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And now, Sir, seeing the want of Shining Wood hath kept me ever since I sent you the former Experiments from making any new ones on, that Subject, I shall, by way of amends, subjoyn some of the Observations, that I heretofore intimated to you, I had made of the Resemblances and Differences between a Live Coal and a piece of Shining Wood; in pursuing of which, you will easily discern, that to those particulars, which my Memory and the former Observations, I had noted down about light and luminous Bodies, had suggested to me, I have added some that have been afforded me by those late Tryals made in my Engine, whereof I sent you an account.
Resemblances.
The things, wherein I observed a piece of Wood and a burning Coal to agree or resemble each other, are principally these Five.
1. Both of them are Luminaries, that is, give Light, as having it (if I may so speak) residing in them, and not like Looking-Glasses or white Bodies, which are conspicuous only by the incident beams of the Sun, or some other Luminous Body, which they reflect.
This is evident, because both Shining Wood and a Burning Coal shiner the more vividly, by how much the place wherein they are put is made the darker, by the careful exclusion of the adventitious light. 'Tis true, that the Moon and Venus appear brightest at or about Midnight, and yet have but a borrowed light; but the difference between those Planets and the Bodies we treat of, in reference to the difficulty we are considering, is obvious enough. For, though the beholder's Eye, that looks upon those Stars, be advantag'd by being in the dark, which enlarges the pupil of the Eye, yet the Object it self is freely exposed to the beams of the Sun, which if they were intercepted, those Planets would quickly be darken'd, as experience manifests in Eclipses.
2. Both Shining Wood and a Burning Coal need the presence of the Air, and are too of such a density; to make them continue shining.
This
