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. n. aperture in the side of box; /, 

 quartz filament; h, horse-shoe magnet; I, 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 mm 



Green 495-545 " 



Yellow 565-620 " 



Red 625-665 " 



