Rontgen rays and the radiation from radio-active substances. 359 



A radium specimen was put in the lead tube R and various 

 intensities of ionization were obtained by putting a number of 

 thin aluminium plates at the bottom of the tube. The time 

 required to reduce the divergence from 80 to 47 was compared 

 with that required from 47 to 21'4. 



The procedure is as follows : the disc was connected with the 

 battery, pushed against the top of the discharging rod, drawn 

 back a few centimetres and earthed, and then the transits of the 

 gold-leaf across the micrometer scale divisions 80, 47, and 214 

 were observed by a stop-watch. The results are given on the 

 opposite page. 



Assuming the constancy of the intensity of the radiation from 

 the radium we see that the current was saturated only in the last 

 experiment, so that it was necessary to work always with about 

 that or a smaller intensity of ionization. In reality I used only 

 those intensities of ionization which produce the fall of potential 

 from 65 to 45 of the scale in about one minute or a longer time. 



§ 3. Firstly, I tried the combination of X-rays and uranium- 

 rays. As before the radium was put in the lead tube R with a 

 proper number of thin aluminium plates at the bottom. An X-ray 

 tube Avas placed below the ionization vessel and enclosed in a 

 thick-walled lead box, which has a hole 8 cm. in diameter just 

 above the tube. 



The hole is guarded by a lead cylinder through which the 

 rays pass from the tube, they also pass through the aluminium 

 leaf at the base of the ionization vessel. 



For the purpose of preventing the ray which passed through 

 the ionization vessel from attacking the conducting wire two 

 large thick lead plates were placed on the vessel, so that the 

 leakage from parts of the apparatus other than that of the dis- 

 charging rod in the vessel may be taken as small. 



It may here be remarked that the complete absence of this 

 leakage, though desirable, is not absolutely necessary for these 

 experiments, so long as we keep the conditions of ionization the 

 same throughout one set of experiments. 



Since the variation of the intensity of X-ra}'S during one set 

 of experiments was unavoidable, the leakage due to X-rays was 

 measured before and after the measurement of the leakage under 

 the combined effect of X-rays and radium-rays, and the mean of 

 them taken. The results are as follows. 



24—2 



