516 RUDBERG ON THE EXPANSION OF DRY AIR. 



then 



h' 4- V — 1 



1 + AT = V^r— ; (1 + GT). 



In the above expression the altitudes h', k', h, k need not be 

 connected for temperature, because the experiment is completed 

 in the short space of an hour and a half, during which the tem- 

 perature of a room will undergo no sensible variation. The only 

 reduction to 0° requisite, is that of the barometric height h', in 

 order to deduce from it the temperature T. 



The experiments which I have made up to the present time, 

 with the above-described apparatus, under very different baro- 

 metric pressures (from 752ni°i-92 at -f l7°-4 to 783«"^-72 at 

 4- 18°), gave for 100 A. the foll(»fting values : — 



0-3640 0-3640 0-3653 



0-3648 0-3656 0-3640 



0-3641 0-3643 0-3664 



0-3648 0-3648 0-3645. 



The mean value of 100 A. is 0-36457. Since this mean value 

 is the same as that given by my foi-mer experiments made in a 

 manner entirely different, I venture to consider it as fully esta- 

 blished, — that the true expansion of dry air between 0° and 

 100° centigrade, is only from 0-364 to 0-365 of its volume at 0°. 



