POLARIZATION OF " X " RAYS 3 



at each break of the current in the coil a small 

 spark at the gap cc\ at the same time as "X " 

 rays are being emitted by the tube. Owing 

 to the flexibility of wires, AI<r, A'lV, the 

 straight line cc\ along which the spark occurs, 

 can be set in any direction we please. A 

 sheet of aluminium foil, 40 cms. square, is 

 interposed between the tube and the spark, 

 so as to prevent any direct influence of the 

 electrodes of the tube on cc\ 



In order to define easily the relative posi- 

 tions of the tube and the spark cc\ take three 

 rectangular axes, of which one, Qz> is vertical. 



Fix the focus tube so that its length, and, 

 consequently, the pencil of cathode rays, coin- 

 cides with OY, the anticathode being placed 

 near the origin, and sending " X " rays in the 

 positive direction of OX. 



Place the gap cc' at a point on the positive 

 side of OX, so that its direction is parallel to 

 OY. The spark being properly regulated one 

 observes that the " X " rays act upon it in such 

 a way as to increase its luminosity, for the 

 interposition of a sheet of lead or glass mani- 

 festly diminishes the brightness. 



