102 Langley and Very — Cheapest Form of Light. 



SecchV at first thought that the spectrum of the glow-worm 

 was monochromatic, but with an improved spectroscope, recog- 

 nized that other colors were present, though feebly and decided 

 that the spectrum was sensibly continuous. 



Quatrefages, 2 in connection with the paper of Secchi, remarks 

 that the previous observations of Spallanzani and Macaire, re- 

 peated with much care by Matteucci and Becquerel, show 

 beyond 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 reappears in contact 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 accompanied by the generation of carbon dioxide. Never- 

 theless he points out that there is a distinct kind of phosphores- 

 cence in the marine ^Noctilucidae, due to the contraction of 

 muscular fiber, the shining tissue being seen through the 

 translucent body wall. This species of phosphorescence is 

 increased by irritants, but is independent of the presence of 

 oxygen and is not extinguished or in any way modified by 

 hydrogen or by carbon dioxide. 



Robin and Xaboidbene 3 find the luminous organs of P. noc- 

 tilucus composed of irregularly polyhedral cells, O04 mm to 

 Q.Qgmm thic]^ between which pass very numerous fine tracheae 

 and nerves. The inner face of the organ is composed of 

 adipose tissue, and the outer of a transparent modification of 

 the ordinary chitinous covering of the insect. The authors 

 conclude that the light is due to chemical decomposition of a 

 nitrogenous body with formation of crystalline urates. 



Jousset de Bellesme* finds that although the phosphorescent 

 cells, when separated from the body of the insect, continue to 

 glow for several hours, yet if crushed they instantly lose their 

 illuminating power, which indicates that for the production of 

 the light, the living cells must retain their integrity, and that 

 they are not mere reservoirs of a phosphorescent substance, 

 but continuous generators of it. He surmises that the light- 

 giving substance may be phosphureted hydrogen. 



Meldola b is quoted by Spiller 6 as having examined the glow- 

 worm spectrum and determined its approximate limits. 



Convoy 1 finds the glow-worm's light green, and in a small 

 direct vision spectroscope showing a continuous spectrum from 

 C to b, appearing like a broad band of green light extending 

 from O^'BlS to 0"*587 with a faint continuous spectrum into 

 the red to 0^656. 



1 C. R., lxxv, p. 321, 1872. * C. R., lxxv, p. 322, 1872. 



3 C. R., lxxvii, p. 511, 1873. 4 0. R., xc, p. 318, 1880. 



5 "Proc. Entomological Soc," p. iii, 1880. 6 "Nature," vol. xxvi, p. 343. 

 7 "Nature," vol. xxvi, p. 319, 1882. 



