Cady — On the Energy of the Cathode Bays. 



9 



the bolometer, should give up their charge to earth through 

 the metallic frame. Although the density of the rays is not 

 perfectly uniform throughout the bundle, still it can be 

 assumed that the distribution of temperature in the thin bolo- 

 metric foil under the influence of the rays and of the electric 

 current is practically identical.* The silver was not dissolved 

 away from the platinum-silver foil until the bolometer had been 

 mounted. 



Fig. 2 shows the arrangement of the bridge. The current- 

 intensity i in the battery branch was measured by means of the 

 ampere-meter 31. Shunting the resistance r parallel to R 

 increased the current from i x to \ and gave an accurate means 

 for measuring the increase. A Thomson galvanometer of du 

 Bois-Rubens type was employed. For the thermal measure- 

 ments two 20-ohm coils mm were used ; in order to get rid of 

 the cathode-current, a point between the two coils was led to 

 earth (contact a, fig. 2) and the resistance T so chosen that with 

 battery disconnected the cathode-current caused no deflection 

 of the galvanometer. Two 2000-ohm coils n served to measure 

 the cathode-current, by closing the contact h, while a remained 

 open. 



Sis a shunt for reducing the sensitiveness of the galvanom- 

 eter when necessary. The bridge resistances were balanced by 

 means of the sliding contacts at D. The manganin wire 

 resistances W were as nearly equal to the bolometric resistance 



F. Kurlbaum, Wied. Ann., lxv, p. 755, 1898. 



