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; /, Nernst light; 
m, wooden diaphragm; n, diaphragm at lens; o, biconvex lens; p, prism; 7, wooden 
diaphragm; s, iron diaphragm; w, window. 
light consisted of a long rectangular box containing near its middle 
a 5 inch biconvex lens, 0, with focal length of 28 inches; a Nernst 
light, J, 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 
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 
Fig. B. Diaphragm box showing the mtersected the spectrum at the 
positions at which one diaphragms for foci of the red, yellow, green, and 
ae A ae - iat ae et blue-violet, respectively (cf. Fig. A). 
were slipped in. Thus when a diaphragm was in- 
serted in its appropriate groove, a 
vertical slot in it coincided with the spectral regicn desired to be used, 
allowing passage to it while the rest of the spectrum was obstructed. 
