3S2 Prof. F. Horton on the Zeleny Electroscope. 



lessen the mass. The axle is a piece (1 cm. long) of fine steel 

 sewing-needle sharply pointed at each end. A hole of the 

 diameter of the needle was drilled through the centre of the 

 aluminium disk, and the axle was placed in position and 

 fixed with a minute piece of sealing-wax on either side of the 

 disk. The axle is supported in two cups at the ends of small 

 brass screws, as shown in the figure. When the instrument 



A, aluminium disk ; G, gold leaf; P, brass plate with carbon facing ; 

 V, pivot to enable plate to be set parallel to leaf; H, high potential 

 terminal ; E, earthing terminal ; L, levelling screw. 



is being used and the gold leaf moves to and fro, the wheel 

 to which it is attached turns with it, so that the leaf always 

 oscillates about a definite axis — that of the wheel. Those 

 who are not skilled in cutting gold leaf from the ordinary 

 sheets may perhaps prefer to use the ribbon which can be 

 obtained | inch wide, but with this, difficulty is sometimes 

 experienced in removing the strip of gold from the paper 

 which separates the layers. 



Prof. Zeleny has pointed out that the surface of the brass 

 plate (P) cannot be left uncovered because the leaf sticks to 

 it ; an effect which appears to be due to coherence caused by 

 the flow of electricity across the points of contact when the 

 leaf touches the plate. Prof. Zeleny was able to prevent 

 this by coating the plate with a layer of Indian ink. The 



