CH. xiv.] RADIUM RAYS 137 



it will possess no features which enable anything 

 like measurement to be made on it, unless some 

 still further ingenious device be employed, such as, 

 for instance, that of Kundt for making experiments 

 on anomalous dispersion. 



The experiments of W. Kaufmann at Gottingen 

 were conducted after this very fashion, and may be 

 summarised thus: an electric and a magnetic field 

 were simultaneously applied, in such a way as not to 

 neutralise each other's effect but to cause deflexions 



FIG. 18. Diagram of the deflexion of high-velocity rays from radium. 

 The radium is in a cavity in a lead block a ; the rays pass through an 

 aperture 6, and are spread out by a magnetic field into a spectrum d : d 2 ; 

 the gamma rays or any uncharged rays produce an impression at c on 

 the photographic plate, cd, placed to receive all the rays. In a uniform 

 field each of the lines abd is a circle. 



at right angles to each other. In that case if the rays 

 from a small point source, after traversing the double 

 field, are received upon a photographic plate at a 

 little distance, it may be expected that the two 

 spectra will be compounded into a single spectrum 

 inclined at some angle corresponding to the relative 

 strength of the two fields. But whether the inclined 

 spectrum thus produced will be a straight line or a 

 curve must depend upon circumstances. All that 

 can be said, without further consideration, is that each 

 point of the spectrum would represent a definite 

 ratio of deflexion, and therefore a definite inertia and 





