400 Mhceihiiieoiia Iiilelligetice. 



clear day ; to keep them out of the rays of the sun, lest tliey 

 should become heated ; and to observe them in the same dark 

 chamber to which he had previously retired. The observations 

 were made in two different seasons, the summer and the winter. 

 The following are the general results, but the account is very 

 much compressed from M. Heinrich's paper. 



Among natural bodies some are phosphorescent, some not 

 phosphorescent. Among the most phosphorescent are some dia- 

 monds, but not all, though no apparent difference in their ex- 

 ternal appearances could be perceived ; some remained lumi- 

 nous from five seconds to one hour. The different effects of 

 the coloured rays were remarkable ; a good diamond exposed in 

 the blue rays acquired a durable phosphorescence, but did not 

 become luminous at all in the red rays. All the fluor spars 

 were highly phosphorescent, and also all the carbonates of 

 lime. 



M. Heinrich observes that the phosphorescence of calcareous 

 combinations varies with the acid in combination. Thus the 

 fluates were very phosphorescent, some of them remaining lumi- 

 nous for one hour. The carbonates follow ; they are dis- 

 tinguished by the clear and white light they emit, which is such 

 in some specimens as to enable a person to read by it, but it 

 does not continue above thirty or forty-five seconds. The sul- 

 phates shine for a short time, but very faintly ; the phosphates 

 are still less favourable for the phenomena of phosphorescence by 

 irradiation. 



The calcareous combinations are succeeded by heavy spar or 

 sulphate, and carbonate of baryta. Pure siliceous, aluminous 

 and magnesian earths are not phosphorescent, though many of 

 their native combinations are feebly so. 



With regard to saline minerals, M. Heinrich considers their 

 phosplioresccnt powers to be determined by the acid and base 

 in combination. With the exception of amber and the diamond, 

 no inflammable fossil becomes phosphorescent by irradiation. 

 None of the metals are phosphorescent ; metallic salts are 

 moderately, and metallic oxides feebly, phosphorescent. 



Vegetable substances are but bad phosphori. The wood of hot 

 countries is better than that of our climate ; the white hazel-tree 

 shines brightly — an old sugar cane, dates, and the inner part of 

 the cocoa nut, become finely phosphorescent. Cotton is very 

 bad ; dried plants are in general very feebly luminous ; vegetable 

 substances bleached are infinitely superior to the same sub- 

 stance not bleached ; this is particularly observable in linen, 

 paper, iSc. Animal substances, containing carbonate of lime, 

 as egg-shells, shells, corals, ^'c, are more phosphorescent than 

 those containing phosphate of lime. 



After the facts, of which the above are the results, follow 

 various interesting observations: thus it is remarked that the 



