336 Mr Orange, On the shape of beams of canal-rays. 



may produce great changes in the electrostatic field, which is 

 known to depend largely on the distribution of ions in the kathode 

 region. 



Consider the effect of the slip in Fig. 3 in the light of this 

 reservation. Beam A, which we hold to originate in the lower 

 part of the region, (kathode-rays from the longest side of the 

 triangle being the primary agent), contains a sharp shadow as 

 shown. Here we can claim that the mica does not interfere at all 

 with the discharge from the longest side of the triangle, and hence 

 the beam A is formed normally, -the mica simply blocking out 

 part of the canal-rays when they have passed through the kathodic 

 interspace. 



But now consider the effect on beam B. Here we have to 

 deal with canal-rays produced in the N.E. corner of the region, 

 the kathode-rays from the medium side of the triangle being 

 responsible. The slip, however, is placed so as to interfere con- 

 siderably with the discharge (including the kathode-rays) from 

 this side. Thus instead of getting a neat shadow in the beam, we 

 get an ill-defined dai-k core which is vaguely indicated in Fig. 3 by 

 a dotted line of elliptical form. 



The details of Fig. 3 are typical of the appearances for various 

 positions of the slip, as may be readily imagined. The effect 

 of placing the slip in a more exceptional position is shown in 

 Figs. 4, 5 and 6, which correspond respectively to decreasing 

 pressures. 



The general tendency is best shown at the lowest pressures, 

 e.g. in Fig. 6. The beams are roughly of the forms which would 

 be obtained if the right-hand corner of the kathode were 

 removed altogether, as indicated by the dotted line in Fig. 7. 



This right-hand corner is certainly fenced off by the mica and 

 the pin so that it is prevented from acting as a double kathode ; 

 the forms of the beams would seem to be in accordance with this 

 fact. The only other feature of interest is the fine pencil of canal- 

 rays coming from the aperture between the mica and the pin, and 

 visible in Figs. 4 and 5. 



These observations would seem to support the view that 

 the constituent csmal-rays are straight. 



I wish to thank Prof. Sir J. J. Thomson for his kindly interest 

 in these experiments. 



