5Y/? WILLIAM SIEMENS, F.R.S. 77 



through the cylinder, without exerting its elastic force upon the 

 piston. To prevent this action, it was necessary to sufficiently 

 increase the temperature of the steam, that it might be expanded 

 through the stroke, without condensation. According to the 

 present well-established law, expressing mechanical force by the 

 quantity of heat, he found, that an increase of temperature of 

 100 Fahr. would suffice to prevent condensation in an ordinary 

 expansive engine. Increasing the heat beyond that point would 

 not be accompanied with any marked economy, and would en- 

 gender many difficulties ; lubrication would become difficult, and 

 friction would be produced. Great stress had been laid upon the 

 peculiar properties of mixed steam, and the advantages which it 

 possessed over superheated steam, but he had never seen any re- 

 markable results from its use. In an engine which he designed, he 

 virtually used the two steams together, inasmuch as, at each stroke, 

 he added to a volume of superheated steam, a certain proportion of 

 saturated steam ; but he never observed any spontaneous increase 

 in the bulk. There was, however, one advantage in the author's 

 system, by mixing ordinary saturated steam with superheated 

 steam, he had the means of regulating the temperature. If, then, 

 a compensating rod was introduced into the steam pipe, so as to 

 limit the admission of steam in proportion to the temperature, 

 beneficial results might be obtained. He was convinced, however, 

 that in simply superheating steam, the ultimate degree of economy 

 would not be reached. The chief advantage of superheating was 

 to prevent condensation in the working cylinder, whereas Mr. Sie- 

 mens's object had been, and still was, to prevent the loss of the 

 latent heat of the steam, by means of the regenerative system. 

 Although he had advanced but slowly, owing to the difficulties 

 and expense attending experiments of this description, he had two 

 engines at work, which gave him every confidence of ultimate and 

 complete success. 



