510 RUDBERG ON THE EXPANSION OF DRY AIR. 



been made as accurately as possible, the measuring apparatus 

 was removed, and the globe, the extremity of the tube being 

 closed with wax, as has been already stated, lifted out of the 

 trough. The difference of altitude of N and S was then accu- 

 rately measured, by means of two graduated scales, placed at 

 right angles to each other, and the globe, with the mercury 

 which had been forced into it, weighed after the wax had been 

 removed. 



When this was accomplished, the tube was bent at the end, 

 so that it could be dipped into a vessel of mercury, the globe 

 filled with it, and all the air expelled, by carefully boiling. When 

 cold it was placed in snow, and completely filled with mercury 

 at 0°. When no more mercury could be introduced (this was 

 known to be the case by the thread of mercury showing itself at 

 the extremity of the tube), a clean empty vessel was placed un- 

 derneath, to receive the mercurj^ that ran out ; the globe taken 

 out, and placed in the boiler. The mercury that escaped be- 

 tween the temperatures of 0° and temperature of boiling deter- 

 mined by the height of the barometric column, was weighed, 

 and the weight of this, added to the weight of the mercuiy re- 

 maining in the globe, consequently gave the weight of mercury 

 contained in the globe at 0°. From these two weights, and the 

 true expansion of mercury, the true expansion of the glass may 

 be calculated. 



Let u be the volume of the globe at 0°, and therefore the vo- 

 lume of the mercury contained in it at that temperature ; h the 

 height of the barometric column, in centimetres, at the instant 

 the tube was sealed ; T the corresponding temperature of the 

 vapour of boihng water; 100 A the true expansion of dry air 

 from 0° to 100° ; 100 G the expansion of glass in volume from 

 0° to 100°. At the instant the end of the tube was closed with 

 wax, let V be the volume of the air contained in it ; q the weight 

 of the mercury contained in it ; ^ the height of the mercury in 

 the barometer ; I the height of the surface of the mercury in the 

 globe above the surface of the mercury in the trough ; p the 

 weight of the mercury contained in the globe at 0°. The vo- 

 lumes, pressures, and temperatures of the air at the time the 

 tube was sealed, and at the time it Avas closed with wax, were 

 as M (1 + G T), v\ h, k — I; T°, 0° respectively, therefore 



