Assimilation in Relation to Radiant Energy. 149 



blue light of the same energy. This problem has been attacked 

 by Kniep and Minder (1909). They used a Rubens' thermopile for 

 the measurement of radiant energy. Light of different colours were 

 obtained by the use of different filters. 



For red a glass filter was used which let through light of wave 

 lengths 620/i/i — infra red, and a little light of wave length 608/*/*. 

 The coefficients of transmission given for different wave lengths 

 were — 



O-S 



^ 0-6 





C 



0% 



130 690. fe50 



folO 570 5iO 490 /(-SO 

 Wave Lengths in fji.fi. 



410 370 



