378 Mr. A. A. Campbell S win ton. 



sealed into the glass of an elongated annex. The tube was exhausted 

 to about O'OOOOOo atmosphere, and the arrangement was such that the 

 paracathodic rays proceeding from A, cast a sharp shadow of B upon 

 the glass at D. The distance from B to D was made long so that a 

 small horse-shoe magnet, held so as to embrace the annex between B 

 and D, would deflect the paracathodic rays without materially affecting 

 the cathode rays passing from C to A. With this arrangement it was 

 found that the shadow of B, cast by the paracathodic rays, was always 

 moved by the magnet in the same direction as it would have been 

 moved had it been cast by cathode rays proceeding from A, thus show- 

 ing that paracathodic rays are magnetically deflected in the same 

 direction as cathode rays. 



This would point to the paracathodic rays consisting of negatively 

 charged particles, as does also the fact, noted by Professor S. P. Thomp- 

 son, with a somewhat similar tube, and confirmed by the writer, that 

 when the wire B is positively or negatively charged from a separate 

 electrical source, the consequent contraction or enlargement of its 

 shadow at D denotes electro-static attraction or repulsion between B 

 and the rays. 



However, as previously noted by the writer,* an exploring pole 

 immersed in the paracathodic rays, acquires a positive charge, and 

 the wire B in the tube illustrated in fig. 1, was found invariably to 

 have a slight positive charge, if tested with an electroscope when the 

 tube was being used as in the first experiment described above. On 

 the other hand, it was found that when the wire B was used as anode 

 instead of A, the latter also acquired a positive charge, though directly 

 played upon by the cathode rays. 



It was therefore decided to determine the nature of the electrifica- 

 tion of the paracathodic rays by means of the Faraday cylinder method 

 employed by Perrin for testing cathode rays. It is generally agreed 

 that this method gives more conclusive results than those obtained 

 with exploring poles, where the effects of induction and possibly other 

 causes appear to introduce errors. 



A tube was therefore constructed as shown in fig. 2, in which C is 

 the cathode and A is both anode and anti-cathode ; F is the Faraday 

 cylinder of brass, pierced by a small aperture through which the para- 

 cathodic rays from A can enter, and connected by means of a wire 

 entirely enclosed in glass, with the terminal T. The Faraday cylinder 

 is enclosed in another coaxial brass cylinder, also having an aperture 

 facing the anticathode, and connected with the terminal B, which 

 during the experiments was connected to earth, so as to screen the 

 Faraday cylinder from outside influence. The Faraday cylinder was 

 connected through T with the leaves of an electroscope, and when the 

 tube was put into action and the paracathodic rays entered the cylinder, 

 * ' Koy. Soc. Proc.,' vol. 63, 1898, pp. 436437. 



