484 Scientific Proceedings, Royal Dublin Society. 



a liquid on the apparatus. A small correction might also be re- 

 quired for the expansion of the glass hy heat. As the whole thing 

 can be made of glass, for even the mirror need not be silvered, 

 it is applicable to such corrosive gases as chlorine, bromine, and 

 iodine. 



It is evident that a large number of applications of the same 

 general principle are possible : as, for instance, by weighing a 

 bulb immersed in a vapour, as in Mr. Joly's calorimeter, in an ordi- 

 nary balance, or by using spring balances to determine the weight 

 of the bulb. A very pretty one might be made by an application of 

 Messrs. Ayrton and Perry's shaving springs, and it might be made 

 very delicate by reading the position of the bulb by reflection from 

 a mirror attached to it. By suspending a thin balloon of collodion, 

 distended by a heavy gas in a gas, the density of the latter might 

 be measured with a very delicate balance that would not bear the 

 weight of a glass^bulb. 



