42 A PHYSICAL STUDY OF THE FIREFLY. 
it seems just as probable that the explanation will be found in biochemical 
phenomena not requiring the production of radiations of low frequency in 
order to produce a given amount of light. Set as we are in our ways of 
thinking, we insist that the methods employed by the firefly to produce its 
light must be similar to our own. We might as legitimately suppose that 
the combustion of food in our bodies, with the resultant formation of COs 
and H:0O, or that the combustion in a growing leaf, must be accompanied by 
a rise in temperature and emission of radiant energy (other than “animal 
heat”) simply because we observe all these phenomena when we light a 
candle or heave coal into the fire. 
Tn recent papers* the writer has published numerous illustrations showing 
that in incandescent solids and in gases excited in vacuum tubes the produc- 
tion of light is accompanied by a very considerable amount of infra-red 
radiation; that in the arc light, especially the “flaming arc’”’ vapors, there 
is little infra-red radiation; and that in the high-frequency spark nearly all 
the radiation is in the ultra-violet. The light of the firefly is not unlike that 
of an ideal radiator at a temperature of 5,000°, differing from it only in the 
density of the radiation. If the specific emissivity of the sun were as low as 
that of the firefly, it is quite possible that no infra-red radiation could be 
detected. ‘The solar corona is another example of this type. Perhaps the 
question may become clearer when we can formulate some ideas on the 
emissivity from a selectively absorbing substance in the region of a band of 
anomalous dispersion. The ideal radiator is one having no reflectivity. 
Only in the region of anomalous dispersion, where the refractive index 
becomes practically nil, is this condition fulfilled, as far as the reflecting 
power is concerned. 
*Jahrb. der Radioaktivitét und Electronik, vu, p. 123, 1910; Illuminating Engineer, 
London, 3, p. 1, 1910. 
