DAY: PIGMENT-MIGRATION IN EYE OF CRAYFISH. 313 
The wiring of the lamp is represented diagrammatically in Fig. D. 
One branch, r, of the circuit ran to a leg of the brass arch of the lamp 
thereby supplying the upper ends of the glowers, while the other 
branch, s, went via the switches a, b, c and the ballasts d, e, f, to the 
back extensions of the three brass posts which connected with the 
Fig. D. Diagram of wiringoflamp. a, b, c, switches; d, e, f, ballasts; r, wire to 
brass arch; s, wire to the ballasts. 
lower ends of the glowers. Switch a controlled the whole circuit. 
The accessory switches b and c were introduced so that either or both 
of the lateral glowers might be extinguished without interrupting 
the circuit for the remaining ones when a different region of the 
spectrum was to be used. 
At this juncture it may be appropriate to remark briefly upon the 
method by which equal intensity of the colors was obtained. 
The radiomicrometer, reduced to simplest terms, is a slender loop 
of wire containing one or more thermal junctions, suspended by a 
delicate quartz filament to hang within a magnetic field. In Fig. E 
the loop, l, was of fine copper wire; the thermal junction was a small, 
blackened platinum disk, p, soldered into the loop with a fusion of 
bismuth and antimony, s; the suspension, f, was an extremely fine 
quartz filament; and the magnetic field was furnished by a horse- 
shoe magnet, h. The principle by which the radiomicrometer operates 
