532 Mr. W. Wilson on the Effect of 'Temperature 



apparatus could be used for examining white light which had 

 a definite vibration form. 



The polarizers were tested with monochromatic light, and 

 using a quarter-wave plate as analyser, the transmitted light 

 was found to be circularly polarized. Removing the quarter- 

 wave plate and using white light, the intensity of the field of 

 view remained constant however the analysing Nicol's prism 

 and polarizer were orientated, providing the azimuth of the 

 incident vibration with respect to the polarizer was kept con- 

 stant and at the requisite amount. Further, using the Bi- 

 trapezoid polarizer to examine an elliptically polarized beam, 

 produced by a Fresnel's rhomb with white light, no trace of 

 tint could be discerned. 



Each form of polarizer is mounted in a metal cylinder 

 which is provided with central square apertures. 



In conclusion I wish to tender my best thanks to Prof. "W. 

 M. Hicks and to Prof. Sir J. J. Thomson for the great 

 interest they have taken in this work. 



Trinity College, Cambridge, 

 October, 1910. 



Note added March 16, 1911. 

 In the Bi-trapezoid polarizer, since the azimuth £1 of the 

 incident vibration depends upon the refractive index, the 

 efficiency of this form is slightly reduced, and becomes very 

 nearly equal to that of Fresnel's rhomb. 



LIX. The Effect of Temperature on the Absorption 

 Coefficient of Iron for y Rays. By W. Wjlson, M.Sc* 



THE following experiment was made in order to determine 

 if the absorption coefficient of iron for y rays varies 

 with the temperature. A negative result was obtained. 



The arrangement of apparatus is shown in fig. 1. 7 rays 

 from a tube S containing about 30 m.g. radium bromide 

 passed through an iron block B 7 cms. in thickness. The 

 block was contained in a muffle-furnace C, and could be 

 heated by means of a blowpipe. The intensity of the rays 

 after passing through the furnace and iron was measured 

 by an electroscope E. The distance from the furnace to the 

 electroscope was 150 cms., and an asbestos sheet D was 

 placed between them as shown. Under these circumstances, 

 the heating of the furnace was found to have no direct 

 influence on the electroscope. 



* Communicated by Prof. E. Rutherford, F.E.S. 



