310 



bulletin: museum of comparative zoology. 



III. Experimental Investigations. 



A. Preliminary Matters. 

 1. Apparatus. The apparatus, Fig. A, for furnishing the colored 



Fig. A. Plan of colored-light generator, d, diaphragm box; I, Nernst light; 

 m, wooden diaphragm; n, diaphragm at lens; o, biconvex lens; p, prism; r, wooden 

 diaphragm; s, iron diaphragm; w, window. 



light consisted of a long rectangular box containing near its middle 

 a 5 inch biconvex lens, o, with focal length of 28 inches; a Nernst 

 light,/, situated in the rear at one focal point; and a prism-bottle, p, 

 containing carbon bisulphide, located about six inches nearer the lens 

 than the focal point at the front end of the box. In dimensions the 



box was six feet long, a foot wide 

 and about a foot deep. In order to 



y_^E 



vi 



^404:^ 



adjust the apparatus to the new 

 direction taken by the light after its 

 passage through the prism, the front 

 end was given an angle of devia- 

 tion from the main axis of about 45 

 degrees. At the point d, where the 

 spectral band came to a focus, a 

 small wooden case, Fig. B, grooved 

 in floor and roof for receiving card- 

 board diaphragms, was situated. 

 The grooves were so cut that they 

 intersected the spectrum at the 

 foci of the red, yellow, green, and 

 blue-violet, respectively {cf. Fig. A). 

 Thus when a diaphragm was in- 

 serted in its appropriate groove, a 

 vertical slot in it coincided with the spectral region desired to be used, 

 allowing passage to it while the rest of the spectrum was obstructed. 



Fig. B. Diaphragm box showing the 

 positions at which the diapliragms for 

 blue-violet (BV.), green (G.), yellow- 

 green (YG.), yellow (Y.), and red (R.) 

 were slipped in. 



