26 MUSCULAR WORK 
and rapidly radiating to the surrounding air. By varying the intensity of the 
magnetic field, a greater or less brake-effect can be produced. In ergometer II 
the resistance of the magnet is 10 ohms, and a current of 1.5 amperes through 
the coil produces substantially the same brake-effect as 1.25 amperes on 
ergometer I. The heat developed in the magnet of ergometer II by magnet- 
ization with a current of 1.5 amperes is 17.8 calories per hour. ' 
With the excessively high rates of speed frequently employed by the 
subject, it was of course impossible to count the ergometer revolutions from 
minute to minute, and hence a counter of a standard make was attached. 
Two of these were employed to insure accurate records, one actuated by 
direct contact with the pedals and the other by a pin on the large sprocket- 
wheel. 
The ergometer was calibrated by using one of the respiration calorimeters 
(the chair calorimeter a ) in the Nutrition Laboratory. The instrument was 
first divested of the handle-bars and pedals, then placed inside the respiration 
chamber, and fitted with a flexible shaft which could be driven from the out- 
side by an electric motor. By exciting the magnet and rotating the disk, heat 
was produced which could be directly measured by the calorimeter as in an 
ordinary calorimeter experiment. Different strengths of current through the 
magnetic field and varying speeds were used in calibrating the two instru- 
ments, a large number of calibration curves being obtained for both ergometers. 
With these curves it is necessary to know only the number of revolutions and 
the intensity of magnetization in order to compute directly and accurately 
the muscular work which is transformed into heat. 
Since the greater number of experiments reported in this book were made 
with ergometer II, a few characteristic calibration curves of this instrument 
are given in fig. 1, i.e., those for currents through the magnet of 0.5, 0.95, 
1.10, 1.25, 1.35, and 1.5 amperes, the six excitations of the magnet used. All 
of the curves for the calibration of both ergometers I and II, with the excep- 
tion of that for 0.5 ampere, are given in detail in an earlier publication. 6 
The ergometer is very accurately constructed and runs without much 
friction. By again employing the respiration calorimeter, friction tests were 
made with both ergometers I and II. Two tests with ergometer I gave as 
results 0.000274 and 0.000157 calorie per revolution respectively; three tests 
with ergometer II gave 0.000355, 0.000182, and 0.000351 calorie per revolu- 
tion. While the calorimeter used for the tests was primarily designed to meas- 
ure the heat production of a man and hence was not as well adapted for the 
measurement of so small an amount as 1 or 2 calories per hour, the values 
obtained for the two ergometers agree reasonably well and are doubtless not 
far from correct. The details have already been published." 
Inasmuch as the question of the internal friction of the legs came into 
discussion, it seemed desirable to rotate the ergometer by means of an electric 
motor so that the legs of the subject would freely move up and down as the 
pedals revolved. For this purpose a split wooden pulley, with a groove around 
the periphery, was attached to the hub of the copper disk and connected 
with a belt brought out to the pulley on the armature shaft of the motor. 
By measuring the intensity of the field, the current through the armature 
a Benedict and Carpenter, Carnegie Institution of Washington Publication No. 123, 1910. 
6 Benedict and Cady, loc. cit., pp. 18-28. 
c Ibid., pp. 21 and 29 
