Optics — Hydrodynamics. 367 



The female of the Lampyris Noctiluca excels all the rest in the beauty 

 of its light. It is of a light bluish or greenish colour, and seems to en- 

 velope the whole of the insect. The malejly has a soft and delicate bluish 

 light. The fire-fly produces two degrees of light, the one fainter than 

 that of the glow-worm, but without intermission. The second is a vivid 

 white light, intermitting instantaneously like vivid sparks of fire suddenly 

 extinguished. Its power of illumination exceeds that of the glow-worm, 

 and all other animal light, as it may be seen in the brightest moonlight. 

 The intermitting light gives the appearance of a membranous veil being 

 removed from the surface of the organ and suddenly drawn over it The 

 larva or even the ova of these insects give out light. 



The glow-worm requires a mean temperature of 50° 7 for its appearance, 

 and the others about 55° 7. 



The power of emitting light resides in a peculiar adhesive matter like 

 animal gluten. Carradori calls it a white pasty matter, and Ma^aire a semi- 

 lucid albuminous matter. It is said to be granular and organized, and 

 according to Maijaire it is penetrated by nerves. When the matter has 

 lost its vital properties, Dr Todd has found it incapable of affording light 

 by any contrivance. 



From these, and many other facts stated by Dr Todd, he concludes that 

 the phenomenon is, in all its bearings, a vital action ; and that external 

 causes only influence it, as they affect the vitality of the animal, and the 

 sensibility of the organ. This result, he conceives, places before us a new 

 power of animal life, resembling nearly the phenomena of animal heat, 

 viz. the power of separating light from its combinations with matter. 



Dr Todd is disposed to agree with Reaumur, in supposing that it is by 

 means of this light that the sexes distinguish each other in the season of 

 sexual intercourse. 



13. Remarkable Phosphorescent Stone. — At a very recent meeting of the 

 Philomathic Society, M. Becquerel exhibited a singular species of fluor 

 spar, sent by M. Leman, and found in the granite rocks of Siberia. It shines 

 in the dark with a very remarkable phosphoric light, which increases as its 

 temperature is raised. Its light augments when it is plunged in water. In 

 boiling water it is so luminous that the letters of a printed book can be 

 seen near the transparent vase which contains it. In boiling oil the light 

 is still greater ; and in boiling mercury it emits such a light that we may 

 read by it at a distance of five inches. M. Eyries mentioned at the same 

 meeting the fact stated by Sir John Mandeville, that at the entrance of a 

 town in Great Tartary were two columns surmounted by stones which shine 

 brightly in the dark.— Le Globe, No. 98. August 8, 1826. 



HYDRODYNAMICS. 



14. Prize oj '1828, for the most important experiments on the Uesisianceof 

 Fluids. — The Academy of Sciences have just announced the following sub- 

 ject for the mathematical prize of 1828. The prize will be a gold medal, 

 of the value of three thousand francs, and will be adjudged on the 1st 

 Monday of June 1828. The memoirs must be sent to the secretaries of 

 the Institute before the 1st of January 1828. 



