lose 
EXPLANATION OF PLATE. 
. Photograph of the spectrum of a carbon glow-lamp, for different exposures. 
. Spectra of: (1) helium vacuum tube; (2) ‘4-watt” carbon glow-lamp; (3) firefly 
Photinus pyralis, taken in 1909; (4) and (7) firefly Photuris pennsylvanica; 
(5) and (6) firefly Photinus pyralis, taken in 1911. 
. Spectra of: (1) helium vacuum tube; (2) from 0.3889u to 0.49224; fluorescence 
spectrum of a substance found in the blood of fireflies, e. g., in Photinus pyralis; 
(2) from o.5015u to 0.66784, spectrum of light emitted by Photinus pyralis; 
(3) same as (2) from 0.50154 to 0.6678, using a shorter exposure. 
. Photographs obtained with short-focus spectrograph: 
Photuris pennsylvanica, 3: 8, 9, 12, 13. II: 9, 10. TII: 310, 11, 12. IV: 6, 7. 
V: 7, 8,9. VI: 2, 5, 6. VIT: 2, 3, 4. 
Photinus pyralis, I: 2 to 7. II: 2 to 8 and 14. III: 2 tog and 13, 14. IV: 
2to5and8to1r4. V: 2to6and roto 14. VI: 7 to 14. VIT: roto 14. 
Photinus consanguineus, 1: 11. Tis 1t,-12., VIT: 5, 6, 7, 8,9. 
Photinus scintillans, 1: 14. 
Glow-worm, IT: 13. 
Helium comparison spectrum, VI: 3, wave-lengths from left to right 0.471, 0.492, 
a 0.587, and 0.667p. I: 10, yellow helium line, \=0.5876y. (0.501p is 
faint. 
In D, column I is made up of two plates. The succeeding columns, II to VII inclusive, 
are reproductions of single plates containing a dozen or more exposures to firefly 
light, with the helium comparison spectrum at the beginning and the end of 
each series. The original negatives are of course much stronger in the red than 
here reproduced, 
