On the Electric Discharge in Rarefied Gases. 367 



produced with the properties of rectilinear propagation, exci- 

 tation of phosphorescence, &c, at openings of any width, if 

 these openings occur in diaphragms or in tubes connecting 

 vessels or introduced into them, the area of which is consider- 

 able in comparison with the diameter of the opening. A con- 

 sideration of these bundles of rays possessing the properties of 

 the kathode-light issuing from wide openings also protects the 

 experiments on narrow openings against the objection that the 

 coincidence of their rays with the kathode-rays depends on a 

 conductive action of particles of the insulating substance 

 which might possibly be torn off from the edges of the opening. 



It has further been shown* that the positive light also pos- 

 sesses the property of rectilinear propagation, and of exciting 

 phosphorescence when the exhaustion has been carried far ; 

 it does not seem to be reasonable to adopt an explanation for 

 the phenomena of the kathode-light the principle of which is 

 not applicable to the exactly similar properties of the positive 

 light. 



The most convincing proof, however, is given by the fol- 

 lowing observation, which I have made in experiments on the 

 kathodic deflection. This last name was proposed in the 

 book referred to above for the deflection of the electric rays 

 there described, of which I have made use f in determining 

 the velocity with which the electricity propagates itself. I 

 may assume it to be known that a kathode of aluminium pro- 

 duces no deposit on the walls of the tube even after several 

 hours' use, whilst a kathode of platinum of no great thickness 

 soon produces a completely opaque metallic deposit on the 

 part of the tube played upon by the kathode-light. Two 

 straight smooth wire electrodes, a and b, are inserted in the 

 end of a cylindrical discharge-tube parallel to the axis of the 

 tube. If both are made at the same time kathodes of the same 

 discharge, then each of the two wires causes a deflection, in the 

 rays of the other which pass by near to it, of the nature of a 

 repulsion. We have then, as already described, two sharply- 

 bounded surfaces, of which the one receives no rays from a, 

 whilst none of the electric rays emitted by b fall upon the 

 other. At the density of gas favourable to the production of 

 phosphorescence, both surfaces are distinctly seen upon the 

 surrounding brilliantly phosphorescing surface. This pheno- 

 menon is also observed when one of the kathodes a is of pla- 

 tinum, until the increasing thickness of the platinum-deposit 

 prevents the phosphorescence of the wall. 



According to the view of Grintl and Puluj, that portion of 

 the glass wall on which no rays fell from the platinum elec- 

 * Phil. Mag. x. p. 236. t Ibid. p. 246. 



