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PROFESSOR E. RUTHERFORD AXD MR. R. K. McCLUXG 
After working the coil for 10 seconds, the platinum plate became red-hot and 
remained fairly constant during the next 30 seconds. It was generally found 
advisable to run the bulb at intervals for a quarter of an hour before beginning 
measurements, in order to get it into a steady state for the emission of rays of 
constant intensity. Under these conditions exj)eriments could be made from day 
day with a maximum variation of intensity of 30 per cent., and generally vdth 
much less. 
Fig. 2. 
The bulb employed gave out rays of great intensity and great j^enetrating power. 
A fluorescent screen was brightly lighted at a distance of 20 feet from the bulb. 
With a “ soft ’’ tube and less intense rays, it would have been difflcult to measure 
the heating effect with accuracy. 
Wehnelt Interrupter. 
The Wehnelt interrupter was of a simple joattern. One lead plate was placed 
inside a thick glass vessel (a Leclauche cell was used) with three holes about 
1 millim. in diameter bored in one side. The glass vessel was placed inside an 
ebonite box with a lead electrode, and was filled with dilute sulphuric acid in the 
usual manner The acid was kept cool by having a water circulation through a 
coil of lead pipe in the ebonite box. By suitably tapering the holes in the glass 
the interrupter was made to work steadily at a slow speed and gave strong dis¬ 
charges in the coil. The E.M.F. employed was 110 volts and the current was about 
15 amperes. The average number of breaks per second was 57. In the course of 
more than six months’ work the glass vessel was only replaced once, on account of 
the gradual increase of the diameter of the holes. 
