76 



Hon. R. J. Strutt. On the Behaviom' of the 



been used which left the anti-cathode at a greater angle. Thus 

 sharper shadows were obtained, and a smaller magnetic deflection 

 could have been detected. 



The tube was arranged with its cathode stream parallel to the magnetic 

 field, so as to avoid any shifting of the source of radiation when the 

 magnet was reversed, owing to an effect of the magnet on the original 

 cathode beam. Such a shifting would have given rise to a spurious 

 effect. The only objection to this was that the shadow-casting wire 

 had to be obliquely placed so as to be in the plane of the anti-cathode. 

 Thus some sensitiveness was lost, 



I shall now give an estimate of the smallest defiectibility which 

 could have been detected. The rays traversed a distance of 65 cm. 

 after leaving the magnetic field. 



It was estimated that a lateral displacement of the shadow of the 

 wire by 0-02 cm. could have been detected. But the wire was in- 

 clined 50° to the resultant magnetic force. Thus the smallest real 



displacement that could with certaint}^ ])e detected was ? cm. 



sm 50 



The smallest angular deflection of the rays which could be detected 

 would be, in circular measure, 



^'^^ = 0-000405. 



65 sin 50 



The length through which the rays were exposed to the magnetic 

 force was 8 cm. If in this distance they were bent through the above 

 angle, the radius of curvature would be 



cm. = 19,800 cm. 



0-000405 



The strength of the magnetic field was determined in the usual 

 manner, by observing the throw of a galvanometer when a small coil 

 of known dimensions connected up with it was suddenly withdrawn 

 from the region between the pole pieces. To reduce the results to 

 absolute measure, the throw due to reversal of an earth-inductor in 

 the same circuit was observed. 



In this way the strength of the field was found to be 



3270 C.G.S. 



It is convenient to exhibit the result by giving the mxaximum field 

 which the experiments indicate as unable to produce a curvature of 

 radius 1 cm. 



Since a field of 3270 does not produce a curvature of radius less 

 than 19,800 cm., we see that the field required to produce a curvature 

 of radius 1 cm. cai^not be less than 



