24 



A PHYSICAL STUDY OF THE FIREFLY. 



of consanguineus. It is possible that when subjected to a thorough analysis 

 the maximum emission of the scintilla ns will be found still farther toward the 

 red, say 0.58/u. From the photometric curve, Fig. 9, obtained by Langley 

 and Very,* the maximum emission (not applying the energy curve of the 

 comparison source) of the Cuban firefly, Pyrophorus noctilucus, occurs at 

 0.538^. Two determinations by Dubois, f using a grating, gave X 0.53JU as 

 the point of maximum emission. 



In connection with the much-discussed question of the physiological effect 

 on the eye, it is of interest to note the description, by Dubois, of the varia- 

 tion in the color of the light emitted by Pyrophorus. He says that when the 

 light diminishes in intensity the red and orange rays disappear and at last 



Plate 5,26,'ll * 



5,27,'H 



6, 19, 'II , 



6,20,'H & 



.52 4 6 8 .60 2/i 



Fig. 10. Spectral energy curves of fireflies and glow-lamp. 



only the green rays persist; and that when the animal begins to emit light 

 the green rays first appear, then the color extends farther and farther into 

 the red, when the light attains its maximum intensity. 



In concluding this section it may be added that for the first time we have 

 substantial evidence that the color of the light of various fireflies is different, 

 the maximum emission varying from 0.55^1 in the bluish light of the Photuris 

 pennsylvanica to 0.58/i in the orange-red light of the Pholinus consanguineus. 

 Evidently, in these extreme cases the eye made no serious mistake in assign- 



*Langley and Very, Amer. Jour. Sci. (3), 40, 1890. Smithsonian Mis. Collections 

 No. 1258, 1901. 



tDubois, Lecons de Physiologie generalc et comparee, Paris, 1898. 



