.svA- nv/././. M/ .SY/-;.)//-:.V.V, /--.as. 35 



Initiation of the curve horizontally (Fig. 1, Plate 5), it would 

 have exhibited continually decreasing volumes, and increasing 

 temperatures, until finally a point would have been reached, where 

 the volume of the steam was equal only to the water producing it. 

 It may be assumed, that the temperature would, at that point, be 

 640 Centigrade (11HO Fahr.), or in other words, that the entire 

 heat of the steam would be sensible. Supposing this steam (which 

 would have at least 2,o()0 Ibs. pressure per square inch) could be 

 introduced below a piston, and in giving out its power be ex- 

 panded, until its temperature was reduced to zero, then the entire 

 640 degrees of heat would have been converted into their 

 equivalent of power, of which the field of the diagram would 

 represent the integral. The theoretical equivalent of mechanical 

 force for heat is thus represented to the eye ; and in computing 

 the area of the entire figure, it is found to coincide nearly with, 

 but somewhat to exceed, the results of abstract calculation and of 

 'Mr. Joule's experiments. That portion of the diagram (Fig. 1) 

 which is shaded darker than the rest, represents the power of a 

 perfect low-pressure condensing engine ; it covers only about l-14th 

 part of the entire area. 



The diagram shows that the expansive steam-engine would 

 be theoretically a perfect engine, if the water was heated in a 

 close boiler to 1180 Fahr., and being then introduced below 

 the working piston, under a pressure of at least 2,000 Ibs., would 

 resolve itself entirely into steam, and was allowed to expand 2000 

 times before it was discharged into a vacuous space, which, in 

 this case, would not necessarily be a condenser. The impracti- 

 cable nature of such an engine is manifest, and it becomes 

 necessary to seek for other means of obtaining from heat its full 

 value of power. 



It may not be considered out of place to mention here, the well- 

 known experiments on steam-guns by Mr. Perkins, which went far 

 to prove the actual possibility of charging water with sufficient 

 heat, in close vessels, that, upon liberation, it would resolve itself 

 entirely into steam. 



Before leaving this part of the paper, it will be necessary to 

 show the effect produced by the expansion of air, or any other 

 permanently elastic fluid, under a working piston. In the 

 diagram (Fig. 3, Plate r>), the figures on the base and vertical 



D 2 



