glass is perfectly dry, it is varnished with a composition, formed by melting together equal quantities of bees’ wax and tallow. The patentee states that, by experiment, he has ascertained that about 18 grs. of nitrate of silver are used for each square foot of glass. It has been urged as an objection to this process, that in the course of a few weeks the surfaces of the mirrors formed by it become dotted over with small brownish-red spots, which greatly injures their appearance. Dr. Stenhouse states that these spots are caused by the metallic silver, whilst being deposited on the surface of the glass, carrying down with it mechanically small quantities of a resinous matter, resulting most probably from the oxidation of the oil. This subsequently acts upon the metallic surface with which it is in contact, and produces the small brown spots already mentioned. Mr. Drayton, however, states that the brown spots only occur when the oil employed is old and unfit for use.] FOOTNOTES [135] The works in which this subject has been already treated are the following:--Eberhartus de Weihe, de Speculi origine, usu et abusu. A compilation formed without taste, of which I gave some account in the Article on Chimneys.--Spanhemii Obs. in Callimachi hymn. lavacr. Palladis, p. 615.--Académie des Inscriptions, t. xxiii. p. 140.--Recherches sur les Miroirs des Anciens, par Menard. A short paper, barren of information.--Saggi di Dissertazioni Accad. dell’ Accad. Etrusca dell’ città di Cortona, vii. p. 19: Sopra gli Specchi degli Antichi, del Sig. Cari. A translation from the French, with the figures of some ancient mirrors. It contains an explanation of some passages in Pliny, where he seems to speak of a mirror formed of a ruby, and some conjectures respecting the mirror of Nero. An anonymous member of the Academy, in an appendix, confirms the former, and considers the latter, very properly, as improbable.--Caylus, Recueil d’Antiquités, iii. p. 331, and v. p. 173. A description and figures of ancient mirrors, with some chemical experiments on their composition.--Amusemens Philosophiques. Par le père Bonaventure Abat. Amst. 1763, 8vo, p. 433: Sur l’Antiquité des Mirroirs de Verre. A dissertation worthy of being read on account of the author’s acquaintance with the ancient writers, and his knowledge of technology; but he roves beyond all proof, and employs too much verbosity to decorate his conjectures. [136] Passages of the poets, where female deities and shepherdesses are represented as contemplating themselves in water instead of a mirror, may be found in the notes to Phædri Fab. i. 4, in the edition of Burmann. [137] Chap. xxxvii. ver. 18. [138] Exodus, chap. xxxviii. ver. 8.