240 APPENDIX B. 



observable quantity. (2) The air which has jusl 

 touched the bowl of the thermometer possibly 

 takes again by its collision with this bowl, or 

 rather by the effect of the detour which it is 

 forced to make by its rencounter, a density equal 

 to that which it had in the receiver, much as the 

 water of a current rises against a fixed obstacle, 

 above its level. 



The change of temperature occasioned in the 

 gas by the change of volume may be regarded as 

 one of the most important facts of Physics, be- 

 cause of the numerous consequences which it 

 entails, and at the same time as one of the most 

 difficult to illustrate, and to measure by decisive 

 experiments. It seems to present in some respects 

 singular anomalies. 



Is it not to the cooling of the air by dilatation 

 that the cold of the higher regions of the atmos- 

 phere must be attributed? The reasons given 

 heretofore as an explanation of this cold are en- 

 tirely insufficient; it has been said that the air of 

 the elevated regions receiving little reflected heat 

 from the earth, and radiating towards celestial 

 space, would lose caloric, and that this is the cause 

 of its cooling; but this explanation is refuted by 

 the fact that, at an equal height, cold reigns with 

 equal and even more intensity on the elevated 



