94 



THE Nature of Rontgen Rays. 



By W. H. Bragg, M.A., F.R.S., Elder Professor of Mathe- 

 matics and Physics in the University of Adelaide. 



[Read June 4, 1907.] 



In a paper read before this Society at its last meeting 

 (May 7, 1907), I pointed out that the properties of the X-rays 

 were, with one important exception, generally consistent with 

 the theory that they were of a material nature, being com- 

 posed of neutral combinations of a and /? particles. But it 

 was difficult to reconcile this theory with the result announced 

 by Marx, viz., that the X-rays possessed the velocity of light. 



On further consideration of Marx's beautiful experiment 

 I find that his result is by no means so antagonistic to the 

 material nature hypothesis as I at first imagined it to be. 

 To see this clearly it will be necessary to consider briefly the 

 details of the experiment. 



An electric pulse is made to travel along a wire, TF, as 

 shown in the accompanying sketch. When it reaches the 

 cathode, C , cathode rays are driven against the anode, A, and 

 X-rays are given out, some of which travel towards the 

 saucer-shaped electrode, B. At the focus of i? is a small Fara- 

 day cylinder, F, connected to an electrometer, E. A small 

 impulse is derived from the wire, Tf", by electrostatic induc- 

 tion at D, and travels down to B. If the various distancea 



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