650 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



4000 



6000 

 WAVE-LENGTH 



Figure 1. Electric Double Eefraction of Carbon Bisulphide. 



The heavy curves show the double refraction observed with carbon bisulphide at 

 11° and at 24°. The dotted curves show how the double refraction was previously 

 supposed to vary, — inversely as the square-root of wave-length. The departure of 

 each observed curve from the dotted one is important, for the dotted curve is an 

 equilateral hyperbola approaching the axes of zero wave-length and zero double 

 refraction as asymptotes, whilst the observed curve rises much more sharply 

 towards the edge of strong absorption in the ultra-violet, and falls much more 

 slowly than the hyperbola towards the red. 



The wave-length is expressed in lO -10 meters ; the double refraction is expressed 

 in per cent of the value of (fi e — /xj at 24°.0 with sodium light, — equal to about 

 7.04 • 10~ 7 ; the field-strength giving these values is 56,000 volts per cm. 



