338 Prof. Wood and Mr. Kimura on Scattering and 



The arrangement of the apparatus is shown in fig. 3, 

 which explains itself. The camera is of course focussed upon 



Ficr. 3. 



Quartz 



corners 



h- 



£23 Double Im. 

 Prism . 

 Double ftefr. 

 , Prism. 



\\ 

 \\ 



,\ \ | \| Fresnef R.L 

 \\\v LJ Prism. 





Sere 



the Fresnel prism, by adjusting the distance as described 

 previously. An exposure of four or five minutes was sufficient 

 to give the two images of the spot of resonance radiation 

 formed by the double-image prism. The presence of two or 

 three per cent, of polarization would be indicated by faint 

 traces of the horizontal dark bands in the images. 



At first we obtained distinct traces of the bands, but their 

 appearance and intensity were very variable, and we finally 

 found that they were due either to a slight deposit of mercury 

 globules on the inner surface in the high temperature expe- 

 riments, or to a slight cloudiness of the inner surface of the 

 prismatic plate near one edge. We finally got things so 

 adjusted that no trace of them appeared at any temperature 

 between 20° and 200°, above which the scattered resonance 

 radiation practically disappears ; and we feel quite certain 

 that there is no trace of polarization in the scattered radiation, 

 even when the incident light is plane polarized, and the 

 density of the vapour is so great that we are approaching the 

 stage at which selective metallic reflexion begins. This 

 seems very remarkable, since, as we shall see presently, if 

 the incident light is polarized, the metallically reflected wave 

 is polarized also. 



This makes it appear probable that we shall have to reject 

 the idea that the reflected wave can be accounted for by the 

 application of the Huygens principle to the waves emitted by 

 the resonators. Moreover, as the vapour density increases, 

 the scattered resonance radiation practically disappears some 



