448 Mr Crowther, On the Transmission of ^-rays. 



varied. In this way curves connecting the intensity of the 

 ;8-radiation passing through the second system with the magnetic 

 field both with and without an absorbing substance between the 

 two systems could be obtained. The experiments were then 

 repeated for different values of the first deflecting field, that is, for 

 different velocities of the incident rays. 



Specimen curves, obtained with aluminium as the absorbing 

 substance, are given in fig. 3. It will be seen that there is a con- 

 siderable broadening of the curves even when there is no absorbing 

 screen in the path of the rays. As the rays emerging from the 

 first system have been shown to be very nearly homogeneous, this 

 broadening is due to the greater latitude of path allowed by the 

 second system owing to the shortening of the tube AD. It will 

 be noticed that for aluminium this broadening of the curves is 

 no greater with than without the absorbing layers. 



Fig. 3 shows the effect of interposing a sheet of aluminium 

 0*47 mm. in thickness between the two systems, for two different 

 velocities of the incident beam. The upper curve in each case is 

 the curve obtained for the incident beam in the absence of the 

 absorbing sheet. The ordinates represent the intensity of the rays 

 passing through the two systems, as measured by the ionization 

 produced ; the abscissae measure the magnetic field acting upon 

 the second system. 



It will be seen that in each case the introduction of the 

 absorbing sheet produces a very definite displacement of the curve 

 in the direction of the smaller velocities. 



The actual figures deduced from these curves are given in 

 Table I. 



Table I. 



Aluminium (0*47 mm.). 



It is evident therefore that there is a small, but perceptible 

 decrease in the velocity of the ^-rays as they pass through 

 absorbing media. 



But though this small decrease in velocity accompanies absorp- 

 tion, it is not sufficient to account for it. The third column in 



