5. In Rome and other cities of the empire, thin leaves of a certain kind of stone called _lapis specularis_ were used. Windows of this material, however, were employed only in the principal apartments of great houses, in gardens, sedans, and the like. Paper made of the Egyptian papyrus, linen cloth, thin plates of marble, agate, and horn, seem likewise to have been used. 6. The first certain information we have of the employment of glass panes in windows, is found in the writings of Gregory of Tours, who flourished in the last quarter of the sixth century. This prelate states that the churches were furnished with windows of colored glass, in the fourth century after Christ. The oldest glass windows now in existence were of the twelfth century, and are in the Church of St. Denis, the most ancient edifice of this description in France. 7. Æneas Sylvius accounted it one of the most striking instances of splendor which he met with in Vienna, in 1458, that most of the houses had glass windows. In France, all the churches had these conveniences in the sixteenth century, although there were but few in private dwellings. Talc, isinglass, plates of white horn, oiled paper, and thinly shaved leather, were used instead of glass. A similar state of things prevailed in England. 8. The glass used for the windows of churches and other public buildings, after the fourth century, was very commonly intrinsically colored or superficially painted. Painting on glass had its origin in the third century, and at first it consisted in the mere arrangement of small pieces of glass of different colors in some sort of symmetry, and constituted a kind of mosaic-work. 9. Afterwards, when more regular designs came to be attempted, such as the human figure, the whole address of the artist went no farther than drawing the outlines of the objects in black on glass resembling in color the subjects to be represented. The art, in this state of advancement, was spread over a great part of Europe. 10. About the beginning of the fifteenth century, a method of fixing metallic colors in glass by means of heat was discovered, and from this the art derived great advantages. It flourished most during the fifteenth and sixteenth centuries; but it declined in the following age, and in the eighteenth century it was very little practised in any country. It has, however, been partially revived, of late, in Germany. A very good specimen of this kind of painting, as well as of colored glass, may be seen in St. John's Church, in Philadelphia. [Illustration: TURNER.] THE TURNER. 1. Turning is a very useful art, by which a great variety of articles are almost exclusively manufactured. Besides this, it constitutes a considerable part of the operations of several trades and occupations, such as the chairmaker, machinist, cabinet-maker, brass-founder, &c., since every substance of a solid nature can be submitted to the process.