Johann Beckmann - A History of Inventions, Discoveries, and Origins, Volume II (of 2)

Of such large mirrors Seneca speaks in his Quæst. Nat. lib. i. Of the like kind was the mirror of Demosthenes mentioned by Plutarch, Lucian, and Quintilian. – Institut. Orat. xi. 3, 68, p. 572.

“Having filtered the solution, I took a part of it, upon which I poured an infusion of gall-nuts, but it produced no change. A solution of gold, which I poured upon another part, made it assume a beautiful green colour; but no precipitate was formed: which is sufficient to prove that there was neither iron nor tin in the mixture.

“On the remaining part of the solution I poured a sufficient quantity of the volatile alkali to dissolve all the copper that might be contained in it. The solution became of a beautiful sapphire blue colour, and a white precipitate was formed. Having decanted the liquor, and carefully edulcorated the precipitate, I endeavoured to reduce it; but whether it was owing to the quantity being too small, or to my not giving it sufficient heat, I could not succeed. I had recourse therefore to another method.

“I took the weight of two drams of the mixture, which I brought to a high state of ignition in a cuppel. When it was of a whitish-red colour, I threw upon it gradually four drams of sulphur, and when the flame ceased, I strengthened the fire in order to bring it to complete fusion. By these means I obtained a tender brittle regulus, whiter than the mixture, in which I observed a few small needles. Being apprehensive that some copper might still remain, I sulphurated it a second time, and then obtained a small regulus which was almost pure antimony.

“It results from these experiments, that the metal of which the ancients made their mirrors was a composition of copper, regulus of antimony, and lead. Copper was the predominant, and lead the smallest part of the mixture; but it is very difficult, as is well known, to determine with any certainty the exact proportion of the substances contained in such compositions.”

[In the examination of an Etruscan mirror, which was placed in my hands for analysis by Professor Gerhardt of Berlin, it was found to consist, in 100 parts, of 67·12 copper, 24·93 tin, and 8·13 lead, approximating closely to an alloy of eight parts of copper to three of tin and one of lead. The oxide of tin obtained in the course of analysis was carefully examined, before the blowpipe, for antimony, but I did not succeed in detecting a trace of that metal. A similar mirror had been likewise analysed by Klaproth; he found 62 per cent. copper, 32 tin, and 6 per cent. lead, but no trace of antimony. – W. F.]

Lib. xxxvi. c. 26, p. 758.

Sueton. in Vita Domit. cap. xiv. p. 334.

Lib. xxxvi. 22, p. 752. – “Cappadociæ lapis, duritia marmoris, candidus atque translucidus, ex quo quondam templum constructum est a quodam rege, foribus aureis, quibus clausis claritas diurna erat.” – Isidor. Origin. 16, 4. Our spar is transparent, though clouds and veins occur in it, like the violet and isabella-coloured, for example, of that found at Andreasberg. Compare this explanation with what Salmasius says in Exercitat. Plin. p. 184.

Lib. xxxvii. cap. 5, p. 774.

Lib. xi. cap. 37, p. 617.

This dissertation of Abat may be found translated in Neuen Hamburg. Magazin. i. p. 568.

Academia di Cortona, vii. p. 34.

Origin. xvi. 7.

Goguet, ii. p. 111. Fabricii Biblioth. Græca. vol. i. p. 70.

Keyssler, i. pp. 17 and 441.

Lib. xxxvii. cap. 7.

De Lapid. § 61.

[This stone acquired its name from its being much used in ornaments by the Incas or Princes of Peru.]

De la Vega, ii. 28.

Montamy in Abhandlung von den Farben zum Porzellan, Leipzig, 1767, 8vo, p. 222, asserts that he saw, in a collection of antiquities, glass mirrors which were covered behind only with a black foil.

Lib. xxxvi. cap. 26, p. 758.

Lib. xxxiii. cap. 9, p. 627.

Trebell. Pollio, Vita Gallien. cap. 12.

Chemical Essays, vol. iv. p. 246.

Plin. lib. xxxiii.: Æs inaurari argento vivo, aut certe hydrargyro, legitimum erat. The first name here seems to signify native quicksilver, and the second that separated from the ore by an artificial process.

Hist. Nat. Supplem. i. p. 451.

Stob. Eclog. Antv. 1575, fol. p. 56.

De Placitis Philos. ii. cap. 20.

In Aratum, cap. 19.

Lib. i. cap. 8.

It is undoubtedly certain, that ὕαλος, which is translated vitreous or glassy , means any smooth polished body capable of reflecting rays of light. Originally it signified a watery body; and because watery bodies have a lustre, it was at length used for glass. See Salmas. ad Solin. p. 771.

More observations respecting the opinion of Philolaus may be found in the edition of Plutarch’s work De Placitis Philosophorum by Ed. Corsinus, Flor. 1750, 4to, p. 61, and p. 23.

Professor Heeren having given me his opinion on this passage of Stobæus, I shall here insert it for the satisfaction of the learned reader. The critics, says he, will hardly be persuaded that the words καὶ τὸ ἀπ’ αὐτοῦ πυροειδὲς κατὰ τὸ ἐσοπτροειδὲς are correct, as they can be translated different ways. With regard to the explanation of the matter, I build only on the plain meaning of the words. The author tells us, that Philolaus thought the sun to be a mirror; but we must conclude that he speaks of a mirror such as were then in use; a smooth plate of metal, and not a globe. In this case the first explanation of a glass globe falls to the ground. This is confirmed by Eusebius, who calls it ὑαλοειδὴς δίσκος, though it is possible that the latter word may be a gloss added by some grammarian, or by Eusebius himself. If we enter further into the explanation, we must adopt the plain idea, that the rays of the sun fall upon this plate, and are reflected to us. I am however of opinion, that ὕαλος ought to be translated glass , ὑαλοειδὴς glassy or vitreous ; for the intention of Philolaus evidently was to define the substance of the sun’s body. The result of the whole is, Philolaus considered the sun as a plain plate of glass which reflected the rays or brightness of the æthereal fire. But that he was acquainted with a proper glass mirror does not thence follow with certainty.

Pourquoy reluient les fenestres de verre si fort? Pourtant que la nature de l’estain, duquel elles sont basties par dedans, fort clere, meslée avec le verre cler aussi de lui mesme reluyst d’avantage; et le quel estain outrepassant ses raïons par les petits pores du verre, et augmentant doublement la face extérieure du dit verre, la rend grandement clere. – Problemes d’Alexandre Aphrod., traduit par M. Herret. Paris 1555, 8vo, p. 50.

Origin. lib. xvi. 15, p. 394.