8 



Professor Apjohn upon a new Method of 



enable us to calculate the specific heat of a gas, when we have observed the sta- 

 tionary temperature to which, when in a state of perfect desiccation, it brings the 

 wet bulb thermometer. The experiments subservient to this method are easily 

 made ; and the gases being dry, their specific heats are not affected by the pre- 

 sence of vapours, the influence of which, by the way, we are probably not in a 

 predicament to appreciate with the necessary degree of precision. 



The method, therefore, which I have, I believe, been the first to adopt, con- 

 sists in determining, by experiment, in the case of the several gases deprived of 

 all hygrometric measure, t and <', and consequently t—t' — d, and deducing in 

 each instance from these data the value of a, the specific heat. 



In order to the determination of rf, the following apparatus, and method of 

 experimenting was, after a trial of several others, finally adopted : — 



a 6 c c? e is a glass tube, 3-lOth of an inch in diameter, and whose vertical 

 arms are each about twenty inches long. Into this inverted syphon oil of vitriol 

 was poured, so as to rise to the height of about two inches in each leg ; and to the 

 horizontal portion of each of these there were connected, through the medium of 

 a three-armed copper tube, two bladders, A and G, furnished with stop-cocks, 

 one of which was filled with air, and the other with the gas which was to be the 

 subject of experiment ; while to the other extremity of the syphon there was at- 

 tached, also by a caoutchouc collar, a glass tube, in which were placed the dry and 

 moist thermometers, as represented at D and W. " Every thing being thus ar- 

 ranged, an assistant pressed by means of a deal board on the air bladder, by which 

 its contents were forced through the oil of vitriol, where they were deprived of 

 vapour, and over the di-y and wet thermometers, producing in the latter a consi- 

 derable fall of temperature ; and the moment that the air bladder was exhausted, 



