On the Absorption of Narrow X-ray Beams. 389 



The hydrogen was generated from zinc and sulphuric acid 

 and was passed through moist glass wool to eliminate acid 

 spray. The oxygen was 99 per cent, pure from a commercial 

 cylinder. 



Some time after the experiment had been completed, a 

 paper by Simons * was noticed in which he has recorded the 

 same result for this particular comparison. 



The results of these four direct tests show that the assump- 

 tion of additive absorption in gaseous mixtures and compounds 

 is justified. 



Summary. 



(1) The total absorption coefficient of silver K radiation 

 has been measured in air, carbon dioxide, sulphur dioxide, 

 methyl iodide. 



(2) Using this silver K. radiation, it has been shown by 

 direct test on four mixtures that, the absorption in gases is 

 atomic (as in the case of solids and liquids) and therefore 

 additive in mixtures and compounds. 



My thanks are due to Professor Sir J. J. Thomson 

 for suggesting this research and for his interest in the 

 exneriments. 



XL. Note on the Absorption of Narrow X-ray Beams. By 

 P. W. Burbidge, M.Sc. (N.Z.), B.A. {Cantab.). 1851 

 Exhibition Research Scholar, Trinity College, Cambridge f.' 



THE experimental data on the scattering of X-rays at 

 small angles is somewhat meagre and the following- 

 rough experiments were clone, at the suggestion of Professor 

 Sir Ernest Rutherford, to ascertain whether at very small 

 angles there was any very large scattering effect which may 

 have escaped observation. 



The principle of the method is that used by Rutherford 

 and Nuttall % in determining the scattering of a rays — the 

 absorption of the rays in some medium is measured (1) with 

 a wide-angle beam, (2) with a very narrow beam. In the 

 case of X-rays the ideal arrangement for the former case 

 w^ould be to have the radiating point at the centre of a sphere 

 and to measure the absorption in a surrounding spherical 

 shell. If the coefficient, so determined were then subtracted 



* Simons, Univ. of Durham Phil. Soc. Proc, 1912-13. 



t Communicated bv Sir E. Kutherford, F.K.S. 



X Rutherford & Nuttall, Phil. Mag. vol. xxvi., Oct. 1913. 



