SPfiCTRAIv ENERGY CURVES OE UGHT EMITTED BY VARIOUS SPECIES. 21 



two samples were obtained from the photographs taken with the small 

 spectrograph, Fig. 8. Knowing the distribution of energy in the spectrum 

 of the glow-lamp given in Fig. lo, it is possible to determine the spectral 

 energy distribution of the firefly by multiplying the energy values of the 



glow-lamp by the ratio of densities, — ^rr-; — , from Fig. 9, at each 



*^ glow-lamp light 



wave-length. The resultant curves are given in Figs. 10 and 1 1 and tabu- 

 lated in Tables i and 2. 



In Fig. 10 the spectral energy curve of Photuris peunsyhanica and Pho- 

 tiniis pyralis are plotted to the same scale in the blue-green. An integration 



Fig. 9. 



-Ratio of densities of photographic plates (firefly lights-glow-lamp light) 

 obtained from the preceding illustrations. 



of these two curves shows that for the same emissivity in the blue the energy 

 curve of the Photinus pyralis is 2.83 times that of the pennsylvanica. To 

 the eye it is apparent that the illuminating power of the Photinus is far 

 greater than that of the Photuris. Whether the Photuris pennsylvanica 

 curve is asymmetrical, as indicated in Fig. 10, or symmetrical is difficult to 

 decide because of the far greater sensitivity of the plate for the region of 

 o.59)Li, and the fewness of the negatives. The same irregularity occurs in 

 the Photinus pyralis, but is somewhat obliterated by the nearness of the 

 maximum of emission. 



