SfK WILLIAM SIEMENS, F.R.S. 29 



ON THE CONVERSION OF HEAT INTO MECHANICAL 



EFFECT. 

 BY CHARLES WILLIAM SIEMEXS,* Assoc. Inst. C.E. 



THIS subject may be considered under three heads. 

 First, an inquiry into general qualitative and quantitative 

 relations between heat and mechanical effect. 



Second, the theoretical and practical consideration of actual 

 engines, including those of Stirling and Ericsson. 



Third, the definition of the characteristics of a perfect engine. 

 The first portion relates to a purely theoretical question, and 

 would, separately considered, fall beyond the usual limits of 

 discussion at this Institution ; but the author is obliged to ask 

 for an exception in his favour, finding it would be impossible to 

 establish the ultimate object in view, without having proved his 

 premises, which are based upon evidence of recent discoveries. 



In discussing the succeeding heads he will have to rely, to a 

 considerable extent, on his individual judgment and experimental 

 researches. 



First. On the relations between " Heat and Mechanical 

 Effect." 



The power obtained from a steam-engine depends upon the 

 increase of volume given to the water in its transformation into 

 steam, by the action of the fire under the boiler. Dr. Black 

 observed, in 17G3, that the effect of the fire was, for the most part, 

 required to effect the conversion, after the water had been raised 

 to the temperature of the steam itself ; and, moreover, that it 

 made no difference whether the evaporation took place in the open 

 air, or in a closed vessel under pressure. Upon these facts he 

 grounded his theory, that steam was a compound of water and heat, 

 which heat, on entering into combination with the water, lost its 

 individual properties, or became latent. 



This " material theory " of heat has been generally adopted, in 

 preference to the " theory of undulation," according to which heat 



* Excerpt Minutes of Proceedings of the Institution of Civil Engineers, 

 Vol. XII. 1852-1853, pp. 571-590. 



