18 



A BICYCLE ERGOMETER WITH AN ELECTRIC BRAKE 



field in the form of curves. Accordingly, in fig. 4 we have all of the ex- 

 periments made with ergometer I with a current through the armature of 

 0.70 and 0.80 ampere. On this diagram the points indicated by circles are 

 those obtained with the earlier calibrations with this ergometer, of which 

 the results are given in table 1. The values indicated by small crosses 

 are those obtained in the tests during June and July of 1911 (see table 3). 



.017 



.016 



.015 



.014 



.013 



012 



60 70 80 90 100 110 120 



Fig. 4. -Heat per revolution of ergometer I for currents of 0.7 

 and 0.8 ampere through field. Ordinates represent heat per 

 revolution expressed in large calories. Abscissa represent 

 revolutions per minute. 



In practically all of the experiments made with a current of 0.70 am- 

 pere, it will be seen that the average speed ranged between 75 and 82 

 revolutions per minute, and that the variations in heat per revolution 

 are not very great. Four of the five experiments made with 0.80 am- 

 pere through the field were between the limits of 71 and 75 revolutions 

 per minute, and hence these values were all clustered around one point. 

 Of particular interest is the fact that the fifth experiment was made with 

 122 revolutions per minute, and in this experiment we find that the heat 

 per revolution was considerably less than when the speed was 71 to 75 

 revolutions. 



In the earlier tests of this ergometer, practically all of the experimental 

 evidence was accumulated at a speed which was found to be the most 

 practicable and comfortable for the subject, namely, from 65 to 80 revo- 

 lutions per minute. On the basis of these calibrations it was believed 

 that the evidence showed that the heat per revolution was constant, 

 irrespective of speed; accordingly it is of interest to note that all of the 

 experiments with a current of 0.70 ampere, and four of the five experi- 

 ments with 0.80 ampere, show essentially this feature, namely, that within 

 narrow limits the results are grouped around a certain value which is 

 practically independent of the speed. On the other hand, we find that 

 in the experiment with a very high speed and a current of 0.80 ampere 

 there is a greatly decreased heat per revolution. 



In fig. 5 are shown the values obtained with a current of 0.90 ampere. 

 With this current the experiments are much more numerous and include, 



