 81 
 
 771 
 
 73 
 
 4 
 
 
 86 
 
 82-3 
 
 73 
 
 4 
 
 
 79 
 
 73-9 
 
 65 
 
 4 
 
 
 84 
 
 79-1 
 
 66 
 
 3 
 
 
 77 
 
 70-6 
 
 58 
 
 3 
 
 
 82 
 
 75-9 
 
 59 
 
 3 
 
 
 75 
 
 67-3 
 
 52 
 
 3 
 
 
 80 
 
 72-6 
 
 53 
 
 3 
 
 
 73 
 
 64-0 
 
 46 
 
 2 
 
 
 78 
 
 69-4 
 
 47 
 
 2 
 
 88 
 
 88 
 
 88-0 
 
 100 
 
 -5 
 
 93 
 
 93 
 
 93-0 
 
 100 
 
 -5 
 
 
 86 
 
 847 
 
 90 
 
 5 
 
 
 91 
 
 89-8 
 
 90 
 
 4 
 
 
 84 
 
 81-5 
 
 81 
 
 4 
 
 
 89 
 
 86-6 
 
 82 
 
 4 
 
 
 82 
 
 78-2 
 
 ' 73 
 
 4 
 
 
 87 
 
 83-4 
 
 74 
 
 4 
 
 
 80 
 
 74-9 
 
 65 
 
 3 
 
 
 85 
 
 80-1 
 
 66 
 
 3 
 
 
 78 
 
 71-6 
 
 58 
 
 3 
 
 
 83 
 
 76-9 
 
 60 
 
 3 
 
 
 76 
 
 68-4 
 
 52 
 
 3 
 
 
 81 
 
 737 
 
 54 
 
 3 
 
 
 74 
 
 65-1 
 
 46 
 
 2 
 
 
 79 
 
 70-5 
 
 48 
 
 2 
 
 89 
 
 89 
 
 89-0 
 
 100 
 
 -5 
 
 94 
 
 94 
 
 94-0 
 
 100 
 
 -5 
 
 
 87 
 
 857 
 
 90 
 
 5 
 
 
 92 
 
 90-8 
 
 90 
 
 4 
 
 
 85 
 
 82-5 
 
 81 
 
 4 
 
 
 90 
 
 87-6 
 
 82 
 
 4 
 
 
 83 
 
 79-2 
 
 73 
 
 4 
 
 
 88 
 
 84-4 
 
 74 
 
 4 
 
 
 81 
 
 76-0 
 
 65 
 
 3 
 
 
 86 
 
 81-2 
 
 66 
 
 3 
 
 
 79 
 
 727 
 
 58 
 
 3 
 
 
 84 
 
 78-0 
 
 60 
 
 3 
 
 
 77 
 
 69-4 
 
 52 
 
 2 
 
 
 82 
 
 74-8 
 
 54 
 
 3 
 
 
 75 
 
 66-2 
 
 46 
 
 2 
 
 
 80 
 
 71-5 
 
 48 
 
 2 
 
 90 
 
 90 
 
 90-0 
 
 100 
 
 -5 
 
 95 
 
 95 
 
 95-0 
 
 100 
 
 -5 
 
 
 88 
 
 86-8 
 
 90 
 
 4 
 
 
 93 
 
 91-8 
 
 91 
 
 5 
 
 
 86 
 
 83-5 
 
 81 
 
 4 
 
 
 91 
 
 88-6 
 
 82 
 
 4 
 
 
 84 
 
 80-3 
 
 73 
 
 4 
 
 
 89 
 
 85-4 
 
 74 
 
 4 
 
 
 82 
 
 77-0 
 
 65 
 
 3 
 
 
 87 
 
 82-2 
 
 66 
 
 3 
 
 
 80 
 
 737 
 
 59 
 
 3 
 
 
 85 
 
 79-0 
 
 60 
 
 3 
 
 
 78 
 
 70-5 
 
 53 
 
 3 
 
 
 83 
 
 75-8 
 
 54 
 
 2 
 
 
 76 
 
 67-2 
 
 47 
 
 2 
 
 
 81 
 
 72-6 
 
 48 
 
 2 
 
 91 
 
 91 
 
 91-0 
 
 100 
 
 -5 
 
 96 
 
 96 
 
 96-0 
 
 100 
 
 -5 
 
 
 89 
 
 87-8 
 
 90 
 
 4 
 
 
 94 
 
 92-8 
 
 90 
 
 4 
 
 
 87 
 
 84-5 
 
 82 
 
 4 
 
 
 92 
 
 89-6 
 
 82 
 
 4 
 
 
 85 
 
 81-3 
 
 74 
 
 4 
 
 
 90 
 
 86'4 
 
 74 
 
 3 
 
 
 83 
 
 78-0 
 
 66 
 
 3 
 
 
 88 
 
 83-3 
 
 66 
 
 3 
 
 
 81 
 
 74-8 
 
 59 
 
 3 
 
 
 86 
 
 80-1 
 
 60 
 
 3 
 
 
 79 
 
 71-6 
 
 53 
 
 3 
 
 
 84 
 
 76-9 
 
 54 
 
 3 
 
 
 77 
 
 68-3 
 
 47 
 
 2 
 
 
 82 
 
 737 
 
 49 
 
 2 
 
92 
 
 METEOROLOGICAL TABLES. 
 
