VOL. XXVI. 1 PHILOSOPHICAL TKANSACTIONS. 409 



kinds of soft animal substances, and found none answer so well as wool. And 

 no new phaenomena offered themselves; for upon drawing the piece of amber 

 swiftly through the woollen cloth, and squeezing it pretty hard with my hand, 

 a prodigious number of little cracklings were heard, every one of which pro- 

 duced a little flash of light; but when the amber was drawn gently and slightly 

 through the cloth, it produced a light, but no crackling ; but by holding a 

 finger at a little distance from the amber, a crackling is produced, with a great 

 flash of light succeeding it; and, what is very surprising, on its eruption it 

 strikes the finger very sensibly, wheresoever applied, with a push or puff^ like 

 wind. The crackling is full as loud as that of charcoal on fire ; nay, five of 

 six cracklings, or more, according to the quickness of placing the finger, have 

 been produced from one single friction, light always succeeding each of them. 

 Now I doubt not, but on using a longer and larger piece of amber, both the 

 cracklings and light would be much greater, because I never yet found any 

 crackling from the head of my cane, though it is a pretty large one ; and it 

 seems, in some degree, to represent thunder and lightning \ but, what is more 

 surprising, though on friction with wool in the day time, the cracklings seem 

 to be full as many, and as large, yet very little light appears, even in the darkest 

 room; and the best time of making these experiments, is when the sun is 18 

 degrees below the horizon ; and then, though the moon shine ever so bright, 

 the light is the same as in the darkest room, which makes me chuse to call it 

 a noctiluca. 



As the artificial phosphorus led me to consider that of amber, so amber 

 directed me to that of a diamond, from its being electral as well as the other, 

 which is also a natural phosphorus, or rather a noctiluca, exceeding all others, 

 and may, without any exception, be called a mineral phosphorus, it being, I 

 suppose, the most pure of all oleosums. A diamond, by an easy slight friction, 

 in the dark, with any soft animal substance, as the finger, woollen, silk, &c. 

 appears in its whole body to be luminous; nay, if you keep rubbing for a little 

 while, and then expose it to the eye, it will remain so for some little time: but 

 if the sun be 18 degrees below the horizon, and any one holds up a piece of 

 baize or flannel stretched tight between both hands, at some distance from the 

 eye, and another rubs the baize or flannel with the diamond swiftly and pretty 

 hard on the other side of it, the light to the eye of him that holds it, seems 

 much more pleasant and perfect than any other way I have yet tried. But, 

 what seems most surprising, a diamond being exposed to the open air in view 

 of the sky, gives almost the same light of itself without rubbing, as if rubbed 

 in a dark room; and if in the open air you put your hand, or any thing else, 

 a little over it, to hinder its communication with the sky, it gives no light. 



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