22 A PHYSICAL STUDY OF THE FIREFLY. 
In Fig. 11 no special significance is to be attached to the tilted appearance 
of the energy curve of the Photinus consanguineus. A slight increase in the 
ordinates of the spectral energy curve of the glow-lamp at 0.60p to 0.654 
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 Pholinus 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 thepresentcurves. ‘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 1. 
Photuris pennsylvanica. Glow-worm (larva of Photuris pennsylvanica). 
Ratio of quate of i 
densities: 0 nsities: 
Wave- cha aistee ton Pind Wave- : seein disceination 
length. | Firefly of carbon oF i fl von!) Jength. | Glow-worm | of carbon of 
Glow-lamp | glow-lamp. MECH Glow-lamp | glow-lamp. | glow-worm. 
(Fig. 9). (Fig. 9). 
0.520n 1.00 3.30 3.30 0.531h 1.50 3.88 5.82 
-528 1.50 3.70 5.55 -534 2.00 3.98 17.96 
-5305 2.00 3.82 7.64 -542 3.00 4.47 13.41 
©5325 2.50 3.98 9.95 .550 4.00 | 4.92 19.68 
5345 3.00 4.02 12.06 2555 3.70 | 5.20 19.24 
541 5.00 4.39 21.95 561 3.00 | 5.61 16.83 
-547 5.75 4.72 27.14 568 2.00 , 6.13 12.26 
-557 5.00 5.33 26.065 -578 1.50 6.92 0.38 
568 3.00 6.10 18.30 598 1.00 8.74 8.74 
+5715 2.50 6.36 15.90 612 -50 10.14 5.07 
576 2.00 6.74 13.48 
«581 1.50 7.15 10.73 
«583 1.33 7-32 9.74 
589 1.00 7.87 7.87 
596 .50 8.50 4.25 
600 50 8.90 4.45 ' 
610 25 9.90 2.47 | 
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 Photinus consanguineus (the lower curve, Fig. 8) 
is irregular at 0.564 and 0.58y, being the highest at thelatter point. Another 
curve showed this same irregularity, but its highest point was at 0.56u. 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. Bur. Standards, 6, a 321, 1909. 
