426 PHYSIOLOGICAL LIGHT. 



Aii organoleptic examination shows, like the physical analysis, that 

 the light of Pyrophorus is undoubtedly superior to that of any artificial 

 sources of light with -which we are acquainted. 



The visual intensity, measured by means of a typographic scale, has 

 been found, when compared with that of a candle, to be much greater 

 than is indicated by the luminous intensity, as determined by the spec- 

 trophotometer. The beautiful clarity of the Pyrophorus does not favor 

 retinal persistence, there are no accidental images, and complementary 

 color images are produced with difficulty. In spite of its greenish hue, 

 it has almost no influence on the color sense, for all tints are easily 

 recognized, except blue and violet, which do not exist in its spectrum, 

 and its rays are perceived at the extreme limits of the visual field. 



•The light of the Pyrophori contains no polarized rays, which proves 

 that the function attributed to the chalky, radio-crystalline layer of the 

 l>hotogenic organs of insects does not exist. On the contrary, it still 

 includes, in spite of the fluorescence of pyrophorine, a sufficient quan- 

 tity of chemical rays to effect the photographic reproduction of objects, 

 but no less thau five minutes' exposure is necessary to produce, with 

 the ventral organ (the most brilliant of the three), a good proof with 

 gelatin-bromide plates that give with solar light an image in a frac- 

 tion of a second (fig. 2). 



The quantity of heat generated by the photogenic organs is infini- 

 tesimal. I have, however, been able to show the presence of a few 

 heat rays by means of an extremely sensitive thermo-electric pile, so 

 arranged as to avoid all causes of error. It has also been possible to 

 show that this small quantity of heat is nearly double that given out 

 by the dark portion of the tegument at the same time. The existence 

 of these calorific rays has been completely confirmed by the use of the 

 bolometer, an instrument which informs us, as it appears, that the 

 quantity of heat given off during ten minutes, by the most brilliant 

 Pyrophorus, is a seven-millionth of a calory. 



The most sensitive instruments fail to show any electric phenomena 

 whatever accompanying the production of the light. 



The experiments, taken together, fully justify the conclusions which 

 we published in 1886, 1 namely, that in contrast with artificial light in 

 which 98 per cent of the energy is employed otherwise than in produc- 

 ing illuminating rays, physiological light employs effectively 98 per 

 cent of energy, with only 2 per cent of loss. Besides this immense 

 economic superiority there should be mentioned the exceptional quali 

 ties (organoleptic or otherwise) which cause the Pyrophori themselves 

 to prefer their own beautiful light to any other, it never causing 



'See Les Elatexides lumineux: Bulletin tie la Socie~td zoologique tie France, Paris, 

 1886. The exactitude of the physical results noted in that work has been fully cor- 

 roborated by the confirmatory researches of MM. Very and Langley published in 

 1890 (see Phil. Magaz., XXX, Series V, p. 200) ; but these scientists were in error "when 

 they said that I had not been able to show the existence of calorific rays. 



