Fifteenthly, Having well excited the Stone, I nimbly plung'd it under Water[a]40], that I had provided for that purpoſe, and perceiv'd it to Shine whilſt it was beneath the Surface of that Liquor, and this I did divers times. But when I indeavour'd to produce a Light by rubbing it upon the lately mentioned Cover of the Box, the Stone and it being both held beneath the Surface of the Water, I did not well ſatisfie my ſelf in the Event of the Trial; But this I found, if I took the Stone out, and Rubb'd it upon a piece of Cloath, it would not as elſe it was wont to do, preſently acquire a Luminouſneſs, but needed to be rubb'd manifeſtly much longer before the deſired Effect was found.
Sixteenthly, I alſo try'd ſeveral times, that by covering it with my
warm Spittle (having no warm Water at hand) it did not loſe his Light.[a]41]
Seventeenthly, Finding that by Rubbing the Stone with the Flat ſide downwards, I did by reaſon of the Opacity of the Ring; and the ſudden Decay of Light upon the ceaſing of the Attrition, probably loſe the ſight of the Stones greateſt Vividneſs; and ſuppoſing that the Commotion made in one part of the ſtone will be eaſily propagated all over, I ſometimes held the piece of Cloath upon which I rubb'd it, ſo, that one ſide of the Stone was expoſed to my Eye, whilſt I was rubbing the other, whereby it appear'd more Vivid than formerly, and to make Luminous Tracts by its Motions too and fro. And ſometimes holding the Stone upwards, I rubb'd its Broad ſide with a fine ſmooth piece of Tranſparent Horn, by which means the Light through that Diaphanous Subſtance, did whilſt I was actually rubbing the Stone, appear ſo Brisk that ſometimes and in ſome places it ſeem'd to have little Sparks of fire.
Eighteenthly, I took alſo a piece of flat Blew Glaſs, and having rubb'd the Diamond well upon a Cloath, and nimbly clapt the Glaſs upon it, to try whether in caſe the Light could peirce it, it would by
appearing Green, or of ſome other Colour than Blew, aſſiſt me to gueſs whether it ſelf were ſincere or no. But finding the Glaſs impervious to ſo faint a Light, I then thought it fit to try whether that hard Bodies would not by Attrition increaſe the Diamonds Light ſo as to become penetrable thereby, and accordingly when I rubb'd the Glaſs briskly upon the Stone, I found the Light to be Conſpicuous enough, and ſomewhat Dy'd in its paſſage, but found it not eaſie to give a Name to the Colour it exhibited.
Laſtly, To comply with the Suſpition I had upon the whole Matter, that the chief manifeſt Change wrought in the Stone, was by Compreſſion of its parts, rather than Incaleſcence, I took a piece of white Tile well Glaz'd, and if I preſs'd the Stone hard againſt it, it ſeem'd though I did not rub it to and fro, to ſhine at the Sides: And however it did both very manifeſtly and vigorouſly Shine, if whilſt I ſo preſs'd it, I mov'd it any way upon the Surface of the Tile, though I did not make it draw a Line of above a quarter of an Inch long, or thereabouts. And though I made it not move to and fro, but only from one end of the ſhort Line to the other, without any return or Lateral motion. Nay, after it had been
often rubb'd, and ſuffer'd to loſe its Light again, not only it ſeem'd more eaſie to be excited than at the beginning of the Night; but if I did preſs hard upon it with my Finger, at the very inſtant that I drew it briskly off, it would diſcloſe a very Vivid but exceeding ſhort Liv'd Splendour, not to call it a little Coruſcation.[a]42] So that a Carteſian would ſcarce ſcruple to think he had found in this Stone no ſlight Confirmation of his Ingenious Maſters Hypotheſis, touching the Generation of Light in Sublunary Bodies, not ſenſibly Hot.
