Dr. Watson[176] also has endeavoured to support the opinion of Abat, but with less confidence and with more critical acumen. His grounds, I think, I have weakened already; but one observation here deserves not to be overlooked, because it suggests an idea that may serve to illustrate a passage of Pliny, which, as I before remarked, has never yet been explained. “If we admit,” says he, “that Pliny was acquainted with glass mirrors, we may thus understand what he says respecting an invention, which was then new, of applying gold behind a mirror.” Instead of an amalgam of tin, some one had proposed to cover the back of the mirror with an amalgam of gold, with which the ancients were certainly acquainted, and which they employed in gilding[177]. He mentions, also, on this occasion, that a thought had once occurred to Buffon, that an amalgam of gold might be much better for mirrors than that used at present[178]. This conjecture appears, at any rate, to be ingenious; but when I read the passage again, without prejudice, I can hardly believe that Pliny alludes to a plate of glass in a place where he speaks only of metallic mirrors; and the overlaying with amalgam requires too much art to allow me to ascribe it to such a period without sufficient proof. I consider it more probable that some person had tried, by means of a polished plate of gold, to collect the rays of light, and to throw them either on the mirror or the object, in order to render the image brighter. Professor Heeren showed me a passage in the Ecloga of Stobæus, which, on the first view, seems to allude to a glass mirror[179]. It is there said, Philolaus the Pythagorean believed that the sun was a vitreous body, which only received the rays of the æthereal fire and reflected them to us like a mirror. When we compare, however, the words of Stobæus with those by which Plutarch[180], Achilles Tatius[181], Eusebius[182], and others, express the same thing, that meaning cannot be drawn from them. It appears, at first, as if Philolaus had considered the sun to be transparent, and supposed that the rays passed through it, and came condensed to our earth, in the same manner as they are brought to a focus by a glass globe. Some commentators have explained the passage in this manner; and on account of the affinity of the Greek words have thought also of a funnel. In that case, however, the comparison of the sun with a mirror would not have been just; and if it be admitted that Philolaus considered the sun as a bright body endowed with the property of reflection, what he says of rays passing or transmitted through it, and of the pores of the sun’s body, will become unintelligible. But even if we adopt the last explanation, that Philolaus imagined the sun to be a mirror, it does not follow that he had any idea of a glass one[183]; and besides, he only speaks of a body capable of reflecting a strong light; and that glass, under certain