TO THE DETERMINATION OF THE EFFICIENCY OF MACHINERY. 705 
by the curves above the line OY measures the work which the steam can do. 
The area enclosed below the line OY in A, measures the work which must be 
done (not by the steam) to pull the engine through the dead arcs. This work, 
in practical cases, is done by the fly-wheel, which, if large enough, might do 
the necessary work without allowing the speed to fluctuate sensibly—a condi- 
tion assumed throughout the calculations. 
The whole work done by the steam is 100°5 x 16x 12, or 3216 inch lbs. The 
area of A, was found to be 3210 inch lbs., showing the error due to defective 
drawing to be very trifling ; the area of A, (being the arithmetical difference 
between the positive and negative areas) is 2974 inch lbs. The efficiency, on 
2974 
p= 0927. 
In curve A; the front and back branches are no longer even approximately 
symmetrical to one another. There is no dead point at the end of the front 
‘stroke, and there is a long dead arc at the end of the back stroke. The maxi- 
mum effect is greater 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; (calculated as for A,) is 3212 inch lbs., 
‘the total error due to imperfect draughtsmanship being only 4 inch lbs. 
Curve A, resembles A; in its general outline, and when these are compared 
with A, and A, they show the effect of the weight and mass of the parts in in- 
creasing friction. The increase in the loss due to friction is not even approxi- 
“Mately 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. More- 
Over, 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, is 2602 inch lbs., so that the true efficiency of the engine 
602 a 
3919 9 810. 
§ 35. Example B, fig. 47, Plate X X VII.—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—Ist, on the assump- 
tion that although the parts resisted acceleration they had no weight ; and, 
| 2d, 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, we should have seen the effect of each element 
vf the problem. This, however, was thought unnecessary, because the effect of 

assumption 2d, is therefore 
Tunning at this speed, and with this low pressure of steam, is 


