322 Prof. J. J. Thomson on the Discharge of Electricity 



the electromotive force in the neighbourhood of the wire is 

 exceedingly large. To make these forces available for pro- 

 ducing an electrodeless discharge, all we have to do is to 

 make the wire connecting the coatings of the jar the 

 primary of an induction-coil of which the discharge-tube 

 itself forms the secondary. The arrangements which I have 

 employed for this purpose are represented in the accompanying 

 diagram. 



Fiar. 1. 



earths 



earth 



In (a) A is the inside coating of a Leyden jar : this is con- 

 nected to E, one of the poles of a Wimshurst electrical machine, 

 or an induction-coil, the other pole F of the machine being 

 connected to B the outer coating of the jar. A C D is a wire 

 connected to the inner coating of the jar, a few turns C 

 (which we shall call the primary coil) are made in this wire ; 

 these turns are square if the discharge-tube is square, circular 

 if the discharge-tube is a spherical bulb. The wire at D is 

 attached to an air-break, the other side of which is connected 

 with the outer coating of the Leyden jar. The knobs of this 

 air-break ought to be kept brightly polished. The loop C is 

 connected to earth. The discharge-tubes, which were in 

 general either rectangular tubes or spherical bulbs, were 

 placed close to the turns of C. When the difference of poten- 

 tial between A and B is sufficiently large, a spark passes 

 across the air-break, and the electrical oscillations set up 

 produce a large electromotive force in the neighbourhood of 

 the coil, sufficient under favourable circumstances to cause 

 a bright discharge to pass through the vacuum-tubes. In some 

 experiments the jars, at the suggestion of Prof. Oliver Lodge, 

 were connected up differently, and are represented by (/3) in 



