investigating the Specific Heats of the Gases. 13 



vitriol, instead of water, and placed upon a table at the distance of three feet from 

 each other, the brass caps, E, F, attached to the bells, being suspended to the ex- 

 tremities of a stout cord passing over a pair of runners, G, H, fixed in the ceiling 

 of the laboratory, the length of the cord being such, that while one of the bells 

 was almost entirely immersed in the oil of vitriol, the other dipped about an inch 

 beneath its surface. Between the lower stop-cocks, m, n, attached to the gasometers, 

 a couple of glass tubes were interposed, connected to the stop-cocks by caoutchouc 

 collars, and fitting at their other extremities to each other by a tight ground joint. 

 In the larger of these tubes the dry thermometer t was permanently placed, and 

 into it also the wet one t! was introduced previous to the commencement of an ex- 

 periment. Matters being, we shall suppose, thus prepared, and the unimraersed bell, 

 c, occupied, ^r5< with atmospherical air, deprived by the oil of vitriol of its mois- 

 ture, pressure was made upon it by an assistant, so as to force its contents in a 

 rapid current into the second bell, D, through the tube containing the wet and 

 dry thermometers. During this operation the observer kept his eye, armed with 

 a lens, steadily fixed on the thermometers, and registered the indications of both 

 as soon as the wet one became and continued stationary for a few seconds. The 

 height of the barometer being now taken, the necessary data were obtained for 

 calculating, from the formula 



J -J e ^30' 



the elastic force of the vapour still existing in the air of the gasometer. The 

 atmospheric air being now replaced by one of the gases which were to be the 

 subject of experiment, and left sufficiently long in contact with the oil of vitriol, 

 the very manipulations and observations just detailed were repeated. This same 

 experiment, with sufficient intervals to allow in each instance of maximum desic- 

 cation, was again and again performed ; and it having been ascertained, after a 

 considerable number of repetitions, that the results were uniform and consistent, 

 and that they might therefore be relied upon, the mean of all the observations 

 was taken, and from this the specific heat of the gas deduced by means of the 

 formula 



<'=C/-/-)X4|3V' 

 that value being assigned to/" which resulted from the preliminary experiments 



