S/X WILLIAM SIEMENS, F.R.S. 43 



to expand the air down to atmospheric pressure, before it is dis- 

 charged, whereby the maximum effect will be obtained. From 

 this gross effect has to be deducted, first the resisting pressure of 

 the atmosphere against the working piston, which is represented 

 by the field a bfe, and secondly the power absorbed by the 

 pumping cylinder. 7?, as represented by the field b g h f. By 

 laying this field of resistance upon the field of power b c df of 

 the working cylinder, there remains the field b c d h g representing 

 the entire effective pressure upon the working piston. This 

 pressure amounts, on the average, to nearly 3 Ibs. per square inch 

 on the working piston. 



In order to estimate the comparative economy of Ericsson's 

 engine, it is necessary to consider the total quantity of heat 

 absorbed for one revolution, the proportion of it which is trans- 

 ferred into useful effect, and the difference between the two, which 

 of necessity escapes in the form of sensible heat. 



If the atmospheric air enters the pumping cylinder at a tem- 

 perature of 60 Fahr., it will be raised, by compression, to 10 Ibs. 

 additional pressure and to a temperature of 111 Fahr., as is 

 shown in the dynamical diagram (Fig. 3, Plate 5). 



This air has to be heated on its passage to the working cylinder, 

 so that its volume is increased in the proportion of two to three, 

 in order that the air delivered by the pumping cylinder may each 

 time suffice to fill the working cylinder. To effect this it must 

 be heated to 391 Fahr. 



The expansion that takes place in the working cylinder will 

 reduce that temperature to 314, which is the temperature at 

 which the pumping cylinder full of air at 60 will fill the working 



508 



cylinder of one-half greater capacity (for + GO = 314). 



z 



The temperature lost, during expansion in the working cylinder, 

 is 391 314 = 77, which must be supplied to it again by the 

 fire, before it reaches the respirator, in order not to cool down its 

 lower extremity, and 25 in addition, to make up for the loss, on 

 account of the imperfect action of the same. 



The air issues into the atmosphere at a temperature 25 

 above that of the upper extremity of the respirator, or at 

 111 + 25 = 136 Fahr., being 136 GO = 76 hotter than when 

 iD entered. 



