APPLICATION OF GRAPHIC METHODS 329 



in the front than in the back stroke. These effects are due to 

 the weight and mass of the connecting rod. A counterbalance 

 might be so placed as to make the front and back branches 

 resemble one another much more closely. The area of the curve 

 A 3 (calculated as for A 2 ) is 3,212 inch Ibs., the total error due 

 to imperfect draughtsmanship being only 4 inch Ibs. 



Curve A 4 resembles A 3 in its general outline, and when 

 these are compared with Aj and A. 7 they show the effect of the 

 weight and mass of the parts in increasing friction. The in- 

 crease in the loss due to friction is not even approximately 

 constant throughout the stroke, but is much greater when the 

 crank is nearly at right angles to the centre line of the engine. 

 The loss is greatest during the back stroke, producing inequality 

 between the useful work done during the back and front strokes. 

 The causes of each departure from symmetry in all these curves 

 can be followed on the diagrams of the dynamic frames, but this 

 paper would be unduly extended if these were all to be printed. 

 Moreover, such directions have already been given for drawing 

 these as will enable any one to investigate the cause of each 

 effect now described or shown on the curves. The area of A 4 is 

 2.GU2 inch Ibs., so that the true efficiency of the engine running at 



2 602 



this speed, and with this low pressure of steam, is ~' o " = O'SIO. 



O I 



35. Example J5, Fig. 47. The effect of the resistance of 

 the masses to acceleration as distinguished from the effect of 

 the weights of the parts might have been exhibited by drawing 

 effort curves 1st, on the assumption that although the parts 

 resisted acceleration they had no weight ; and, 2nd, on the 

 assumption that although the parts had weight they offered 

 no resistance to acceleration, or were moving at an infinitely 

 slow speed ; then, comparing these curves with A 4 , we should 

 have seen the effect of each element of the problem. This, 

 however, was thought unnecessary, because the effect of the 

 resistance of the masses to acceleration is strikingly shown by 

 the curves B 3 and B 4 , being the effort curves of the same 

 engine, with the same pressure in the cylinder, but running 

 four times faster. When making one revolution per second, the 

 resistances to acceleration are smaller than the weights of the 

 elements in motion, as may be seen in Table I. of the Appendix, 



