APPENDIX B. 239 



seems to be due to the condensation of the watery 

 vapor caused by the cooling of the air. 



(2) The inflammation of German tinder in the 

 so-called pneumatic tinder-boxes ; which are, as 

 we know, little pump- chambers in which the air is 

 rapidly compressed. 



(3) The fall of a thermometer placed in a space 

 where the air has been first compressed and then 

 allowed to escape by the opening of a cock. 



(4) The results of experiments on the velocity 

 of sound. M. de Laplace has shown that, in 

 order to secure results accurately by theory and 

 computation, it is necessary to assume the heating 

 of the air by sudden compression. 



The only fact which may be adduced in opposi- 

 tion to the above is an experiment of MM. Gay- 

 Lussac and Welter, described in the Annales de 

 Chimie et de Physique. A small opening having 

 been made in a large reservoir of compressed air, 

 and the ball of a thermometer having been intro- 

 duced into the current of air which passes out 

 through this opening, no sensible fall of the tem- 

 perature denoted by the thermometer has been 

 observed. 



Two explanations of this fact may be given: 

 (1) The striking of the air against the walls of the 

 opening by which it escapes may develop heat in. 



