328 THE SCIENTIFIC PAPERS OF 



one-fifth to one-sixth part of the theoretical duty of the heat 

 expended. The reason was that all the air cooled and heated 

 alternately did not enter the working cylinder ; but the diagram 

 of the force obtained in the working cylinder formed only a sixth 

 part of the diagram that would be produced if the whole of the 

 air were allowed to expand behind a working piston and between 

 the same limits ; and that proportion really indicated the dynamic 

 value of the engine. Therefore, although he admired the ingenuity 

 with which the author had enlarged the available heating surfaces 

 of Stirling's arrangement, and elaborated the best form of regene- 

 rator for the purpose, he could not agree in the application of that 

 principle to refrigeration. He believed better results would have 

 been obtained if the compressing apparatus had been separated 

 from the expanding apparatus as had been done by others. That 

 opinion appeared to be corroborated by the results given in the 

 paper. With 37 h.-p. 20 gallons of water were reduced from Gl 

 to 47^ per minute, which was equal to 2'8 Ibs. of ice per hour, 

 whereas the Windhausen engine was said to produce 20 Ibs. of ice 

 with 1 h.-p. Generally speaking, he believed the air-compressing 

 engine, on the purely mechanical mode of producing refrigeration 

 was applicable with the greatest advantage where moderate re- 

 frigeration was required. Where the production of ice in large 

 masses was desired, he believed the method adopted by Siebe and 

 by Harrison was superior, for this reason : in compressing and 

 expanding air, 25,000 cubic feet of air were required to produce 

 the effect of 1 Ib. of ice ; whereas, in compressing sulphuric ether 

 after evaporation, only 5,100 cubic feet were required, the reason 

 being that when sulphuric ether was transferred from the liquid 

 into the gaseous condition, the whole of the latent heat was 

 obtained. A much higher result was arrived at by using a still 

 more volatile substance methylic ether which at a depression of 

 temperature equal to 15 Centigrade had a pressure of \\ atmo- 

 sphere, and the displacement of piston to produce the same effect 

 was only about 340 cubic feet. Therefore a pumping engine, with 

 a displacing capacity of piston of 340 cubic feet per minute, 

 would produce the same effect as an air engine of 25,000 cubic 

 feet displacement per minute, and of 5,000 cubic feet in the case 

 of a sulphuric-ether engine. This meant a much smaller engine 

 and a less costly machine in the case of the methylic ether pump, 



