122 



RELATIONS OF PLANTS TO LIGHT 



the capacity of chlorophyl for absorbing rays of one wave-length 

 and emitting others of greater length, or of converting rays from 

 the upper part of the spectrum to the lower red. 



189. Absorption Spectrum of Chlorophyl. Adjust an Abbe, or 

 any convenient spectroscopic eyepiece to a microscope fitted 

 with a low power objective. The instrument should stand on 

 a table in a strong diffuse light and the mirror of the micro- 



Fig. 59. Abbe micro-spectroscope, a, b, screws for regulating the slit through 

 which light passes, c , screw for clamping apparatus to tube of microscope, d', spring 

 which, loosened, allows the ocular portion to swing around on the pivot, d. E, phial 

 containing solution to be tested. S, mirror for reflecting light upon solution. S', 

 mirror for illuminating scale, p, screw for manipulating Amici prism, and the ex- 

 tended drum into which the screws a, and 6, project contains the comparison prism 

 which receives light from the objective of the microscope, and throws a solar spec- 

 trum alongside that which has come from the light passing through the solution aXE. 



scope should be arranged to give a plain solar spectrum. Light 

 from the sun should be thrown on the lateral mirror of the 

 spectroscope by means of a heliostat, or a strong artificial 

 light from a welsbach or argand burner should be provided. 

 The spectrum of the second should be of the same intensity 