 1*1 
 
 ill 
 
 S 3 
 3- 
 
 c . 
 
 
 
 
 11 
 
 ll 
 
 's 
 
 <; 
 
 
 
 
METEOROLOGICAL TABLES. 
 
 93 
 
 TEMPERATURE OF SOME NOTED PLACES. 
 
 
 Latitude. 
 
 Winter's 
 Mean. 
 
 Summer's 
 Mean. 
 
 Annual 
 Mean. 
 
 EUROPE. 
 St Petersburg, . . 
 Copenhagen, . . . 
 Edinburgh, .... 
 Berlin, 
 
 N.L. 59 56' 
 
 ... 55 41' 
 ... 55 57' 
 .. 52 31' 
 
 18 
 31 
 38 
 31 
 
 61 
 62 
 
 57 
 64 
 
 39 
 46 
 47 
 
 48 
 
 Dublin, 
 
 ... 53 23' 
 
 40 
 
 59 
 
 49 
 
 London, 
 
 ... 51 30' 
 
 39 
 
 60 
 
 50 
 
 Paris, 
 
 48 50' 
 
 38 
 
 64 
 
 51 
 
 Vienna, . 
 
 48 12' 
 
 32 
 
 69 
 
 51 
 
 Constantinople, . . 
 Gibraltar, .... 
 
 ASIA. 
 Pekin, 
 
 ... 41 0' 
 ... 36 7' 
 
 N L 39 54' 
 
 41 
 56 
 
 28 
 
 71 
 73 
 
 75 
 
 56 
 
 64 
 
 53 
 
 Canton, . 
 
 23 7' 
 
 54 
 
 82 
 
 69 
 
 Bagdad, . 
 
 33 19' 
 
 49 
 
 93 
 
 73 
 
 Bombay, ... 
 
 18 56' 
 
 77 
 
 83 
 
 81 
 
 Calcutta, 
 
 ... 22 33' 
 
 72 
 
 86 
 
 82 
 
 AFRICA. 
 Cape of Good Hope, . 
 Cairo, 
 
 S.L. 34 11' 
 N.L. 30 2' 
 
 58 
 58 
 
 74 
 
 85 
 
 66 
 
 72 
 
 AMERICA. 
 Melville Island, . . 
 Quebec, 
 
 N.L. 74 47' 
 ... 46 49' 
 
 -28 
 + 14 
 
 37 
 
 68 
 
 41 
 
 New York, .... 
 New Orleans, . . . 
 Eio Janeiro, . 
 
 AUSTRALIA (Hobart ) 
 Town), . . . . J 
 
 ... 40 42' 
 ... 29 57' 
 S.L. 22 54' 
 
 S.L. 42 53' 
 
 30 
 55 
 
 68 
 
 42 
 
 71 
 82 
 79 
 
 63 
 
 51 
 69 
 73 
 
 52 
 
INDEX, 
 
 PAGE 
 
 Actinism, ....... 74 
 
 Aerolites, ....... 64 
 
 Agency, Divine, ...... 79 
 
 Agents, imponderable, ...... 70 
 
 Alcoholic thermometer, its defects, . . . .21 
 
 " Apparent" reading of Barometer, .... 7 
 
 Aqueous vapour, invisible, ..... 32 
 
 its beneficial effects, . . . . .57 
 
 Aristotle's idea of Heat, . . . . .70 
 
 Armstrong (Sir William's) Theory, . . . .67 
 
 Atmosphere, ....... 1 
 
 its height and weight, ..... 2 
 
 its component parts, . . . . .60 
 
 its colour, ....... 72 
 
 Atomic Theory, ....... 69 
 
 Aurora Borealis, ...... 54 
 
 Balloon excursions, .....; 44 
 Barometer, ....... 3 
 
 " corrected and reduced," ..... 7 
 
 allowance for temperature, .... 8 
 
 allowance for elevation, ..... 6 
 
 dial-faced, and standard, . . . . .10 
 
 - diameter of tube, . . . . . .11 
 
 hourly fluctuations of, . . . . .15 
 
 how affected by temperature, .... 9 
 
 how and where to hang it, . . . .12 
 
 its indications, . . . . . .14 
 
 manner of observing, . . . . .14 
 
 testing before hanging, .... 11 
 
96 INDEX. 
 
 PAGE 
 
 British rain-fall, Mr Synion's, . . . . .47 
 General Table of, . . . . . .92 
 
 Calendar of nature, . . . . . 77 
 
 Callander, rain-fall at, . . . . . .50 
 
 Calm at Equinox, . . . . . .53 
 
 Casella's thermometers, . . . . .29 
 
 new mercurial minimum, . . . . .30 
 
 Climate, and organic development, . . ... 68 
 
 Clouds, classes of, . . . . .51 
 
 Colours, the primary, . . , . . .74 
 
 Comparative Dryness (Summer and Winter), . . .43 
 
 Crieff, elevation of, ...... 6 
 
 Cylinders for snow measurement, . . . .48 
 
 Daily hour of observation, ..... 
 
