ivith the Brush Discharge. 47 



the leaves is not produced. If the sheet be placed near to 

 the electroscope {within 10 centims.) no effect is produced on the 

 leaves, but as the distance is increased the leaves diverge more 

 and more ; thus at 50 centims. the effect is nearly as much as 

 when the board is midway. It is impossible while witnessing 

 these experiments to avoid calling to mind the similarity of 

 the effects produced to those which one sees on the coast when 

 a long billow rushing onwards towards the shore meets with 

 a solitary rock in its path. The rock is grasped on all sides, 

 but while immediately behind it the water is comparatively 

 still, the waves soon curl as it were round the sides and meet 

 each other at a short distance behind. The result being that 

 the effect of the rock is to interfere with the wave for only a 

 short distance immediately behind it. Beyond that there is 

 as much commotion in the line from the middle of the rock to 

 the shore as at the edges. 



If while the electroscope leaves are diverged and the 

 machine working, a person walks between the point and the 

 instrument, the leaves will sway with his movements, but will 

 not fall together. 



The production of the effect all round the point extends to 

 positions under the machine, for I have repeatedly obtained 

 the divergence of the leaves when the electroscope was placed 

 directly under the machine, which stood on an inch board on 

 the bench, which had a two-inch top. 



4. Chemical Action produced by the Brush-Discharge. 



The formation of ozone by the working of an ordinary 

 electrical machine is well known, but whether positive or 

 negative is more active in its production has not been 

 investigated. It was therefore determined to examine the 

 action of the brush-discharge in producing this and other 

 chemical changes. The whole of the work contemplated has 

 not been completed, but some results of interest may be 

 mentioned. Considerable difficulty was experienced, in con- 

 sequence of the high potentials used, in preventing leakage. 

 In some cases leakage took the form of brushes at other 

 places than the points required. In such cases the results 

 were useless. In consequence of this, whenever it was 

 necessary to lead the brush away from the point only the 

 most strongly insulated wire was used, and this was first 

 specially examined in order to see if any cracks or thin 

 places were in it. Whenever the wire had to be led into 

 flasks or bottles it was found that the best material for bungs 

 was solid paraffin. But it was found very difficult to produce 

 good brushes inside glass vessels, because the interior surface 



