52 Prof. Thomson, On the motion of a charged ion. 



greater than that of the positive ; and I have shown in a 

 paper in the Philosophical Magazine for March 1899 that this 

 difference in the velocities of the positive and negative ions would 

 account for many of the differences between the phenomena at 

 the positive and negative electrodes in a vacuum tube. The 

 preceding analysis shows that the same hypothesis will account 

 for the difference in behaviour of the negative glow and of the 

 positive column when in a magnetic field. Plucker showed that in 

 strong magnetic fields the negative glow follows the lines of 

 magnetic force ; the positive column on the other hand does not 

 do so, but pursues a more or less spiral path. This is what we 

 should expect if the negative glow marks the path of the rapidly 

 moving negative particles for which Hv is large ; while in the 

 positive column (where we have to do with the more slowly 

 moving positive ions for which Hv is not so large, not large 

 enough to allow us to neglect the components of the velocity 

 along the lines of electric force, and in the direction at right 

 angles to the electric and magnetic forces in comparison with the 

 component along the lines of magnetic force) the path of the 

 particles will be spirals. 



The formation of clouds with ozone. By John S. Townsend, 

 M.A., Cavendish Laboratory, Cambridge. 



[Received January 13, 1899. Head January 23, 1899.] 



1. The properties of the clouds which are formed with oxygen 

 containing ozone have been investigated by many experimenters 

 and very different conclusions have been arrived at as to the 

 cause of their formation. The methods by which these clouds can 

 be obtained are very numerous, but the following experiments deal 

 only with three of the principal cases. 



When oxygen containing ozone is bubbled through a solution 

 of potassium iodide a cloud begins to appear over the surface of 

 the solution after the bubbling has been going on for a few 

 minutes. No such effect is observed when the gas is passed 

 through pure water. Meissner explains this result by supposing 

 that there are two allotropic forms of oxygen made by the silent 

 discharge, — ozone and antozone, the latter of which has the power 

 of condensing water to form a cloud when the ozone is removed. 

 Thus, when ozone is removed from oxygen by passing the gas 



