﻿198 Mr. A. S. Eve on the Radioactive Matter 



In this table the values of Q have for convenience been 

 repeated from an earlier part of this paper. Q denotes the 

 number of ions produced per c.c. per second in the vessels 

 when 14*3 mg. of radium bromide were placed at 303 cms. 

 from the centres of the vessels. 



The six equal results in the third column are the mean of 

 very many observations. Their equality is based on the fact 

 that by comparative measurements no difference could be 

 detected between the metals observed under identical con- 

 ditions. Further experiments are in progress on the effect 

 of screening the vessels and on the values of g for various 

 diameters. 



In several cases a gradual increase of ionization occurred 

 due to an emanation proceeding from the sides of the vessel. 

 Sometimes the rise curves had the character of those of 

 radium emanation. The presence of an emanation has been 

 noted by McLennan, Burton, and others. Further investi- 

 gation of this emanation may throw light on the activity 

 of metals. The effects were irregular, but they could always 

 be eliminated by pulling dry clean air through the vessels 

 for a few hours. 



Ionization in the Atmosphere. 



In a previous paper* the writer gave an account of the 

 measurement of the number of ions produced per c.c. per 

 second in a large iron tank, 2*5 cms. thick, 8 x 1\ x 1^ metres 

 in dimensions. The value obtained was q = 9'6 ; and as the 

 active matter collected in the tank was sufficient to account 

 for such ionization, the greater part of it was attributed to the 

 emanation in the air in the tank. Mr. 1ST. R. Campbell dis- 

 sents from this view, writing thus : — " Surely if the quantity 

 of emanation in the small volume of air inside the vessel 

 causes an effect so large, the far larger quantity outside the 

 vessel must have an appreciable effect even though the walls 

 are so thick as to cut out all a rays." 



This criticism arises from a misconception. The a. rays 

 are much more effective in producing ionization than the 

 7 rays. The experiments and calculations given in this paper 

 show that the a radiation of the emanation in the tank, 

 despite its limited range, produces a much greater effect in 

 the tank than the y radiation from the emanation in all the 

 air both inside and outside the tank to any distance, even 

 supposing the walls of the tank were thin ; and they were 

 2*5 cms. thick. And since Cooke found that 5 cms, of 



* Eve, Phil. Ma#. July 1905. 



