20 



A BICYCLE ERGOMETER WITH AN ELECTRIC BRAKE 



variations in resistance that could be experienced. The values obtained 

 in five tests with a current having a strength of 1.1 amperes are presented 

 in fig. 6, only one of these observations being made in the earlier cali- 

 bration tests. The general trend of this curve has a striking similarity 

 to that observed with a strength of current of 0.90 ampere. 



By far the greater number of the work experiments performed with 

 ergometer I and published in the earlier report were made with a current 

 through the field of 1.25 amperes, and hence in the later calibration tests 

 of this instrument, especial care was taken to secure values at different 

 rates of speed with this strength of current. On fig. 7 are plotted the 

 points for the earlier observations ranging between the speeds of 72 and 

 102; these are more or less grouped about the high point of the curve, 

 which is somewhat flat, and therefore again gives justification for the 

 assertion that the heat per revolution is constant irrespective of speed 

 between 70 and 100 revolutions per minute. The points determined 

 in the later calibrations, with the speed varying from 39 to 119 revolu- 

 tions, indicate the same general form of curve, with a maximum between 

 70 to 90 revolutions per minute. 



.024 

 .023 



.022 



.021 



.020 



.019 



.018 



' 30 40 50 60 70 80 90 lOO 110 120 



Fia. 7. Calibration curve of ergometer I for magnetizing current of 1.25 amperes. 



It is a matter of some interest that all of the more recently determined 

 points are slightly lower than those determined in the earlier observations. 

 While this is not strikingly shown in the preceding curves, it is possibly 

 due to the fact that the apparatus may have been a little better lubricated 

 during the last test, since it had been put in thorough working condition 

 after several years of use and a smaller and more accurate calorimeter 

 was used. Furthermore, certain of the earlier friction tests appear to 

 show that the apparatus was distinctly not so free from friction as it should 

 have been, since the later friction tests indicated a very much smaller 

 value than that originally found. It should be stated, however, that the 

 two friction tests made and reported in the earlier publication were by 

 no means sufficient in number or extent to justify definite conclusions. 



