140 THE PHOSPHORESCENCE OF BODIES. [MEMOIR VIII. 



a very elaborate memoir by Osann (Poggendorff s Anna- 

 len, 1834, vol. xxxiii., p. 405), in which he discusses the 

 various theories of combustion, absorption, excitation, 

 etc., and gives many new facts. 



(Respecting the phosphorescence of diamonds, I have 

 recently had an opportunity of making a curious obser- 

 vation. A lady, a relative of mine, has a pair of ear- 

 rings in which are set two large and beautiful gems, 

 both of which phosphoresce after exposure to an electric- 

 al spark; she has also another pair in which both the 

 diamonds in like manner phosphoresce. Judging from 

 these four instances, one might regard this property as 

 very common. Curiously enough, the necklace belong- 

 ing to this set, containing thirty-eight stones of very fine 

 water, has only one that will phosphoresce. This neck- 

 lace would, therefore, lead us to reverse the conclusion 

 to which the ear-rings had led us, and to infer that phos- 

 phorescing diamonds are comparatively rare.) 



All solid substances, except the metals, possess the 

 phosphorescent quality. We may, however, by making 

 a judicious selection of the bodies which are to serve as 

 our means of experiment, disembarrass the inquiry of 

 many of its complications. If we employ the Bolognian 

 stone (barium sulphate) or Canton's phosphorus (cal- 

 cium sulphide), or, indeed, any other substance liable 

 to undergo chemical changes in the air, we introduce 

 unnecessary phenomena, and cannot distinctly prove 

 whether the shining is due to a direct combustion of 

 the parts or to other causes. 



Among selections that might be made, diamond and 

 fluor-spar possess qualities rendering them very eligible 

 for these purposes unchangeability in the air and 

 under water. Even between these there is a choice, for 

 fluor-spar possesses all the good qualities of diamond. 

 It might be said, considering the chemical relationships 



