THK CHEAPEST FORM OF LIGHT. i 



concludes, from tlie apparent continuity of the spectrum of the light 

 from phosphorescent animals, that their light approaches nearer to that 

 of ordinary incandescence — a deduction which the following result 

 renders unnecessary. 



C. A. Yoim;-^ states that the "common" fire-fly gives a continuous 

 spectrum, extending from a little above Fraunhofer's line Cin the scarlet, 

 to about F in the blue, gradually fading out at the extremities. He 

 observes that it is noticeable that ))recisely this portion of the spectrum 

 is composed of rays, which, while they more powerfully than any others 

 affect the organs of vision, produce hardly any thermal or actinic effect. 

 In other words, very little of the energy expended in the flash of the 

 fire-fl}'' is wasted. 



(This is a most important and interesting inference, l)ut it will be ob- 

 served that this is necessarily rather assumed as highly probable than 

 actually demonstrated, since the method did not permit the dealing 

 with the invisible rays except by inference.) 



It is quite different with our artificial methods of illumination. In 

 the case of an ordinary gas light, experiments show that at most, one 

 per cent of the -radiant energy consists of visible yhys, the rest being in- 

 visible heat ; that is to say, over ninety-nine pev cent of the gas is wasted 

 in producing ravs that do not help in making objects visible, f 



Seechi'l at first thought that the si)ectrum of the glow-worm was 

 monochromatic, but with an improved spectroscope, recognized that 

 other colors were present, though feebly, and decided that the spectrum 

 was sensibly continuous. 



Quatr(]fnges,% in connection with the paper of Secchi, remarks that the 

 previous observations of Spallanzani and Macaire, repeated with much 

 care by ^latteucci and Becquerel, show be3^ond doubt that the light of 

 glow-worms and elaters is due to slow combustion. Thus the light is 

 extinguished in a vacuum, and in irrespirable gases, it reapi^ears in con- 

 tact with the air, it is perceptibly increased by the presence of pure 

 oxygen, it persists after the death of the creature, and finally it is ac- 

 companied by the generation of carbon dioxide. Nevertheless, he points 

 out that there is a distinct kind of phosphorescence in the marine Noc- 

 tilucidffi, due to the contraction of muscular fiber, the shining tissue- 

 being seen through the translucent body wall. This species of phos- 

 phorescence is increased by irritants, but is independent of the presence 

 of oxj'gen and is not extinguished or in any way modified by hy<lrogen 

 or by carbon dioxide. 



*The Amerioan Natl^ralist., Salem, 1870, vol. iii, p. 615. 



fS. P. Langley has shown that the waste is in fact even greater than this ; see 

 "Science," vol. i, No. 17, p. 482, 1883. 

 tC. R., Ixxv, p. 321, 1872. 

 ?C. R., Ixxv, p. 322, 1872. 



