DAY: PIGMENT-MIGRATION IN EYE OF CRAYFISH. oll 
By regulating the width of the slot in each diaphragm the radiant 
energy in the various regions of the spectrum could be reduced (e. g. 
in red) or enhanced (e. g. in blue-violet) until an equality, as deter- 
mined by the radiomicrometer, was established between them. Be- 
sides the coat of dead black paint on the interior of the box, three 
diaphragms, two permanent ones of wood at m and r, Fig. A, and a 
removable one of sheet-iron at s, reduced internal reflections from the 
walls to a minimum. A small window, w, on one side and near the 
rear, together with an aperture cut in the lid and surmounted by a 
metal chimney, served as ventilators to reduce the heat from the lamp. 
Metal flanges in the chimney and at the side aperture were so over- 
lapped as to prevent any appreciable leakage of light. By means of a 
metal peg projecting upward from the table and inserted in a hole in 
the floor of the box at a point directly beneath the center of the prism, 
the apparatus was so pivoted that the beam of monochromatic light 
could be directed at will. 
Illumination was furnished by three 220-volt Nernst filaments of 
the pattern used in the Schwann lamp and so arranged that they 
might be used either in combination of three, for blue-violet and green, 
two, for yellow, or singly, for red light. The feebleness in radiant 
energy of the blue end of the spectrum necessitated not only a wide 
slot in the blue diaphragm but, in addition, this reénforcement by 
triple combination of glowers to obtain sufficient energy to equal 
that furnished by the single glower and a narrow diaphragm-slot 
in the red. A front perspective view of the lamp devised for facili- 
tating these combinations is shown in Fig. C. At one end of a wooden 
base, a, was erected an arch of brass, b, about six inches high. The 
three L-shaped posts, p, p’, p’’, and the arms, 7, 7’, r”’, above were 
also of brass. The middle arm, r, and post, p, were screwed firmly 
to the underside of the brass arch and to the wooden base, respectively. 
On the right side of this central combination, rfp, the arm r’ was 
fastened to the arch with a thumb-screw and nut so placed that 
the pivoting point m plumbed exactly with the screw n in the post 
p below. The wooden column h, sheathed with blackened asbestos, 
connecting the backward extensions of r’ and p’, so firmly united 
these two parts that they could be rotated coérdinately about mn 
as an axis. Whereas the upper platinum connection of the glower f’ 
was wedged into a hole in the arm?’ with a copper plug, e, the lower 
connection, in order to allow for the expansion of the filament when 
heated, was suspended freely in a mercury-filled cup, c. This brass 
cup was bound with copper wire to the post p’.. The whole system 
