Thirteenthly, Having purposely rubb'd it upon several Bodies differing as
to Colour, and as to Texture, there seem'd to be some little Disparity in
the excitation (if I may so call it) of Light. Upon White and Red Cloths it
seem'd to succeed best, especially in comparison of Black ones.
Fourteenthly, But to try what it would do rubb'd upon Bodies more hard, and
less apt to yield Heat upon a light Affriction, than Cloath, I first rubb'd
it upon a white wooden Box, by which it was excited, and afterwards upon a
piece of purely Glazed Earth, which seem'd during the Attrition to make it
Shine better than any of the other Bodies had done, without excepting the
White ones, which I add, lest the Effect should be wholly ascrib'd to the
disposition White Bodies are wont to have to Reflect much Light.
Fifteenthly, Having well excited the Stone, I nimbly plung'd it under
Water[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.
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