A PHYSICAL STUDY OF THE FIREFLY. 
CONTENTS. 
Page. Page. 
I. Introduction............ 00... cece eee e ee eee 3 VII. Spectral Energy Curves of the Light 
II. Habits of the Various Species Investigated... 5 emitted by Various Species of Fireflies.. 18 
ILL, Composition of the Light of Fireflies........ 6 ; VIII. Luminous Efficiency and Candle-power 
IV. The Function of the Light emitted by Living Measurements. ....... 06.0. cc sees eae eees 26 
Organisms s cixisisc'son selector aa ensinee 9 IX. Radiationand Temperature Measurements. 29 
V. Histology of the Light Organs.............. 10 X. The Fluorescent Substance in Fireflies.... 37 
VI. Methods of Investigation of the Light XI. Infra-red Absorption Measurements....... 40 
GMb O Deca iss dome csscetessemisind aessunciancnannians 14 XII. Nature of the Light emitted.............. 43 
I, INTRODUCTION. 
During the latter part of the summer of 1908 the first attempt was made 
to measure the radiation from the local species of firefly. The season was 
late and but little was accomplished beyond the acquisition of some knowl- 
edge of the habits of these interesting insects. The following summer, in 
collaboration with Dr. H. E. Ives,* the spectral energy distribution of the 
light from the species Photinus pyralis was obtained by photographic pho- 
tometry. Last year an attempt was made to obtain photographically the 
spectral energy distribution of the species Photuris pennsylvanica, which 
comes earlier in the year. As mentioned elsewhere,} the work was begun 
too late in the season, and in the course of only a few days this species had 
disappeared for the year. However, in spite of the lack of sensitiveness of 
the photographic plates in the red, there was considerable evidence that 
thelight fromthe Photuris, which to the eye appears a greenish blue, is quite 
monochromatic, being deficient in the yellow and red rays which are promi- 
nent in the light of the Photinus. Whether the maximum emission is very 
different in these two genera remained undetermined until this year. ‘The 
work requires an intimate knowledge of the habits of the various species, 
the lack of which has been the cause of most of the delays in reaching some 
conclusion in regard to the various questions under discussion. 
One of the foremost problems which now occupies the attention of investi- 
gators is the improvement of our methods of illumination. It is recognized 
that our present methods of light production are of the most primitive type, 
and yet we seem helpless in the matter. Recognizing our helplessness, we 
should not hesitate to turn to other animals having photogenic systems 
which apparently are far more efficient than our own, and try to learn their 
methods of operation. It may be that in the ultimate analysis the efficiency 
*Bull. Bur. Standards, vol. 6, p. 321, 1909. 
fElectrical World, 56, p. 1012, Oct. 27, 1910. 
