A Calorimeter for the Human Body. 237 



at the end of the experiment in the temperature of the air of the 

 copper chamber was not of great moment from the low specific heat 

 of air ; indeed, such a difference would only yield 214 calories, which 

 is but trifling on say, 90,000 calories given out in one hour. On the 

 other hand, a slight difference in the temperature of the copper 

 proved of importance on account of the mass of metal. 



There was no difficulty, however, in maintaining the temperature 

 of the copper within 0'3 or 0'4 of its original reading before the 

 experiment. Should it accidentally run up beyond that figure, a 

 very rare occurrence, this only lasted a minute or two, and by 

 increasing the blast through the ice, the temperature of the copper 

 was soon brought down to its initial reading. A similar remark 

 applies to falling temperatures of the copper ; by stopping the 

 draught through the ice they soon rose to the initial reading. Of 

 course, constant attention to the temperatures was required during 

 the whole experiment, which, with but few exceptions, lasted one 

 hour. 



There remained, however, a serious difficulty to contend with, 

 owing to the heat produced by .the action of the ventilators or 

 agitators. 



At first the friction of the bearings on which the fans rotate was 

 thought to be the main cause of this heat ; and, in consequence, their 

 position was altered so as to be placed entirely outside the wooden 

 chamber. This, however, failed to mend matters, and it became 

 evident that the friction of the revolving blades against the air was 

 the source of the heat produced. The only method of overcoming 

 the difficulty was to determine the heat produced exclusively by the 

 agitators and subtract it from the total heat obtained in each experi- 

 ment. 



It was now found necessary to introduce counters registering the 

 number of revolutions for each of the ventilators up to 1,000,000 

 turns. The inquiry necessitated by the ventilators (say agitators) 

 took up a considerable portion of the winter 1896-97. 



These experiments were carried out exactly in the same way as 

 those made on the living body, with this difference, that while from 

 10 to 15 Ibs. (4'5 6'8 kilograms) of ice were wanted when a human 

 subject was under experiment, from 500 to 800 grams of ice only 

 had to be used with the agitator experiments. The following is the 

 result of one experiment taken at random amongst a great many 

 others : 



-0-04 +0-02 +0-15 



