332 



Mr Horton, The emission of positive rays 



field was investigated. For this purpose the apparatus dia- 

 grammatically represented in Fig. 2 was used. The rays leaving 

 A were made to shoot through the hole in the earth-connected 

 screen S, and then between the parallel plates Pj, P^, which were 

 about 3 cms. long and placed about 1 cm. apart. A strong electric 

 field could be created between these by connecting them to the ter- 

 minals of a battery of small accumulator cells. Z is a zinc-blende 

 screen by means of the phosphorescence of which the deflection 

 of the rays could be observed even when the illumination along 

 their path was very faint. 



s A 



Fig. 2. 



A, anode. S, earth-connected screen. Z, zinc-blende screen. 



C, cathode. Pj, P2, parallel aluminium plates. 



As with the former apparatus it was found that there was no 

 fine pencil of rays given off by the anode. The rays getting 

 through the hole in the screen S were always deflected towards 

 the positive plate by the electric field, showing that they were 

 negatively charged. They were, no doubt, ordinary cathode rays 

 formed by the reversals of the induction coil. The impossibility 

 of obtaining anode rays from these phosphates seems to show that 

 there is no connection between the anode rays and the positive 

 electrification emitted by salts when heated, but it was thought 

 worth while seeing whether anode rays could be obtained from 

 other compounds of phosphorus, because these, as well as phosphorus 

 itself, have the power of emitting positive ions when heated on 

 the anode of a vacuum tube. 



Some experiments were therefore made in which calcium 

 phosphide mixed with a little graphite was used as the anode 

 in the apparatus of Fig. 1. At a low pressure a distinct torch 

 of rays was seen surrounding the anode, and, after a few minutes, 

 from the midst of this torch there came a fine pencil of rays 

 shooting right across the bulb and causing phosphorescence of the 

 glass where they struck. This pencil seemed to have its origin 

 at a spot on the surface of the anode which was hotter than the 

 rest of the surface. It was not deflected in a weak magnetic field, 



