86 Mr. J. Ivory on the Constitution of the Atmosphere. 



makes the heat of the atmosphere decrease more rapidly than 

 the altitude increases. It is difficult to determine this point 

 in a satisfactory manner by a comparison of actual measure- 

 ments, if we confine our attention to small heights above the 

 earth's surface. The irregularity in such cases is so great, 

 that by a proper choice of instances the result may be made 

 to flivour either an accelerating or a retarding scale of heat*. 

 But o-reat altitudes lead unequivocally either to an equable 

 gradation, or to one continually decreasing in its rate. Thus 

 in the instances collected by Ramond, the mean height for 

 one degree of depression is upon the whole 90 fathoms ; but 

 in the great altitude ascended by Gay-Lussac, taken by itself, 

 the like quantity is 95 fathoms, which is incompatible with an 

 accelerated rate of decrease. The opinion that the decre- 

 ments of heat are more rapid the higher we ascend in the at- 

 mosphere, — which Professor Leslie has adopted, and which he 

 has illustrated with a profusion of elementary geometry, — was 

 no doubt suggested by his formula, from which it follows as a 

 necessary consequence. But the experimental investigation 

 of the formula itself is merely an ingenious chimera, which 

 leads to an inexact result. The real foundation of it is the 

 barometrical theory, to which it makes no addition, and the 

 Conclusions of which it cannot, with any pretension to right 

 reasoning, be employed to overturn. 



Dr. Young has followed Professor Leslie in adopting an 

 accelerated decrease of heat, which seems to favour some of 

 his pecuUar notions about the astronomical refractions. He 

 quotes the authority of Humboldt in support of his opinion. 

 As the quotation is general, it might not be easy to find the 

 particular passage alluded to; but in Ramond's work I find 

 the following words relating to the same point. 



" An voisinage de la terre, le decroissement de la chaleur 

 est ordinairement d'une lenteur extreme, et quelquefois d'une 

 singuliere rapidite. II s'accelere communement a une cer- 

 taine hauteur, et le maximum de I'acceleration se rencontre 

 dans une couche d'air dont I'elevation absolue pai'ait varier 

 suivant le climat. Vers I'equateur, M. de Humboldt a recon- 

 nu cette couche entre 2500 et 3500 metres d'elevation. Dans 

 les Pyrenees, j'ai cru la trouver entre 2000 et 3000 metres. 

 .Plus haut il se ralentit de nouveau." — Ramond, sur la Form. 

 Barom. p. 184. 



* Professor Plajfair, who had no S3'steni to support, adopts an opinion 

 with regard to the gradation of heat quite opposite to that of Professor 

 Leslie. It is curious that both of them draw theii" conclusions from the 

 same observations of Saussure on Mout Blanc. — Outlines of Kat. Phil. 

 vol. i. p. 251. 



Now 



