

A/A' WILLIAM S7/-M/-~\\ /.A'.X. 329 



although the expenditure of power might be the same ; but, on 

 the other hand, there was the set-off of having to deal with a 

 highly inflammable material like methylic ether instead of with 

 atmospheric air. For producing a depression of temperature in 

 houses or breweries he believed the air engine was the best con- 

 trivance that could be adopted. 



MR. SIEMENS explained that he had no desire to disparage 

 Mr. Kirk's ingenious contrivance on the contrary, he wished it 

 every success but he could not help observing upon the draw- 

 backs which he conceived were incidental to the construction of 

 the machines. He admitted that the construction had the advan- 

 tage of giving a greater amount of power in a limited space than 

 the Windhausen machine, but, as a set off, the greater back 

 pressure or lost effect incidental to the engine must be taken into 

 account. Other speakers had alluded to the thermo-dynamic 

 theory, and had argued that, inasmuch as a unit of heat could 

 only develop 772 units of force, so 772 units of force were necessary 

 to abstract one unit of heat in the production of ice. If the 

 object was to create a unit of heat he could agree with these 

 remarks, but refrigeration meant only the displacement of heat 

 from one temperature to another, and involved the amount of 

 force necessarily due to that step. In starting from the absolute 

 zero point water of the ordinary temperature of 00 was in reality 

 just about 500 hot ; and in depressing this temperature to 10, 

 work had to be accomplished amounting to T a c % or but little more 

 than Jyth of the mechanical equivalent of the heat so transferred. 

 This proposition could be verified by means of two diagrams, one 

 representing the curve of air compression with simultaneous 

 injection of cold water, and the other the air expansion after 

 cooling ; the difference of magnitude between the two was only 

 -roth of the air compression diagram, and -J-th of the air expansion 

 diagram, which latter represented the work of refrigeration which 

 was accomplished. This result followed generally from the formula 

 by Clausius just submitted by Mr. Thomson. 



