Rays of Positive Electricity. 231 



Hence, as the minimum electrostatic deflexion is the same 

 for all the particles, we conclude that the maximum potential 

 difference through which each set of particles has fallen is 

 the same. 



(2) The second type of curve to be seen on the plate are 

 curves which pass through 0, the point on the plate struck by 

 the rays when they are not deflected by either electric or 

 magnetic forces. The portions of these curves near are 

 straight lines when the electric and magnetic fields are co- 

 terminous. If the magnetic field overlaps the electrostatic 

 the shape of the curve is that shown in fig. 6. In my paper 



in the ' Philosophical Magazine ' for October 1910 I gave 

 reasons for thinking that these curves represent secondary 

 positive rays produced by the passage of the primary rays 

 through the gas on the way to the plate, and that the parts 

 of the curve near which are produced by particles which 

 have suffered only small deflexions were produced by rays 

 which had not traversed the whole of the magnetic and 

 electric fields, but had been generated towards the ends of 

 these fields. If this view is right, then, if we shorten these 

 fields, we ought to diminish the intensity of these curves 

 near 0. To test this point the magnetic field was red need 

 from the length of 25 mm., the value it had in most of the 

 experiments, to 6 mm. The arrangement used is represented 

 in fig. 7(p. 232). The pole-pieces A, B, 6 mm. in diameter 

 and 1 mm. apart, came through sealing-wax joints in the side 

 tubes D and E ; the other ends of A and B were screwed 

 into the pole-pieces of a powerful electromagnet. On one 

 of the poles, A. a thin piece of brass was fastened by a thin 

 layer of sealing-wax which insulated it from the pole-piece : 

 the brass was connected with one terminal of a battery of 

 small storage-cells, the other terminal of which was connected 

 with the earth and with the other pole-piece, B. In this 

 way an intense electric field coterminous with the magnetic 



