CALIBRATION TESTS 



29 



constancy in the apparatus. We feel justified, therefore, in heartily 

 recommending its use when a constant amount of work is to be done and 

 uniformity in muscular work is essential. Furthermore, the amounts of 

 energy computed from the speed of the magnetizing current are accu- 

 rate to within about 2 per cent. 



FRICTION TESTS WITH ERGOMETER II. 



Although it was doubtful if a knowledge of the heat per revolution 

 due to friction would be of any particular value, it seemed desirable to 

 make measurements of the friction of this apparatus if only for com- 

 parison with those made with ergometer I, and for checking the recent 

 experiments with the latter. Three friction tests were accordingly made 

 with ergometer II on December 18, 20, and 22, 1911, the results being 

 reported in table 6. As in the friction tests with ergometer I, the amounts 

 of heat measured were so very small that but little reliance can be placed 

 upon the results for individual periods; and it is not surprising that we 

 find variations of 50 per cent between the heat per revolution found on 

 December 18 and December 22 when compared with that in the test on 

 December 20. When we consider, for example, that through a whole 

 experiment lasting from 10 h 14 m a. m. to 2 h 15 m p. m. only a sum total of 

 7 calories was measured, the numerical values found are certainly not 

 of great significance. The important thing is that these results show 

 an average of heat per revolution not far from 0.0025 calorie, which is in 

 reasonably close agreement with those found with ergometer I in the 

 calibrations inside of this identical calorimeter. In general, the frictional 

 heat per revolution is not far, therefore, from 1 to 2 per cent of the total 

 heat produced when the apparatus is used with the field magnetized at 

 1.5 amperes. 



Table 6. Friction test, ergometer II. 



