MECHANICAL EFFICIENCY OF THE HUMAN BODY 
143 
when experiments are made at the same speed, preferably from 70 to 80 
revolutions per minute, and changing from moderately severe to severe mus- 
cular work. 
COMPARISON OF THE EFFICIENCY EN THE EARLIER AND LATER 
EXPERIMENTS WITH THE ERGOMETER. 
Since this is the second research carried out by means of this type of 
ergometer, a comparison of our results with those obtained earlier are of un- 
usual interest. As has already been pointed out, 6 the friction of these ergom- 
eters is so low that in calibrating them it was extremely difficult to measure 
the heat produced by means of the apparatus employed. In general the 
friction per revolution is not far from 1 to 2 per cent of the total heat produced. 
Under these conditions, it seemed to be entirely unjustifiable to utilize this 
figure in any of the computations, and hence in no experiment does the ques- 
tion of friction enter. 
At this point the gross errors resulting from the use by Benedict and 
Carpenter c of an erroneous value for the friction of the machine should be 
again pointed out. Their entire discussion of the mechanical efficiency based 
on "coasting" or no-load experiments is vitiated by the fact that in deducting 
the "coasting" value from the total heat produced, they attempted to deduct 
the heat produced by friction from that produced by the external muscular 
work. Their values, which have been given in table 110, d have been recom- 
puted by us and are given in table 127, in which it can be seen that the per- 
centage efficiency based upon the so-called coasting values averages not far 
from 26 per cent as against the 24 per cent found and reported by them. 
Furthermore, their discussion of the internal friction of the legs e is entirely 
unwarranted owing to this erroneous value for the friction of the apparatus. 
Our observations do, however, furnish interesting comparisons since the 
general thesis that the gross efficiency for bicycle riding is approximately 
12 to 13 per cent and the net efficiency not far from 20 per cent confirms fully 
the values given for the previous research. 
Table 127. — Mechanical efficiency based on coasting experiments of Benedict and Carpenter. 
Subject. 
Efficiency. 
Friction 
value 
deducted. 1 
Recomputed 
without cor- 
rection for 
friction. 
X.B 
p. a. 
24.6 
p. a. 
26.4 
26.0 
26.2 
28.4 
23.2 
N. B 
23.7 
23.4 
24.6 
21.6 
N. B 
N. B.. . 
A. L. L 
t The friction value used by Benedict and Carpenter in these computations 
(0.001547 per revolution) was erroneous. 
One discrepancy between the earlier work and the more recent observa- 
tions is in the computation of the effect on the efficiency of increasing the 
a Benedict and Carpenter, U. S. Dept. Agr., Office Expt. Stas. Bull. 208, 1909. 
b Benedict and Cady, Carnegie Institution of Washington Publication No. 167, 1912, pp. 21 and 29. 
c Benedict and Carpenter, loc cit., p. 39. 
d See p. 110. 
e Benedict and Carpenter, loc. cit., pp. 40 and 41. 
