THE ACTION OF LIGHT 



549 



B 



FIG. 176. ULTRA-VIOLET ABSORPTION BY ANTHRACENE. 



A, Series of photographs of ultra-violet absorption spectra of anthracene. Below each one there is a normal 

 spectrum. The relative intensities of the two spectra are varied in known ratio by means of rotating adjust- 

 able sectors. At a certain wave length in each pair, marked with a white spot, the intensities of the light are 

 equal. 



B, Absorption curve drawn from the above photograph. 



Ordinates amount of absorption corresponding to the frequency of vibration of light indicated by the 

 abscissae. 



(See Catalogue of Messrs Adam Hilger, 1914. ) 



green light, yellow gold chloride by blue light, blue starch iodide by yellow light. Each is 

 attacked by light of the colour complementary to its own colour, that is, by the light which 

 it absorbs. 



