334 APPLIED SCIENCE 



half of each stroke. The resistance to acceleration is not, how- 

 ever, so large relatively to the steam pressure as to produce 

 negative ordinates, such as were found in cases B and D. The 

 action of the reciprocating masses is, therefore, on the wh< le, 

 beneficial, and we find the efficiency of the engine to be 0*917, 

 or somewhat higher than in Example E. Much care has been 

 taken in the computations to check this rather remarkable result, 

 but there seems no reason to doubt its accuracy. The impor- 

 tant conclusion to be drawn does not, however, depend on trifling 

 differences such as that between 0-917 and 0-913. It is that 

 high speeds do not necessarily entail low efficiency, so that by 

 judicious arrangement of the masses we can have small engines 

 running rapidly with high expansion which, so far as friction al 

 resistances are concerned, may be at least as efficient as the same 

 engines running slowly, and necessarily more efficient than larger 

 engines doing the same work. 



39. Examples G and H, Figs. 53 and 54. The unexpected 

 results obtained rendered it desirable to investigate the case of 

 infinitely slow speed, or that in which the effect of inertia was 

 wholly disregarded. Curves G 3 and G 4 show the efforts with 

 and without friction for the practical distribution of steam 

 assumed in cases E and F. The total work done by the steam is 

 30,770 inch. Ibs., the useful work 28,120, and the efficiency 0'914 

 a result hardly differing sensibly from that obtained with the 

 high speed of 4 revolutions per second. 



40. Example H. Lastly, curves H 3 and H 4 show the efforts 

 with and without friction when the engine is modified so as 

 to make the connecting rod only 28 in. long, or 3^ times the 

 stroke. The weight of the new rod is taken as 28 Ibs., and its 

 centre of gravity 14" from the crank end, and its radius of 

 gyration about the crosshead 18-83 inches. The speed assumed 

 was 1 revolution per second. 1 As calculated from the areas of 

 the curves the whole work done by the steam is 30,740 inch Ibs., 

 the useful work 27,920 inch Ibs., and the efficiency 0-908. 



This result is of considerable practical value, showing that 

 the efficiency of the engine is hardly diminished by shortening 

 the connecting rod to this extent. 



1 The initial steam pressure, the ratio of expansion, and the back prc-sMi 

 were assumed to be the same as in Example E. 



