ON ENERGY OF RONTGEN AND BECQIIEREL RAYS, ETC. 
29 
Arrangement oj Apparatus. 
Fig. 3 shows the general arrangement of the experiment. The bulb and coil 
were completely enclosed in a small lead-covered room connected to earth. Tlie 
rays passing through a circular hole in the lead, covered with aluminium, fell on 
one of the platinum grids A. A pencil of the rays, after traversing the grid, passed 
through a rectangular hole in the thick lead plate B, and made the air a partial 
conductor inside the discharge cylinder D. The vessel D merely served as a means 
of testing the constancy of the rays given out by the bulb by noting the current 
produced between the charged electrodes. The discharge apparatus will he described 
in detail later. 
Fig. 3. 
The two grids A and A' formed two arms of a Wheatstone Ijridge (fig. 4). Tlie 
other two arms were formed by a manganin cylinder potentiometer of 22 ohms, 
corresponding to a length of about 25 metres of wire. A sensitive low-i'esistance 
galvanometer was employed, and the deflection read with a telescope and scale. 
Tlie balance was first ol3tained for a momentary passage of the battery current. 
The rays were tlien turned on for a given time, generally either 30 or 45 seconds. 
The rays falling on the grid A were partly absorbed and heated the platinum to a 
slight extent, and the resistance consequently changed. The deflection from zero 
was noted immediately after the cessation of the rays. 
In order to obtain a measure of the heating efiect, a steady current was sent 
through the grid A for the same time as the rays acted. The magnitude of this 
current was adjusted until the deflection from zero was the same as for the rays. 
