The Prevalence of Green Color in Plants 



33 



in sunlight have been stopped by the chlorophyll excepting only 

 the green. But the human eye is far too crude an analyzer of 

 color to be scientifically trustworthy, and we turn for aid to an 

 instrument which science has devised for the exact analysis of 

 light, the spectroscope. I confess, it is only with reluctance that 

 I refrain from explaining to the reader the principle of this beauti- 



FIG. 5. Diagrams to illustrate analysis of light by the spectro- 

 scope, a. Spectrum of pure sunlight. 6. Spectrum of sun- 

 light passed through chlorophyll. 



ful instrument, one of the most delicate and exact, but withal one 

 of the simplest in theory, of all that have yet been evolved 

 in the progress of science. It must suffice to say that the spectro- 

 scope takes any mixture of colored lights, no matter in what 

 complication, and, through the mediation of a prism, spreads 

 them out in a band (called a spectrum), each color by itself. So, 

 when a ray of white sunlight is sent into this instrument, it is 

 made to fringe out into its red, orange, yellow, green, blue, in- 

 digo and violet constituents, all beautifully clear and distinct, as 

 shown diagrammatically in our accompanying figure 5, a. Now 



