1823.] Mr. DanielVs Meteorological Essays. 457 



We have thus endeavoured to give a concise view of a theory- 

 framed to account for the changes which are constantly taking 

 place in the pressure of the atmosphere. It has certainly the 

 merit of ingenuity, and, so far as we are aware, of novelty, but it 

 rests upon the sandy foundation of assumed partial changes of 

 temperature in the higher regions of the atmosphere, of the ex^ 

 istence of which we have very insufficient evidence, and which, 

 moreover, if they were by any train of reasoning rendered proba- 

 ble, could scarcely be considered as adequate to explain the 

 phenomena. For to evolve so much heat as would raise the 

 temperature of a considerable mass of air, and cause it to diffuse 

 itself rapidly into distant regions, would require the condensa- 

 tion of a greater quantity of aqueous vapour than is hkely to be 

 present in any given space, and also that this condensation 

 should not be gradual, but should take place suddenly to a very 

 great amount. There can be no discredit, however, to any one 

 v/ho fails to unfold the causes of phenomena which have been 

 acknowledged by one of the first philosophers of the present 

 times * to have hitherto baffled all attempts to reduce them to 

 fixed principles. The data for a sound and stable theory are, it 

 appears to us, still wanting, and must be supplied chiefly by a 

 very extensive series of simultaneous observations on the state 

 of the barometer, in various and distant parts of the world. 



We may remark, by the way, an error, as it seems to us, into 

 which not only Mr. Daniell (p. 8), but Mr. Leshe, has fallen, 

 viz. " that the particles of air in passing over the surface of the 

 globe do not for a moment cease to gravitate, and that no hori- 

 zontal movement of them will produce the slightest derangement 

 in a perpendicular direction." Now it is well known that any 

 body, to which a projectile motion of five miles per second has 

 been imparted, would revolve around the earth like a planet, and 

 would cease to exert any pressure on its surface. Any less 

 velocity must produce a proportional decrease of weight in the 

 particles of air, which is known to move at the rate of from 60 to 

 100 miles per hour. 



We venture also to suggest, with submission, that the third 

 table in Part I. is founded on an erroneous principle. In calcu- 

 lating the influence of a decreasing temperature on the weight of 

 the atmosphere at different heights, Mr. Daniell has deducted 



TTT^ of the lenscth of the mercurial column for each decree of 



480 ^ ^ ^ 



depression due to the elevation. Now it appears to us, that a 

 mean ought to have been taken between the temperature at the 

 base, and that at the summit of the atmospheric column. For 

 example, the weight of a column of air of 5000 feet, supposed of 

 an uniform temperature of 32°, and decreasing in density from 

 the surface upwards, according to statical laws, is equal to 



• M. Biou 



