THE AM ERIC A \ XATURALIST. [Vol. XXXVI I L 



has arisen independently in different organisms, it would not 

 seem strange that the light of such widely separated forms as a 

 marine mollusk and a terrestrial insect, though in both cases a 

 process of oxidation, might be produced in a different manner. 



The physical properties of the firefly's light have been studied 

 by Dubois, Langley and Very, Young, and Watase, with essen- 

 tially the same results. The spectrum given by the light of the 

 Lampyridae is perfectly continuous, without any trace of lines, 

 either bright or dark. It lies within that portion of the spectrum 

 which most powerfully affects the organs of vision, though 

 having small thermal or actinic effect. Dubois has demonstrated 

 by photography the presence of some actinic rays in the light of 

 Pyrophorus. A single insect was used, and five minutes was 

 required for printing from a plate which would have taken only 

 a fraction of a second with sunlight. Dubois attributed the 

 presence of actinic rays to a fluorescent substance which he 

 found in the blood. 



Most careful and elaborate experiments have failed to show 

 more than an infinitesimal amount of heat connected with the 

 light. One authority even goes so far as to say that not more 

 than one-thousandth of the energy expended in the flash of the 

 firefly is converted into heat waves. When one considers that 

 m our ordinary oil or gas lamps more than ninety-nine per cent 

 of the energy is lost as regards illumination, and that even in the 

 arc light only about ten per cent, of the waves are visible, the 

 mterest which this '« cheapest form of light " arouses from the 

 economic point of view is very apparent. It is also an alluring 

 problem to the student of physics to determine by what process 

 the medium wave lengths are produced independent of the longer 

 and shorter waves. If this "secret process" could be wrested 

 from nature, its economic value would prove almost inestimable. 



While the phenomena of biological light early attracted the 

 attention of observers of nature, as Aristotle, Democritus and the 

 naturalist Pliny, it is only within the last century that any serious 

 study has been given to the organs which produce it. The dis- 

 covery of their cellular nature may be credited to Peters. In 

 1841 he refuted the theory of Carrara ('36) that the light was 

 dependent upon an air-sac extending from the mouth to the light- 



