^4 Mr. C. W. Siemens^ on a [April 11, 



was, strictly speaking, a combustible material. The pyropherus 

 or finely divided metallic iron, took fire spontaneously on exposure 

 to the atmosphere, a chip of iron was ignited in flying through the 

 flame of a candle ; an iron tea-kettle was destroyed by exposing it 

 (unfilled with water) to a kitchen fire ; whereas, in forging a crank 

 shaft, the solid mass of iron withstands the white heat of the forge 

 fire for several weeks without deteriorating. A heating vessel, 

 properly constructed and protected, might be heated with safety to 

 700^ Fah., at which temperature it would be almost as able to 

 resist pressure, as at the ordinary temperature of the atmosphere, 

 the point of maximum strength of iron being at SoO'^ Fah., as had 

 been proved by experiments made for the Franklin Institute. 

 The construction of a heating vessel combining these desiderata 

 was of paramount importance for the success of Mr. Siemens' engine, 

 and had not been accomplished without combating against consider- 

 able 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 Ziirich, and implies at least the partial truth of '' Car- 

 net's theory." In the " regenerative steam-engine," provision 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 respi- 

 rator remains proportionateHo the condensing 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 rege- 

 nerative steam-engine, on account of its apparent similarity in prin- 

 ciple 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 temperatures ; 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 lipon 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 the probable failure of that 



