12 A BICYCLE ERGOMETER WITH AN ELECTRIC BRAKE 



When placed in the calorimeter, the ergometer was divested of the 

 handle-bar and pedals, and usually of the front support. Furthermore, 

 in order to secure it properly inside the calorimeter, it was necessary to 

 place it on end. This position is shown in fig. 3. A somewhat diagram- 

 matical representation of the electric motor and of the pulley systems 

 used to reduce the speed is also shown in the lower part of the figure. 

 In actual practice the motor, instead of being bolted to one of the calorim- 

 eter supports, was fastened to the laboratory floor. A separate support 

 for the pulleys and shafting was likewise arranged so that the entire 

 driving-mechanism was independent of the calorimeter, the only con- 

 nection between the ergometer and the driving-mechanism being the long 

 shaft passing out through a small hole in the front of the calorimeter. 

 This shaft was so adjusted as to have free clearance at all points. The 

 temperature of the calorimeter room was also carefully controlled, so 

 that it would be equal to the temperature inside the calorimeter, thus 

 preventing any interchange of heat along the metallic shaft. 



By means of an adjustable resistance in the motor circuit, it was pos- 

 sible to regulate the speed of the motor so as to have the rotation of the 

 pedals vary from 11 to 120 per minute. The particularly low speeds 

 were used only in calibrating the new ergometer, being especially utilized 

 for studying the magnetic conditions in the field during calibration. 



THE TECHNIQUE OF A CALIBRATION EXPERIMENT. 



In order to bring the ergometer and the calorimeter into temperature 

 equilibrium, a preliminary period of approximately 1 hour was necessary, 

 during which time the ergometer was rotated at the desired speed, the 

 rate of flow of the water-current through the heat-absorbing coils inside 

 the calorimeter adjusted, and the temperature of the calorimeter regu- 

 lated so that the heat brought away was exactly equal to the heat devel- 

 oped by the ergometer. The current through the magnet was likewise 

 adjusted to constancy. When complete temperature equilibrium had 

 been established, the experiment proper began. An automatic counter 

 recorded the number of revolutions of the shaft outside the chamber; at 

 the exact moment of beginning the period, a reading of this counter was 

 taken, the current of water to bring away the heat was deflected into a 

 large can on a platform balance, so that the amount of water passing 

 through the heat-absorbing coils could be accurately weighed, and the 

 initial temperature of the air inside the calorimeter was carefully recorded, 

 all of these records being continued for several successive series of 1-hour 

 periods. Every 4 minutes the temperatures of water entering and leaving 

 the chamber were recorded, and the temperature of the zinc wall was ad- 

 justed whenever necessary to bring it to the temperature of the copper 

 wall, so as to maintain adiabatic conditions throughout the whole ex- 

 periment. Usually each calibration test occupied five or six 1-hour pe- 

 riods. At the end of the experiment the calorimeter door was opened 