 Daniell's Hygrometer, . . . . . 
 
 Decimal Notation, . -. . . 
 Dew-point Hygrometer, 
 
 by calculation, . . . . 
 
 by observation, . . . . . . 
 
 Dynamical theory of Heat, . . . 
 
 Earth's rotation, affected by Heat, - . 
 
 internal heat, ...... 
 
 magnetic sympathy with the Sun, . . 
 
 Electricity, atmospheric, . . . 
 
 English Temperature. (See Table III.) 
 Equinoxial Gales, ...... 
 
 Etherial Hygrometer, ...... 
 
 Expansion of water, Law of, 
 
 Forces, imponderable, ...... 
 
 Funnel of Eain-gauge, . . . 
 
 Fusion (subterranean), ...... 
 
 Gulf Stream, . . . 
 
 Hurricanes, ....... 
 
 Hydrogen, presence in the air, ..... 
 
INDEX. 9 
 
 PAGE 
 
 Hydrometer, meaning of, .... 32 
 
 its variations, ...... 36 
 
 use in sick-rooms, ...... 45 
 
 use in hot-houses, ..... 45 
 
 factors for Dry Bulb, ... 40 
 
 Ice floats, why ?..... 56 
 
 on the wet bulb, ...... 3 
 
 Insects, first appearance to ba noted, . . . .77 
 
 Law implies Mind, . . . . . .77 
 
 Leslie (Sir John's) Theory, . ... 67 
 
 Light, its decomposition, ..... 73 
 
 theories respecting, . . . . .71 
 
 Makers of Thermometers, ..... 27 
 
 Meteoric Stones, . ' . . . .64 
 
 Mistral, . . . . . . .54 
 
 Moisture, atmospheric, ...... 41 
 
 Ozone, what it is, . . . . . .63 
 
 Ozonometer, ....... 63 
 
 Primary Colours, ...... 74 
 
 Psychrometric Hygrometer, ..... 35 
 
 Radiation, solar, ...... 22 
 
 terrestrial, ...... 23 
 
 Rainbow, cause of, . . . . . .73 
 
 Rain-fall, unequally distributed, . . . . 5( > 
 
 Rain-gauge, ....... 46 
 
 Range of temperature, . . . . . 19, 43 
 
 Record of observations, ..... 25 
 
 Saturation, degree of. (See Table IV.) . . . 84, etc. 
 
 Simoom, ....... 54 
 
 Sirocco, ........ 54 
 
 Snow measurement, ...... 48 
 
 Standard Barometer, . . ... . 10 
 
 Sun's heat, how renovated, . 50 
 
 
98 INDEX. 
 
 Tables. (See end of the volume.) 
 No. I. Strathearn Winds, 
 No. II. Six years of Barometer, 
 No. III. Seven years of Thermometer, 
 No. IV. Dew-point and Saturation, . 
 
 Temperature, 
 
 of the ground, 
 
 of deep mines and springs, 
 
 - - of the Arctic Regions, 
 
 of noted places, Table of, . 
 
 Thermometers, description of, . 
 
 mercury better than alcohol, 
 
 where to place them, 
 
 . manner of observing them, 
 
 Tornado, .... 
 
 Twilight, cause of, 
 
 Tyndall's (Professor) theory, 
 
 Typhoon, 
 
 Use of Meteorology, 
 
 Velocity of Light, 
 
 of Sound, . .. . . 
 
 of Wind, .... 
 
 Vernier, its form and use, 
 
 Winds, how they modify heat, . 
 in Strathearn. (See Table I.) 
 
 Zero, above and below, . 
 
 BY XKILL AND CoMl'ANY, KDIXBl'KMI 
 
SITY OF CALIFORNIA 
 
 ft) 
 
 LIBRARY OF THE UNIVERSITY OF CALIFORNIA 
 
 h< 
 
 SITY OF CALIFORNIA LIBRARY OF THE UNIVERSITY OF CALIFORNIA 
 
 fb 
 
VXD 
 
 UNIVERSITY OF CALIFORNIA LIBRARY OF THE UNIVERSITY OF CALIFOR 
 
 UNIVERSITY OF CALIFORNIA 
 
 LIBRARY OF THE UNIVERSITY OF CALIFOR