296 



Ml!. C. T. II. NVII.soN i>X TIIK KrTK'IKM'Y AS n>XI>KXSATIOX 



RAYS turned off before expansion. Difference of potential lift ween plates, 



1 Leclanch6 cell. 



The effect of the positive ions begins to l>e detected when v-,/v t amounts to alx>ut 

 1*32 or 1 "33 ; below that point no more drops are seen than in the absence of the rays. 



The next series shows the point at which the positive ions first begin to be 

 detected more sharply defined. 



RAYS turned off before expansion. Difference of potential between the plates, 



1 Leclanche cell. 



Positive ions begin to be caught when v^/Vi is between T31 and 1'32. 



A double apparatus was now constructed, to allow of the comparison of fogs 

 produced simultaneously in the presence of positive and negative ions respectively. 



The arrangements for causing the sudden expansion were the same as before. The 

 general form of the rest of the apparatus is indicated in the diagram (fig. 2) which is 

 drawn approximately to scale. 



The vessel in which the clouds were observed was nearly spherical, and about 

 5 '8 centims. in diameter. It was divided into two equal chamlxjrs by a partition 

 of brass (about 1 inillim. thick) in the equatorial plane ; the vessel was cut in two to 

 allow of its insertion, the edges of the two halves being ground smooth, to allow 



