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LXXXIII. Some Experiments on Polarized Rontgen Ra- 

 diation. By J. Crosby Chapman, B.Sc, Tutor in Mathe- 

 matics, Kings College, London; late Research Student of 

 Gonville and Caius College, Cambridge *. 



Introduction. 



ALL the experimental evidence obtained within the last 

 few years indicates the fundamental identity of X-rays 

 and light : this evidence includes experiments on the 

 properties of the scattered, fluorescent, and corpuscular 

 radiations, as well as on the polarization, interference, 

 reflexion, and the velocity of X-rays. These seem to establish 

 the theory that X-rays are merely light-waves of exceptionally 

 short wave-length. Previous to the recent experiments on 

 interference, one of the most significant properties which 

 Rontgen rays had been shown to possess was that of polariz- 

 ation. Barkla f, as early as 1906, showed that it was 

 possible to produce a secondary beam of X-rays which shows 

 fairly complete polarization. 



Up to the present all experiments on the rotation of the 

 plane of polarization have been made using light of a wave- 

 length of the order of that found in the visible spectrum. 

 The results indicate that the magnitude of the rotation in 

 quartz and other active substances varies inversely as some 

 power of the wave-length. This power over a considerable 

 portion of the spectrum examined is the square, but it does 

 not hold over a wider range. 



On the assumption that Rontgen radiation is merely light 

 of exceptionally short wave-length, it seemed possible that 

 a great rotation of the plane of polarization of X-rays might 

 be obtained under suitable conditions. 



The object of this present research, suggested by Professor 

 Barkla, was to test directly whether anything corresponding 

 to a rotation of the plane of polarization could be obtained 

 with X-rays. 



Apparatus. 



The apparatus was essentially similar to that used in 

 previous experiments on X-ray polarization. X-rays from 

 the anticathode of an X-ray tube passed through the slits 

 Sx and S 2 in lead screens on to the first radiator Rj ; a 

 portion of the rays scattered from this radiator passed through 

 the slits S 3 , S 4 , and S 5 in further lead screens, on to the 

 radiator R 2 . At equal horizontal and vertical distances of 



* Communicated by Prof. C. G. Barkla, F.R.S. The expenses of this 

 research have been partly covered by a grant from the Roy;il Society. 

 t Baikla, Proc. Roy. Soc. Series A., vol. lxxvii. pp. 247-255 (1906). 



