270 Messrs. Langley and Very on the 



elsewhere*. The insect turned so as to show the abdominal 

 light is depicted in fig. 2. 



Fig. 3. 



-240-1 



-220-j 



-200-1 



-180-i 



I6CH 



-140-1 



-120-f 



-100-1 



- 20-i 



PHOTOMETRIC CURVES. 

 FOR EQUAL TOTAL AMOUNTS OF LIGHT. 



A — Sun-light. 

 B— Fire-fly light. 



Abscissae— Wave Lengths. 

 Ordinates.— Luminous Intensities. 



B. Tire-fly Spectrum. 



The observer waited for some time in a wholly darkened 

 room, and to the eye, thus rendered sensitive, the visible 

 spectrum, before magnification, was about 2 millim. high and 



* See this Journal, March 1883, p. 173. 



