Chemical Science. 401 



duration of the light differs very much; the diamond and fluor 

 shine for above an hour, no other fossil for more than a minute. 

 Vividness and duration are in no relation to each other. With the 

 exception of the diamond, the light of fossils is always white, 

 whether they be illuminated by coloured rays or not. Sun-light 

 is more effectual in producing the phenomena than day-light, 

 but too long an exposure is disadvantageous. White bodies act 

 more powerfully than coloured, and light coloured more than 

 dark coloured. Bodies that are shining continue to shine when 

 immersed in water. Difference of temperature has but little 

 effect ; ice is phosphorescent, at the same time it is observed, 

 that heat augments the intensity and diminishes the duration 

 of the phosphorescence ; cold has a contrary effect. Pure water 

 and transparent fluids do not shine. The light appears to pe- 

 netrate the substances considerably ; for when shining, if a 

 grove be cut a line deep in the substance, it will be as luminous 

 at the bottom of it as at the surface ; finally, polishing injures, 

 and in some cases destroys, the phosphorescent power. 



M. Heinrich then speaks of artificial phosphori, and de- 

 scribes the process for preparing the Bolognian compound, and 

 those of Canton, Baldwin, ^c. Among animal and vegetable 

 substances, many not linninous at first, became so by being- 

 cooled or heated; some of these are the flesh of birds ; dried 

 tendons, burnt bones and horns, yolk of eggs, toasted cheese, 

 roasted coftee, chestnuts, pease, S,c. 



M. Heinrich considers these phenomena of phosphorescence 

 to be occasioned by the mere restitution or emission of the light 

 absorbed by the phosphori during exposure to external sources. 

 Among those which are most difficult to explain are the pre- 

 servation of the light, by enveloping the luminous body per- 

 fectly ; and its increased emission by the application of heat. 

 If a diamond, the fluor spar of Siberia, or chlorophane, be ex- 

 posed to light for some minutes, and be then covered with 

 black wax, ink, or any substance, which will perfectly exclude 

 air and light, on removing the envelope, after some days, the 

 body will still be found emitting light. This fact was known to 

 Kircher and Beccaria. The second fact is the following : 

 When fluor spar which has been exposed to light has ceased to 

 become luminous, it may be made to emit light by merely 

 warming it with the breath or the hand. This effect may be 

 obtained many times successively after only one irradiation, 

 especially if, at each time, the warmth be a little increased ; at 

 last, warming ceases to produce the effect, but the simple ex- 

 posure of the spar to the sun enables it anew to present the 

 same appearances as before. — Bib. Univ. xv. p. 247. 



22. To the Editor of the Journal of Science. 

 Sir, 



In page xiii of the Introduofion to the Dictionary of Che- 



