THE CALORIMETER SYSTEM, AND MEASUREMENT OP HEAT. 127 



by volume, by alternately filling and emptying two copper cans grad- 

 uated in liters. This method involved a not inconsiderable error, i. e. , 

 neglect of the variation in density of water at different temperatures. 

 For a more accurate determination of the quantity of heat, therefore, it 

 is essential to measure the quantity of water by weight. For this pur- 

 pose the water-meter or balance shown in figure 34 was devised. 



A copper can holding about 10,000 grams of water is suspended on 

 one arm of an equal beam, and a lead counterpoise, equal in weight to 

 the weight of the can and about 9,800 grams of water, is suspended 

 from the other end. In addition, the remaining weight of water is 

 taken by a spring balance, which indicates about 400 grams for a com- 

 plete revolution of the pointer. When the can is nearly filled with 

 water and the weight of the counterpoise has been overcome, the beam 

 begins to settle. As it settles, a flexible cord attached to one arm of 

 the beam throws the weight upon the spring balance, and the pointer on 

 the dial indicates the exact amount of weight taken care of by the 

 spring. The dial is graduated into 100 divisions, and the differences 

 between divisions can be read easily by halves. 



To make the meter as nearly automatic as possible and not to inter- 

 rupt the flow of water through the calorimeter, two cans are provided, 

 as is shown in figures 34 and 35. 



The cans and balances are mounted side by side on a stout wooden 

 frame. In the front view, figure 35, the two cans with their respect- 

 ive balances are shown. In the side view one can, the equal beam, and 

 the lead counterpoise are shown. The equal beams were specially made 

 by the E. & T. Fairbanks Company, of Saint Johnsbury, Vermont. It 

 was found by preliminary tests that with a load of nearly 20 kg. on each 

 arm, differences of one gram could be detected. The spring balances 

 were made by the John Chatillon Company, of New York. These are 

 also quite sensitive. 



In experiments with man the amount of water passing through the 

 heat-absorber varies greatly at different times in the same experiment, 

 and especially with experiments of different nature. When the sub- 

 ject is asleep in the middle of the night, 10 kg. of water passing through 

 the absorber system above described will suffice to bring away the heat 

 as fast as it is generated for over an hour, and at times the rate of flow 

 may even be cut down to 10 kg. in 2 or 2^4 hours. This is the slowest 

 rate. During periods when the subject is hard at work, on the other 

 hand, the rate is much faster, a flow of 10 kg. in 7 minutes being some- 

 times necessary. In devising the water-meter, therefore, the problem 

 was to provide for the accurate weighing of as much as 80 kg. of water 

 in an hour. Furthermore, in order that the observer may be relieved 



