34 



BRIGGS: A DIFFERENTIAL TELETHERMOGRAPH 



the bulbs, such changes do not affect the reading of the instru- 

 ment, providing the springs do not differ substantially in tem- 

 perature at any time during this change. To secure this equality 

 in temperature of the two springs as nearly as possible, the 

 instrument is provided with a metal cover blackened inside, and 

 the interior is given an open construction. The two copper 

 capillaries can also be kept at the same temperature for the 

 greater part of their length. The differential temperature 



Fig. 1. A mechanical differential telethermograph. Capillary tubes much 

 longer than those shown in the illustration may be used. 



recorded is, therefore, substantially that represented by the 

 difference in temperature of the two bulbs. 



APPLICATIONS 



Two applications of this instrument have been made during 

 the past year in connection with investigations in bio-physics. 



Recording the depression in temperature of the ivet-bulb thermome- 

 ter. One use of the instrument consists in recording changes in 

 the depression in temperature of the wet-bulb thermometer. 

 For this purpose the apparatus is placed in a ventilated instru- 

 ment shelter. One bulb is covered with muslin and kept con- 



