the Transformation of Energy . 113 



from M. Regnault's experiments the effect of cohesive force, I 

 have found that they indicate that perfect gases possess an elas- 

 ticity, independent of heat, corresponding to that due to about 

 2*^*1 of the Centigrade thermometer; that is to say, that the 

 temperature of total privation of heat is about 2°'l Centigrade 

 above the absolute zero of a perfect gas-thermometer, or 2732-° 

 Centigrade below the freezing-point. 



In applying the law of the efficiency of machines to the case of 

 expansive heat, we must put the following interpretation on the 

 symbols : — 



Let Qi denote the total heat present in the expanding body 

 during the period of receiving heat from without ; 



Qg the total heat during the period of emitting heat ; 



Hj the whole heat received; 



Hg the whole heat emitted ; so that 



Hi — H2 is the useful effect of the engine, or the heat perma- 

 nently converted into expansive power ; then the proportion of 

 the useful effect to the whole heat received is, as in equation (7), 



Hi — Hg _ Qi — Qg 

 Hi - " Qi • 



If we admit the principle, which appears to me to be demon- 

 strable, that the heat present in a body varies with temperature 

 according to the same law for all substances, the above formula 

 leads immediately to Carnot^s law, as modified by Messrs. Clau- 

 sius and Thomson. If we, further, adopt the hypothesis that 

 expansive heat consists in vortices or eddies in atmospheres sur- 

 rounding centres of molecular attraction, we are led to the con- 

 clusion, which is borne out by our present experimental know- 

 ledge so far as it extends, that the quantity of heat in a body is 

 proportional simply to the temperature, as measured from the 

 point of total privation of heat already mentioned. Let k denote 

 the position of this point on the thermometric scale ; then the 

 greatest proportion of heat which can be rendered effective by 

 any expansive engine, receiving heat at the temperature Tj and 

 emitting it at Tg, is 



~7' • • • (8) 



being the formula which, in the fifth section of a paper on the 

 Mechanical Action of Heat, I have deduced directly from the 

 hypothesis above mentioned. 



Application to Current Electricity, 



(8.) In order to apply the general law of the transformation 

 of energy and its consequences to current electricity, we must 



