596 



Mr. Alan A. Campbell Swinton 



[Feb. 4 



velocity of the atoms that form the cathode rays, and the more pene- 

 trative are the Rontgen rays produced. Further, so far as the moving 



Fig. 20. — Diagram showing how the rosislance of a lube is altoved 

 by varying the position of the cathode. 



cathode is concerned, the supply of atoms appears to be of great im- 

 portance. If penetrative Eontgen rays are desired the access of 

 atoms to the cathode must be restricted. If only a few atoms can 

 get to the cathode these are projected at great velocity ; if there is 

 too ready access the atoms crowd in upon the cathode and the electri- 

 cal charge of the latter is unable to throw them off with much speed. 

 It is possible to restrict the supply of atoms to the cathode either by 

 bringing the latter back into a recess or annex, as in the tube just 

 shown, or a tube such as is illustrated in Fig. 21, in which both 

 cathode and anti-cathode are fixed, but in which there is a movable 

 conical glass shield which can be brought up from behind the cathode 

 so as to impede the access of the atoms, which, as we have seen, come 

 in round the edges of the cathode, to any desired extent. This tube 

 regulates just as did the adjustable cathode tube, and its efficacy goes 

 a long way to prove that the theory as explained above is substantially 

 correct. 



In order to produce sharply defined Eontgen photographs it is of 

 course of the utmost importance that the rays should be given off 



