390 Mr. A. A. Campbell Swinton on the Circulation of 



might, however, be argued that this stream, though coming 

 from the anode, is in reality a cathode- stream due to oscil- 

 lations in the electric discharge causing the anode to be at 

 limes negatively charged. Against this view it should be 

 stated that the effects are produced quite as well by the silent 

 discharge from a small Wimshurst machine as with Ruhmkorff- 

 coil discharges. It has further been noted that the wheel 

 rotates in the proper direction with either the flat plate or the 

 concave cup employed as cathode, the other being used as 

 anode ; and any cathode-rays given off by the concave cup 

 would be concentrated, and could not therefore reach the 

 wheel in the position in which it is used to show the stream 

 from the anode. Again, it might be supposed that the ro- 

 tation is due to heat-radiation from the anti-cathode. In this 

 case, however, the rotation should occur when the side anode 

 is employed, which, as mentioned, is not the case. Further, 

 even when such powerful discharges are used as to make the 

 anti- cathode visibly red hot, the rotation of the wheel ceases 

 almost immediately the current is interrupted, the movement 

 that continues being obviously due to the momentum of the 

 wheel. 



The experiments therefore appear to establish the existence 

 at high exhaustions of a true anode-stream which travels from 

 the anode to the cathode, just as does the cathode-stream 

 from the cathode to the anti-cathode, the anode-stream passing 

 round the exterior of the cathode-stream at a considerably 

 lower velocity than the latter, but at a greater and greater 

 velocity the higher the exhaustion. 



It also appears that while, as is well known, the cathode- 

 stream is negatively charged, the anode-stream is charged 

 positively. 



For the purpose of ascertaining this a tube fitted with 

 exploring-poles, as used by Sir William Crookes, was em- 

 ployed. These poles were, however, somewhat differently 

 arranged to any described in Sir W. Crookes's papers, while 

 the exhaustion, which was taken to the degree required for 

 Rontgen-ray work in which the negative dark space appears 

 to fill the whole tube, was probably much higher than that 

 Sir W. Crookes employed. Such a tube is illustrated in 

 fig. 2, and contains the usual aluminium cathode-cup and 

 anode-plate. The exploring-poles consist of aluminium wires 

 tipped with platinum plates enclosed in glass tubes, which are 

 blown out into small bulbs at the free extremities so as to 

 contain and shield the platinum plates, the bulbs having, how- 

 ever, each an aperture exposing the platinum on one side. 

 One platinum plate is arranged just opposite to the centre of 



