30 LETTERS TO MARCO v 



found most in the blue and violet parts of 

 the spectrum and far less in the yellow and 

 orange ; hence in the negative photograph 

 blue and violet objects, being most affected, 

 come out intensely dark, whereas reds, 

 yellows, and greens are rendered fainter ; 



Relative proportions of Yellow, Blue, and White Crocuses. 



of course in the positive this is reversed, 

 the blue and violet parts being extra light, 

 whilst reds, greens, etc., print dark. Now 

 I cannot help thinking that this actinism 

 affects the blooms of plants, if it is not 

 indeed itself the retarding force in the ray 



