6 ROYAL SOCIETY OF CANADA 



The active wire was placed in a slot V at a distance of 2 cms. 

 below a narrow slit S. The photographic plate P was supported at a 

 definite distance above the slit. The whole was enclosed in a brass tube 

 T, which could be rapidly exhausted to a pressure of a fraction of a 

 millimetre by means of a Fleuss pump. The whole apparatus was 

 placed between the rectangular pole pieces of a large electromagnet, so 

 that the uniform field extended from a distance of 1 cm. below the slit 

 to the top of the tube T. 



In practice, the photographic plate was placed in position and the 

 active wire then placed in the slot. The outer tube was then rapidly 

 waxed down to a base plate and exhausted. The whole operation took 

 less than five minutes, and the magnetic field was then applied parallel 

 to the plane of the wire and slit. The field was reversed every ten 

 minutes for a period of about one hour. On developing the plate, 

 two narrow bands were observed, and the distance between the centres 

 of these bands represented twice the distance of deflection from the 

 normal of the pencil of rays by the magnetic field. The strength of the 

 magnetic field was about 9470 C.G.S. units, and this produced a well 

 marked separation of the bands. For example, when the photographic 

 plate was 4 cms. from the slit, the distance between the bands on the 

 plate was 4.7 mms. 



The /? and y rays from the active wire Avere found to produce a 

 small photographic effect compared with the a rays themselves. The 

 width of the band on the plate was found to be the same whether the 

 magnetic field was on or not. This shows that the rays were all bent 

 to the same extent, that is, the a particles were all projected at the 

 same speed. This result has been observed in a number of experiments 

 and confirms the conclusion arrived at by Bragg in a different way, 

 viz., that the a particles from each product are all projected with the 

 same velocity. We may conclude from this that each « particle at the 

 moment before its expulsion from the atom, is moving at a definite 

 velocity within the atom, which is the same for all the atoms of that 

 particular substance. 



The radius of curvature of the path of the rays is readily calculated. 



Let 2d = distance between centres of images. 



d^=z " of plate above slit. 



d2= " of elit above the beginning of the magnetic 

 field. 



p = radius of curvature of path of the rays. 

 Then 2 pd = d^ (d, + (/j). 



