CALIBRATION TESTS 



25 



curve, and from these observations it would appear as if the rotation of 

 the disk somewhat out of the center of the air-gap caused a very slightly 

 larger amount of heat per revolution. The general form of the curve 

 shows again a tendency toward a maximum heat per revolution with a 

 speed of approximately 60 to 80 revolutions, and a tendency to fall off 

 when the ergometer is running at a high speed. 



With a magnetizing current of 1.10 amperes, we have two series of 

 observations that are by no means concordant (fig. 10), and yet both 

 indicate a noticeable falling off in the heat per revolution at high speed. 

 We are unable at this time to account for the marked discrepancy be- 

 tween these two sets of observations, but since this current is not used 

 at present in actual experimentation with man and since the curve agrees 

 with the others in its general form, it is deemed inadvisable at this time 

 to repeat the calibration test. 



The calibrations made with a current of 1.35 amperes lie for the most 

 part on a very definite curve (fig. 11). In one single observation at 80 

 revolutions per minute, it is approximately 5 per cent too high. The gen- 

 eral form of curve noted for the other calibrations is here markedly shown, 

 namely, a low heat per revolution with a low speed, a fairly constant 

 heat per revolution between 60 and 80 revolutions per minute, and then 

 a falling off in the heat per revolution as the speed is increased. 



.022 



.021 



020 



.Ol 9 



.01 8 



.01 7 



.016 



40 50 60 70 80 90 100 HO 120 



Fig. 11. Calibration curve of ergometer II for magnetizing current of 1.35 amperes. 



X 



The observations with the strongest current through the field, namely, 

 1.50 amperes, are shown in fig. 12. One observation, characterized by a 

 circle, was made when the disk was rotating near the rear pole, i.e., out of 

 center of the air-gap, but the variation from the normal is so slight as to 

 make it almost imperceptible. In this curve we again find a low heat 

 per revolution with low speed, a fairly constant heat per revolution be- 

 tween 60 and 80 revolutions per minute, and a decrease in the heat per 

 revolution as the speed is further increased. 



