28 



A BICYCLE ERGOMETER WITH AN ELECTRIC BRAKE 



the heat per revolution is sufficiently constant between these limits, irre- 

 spective of speed, although reference should be made to the calibration 

 curves if the speeds are below 60 or above 80. The abnormal appearance 

 of these curves led to much speculation as to the cause. In Part III of 

 this report it will be shown that a complete explanation of the observed 

 effects is found in the magnetic reaction of the eddy currents induced in 

 the copper disk. 



.023 



.022 



.021 

 .020 

 .019 

 .018 

 .017 

 .01 6 

 .015 

 .01 4 

 .01 3 



.012 



.01 1 



30 40 50 60 70 80 90 100 110 120 



Fio. 14. Calibration curves of ergometer II for magnetizing currents of 0.95 to 1.50 amperes. 



For physiological experimenting, the apparatus is most satisfactory, 

 since the constant brake-effect gives a constant heat production. Although 

 unfortunately it is not everywhere possible to determine the absolute 

 values by means of calibration tests inside a large calorimetric chamber, 

 yet it may be that by driving the ergometer with an electric motor of 

 known efficiency and measuring the input of electrical power, an approxi- 

 mate idea can be obtained of the actual power required to rotate the 

 pedals. We have made some rough tests of this sort. The chief diffi- 

 culty lies in running the disk at a sufficiently low speed without the 

 various losses becoming disproportionately large. 



In connection with these observations it is of especial interest to note 

 that ergometer I remained essentially constant in its electrical and mechan- 

 ical properties over a period of some 8 years, thus showing a remarkable 



