202 THE SCIENTIFIC PAPERS 01' 



Probable loss expressed in H.P. 



1. By throttled air passages .... say 2 '5 



2. agitation and friction of piston . . . . 1>5 



3. condensation of vapour in expanding cylinder . O'o 



4. ,, cold air escaping ....... 2'5 



5. ,, heat absorbed by radiation .... 2*0 



9-0 

 Gross power of expansion ... . . 25'2 



Leaves effective refrigerating power . . .16*2 

 which is capable of producing 258 Ibs. of ice per hour. 



" The production of ice may, however, be increased 25 per 

 cent, in working the apparatus at the rate of twenty revolutions 

 per minute, which the increased passages, &c., admit of. It is 

 hardly necessary to draw your attention to the gain of engine 

 power which the proposed alterations are calculated to effect. In 

 order to reduce the engine power required to its proper limit, I 

 should propose considerable modifications in the general arrange- 

 ment of the apparatus, consisting chiefly in attaching the three 

 pistons upon one rod, in accelerating the speed of the pistons, and 

 in compressing the air to only about 30 Ibs. per square inch. 



" COST. An apparatus so constructed would be considerably less 

 complicated and costly than our present apparatus. The ex- 

 panding cylinder might be made of cast iron, the two injection 

 pumps and one air reservoir would be suppressed, and in their 

 stead the comparatively cheap exchanger of temperatures or 

 reciprocator be added. The engine and moving gear would, 

 moreover, be greatly diminished. The proposed alterations in the 

 existing apparatus would not cost above 200 (I consider), taking 

 into account the value of materials of the present expanding 

 cylinder and injection pumps. London, 28th July, 1857. 



Signed, C. W. SIEMENS. 



To WOLLASTON BLAKE, Esq., F.E.S. &c. 



Mr. David Thomson said he had been much interested in the 

 paper, the theoretical part of which he thought was quite correct. 

 Dr. Siemens had thrown some doubt upon the formula as given in 



