Barometric Pressure. 



23 



of diurnal air movements analogous to the annual ones is sufficiently 

 substantiated by facts to explain the diurnal variations of the 

 barometer. 



Coming now to the P — V theory, we raise the dust of ancient 

 polemics. Is the spring of the air the same as its gravity ? Is the 

 total pressure of a mechanical mixture of gases equal to the sum 



