314 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
is in general this:— if a beam of light falls upon the thermal junction 
(via aperture a in side of box), an electric current is generated in the 
circuit; and since a wire carrying a current is surrounded by a magnetic 
field, this loop, being converted into a temporary magnet and free 
to rotate will adjust itself like a magnetic needle to the influence of 
Fig. E. Diagram of the radiomicrometer. a, aperture in the side of box; f, 
quartz filament; h, horse-shoe magnet; /, loop; m, mirror; p, platinum disk; s, 
couple. 
the stationary magnet. The amount of rotation is proportional to 
the radiant energy of the light which strikes the thermal junction, 
and can be measured on a scale reflected into a telescope by a tiny 
mirror, m, included in the suspended system. By this instrument 
the intensity of the colored lights was registered in the same units. 
After reducing a color to the common thermal equivalent, it was 
examined with a spectroscope and its spectral range was recorded 
upon the diaphragm used. Whenever a Nernst filament was replaced 
and the lights were again balanced on the radiomicrometer, these 
spectral ranges had to be modified slightly. Through the first part 
of the investigations four spectral regions were employed whose 
ranges in wave-length were:— 
Blue-violet 430-490 pu 
Green 495-545 “ 
Yellow 565-620 “ 
Red 625-665 “ 
ee 
ote ——— 7 a ee - oe 
