TRANSACTIONS OF THE SECTIONS. 51 



goes round, the barometer rises or falls according to the direction or strength of the 

 wind. Supposing a diagram to represent 36 hours, and divided into spaces of three 

 hours each along the upper horizontal line ; while below, points of the compass are 

 shown, from north around by east to north again, and continued to south ; and at 

 the side a scale of inches and decimals, from 28 to 31. Then suppose that the wind 

 has gone round the compass once, or say once and a half, as happens occasionally ; 

 and that it has been an extreme case of depression, as in a storm. Then, if from 

 (say) 303, with the wind at north, a shifting occurs, first towards the north-east, 

 and then onward in the same direction around the compass — as the wind so 

 shifts to the north-east, and is about to shift towards the east and south, the baro- 

 meter foretells it, or falls beforehand. When the wind is north-east the mercury is 

 lower, probably, than when it was at north. As it gets to the east the mercury falls, 

 and gets lower still at south-east, and falls still more to south and south-west, where 

 it is probably the lowest, because it feels the effects of the south-westerly or equa- 

 torial current most then, and may be down, let us suppose, to 28 - 2 inches. As the 

 wind shifts round to south-west, west, north-west, the column in the tube rises, till, 

 perhaps, the wind is north, or even north-east, when it may be as high as 30"8 : it 

 has been known in this country as high as 30'9. As the wind goes round again to 

 the east and south-east and south, the barometer falls as before, and a line or curve 

 traced upon paper, representing these falls and rises, or oscillations of the barometer 

 during a certain time, say these 3C hours, has an appearance like the outline of a 

 wave of water ; but as these apparent waves or undulations take place exactly as the 

 wind shifts, and proportionally to its strength, and as, if the wind remains in one 

 quarter for some days, or say two or three weeks together, the curve becomes almost 

 a direct line, remaining at about the same elevation, it seems that there is an intimate 

 and immediate connexion between such a curve or wave-line and the oscillation of 

 the mercury, though not necessarily between the curve and any undulatory move- 

 ment of the atmosphere above our heads. If a body of the atmosphere above us 

 swelled upwards, like a wave, and fell again, as some suppose, as it were in " crests " 

 and " troughs," how should we reconcile it with the fact of there being various cur- 

 rents passing over each other in the atmosphere from different directions ? Aeronauts 

 who have been up in balloons know that from one stratum of air they passed into 

 another and another, and perhaps a fourth also, moving in different directions. 

 There cannot be vacancies between the undulations of various strata of air. These 

 different bodies of atmosphere could hardly be undulating like waves while having 

 spaces between them, and interferences of cross movements. Waves of ocean have 

 only elastic air above them, which does not impede their rise and fall materially ; and 

 they are only superficial, not reaching far down. 



Were there a raising of any part of the mass of air, the lighter or equatorial portions, 

 or winds, would rise the highest, and would expand ; but, according to the " Wave 

 theory " (here controverted), the reverse is the fact ; you have the lowest part of 

 the apparent trough of the wave, with the lowest barometer, that is, with the air, 

 which is the lightest and most expanded, and ought therefore to rise up the highest ; 

 and you have, coincident with the heavy dry air, the highest part, or what is called 

 the " crest " of the wave. Considering then these facts, and the exact correspondence 

 of the movements of the mercury with the wind's direction, besides noticing the 

 extreme variability traceable in such an atmospheric wave (which can hardly be 

 conceived to be motionless for weeks, as in the case of a steady north-easterly wind, 

 and then going into extraordinary irregularity during a day or two), we are led to the 

 belief and assertion that what are commonly called " atmospheric waves " are rather 

 delusive ; and that there are waves in any line indicating oscillations of the barometer, 

 but not such, in the atmosphere itself, as are usually adverted to by the expressions 

 "trough" and "crest." 



Mr. Birt drew particular attention to these supposed undulations of atmosphere, 

 by papers read at meetings of the British Association, and by a special Article in the 

 ' Admiralty Manual of Science.' Sir John Herschel, Le Verrier, and other great au- 

 thorities then countenanced Mr. Birt's theory and apparently sanctioned his opinion. 

 Yet there is so much argument against those views, that even the highest names 

 scarcely warrant their implicit adoption. That there must be undulations in the 

 atmosphere — constituted as it is — cannot be doubted ; but that the curve traced on 



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