﻿Direct or Indirect Nature of Ionization by X-rays, 



647 



geometrical form, the construction I have devised is repre- 

 sented in the accompanying diagram. 



Take any angle bac and at regular distances from a describe 

 the arcs fg, de, and be, with a as centre. Join, respectively, 

 the points bg, ef, dg, and ef. The line aih, of course, bisects 

 the angle bac. With radius ah and a as centre, describe the 

 arc JK, cutting dg and ef at j and k. The lines al and ami, 

 drawn respectively through j and £, trisect the angle bac. 



St George's Hall, W., 

 Dec. 11, 1911. 



LIV. On the Direct or Indirect Nature of the Ionization 



by X-ray Si 



To the Editors of tlie Philosophical Magazine. 

 Gentlemen,' — 



IN the February number of the. Philosophical Magazine 

 Dr. Barkla criticises some results obtained hj Mr. Porter 

 and myself. We had shown that all the ionization in oxygen 

 due to X-rays could be ascribed to an indirect action of the rays, 

 effected through ft rays originated in the gas by the X-rays, 

 provided that the ratio of the absorption coefficients of the 

 X-rays in silver and in oxygen was about 34. According ro 

 our experiments the value of this ratio was 36*3 : and we 

 therefore looked upon our work as confirming the deduction — 

 made previously as the result of an entirely different argu- 

 ment — that the action of X-rays was mainly, it' not wholly. 



