Mr. J. Gill on the Dynamical Theory of Heat. 7 



ninety-three revolutions per minute, and producing the constant 

 work of 90 horse-power, showed the steam used to be k . 0*1902 

 per second in one case, with an observed loss of heat equal to 

 21*5 calories; and in another case the consumption of steam 

 was k. 0*229 per second, with a loss of heat equal to 22*58 

 calories. 



Iu the most economical of the above experiments a constant 

 amount of work equal to 116 horse-power was obtained from 

 k. 0*23548 of steam per second, the steam, of five atmospheres' 

 pressure, being superheated 93° C. (from 152° to 245°) and 

 cut off early, so that the expansion was as 6 : 1 . In another ex- 

 periment, the steam being equally superheated and cut off near 

 the end of the stroke, so that the expansion was only as 1*15 : 1, 

 the rate of work being kept constant by throttling or wire-draw- 

 ing the steam, the same 116 horse-power required the con- 

 sumption of k. 0*32307 of steam per second, being 36 per cent, 

 more than in the former case. Now, everything else being 

 equal, the furnace must furnish in the second case one-third 

 more heat than in the first case. If, therefore, reasons M. 

 Hirn, we find in the condenser-water also one-third more heat, 

 we may fairly deduce that the amount of heat consumed in its 

 passage through the engine depends entirely on the quantity of 

 external work produced ; for by this mode of experimenting, the 

 quantity of work obtained being constantly 116 horse-power, 

 the proportion of loss from friction &c. should be the same in 

 all cases, and therefore need not be calculated. Now the heat 

 which disappeared was nearly equal in both experiments, being 

 30*51 calories in the first case, and 32*13 in the second; and 

 the mean of all the experiments showed a still nearer approach 

 to equality. It was therefore deduced that in all cases an exact 

 proportionality exists between the work produced by the engine 

 and the difference between the quantity of heat furnished before 

 the steam enters the cylinder and the quantity of heat remain- 

 ing in the steam as it leaves the cylinder. 



As a result of my own experiments, and from what I have 

 understood of the experimental investigations of Seguin and of 

 Hirn on the working of steam-engines, I have for many years 

 entertained the opinion that the direct change of heat into work 

 has not been satisfactorily shown by experiment ; and it still 

 appears to me that when the heat employed in working the en- 

 gine is supposed to be merely the heat of the steam as it enters 

 the cylinder (whether saturated or superheated), and when the 

 steam works at full pressure throughout the whole stroke, none of 

 this heat should disappear theoretically in the production of 

 work, as in this case all the heat of the steam which passes 

 through the cylinder should be found in the condenser. Con- 



