1908] on the Carriers of Positive Electricity. 199 



the pieces of gauze, acquire considerable kinetic energy when they 

 reached the lower gauze, they would travel some distance after 

 passing through before they were stopped and brought back to the 

 gauze, and would thus have an opportunity of ionizing the gas below 

 the gauze by collision. The negative corpuscles produced in this 

 way would be repelled from the lower gauze and might acquire 

 sufficient energy to produce fresh ions by collisions, and thus give 

 rise to the luminosity observed below the gauze. To eliminate this 

 source of ionization, a strong magnetic field was used to prevent 

 any of the secondary cathode rays from straying into a region where 

 they could affect the ionization in the region under observation. 

 Two arrangements were used for this purpose. In the first, the 

 tube with the hot lime cathode (Fig. 8) was used. The primary 

 cathode rays were coiled up into a small bunch by means of a strong 

 electromagnet placed just under the tube, from which the cathode 

 rays emerge, the cathode rays in the early part of their path were 

 screened from the effect of the magnetic force by thick iron plates. 

 The magnetic force was strong enough to prevent the primary 

 cathode rays, which were produced under a potential-difference of 

 about 250 volts, from travelling more than 2 or >> millimetres across 

 the lines of force. The path of the rays when not under the 

 influence of magnetic force never approached within this distance 

 of the two pieces of gauze, and the deflexion of these rays by the 

 magnet was away from the gauze. No luminosity could be seen 

 close to the gauze next to the discharge-tube. Nevertheless, when 

 the lower gauze N was at a potential of about 200 volts, the upper 

 gauze being earthed, there was a perceptible luminous discharge in 

 the side tube, showing that in spite of the strong magnetic field 

 something must have passed across the gauze and ionized the gas in 

 the side tube. A modification of this experiment was tried, in which 

 the two pieces of gauze were connected together and with the earth, 

 and an insulated plate connected with a charged electroscope was 

 placed in the side tube at some distance from the gauze ; the ioniza- 

 tion in the side tube produced a leak of the electroscope. It was 

 found that even when the primary cathode particles were coiled up 

 by the strong magnetic field into a small bundle at the mouth of 

 the tube from which they emerge, there was a rapid leak of the 

 electroscope showing that the gas in the side tube was ionized. The 

 leak was more rapid when the electroscope was positively than when 

 it was negatively charged. 



A somewhat similar experiment was also tried with the apparatus 

 represented in Fig. 6. A magnetic field of 1200 was established 

 between the pole-pieces, and the plates L, M, N connected with the 

 earth, so that there was no electric field in the ionizing vessel. 

 Under these circumstances neither the cylinder nor the disk received 

 any electric charge when the electric discharge passed through the 

 upper tube. The Faraday cylinder was then disconnected from the 



