SfK WILLIAM SIEMENS, F.K.S. 59 



been accomplished without combating against considerable practical 

 difficulty. 



Although heat may be entirely converted into mechanical effect, 

 it would nevertheless be impossible to construct an engine capable 

 of fulfilling this condition without causing at the same time a 

 portion of heat to be transferred from a hotter to a cooler body, 

 and which must ultimately be discharged. This necessity has 

 been generally proved, and in a very elegant manner, by Professor 

 Clausius, of Zurich, and implies at least the partial truth of 

 " Garnet's theory." In the " regenerative steam-engine," pro- 

 vision had been made for absorbing this quantity of heat, arising 

 in this case from the circumstance, that the saturated steam enters 

 the respirator in a state of greatest density or compression, and 

 returns through it (expanding into the regenerative cylinder) at 

 a gradually diminishing density, although the temperature of the 

 extreme edges of the respirator remains proportionate to the con- 

 densing point of the steam of greatest density, by providing 

 water chambers about the cover of the working cylinder, and around 

 the regenerative cylinder, which are in communication with the 

 steam- boiler. The heat absorbed from the slightly superheated 

 steam is thus rendered useful to generate fresh steam. 



Objection had been raised by casual observers against the re- 

 generative steam-engine, on account of its apparent similarity in 

 principle to the "air-engines" of Stirling and Ericsson, implying 

 similar sources of failure. The apparent similarity in principle 

 arose from the circumstance that both Stirling and Ericsson, as 

 well as himself, had employed the respirator and high tempera- 

 tures ; but these were but subordinate means or appliances, that 

 might be resorted to in carrying out a correct as well as an 

 erroneous principle. 



In the winter of 1852-53, when Ericsson was engaged upon 

 his gigantic experiment in America, the speaker had had occasion 

 to read a paper to the Institution of Civil Engineers, entitled " On 

 the conversion of heat into mechanical effect," wherein he had 

 endeavoured to set forth the causes of probable failure of that 

 experiment, and to guard against a sweeping condemnation on 

 that account of some of the means Ericsson had employed. 



According to the dynamic theory of heat, the elastic medium 

 employed in a perfect caloric engine was a matter of indiffcr- 



