462 



Miss Slater on the Emission of Negative 



collapse observed through a window in the silver lining of the 

 bulb, by means of a microscope with micrometer eyepiece. The 

 potential used was generally + 200 volts. The average rate of 

 leak when the leaf was positively charged was 6 scale-divisions 

 per hour, the negative leak being only 1*7. It is evident that 

 with the arrangement above described, a large proportion of the 

 radium emanation would distil over into the side-tube H, and 

 have very little effect on the leak in the bulb. To prevent this the 

 liquid air was removed, and the observations repeated. The 

 average + leak was now 47 divisions per hour, the — leak 7*3, 

 Any ionization leak due to air remaining in the bulb would 

 equally tend to discharge both positive and negative electricity, 

 so that this large difference shows clearly that there must be 

 a very considerable emission of slow cathode rays from the 

 radium products in the bulb. It was shown that the effect 

 was not due to the direct action of /3 rays from the excited 

 activity in the tube G by placing a thick lead screen between 

 this tube and the testing bulb ; the leak was not appreciably 

 altered. 



These experiments gave no indication as to whether the 

 emission of the negative rays was due to the emanation or to 

 the excited activity, since throughout the experiment both 

 substances must have been present. To test this point, a 

 rather different arrangement was used. (Fig. 2.) 



The radium was placed in a 

 small tube (A) ending in a 

 very thin bulb drawn out to a 

 fine point ; this was exhausted 

 on the pump and sealed up. 

 It was then placed in a wide 

 tube (B) with a short side 

 branch holding a lump of soft 

 iron; this tube was sealed onto 

 the bottom of the testing bulb, 

 and the whole exhausted as 

 before. The direct effect of 

 the radium in this position was 

 found to be negligible, the leak, 

 both 4- and — , being too small 

 to be measured. 



By means of an electro- 

 magnet, the iron was now moved 

 from its place, and made to fall 

 on the little tube containing 

 the radium; the thin bulb was broken, and the accumulated 



Fi<y. 2. 



