March 4, 1898.] 



SCIENCE. 



307 



is about the same. The curves then di- 

 verge, the 3-to-l compound reaching a mini- 

 mum steam consumption at 75 horse-power, 

 of 18 pounds. The minimum points on the 

 other curves, owing to their larger low- 

 pressure cylinder volume, lie further along, 

 and are 15.8 pounds for the 7-to-l com- 

 pound, and 13.7 pounds for the triple-ex- 

 pansion engine. We have thus a gain of 

 2.2 pounds of steam per indicated horse- 

 power per hoar of the 7-to-l over the 3-to-l 

 compound, and a gain over the former by 

 the triple-expansion engine of 2.1 pounds 



are given as the relative efficiencies of these 

 three engines, in terms of steam demanded, 

 or of weight of feed-water consumed per 

 horse-power per hour : 



24 

 \ogp 



27 

 logp 



For the triple-expansion engine, 

 For the standard compound, 



TF=: 



W= 



(1) 

 (2) 



For the special form of compound, W = 



log J) 



(3) 



"The latter is seen, on examination of 

 its proportions, to be a form of engine de- 

 signed for an abnormally high total ratio of 



Indicated Horse Power 

 •iciENCY OF Multiple-Cylinder Engines. 



of steam per indicated horse- power per 

 hour. 



Comparing the best work of each type, 

 as given by the records to the date of the 

 preparation of this paper, the best work of 

 good engines of each class may be taken as, 

 approximately, measured by the weights of 

 steam, per horse-power per hour, or by 

 the number of thermal units, proportional 

 to the reciprocal of the logarithm of 

 the pressure adopted. Thus, the following 



expansion at the proposed pressure, and as- 

 signed an abnormally heavy load ; so that 

 vphen actually in action under its average 

 load it must work with a low ratio of ex- 

 pansion in the high-pressure cylinder, and 

 must exhibit an abnormally large ' drop ' at 

 its exhaust." 



The outcome of the investigation is that 

 it is concluded that this novel, intermedi- 

 ate form of multiple-cylinder engine is also 

 intermediate in its economical performance 



