22 



A PHYSICAL STUDY OF THE) FIREFLY. 



In Fig. 1 1 no special significance is to be attached to the tilted appearance 

 of the energy curve of the Photiniis consanguineiis. A slight increase in the 

 ordinates of the spectral energy curve of the glow-lamp at 0.60^ to 0.65/1 

 would obliterate this effect. Then, too, the negatives are too small, and any 

 slight shift from the point of reference in making the photometric measure- 

 ments would change the symmetry of the curve. The first published curve* 

 of Photiniis pyralis was more asymmetrical than the present one, owing to 

 the fact that the spectral energy curve of the glow-lamp, as then used, was 

 steeper in the red than the one used in the present curves. The energy curve 

 of the firefly then published does not superpose nicely upon the present one, 

 being too flat at the top. From the present work it appears that this is due 

 to the use of too greatly overexposed and underexposed photographs in 



Table i. 



making up the composite curve. This made no difference in locating the 

 maximum, which is practically the same as in the present determination, but 

 the energy curve is distorted and flattened at the top. The irregularities 

 in the old curve are similar to those obtained in the present work. 



The "density" curve of Photiniis consanguineus (the lower curve. Fig. 8) 

 is irregular at 0.56/4 and 0.58/i, being the highest at the latter point. Another 

 curve showed this same irregularity, but its highest point was at 0.56/x. It 

 is therefore doubtful whether there are two emission maxima in the consan- 

 guineus, although indicated by dotted lines in Fig. 11. In Fig. 8 the density 

 curves of the carbon lamp found with the large spectrograph were used, while 

 the photographic curves of the insects were obtained with the small spectro- 

 graph. This might make some difference in eliminating the small irregu- 

 larities of the plate, but it can not have a marked effect upon the position 

 of the maximum. 



*Ives and Coblentz, Bull. Btir. Standards, 6, p. 321, 1909. 



