604 EXPERIMENT STATION RECORD. 



The heating effect in the wire that heats the water flowing toward 

 the absorber is thus regulated to give the exact degree of lieat desired, 

 the amount of heating being that required to produce a balance of 

 resistance in the AVheatstone bridge. The mechanism actuating the 

 rheostat can be set by means of a graduated slide wire on the bridge 

 to control the heating to five one-hundredths degree, or even less. 



The new device which records the increase in temperature of the 

 water after flowing through the heat absorber is likewise electrical, 

 is automatic in its operation, and furnishes a continuous record. 

 E«sistance thermometers are placed in the water at the points where 

 it enters and leaves the heat absorber. These thermometers repre- 

 sent two arms of a AMieatstone bridge, the galvanometer of which 

 is connected with a mechanism which actuates a pen on a moving 

 record sheet. In accordance with the deflection of the pointer of 

 the galvanometer the pen is deflected to the right or left, the total 

 movement of the pen depending on the difference in the temperature 

 of the two thermometers, i. e., on the increase in temperature of the 

 water after flowing through the heat absorbers. 



The pen responds to a change of five one-thousandths degree, and 

 the device gives a reading every seven secon-ds, or practically a con- 

 tinuous record in place of the old reading every two minutes. The 

 record shows to one one-hundredth degree the temperature differences 

 in the water at entering and leaving the heat absorbers. From the 

 average of these differences for a given period, measured by a 

 planimeter, and the amount of water passing the absorbers, which is 

 determined by weight, heat eliminated by the subject in the chamber 

 is determined with great accuracy. 



These two devices, for controlling the temperature of the water 

 entering the calorimeter chamber and for recording its increase in 

 temperature in passing through the heat absorbers, represent a marked 

 advance in calorimetry and in the development of the apparatus. 

 They do away with a large amount of labor attendant upon operating 

 it, and eliminate the possibility of errors of observation and record. 

 The observer operating the calorimeter now devotes his attention 

 chiefly to maintaining the temperature of the zinc wall in equilibrium 

 with that of the copper wall and in weighing at intervals the water 

 which comes from the heat absorber. Plans have been perfected in 

 detail for regulating the temperature of the zinc wall automatically. 



The installation of a refrigerating plant in connection with the 

 respiration calorimeter is another decided improvement. This is 

 employed for lowering the temperature of the water used in cooling 

 the air space, which will materially extend the season through which 

 the apparatus can be operated. With a human subject the respira- 

 tion chamber is maintained at a temperature of approximately 68° F., 

 and in warm M-eather it has heretofore been impossible to operate the 

 apparatus on account of the temperature of the water. 



