[759] In the time of Job, pearls were accounted to be of great value. Job, chap. xxviii. ver. 18.
[760] [When the surface of pearl is examined with a microscope, it is found to be indented by a large number of delicate grooves, which by their effect upon the light give rise to the play of colours; and if impressions of them be taken upon wax, fusible metal, lead, balsam of Tolu, &c., the impressed surface exhibits the prismatic colours in the same manner as the pearl. This principle has been applied by Mr. Barton and others to the making of ornaments, in the form of buttons, artificial jewels, &c., by grooving the surface of steel with a very fine cutting machine. The theory of the production of the colours is this: the surfaces of the grooves, from their varied inclinations, reflect the incident white light at various angles, hence the correspondence of the luminous undulations is interrupted and some of them check or interfere with one another, others continue their course. Now, ordinary white light being a mixture of coloured rays, when some of these are checked or interfered with in their progress, the remainder continue their course and appear of that colour which results from the ocular impression communicated by them.]
[761] [One of the most remarkable pearls of which we have any authentic account, was bought by Tavernier at Catifa in Arabia, a fishery famous in the days of Pliny, for the enormous sum of £110,000. It is pear-shaped, regular, and without blemish. It is rather more than half an inch in diameter at the largest part, and from two to three inches in length.—Waterston’s Encyclopædia of Commerce.]
[762] Philostrat. in Vita Apollon. lib. iii. cap. 57, edit. Olearii, p. 139. Conrade Gesner, in his Hist. Nat. lib. iv. p. 634, gives a more correct translation of the passage.
[763] Tsetzes Variorum, lib. ii. segm. 373.
[764] See Dr. Joh. Mayer’s Bemerkungen, in the fourth part of Abhandlungen einer Privatgesellschaft in Böhmen, p. 165.
[765] Abhand. der Schwed. Akadem. der Wissenschaften, vol. xxxiv. p. 89. The author of the paper alluded to had a mussel with such artificial pearls, which had been brought from China. It was a Mytilus cygneus, the swan-mussel, or great horse-mussel. Mention is made also in Histoire de l’Académie des Sciences de Paris, année 1769, of a stone covered with a pearly substance which was found in a mussel.
[766] A kind of cockles.
[767] J. C. Fabricius Briefe aus London, Dessau, 1784, 8vo, p. 104.
[768] See Schlözer’s Briefwechsel, number 40, p. 251.