no inconfiderable knowledge of the fubjects in queftion. * Horace likewife fpeaks of the clearness, and brightnefs of glafs, in terms that fhew the art to have been arrived at a high degree of perfection. Martialt mentions glafs in fuch a as fhews it to have been not uncommon in his time, for drinking veffels, and alfo of fo clear and tranfparent a texture, as to admit an accurate examination of the liquor contained in them. manner, Seneca well understood the magnifying powers of glass, when formed into a convex fhape. A glafs globe, he fays, filled with water, makes letters viewed through it, appear larger and brighter. The magnifying power of glass, confidered as a more denfe, and, of course, a more refrangible medium than air, was not unknown to him. Fruits, fays he, viewed * Perlucidior vitro. Hor. Carm. I. Od. 18. + Nos bibimus vitro, tu myrrha Pontice, quare? Prodat perfpicuus ne duo vina calix. Mart. Epig. IV. 86. Literæ quamvis minutæ et obfcuræ per vitream pilam aqua plenam majores clariorefque cernuntur. Senec. Nat. Quest. I. 6. Queft. Nat. L. I. C. 3. 6. through through glafs appear much larger, and the intervals between pillars longer. The ftars, alfo, appear magnified in a humid atmosphere. If a ring be put into a bowl of water, and viewed there, it feems to approach to the eye, or in other words is magnified, which, the fame author obferves, is the cafe with every body viewed through a fluid. Seneca fays here exprefsly, that water, as a medium, has the fame effect with glass. There is a remarkable paffage in Seneca,* relative to the effect of glafs cut angularwife, or into a prifmatic form, in feparating the rays of light, when held tranfverfely in the fun's rays. From the expreffion he ufes concerning it, we may think fuch inftruments were not uncommon. Pliny, however, feems to have had the most complete information concerning glafs. He mentions its being of Phoenician origin, like many other great difcoveries. It was firft made of fand, found in the river Belus, or Belcus, a small river of Galilee, running from the foot of Mount Carmel, as is teftified by a variety of * Virgula folet fieri ftricta vel pluribus angulis in modum clave torofa; hæc fi ex tranfverfo folem accipit colorem talem qualis in arcu videri folet. Sence. Quæft. Natur. L. I. 8. + Strabon. L. XVI. Jofeph. L. II. C. 10. § 2. Plin. Hift. Natural. L. XXXVI. C. 26. Taciti. Hiftor. L. V. C. 7. H 2 authors. authors. The invention of it is faid to have been owing to fome merchants, who, coming thither with a fhip laden with nitre, or foffil alkali, ufed fome pieces of it to fupport the kettles, in which they were dreffing their meat upon the fands. By this means a vitrification of the fand beneath the fire was produced, and thus afforded a hint for this manufacture. Clear pebbles, fhells, and other kinds of foffil fand, were also employed. In India, rock crystal was used, and, on that account, the 'Indian glass was preferred to any other. It was first melted with the foffil alkali, in proportion of three of the latter to one of the former, (which has continued to be the flux for glafs from the earliest to the prefent times) in furnaces, into maffes of a dull black colour. These were again melted by the refiners, either into a colourlefs glafs, or tinged of any hue they thought proper. The grofs mafs, from the firft fufion, feems to have been called ammonitrum, and probably did not differ much from the Lapis Obfidianus, which is faid to have been of Æthiopian or Egyptian origin. It is faid to have been a kind of black vitreous fubftance, but still pellucid, which was used for cafting into large works. Pliny fays, he faw folid ftatues of the Emperor Auguftus made of this material; and the fame Emperor dedicated four elephants of the fame fubftance in the Capitol. It appears to have been known from great antiquity, as Tiberius Cæfar, when he governed that country, found a ftatue of Menelaus of this compofition. Xenocrates likewife, according to Pliny, fpeaks of the fame compofition, as in ufe in India, Italy, and Spain. Sidon in Phoenicia had been, in early times, famous for glafs. In the time of Pliny, that of the Bay of Naples was preferred. The Romans were acquainted with the art of engraving upon, or cutting glafs, which is exprefsly mentioned by Pliny, and confirmed by the antique gems fo frequently found. It was formed either by blowing it with a pipe, grinding it in a lathe, or cafting it in a mold like metal. The colours principally in ufe were an obscure red glass, or perhaps rather earthen ware, called hæmatinon; one of various colours called myrrhinum, a clear red, a white, a blue, and indeed most other colours. The perfectly clear glafs was, however, most valued. Nero gave for two cups, of no very extraordinary fize, with two handles to each, upwards of fix thousand feftertia, or above fifty thousand pounds fterling. But, though the fineft kinds of glass were fo valuable, and rare, yet I apprehend, from the frequent mention of glass in Martial, and from what Pliny fays, that glafs for drinking veffels had nearly fuperfeded the use of gold and filver, fo that the inferior forts must have been common enough. Pliny likewife mentions the effects of hollow glafs globes, filled with water, in concentrating the rays of light, fo as to produce flame in any combuftible fubftance, upon which the focus fell, and relates, that fome furgeons in his time made ufe of it, as a cauftic for ulcers and wounds. He was alfo acquainted with the comparative hardness of gems and glafs, as he obferves, that the Lapis Obfidianus would not fcratch gems. And he likewife mentions the counterfeiting of the natural gems by glafs, as a very lucrative art,* and in high perfection in his time; and the fame feems to be confirmed by Trebellius Pollio.† Vopifcus fays, that Firmus furnished his houfe with fquare pieces of glafs, faftened together with bitumen or other fubftances; but, whether they were to ferve for windows, or as reflectors of the light and objects does not appear. As fpecula, or metal reflectors, in the prefent age, bear fome reference to glafs, and as they were in confiderable ufe among the ancients, I fhall here fubjoin a few words concerning them. *Plin. Hift. Nat. XXXVII. 12. Trebell. Poll. Gall. duo. It is worth obferving, that Pliny advises the fame cement for broken glafs veffels that is now in use, viz. the mixture of a white of an egg with quicklime. He likewife notices a fact, which later experience has confirmed, that hot water may be fafely poured into a glass veffel, provided it be immediately before moistened with. cold water. The |