5/y? WILL/AM \/AM//-;.V\, /-;A'..V. 



105 



theory of heat was the true one, I adopted it boldly, and by its 

 means arrived at sound conclusions regarding the relative merits 

 of the various steam and air-engines of known construction, by 

 showing what proportion of the heat employed was actually 

 converted in each case into mechanical effect, and what other 

 proportion must necessarily go to waste, notwithstanding the 

 application of an economiser or regenerator, which as I expressed 

 it, " is undoubtedly a useful agent for recovering the free, or 

 otherwise unproductive heat of a caloric engine." On reference to 

 the paper in question, Vol. XII., Minutes Inst. C.E., you will 

 find graphic representations, showing the proportion of heat lost, 

 and that converted into useful effect, similar to those employed in 

 your article in reference to Stirling's engine, but more complete 

 in that they take into consideration the simultaneous action of 

 the two cranks, which you neglect, for the sake, I presume, of 

 simplicity of demonstration. 



In a table I gave the relative merits of different kinds of 

 engines as follows : 



And although Rankine, Clausius, and others have since then 

 handled the dynamical theory of heat in its application to thermo- 

 motors in a much more comprehensive and elegant manner, they 

 in no way disprove the conclusions at which I had arrived, and 

 which I fully maintain. 



Two other papers were presented to the Institution at the same 

 time as my own (one of them by a member of the French Institute 

 through the Secretary), in which it was attempted to clear up the 



