Mr Crowther, On the Transmission of ^-rays. 



443 



Schmidt placed at J. a screen covered with radium E ; 

 measured the ionization produced above B, for different values 

 of the magnetic field, and so obtained a curve connecting the 

 intensity of the radiation passing through B with the magnetic 

 field. The curve he obtained shows a fairly sharp maximum 

 ionization for a certain definite field from which it falls away 

 gradually to zero, as the field is increased or diminished. 



Various thicknesses of aluminium were then interposed between 

 the radium E and the aperture A and the experiment repeated. 

 In every case the curves, though decreasing in height as the 

 absorption increased, were exactly similar in shape and there was 

 no perceptible shift of the maximum in either direction. From 

 this result it was argued that no change in the velocity of the 

 rays occurred during their passage through the aluminium. 



There is, however, a certain ambiguity connected with the 

 use of the magnetic deflection method, which under the best 

 of circumstances can only be minimised, and never completely 

 eradicated. 



If the apertures have a finite size, as must always be the case 

 in practice, the path J. (75 is not the only possible path for rays to 

 follow in order to emerge through B. A little consideration will 

 show that rays of uniform velocity, but entering the field obliquely, 



