THE CALORIMETER SYSTElt AND MEASUREMENT OF HEAT. 125 



pipe of the heat- absorber, passes once around the chamber, then enters 

 the upper pipe and makes another circuit of the chamber, and finally 

 passes out of the chamber by way of the wooden plug through another 

 brass pipe connected by the rubber tube W 2 . With this arrangement 

 the water absorbs heat very rapidly, although the actual mass of water 

 inside the calorimeter at any one time is kept at a minimum, i. <?., the 

 contents of the pipe of the absorber, about 400 grams. 



REGULATION OP RATE OF ABSORPTION OF HEAT. 



In order that the temperature of the chamber may be kept constant, 

 it is necessary to provide that the rate at which heat is absorbed may 

 be varied in accordance with that at which it is produced. This is accom- 

 plished in different ways. The coarser regulations are easily made either 

 by increasing the flow of water through the system or by lowering the 

 temperature of the ingoing water. The finer regulations that are essen- 

 tial for maintaining a constant balance between heat production and 

 heat absorption are made by increasing or diminishing the amount of 

 heat-absorbing surface exposed, by lowering or raising shields (Sd, in 

 n g- 33) provided for the purpose. When the shields are raised the air 

 in them is cooled, and, serving as heat insulation, retards the absorp- 

 tion. When the shields are lowered the absorbing surface is exposed 

 directly to the heat. 



The shields are constructed of sheet aluminum. The shorter ones, 

 which protect the absorbers on the ends of the chamber, are raised or 

 lowered when necessary by the subject inside the chamber. Those on 

 the sides are operated by the observer outside. A flexible cord attached 

 to each of these side shields travels over pulleys and connects with an 

 iron quadrant on the rod which extends through the wall of the appa- 

 ratus and transmits the motion of the hand lever, shown in figure 

 32. It is thus possible, by raising or lowering this lever, to raise or 

 lower the long shields inside the chamber, and the distance through 

 which these shields are raised or lowered determines the area of the 

 absorbing system, either exposed or covered up. A graduated arc over 

 which the hand lever travels permits of very slight motions in the 

 movement of the lever, and consequently of the most delicate adjustment 

 of the position of the shields. 



In ordinary experiments the two end shields are always up, and all 

 the finer regulation is done by means of the two long shields. During 

 the night, and when the subject is sound asleep, it is necessary to raise 

 these shields to the highest point, cut down the rate of flow of water 

 to a minimum, and raise the temperature of the incoming water until 

 it is nearly at the top of the scale on the incoming water thermometer. 

 During work experiments all the shields are lowered as far as they 



