Some Notes on Ancient Ideas concerning the Diamond. 313 
operation, brightly phosphorescent, as much so as an isolated fragment of 
sulphide of zinc. Not one of the Cape diamonds was phosphorescent. 
The non-phosphorescence of the Cape diamond is, however, not absolute, for 
after one has remained in the dark for at least twenty minutes in order to 
rest the eyes ... a very slight phosphorescence on nearly half of 
them is detected. This phosphorescence is on the border of the perceptible 
minimum of light."* Le Bon attributes phosphorescence to the presence 
of infinitesimal proportions of certain foreign bodies. He claims that 
Bahia diamonds are worth 40 per cent, more than Cape diamonds, apparently 
meaning those of one colour and size : " Cape diamonds, often as colourless 
as those of Brazil, and sometimes larger, are always very inferior to the 
Brazilian, not only by their hardness but also by their brightness." If this 
statement were true — and it wants a deal of proving — we should have to 
admit that the superior qualities of the Brazilian stones arise from the 
presence of impurities. " Sometimes larger " is good. Crookes, in his 
Kimberley lecture, remarked that " some diamonds are fluorescent, appearing 
milky in sunlight. In a vacuum, exposed to a high-tension current of 
electricity, diamonds phosphoresce of different colours, most South African 
diamonds shining with a bluish light. Diamonds from other localities 
emit bright blue, apricot, pale blue, red, yellowish-green, orange, and pale 
green light. The most phosphorescent diamonds are those which are 
fluorescent in the sun. One beautiful green diamond in my collection, 
when phosphorescing in a good vacuum, gives almost as much light as a 
candle. . . . Diamonds which phosphoresce red generally show the yellow 
sodium line superposing on a continuous spectrum. In one Brazilian 
diamond phosphorescing a reddish-yellow colour, I detected the citron line 
characteristic of yttrium." 
In the remarkable mixture of truth and error contained in the old 
writings discussed by Laufer it is not altogether improbable that the language 
was framed, in the first instance, to hide trade secrets, and with deliberate 
intent to deceive. The persistence of the stories was only an aspect of the 
dominion of classical literature over the thought of the middle ages, and, 
moreover, the guild interests of lapidaries and alchemists were concerned in 
keeping the half truths and errors alive. The alchemists knew a good deal 
more, no doubt, than they told to outsiders. Soddy, indeed, has argued that 
they knew something about radium. 
* ' The Evolution of Forces/ 1908, p. 233. 
28 
