268 Prof. Apjohn on the Specific Heats of the Gases, 

 cent, of air. Hence, the specific heat of the hydrogen sup- 

 posed pure, as deduced from the equation a' = a-{- > , 



becomes -4151. And as -2767 : '2670 : : 4151 : '4005, the 

 specific heat of hydrogen compared to that of an equal volume 

 of air under a pressure of 30 when water is represented by 

 unity, or, what amounts to the same, when air is '267. 



In order to the determination of t and /' the wet and dry 

 thermometers were introduced into a glass tube through which 

 the gas, first dried by bubbling through oil of vitriol, was 

 made to pass in a rapid current, by means of pressure with 

 a board upon a large bladder in which it was contained; and, 

 as soon as the wet thermometer, which by exposure to the 

 dry air or gas rapidly falls, acquired a stationary temperature, 

 its indication and that of the dry instrument were registered. 

 In the case of air there was no difficulty in reaching this sta- 

 tionary point, it being obviously only necessary to maintain 

 the blast sufficiently long. It would, however, have been in- 

 convenient to employ a sufficient quantity of the other gases 

 to ensure the production in each case of a maximum degree 

 of depression ; so that, when for any of these t and t' had to be 

 observed, the wet thermometer was first brought nearly to its 

 stationary point by a current of atmospherical air. The de- 

 pression proper to the gas was now easily obtained by causing 

 the blast of air to be immediatelij succeeded by one of the gas, 

 and which in consequence of this contrivance it was, generally 

 speaking, found necessary to maintain only for a few seconds. 

 For a more detailed description, and a wood-cut of the ap- 

 paratus, I must refer to the report published by the British 

 Association of its proceedings in Bristol. The results ob- 

 tained by the method just explained are presented in the 

 following tables. Table (1.) relates to atmospheric air alone; 

 table (2.) to the other gases. In table (3.) we have the mean 

 results given in table (2.) referred to atmospheric air repre- 

 sented both by "267 and by unity. The numbers in the last 

 column of table (3.) are the specific heats of equal weights, 

 and are got by dividing the numbers in the preceding column 

 by the specific gravities of the gases to which they respectively 

 belong. 



