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<p>A careful investigation is made of the light emitted by the firefly. The spectrum of "Photunis Pyralis" has been photographed on plates sensitive to the whole visible spectrum. The spectrophotometric curve of the firefly is compared with that of a carbon glow-lamp. The distribution of radiant energy in the carbon glow-lamp has been determined, and hence the distribution of the radiant energy of the firefly has been found. The light is found to consist of an unsymmetrical structureless band in the yellow-green of the spectrum, with a maximum at 0.57mu, and a range extending from 0.51mu to 0.67mu. The luminous efficiency is computed to be 96.5 per cent. This compares with 0.4 per cent. for the carbon glow-lamp, and 4 per cent. for the most efficient artificial illuminant. This val
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<br>Subjects: photometry; spectra</div>
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