Electricity carried by a Gaseous Ion. 



353 



one-half its value, i. e. -J- of a volt per cm., and the electro- 

 meter deflexions again determined : as these were found to be 

 just half the value with the double force, it was concluded 

 that with the weak fields used in these experiments the value 

 of n was sensibly the same as that without fields. 



To test whether the secondary ionization due to the inci- 

 dence of the radiation on the aluminium was appreciable, the 

 observations were repeated with the lower plate covered with 

 wet tissue-paper. It was found, however, that the results 

 obtained with the wet paper were the same as those without. 



The following are the results of experiments made to deter- 

 mine the number of ions per c.c. due (1) to a specimen of 

 radium A placed 10 cms. above the top of the chamber in 



Expansions greater than 1-33. 



Pressure 





of atmo- 



Temp. 



sphere. 





773 



19-5° 0. 



753 



19 



749-5 



19 



761 



19 



772 



19 



768 



19'5 



Difference in 



Expan- 



pressure 



be- 



sion. 



and after 



ex- 





pansion. 







193 



1343 



185 





1-335 



184 





1-336 



185 





1-33 1 



193 





1-343! 



193 





1-344 



Time taken by 

 cloud, to fall 1 cm. 



Radium Radium 

 A. E. 



9'65 sec. '. 186 sec. 

 10 



1025 

 10 



9-5 



9-75 



18-25 

 17-25 

 18-5 



Mean ... 



Ions per c.c. 



Radium Radium 

 A. B. 



63 Xl0 4 

 6-65 xlO 1 

 6-8 xlO* 

 6-66 xlO 4 

 6-3xlO i 

 6-4 xlO 4 



65x10* 



17x10 s 



16-3x104 

 15-5 X10 4 

 16-9 XU> 



16-42x10' 



Expansions less than 1*33. 



Negative ions 

 per c.c. 



768 

 773 



772 



19-5 

 19-5 

 19 



1(13 

 163 

 167 



I 1-277 



7 



i 1-276 



6 



1-28 



7-125 



13 33x10 



13-5 !2-6xlO J 

 12-5 i3-3xuT 



Mean... 3-0x10^ 



8-6x10* 

 S-9 x 10 4 



8-2x10* 



8-5X10 1 



which the cloud was produced. (2) to another specimen (B) 

 placed at a height of 15 cms. above the cloud-chamber. 

 The first table contains the number of positive and nega- 

 tive ions caught by expansions greater than 1*33, the second 

 the number of negative ions caught by expansions less 

 than 1*33. 



If we take the mean of the results, we find the radium A 

 produces at a distance of 10 cms. 6*25 x 10" 1 ions per c.c, v\ hile 

 radium B produces 16*75 x ]()\ 



