PHYSIOLOGICAL INVESTIGATIONS 



ARISING FROM THB 



MECHANICAL EFFECTS 



ow 



ATMOSPHERICAL PRESSURE 



ON TBI 



ANIMAL FRAME. 



BY JOHN DALTON, F.R.S. 



(Read January eth, IB30.) 



A PERIOD of a century and a half has 

 elapsed since the inventions of the Barometer 

 and the Air-pump. In this time the weight of the 

 atmosphere, its elasticity, its specific gravity, 

 and many other properties have been ascertained 

 experimentally with almost mathematical pre- 

 cision. The weight of the atmosphere, that 

 quality we have more particularly to consider 

 in the present essay, is not constantly the 

 same, as is proved by the rising and falling of 

 the barometer. It varies in this part of the earth 

 from 1-1 2th to 1-1 5th of the whole weight at 

 certain times ; but those variations are gradual, 

 3o2 



