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



difficulty. The quantity of steam furnished to the engine per 

 second with the throttle-valve full open, and consequently the 

 maximum amount of cut-off to produce the given constant 

 amount of work, was ascertained by keeping the engine in con- 

 stant action during a whole day ; and the number of strokes made 

 by the engine during this period was taken by a counter. By 

 dividing the whole quantity of water by the whole number of 

 strokes of the engine, the weight of steam for each stroke was 

 ascertained. 



It was much more difficult to ascertain the quantity of steam 

 furnished to the engine in a given time while working with- 

 out cut-off, and regulated to the same constant rate of work 

 by throttling or "wire-drawing" the steam. In this case the 

 consumption of steam, and consequently the consumption of fuel, 

 increased ; the furnace adapted for the more limited rate of com- 

 bustion which sufficed for the more economical mode of working 

 was not sufficient for the larger consumption; and under these 

 circumstances the difficulty of maintaining the conditions of the 

 supply of steam constant during a whole day's work was so great 

 as to render it almost impossible to ascertain accurately by the 

 former method the quantity of steam supplied ; consequently an- 

 other method was adopted for the purpose. The quantity of cold 

 water supplied to the condenser, and the tepid water discharged 

 from the air-pump in a given time, were each accurately gauged, 

 the respective temperatures being taken into account ; and the 

 excess of the latter quantity over the former, representing the 

 steam passing through the engine, being divided by the number 

 of strokes in the given time, showed the weight of steam used 

 per stroke. 



The first series of experiments described by M. Hirn were made 

 with a large engine making twenty-seven strokes or revolutions 

 per minute, and producing the constant work of 150 horse-power, 

 as shown by a friction-brake. Under the most economical con- 

 ditions of the action of the engine this work was produced from 

 k. 0*34554 of steam per second, representing 228*16 French 

 thermal units or calories • and under the least economical condi- 

 tions the steam used was k. 0*46927 per second, equal to 286*38 

 calories. In the former case a disappearance of 40 34 calories 

 was observed ; and in the latter case heat equal to 38*08 calories 

 disappeared. 



A second set of experiments with the same engine, producing 

 work equal to 116 horse-power, showed a consumption of 

 k. 0*23548 of steam per second in one case, and k. 0*32307 in 

 another — the observed loss of heat being 30*51 calories in the 

 first case, and 32*13 calories in the second case. 



Another set of experiments with a smaller engine, making 



