Page:Popular Science Monthly Volume 77.djvu/120



HERE are probably but few if any of the readers of this magazine who have not seen and admired at least one of the many manifestations of "physiologic light" of which the most common to us is the firefly. Indeed, from the earliest times the phenomenon of the emission of light by animals and plants has attracted man's attention, and a large amount of scientific work has been done upon the subject. An attempt to compile a complete bibliography of the subject has resulted in the remarkable discovery that there are over seven hundred references to the literature bearing on the emission of light by organized bodies, and "the end is not yet." The work has embraced the physical, chemical, physiologic, histologic and entomologic sides, and much valuable information and many interesting facts have been secured. Among the names of the early writers who refer to some phase of this phenomenon are Aristotle, Pliny the Younger and Josephus; the more recent names include those of Robert Boyle, Sir Humphry Davy, Faraday, Pasteur, Kölliker, Dubois and the late S. P. Langley, and indeed a host of others whose names are more or less widely known. Several extensive treatises on the subject have appeared, some of which are really quite good, though regrettably they are for the most part out of date at this time. For the benefit of those who may care to read further, the names of a few of these are given below.

The phenomenon of physiologic light has been variously termed "phosphorescence," "luminosity," "photogenic function," etc., by different authors. As these are, for the most part, interchangeable in meaning, they will be used in this paper to refer to the same thing. The term "phosphorescence" is unfortunate, since it implies that the light is due to the presence of the element phosphorus—which it is not—and has become still more objectionable recently owing to its application by physicists and chemists to another totally different phenomenon of light emission.

It was my good fortune during the summer of 1909 to be associated with Professor J. H. Kastle, of the "University of Virginia (then chief