Phosphorescence of Precious Stones 63 



produces diamonds, the lustre of which illuminates the dark night. 

 According to Chao Ju-kua, 1 the King of Ceylon possessed a gem five 

 inches in diameter, which could not be consumed by fire, and at night 

 emitted a brilliancy like a torch. As incombustibility was credited to 

 the diamond, this jewel shining at night, in all probability, was a 

 diamond. 2 Another reason why the diamond should be included in 

 this class will be discussed in the following section. 



Phosphorescence of Precious Stones. — As this subject of stones 

 "luminous at night" has heretofore not been properly comprehended 

 by sinologues and others, it may not be amiss to add some explanatory 

 notes. 8 As a matter of fact, of course, stones cannot shine at night : 

 the lustre of any gem is an optical property, and depends upon the 

 effects of light, solar or artificial, which is reflected back to the human 

 eye. 4 The classical and Chinese reports of stones emitting rays of light 

 in darkness, accordingly, have nothing to do with optical phenomena, 

 or, in particular, with so-called "adamantine lustre." If these stories, 

 partially, should refer to a phenomenon of reality, there is but one that 

 can come into question, — that of phosphorescence. This is a property 

 of some gems, which, after rubbing, heating, exposure to light, or an 

 electrical discharge, radiate a light known as phosphorescence; since the 

 glow, although often of different colors, resembles that of phosphorus. 

 This property is particularly exhibited in the diamond, which, on being 

 rubbed with a cloth or across the fibres of a piece of wood, gives out a 

 light plainly visible in a dark room. It is, however, not a general 

 property of all diamonds, but only efficient in certain stones. 5 Though 



1 Chufan chi (ed. Rockhill), Ch. A, p. 10; translation of Hirth and Rockhill, 

 P- 73- 



* An indirect testimony for the diamond being counted among the night-shining 

 stones in the West may be deduced from the passage in the Physiologus, that the 

 diamond is not found in the daytime, but only at night, which may imply, that, in 

 order to be found at night, it must then emit light (compare F. Lauchert, Geschichte 

 des Physiologus, p. 28; E. Peters, Der griechische Physiologus, p. 96; F. Hommel, 

 Aethiopische Ubersetzung des Physiologus, p. 77; K. Ahrens, Buch der Naturgegen- 

 stande, p. 82). — D'Herbelot (Bibliotheque orientale, Vol. IV, p. 398) already 

 knew that it was a natural property of the diamond to shine in darkness. 



* The subject in general has been dealt with by G. F. Kunz (Curious Lore of 

 Precious Stones, pp. 161-175). 



4 The Chinese scholar Sung Lien (13 10-81) had a certain idea thereof. In a 

 Dissertation on Sun, Moon, and Stars (Ji ytie wu sing lun) he speaks of a "gem like 

 the full moon" {ytie man ju chu), whose substance, in principle, has no lustre; but 

 it borrows its lustre from the sun, that half of it turned away from the sun being 

 constantly dark, and the other half turned toward the sun being constantly bright 

 (P'ei win yiinfu, Ch. 7A, p. 109). 



6 Compare Farrington, Gems and Gem Minerals, pp. 34, 70. Among all 

 minerals, phosphorescence is best exhibited by fluorite, nearly all specimens of which, 



