512 



HENRY LAURENS AND HENRY D. HOOKER, JR. 



box is open and holes are bored in the top and bottom for ventilation. 

 The light-box and spectrometer, with the exception of the ocular end 

 of the telescope, are sm^rounded by heavy black curtains, reaching almost 

 to the ceiling of the room.. In order to obtain colored lights of the 

 desired number of wave-lengths, diaphragms of appropriate width 



E" 



5- 



Fig. 1. L, lamp in box; S, collimator slit; C, collimator; P, prism; D, wave- 

 length drum; T, telescope; S', slit in telescope just behind cross-hairs; 0, 

 ocular; Th, thermopile, DK, double-key; G, galvanometer. 



(twenty-three in number, one for each light), are placed at the focal 

 point, directly behind the cross hairs, in the telescope, thus converting 

 the spectrometer into a monochromatic illuminator. These diaphragms 

 consist of cylindrical tubes of blackened cardboard adjusted to fit 

 snugly inside the telescope tube, in the ocular end of each of which a 

 disk of blackened cardboard, with a slit of appropriate width and 8 



