ON ENERGY OF RONTGEN AND BECQUEREL RAYS, ETC. 
81 
In order to measure the amount of heat corresponding to this deflection of the 
galvanometer, a steady current from a separate battery was passed through the grid 
previously exposed to the rays and for the same time. 
Fig. 4 shows the connections. As it was necessary to determine the change of 
zero immediately after the passage of the current for a definite time, the arms of 
the bridge were undisturbed, and consequently a portion of the heating current 
passed through the grid R,,. 
Fig. 4. 
Resistance of grid R| exposed to rays = 4'2 ohms. 
,, second grid R^ = 4'28 ohms. 
Total resistance of the other two arms and leads, S = 23‘04 ohms. 
If ^ be the current from the battery supplied for heating purposes then. 
Current through R^ = "867 i. 
,, ,, R^ = T33 h 
Heating effect on R^ = 752 gramme calories. 
„ „ R^i^-OlSr 
Difference in amount of heat sujqDlied to R^ and R^ = ‘734 
We thus see that most of the heating effect is confined to the grid Rj. 
From a special series of experiments it was found that the deflection from zero of 
the galvanometer in a given time due to the heating by the current was very closely 
proportional to the square of the current. It was therefore not necessary to find 
experimentally the exact value of the current to give the same deflection as the rays, 
but from observations on one known current the results could be obtained by 
interpolation. 
It was found that under the same conditions as the table given above, a current 
i — -0200 ampere gave a mean deflection from zero in 30 seconds of 37‘4 divisions. 
The mean deflection due to the rays was 17'9 divisions. 
