29. In modern times, the manufacture of glass was confined principally to Italy and Germany. Venice became particularly celebrated for the beauty of the material, and the skill of its workmen; and as early as the thirteenth century, it supplied the greatest part of the glass used in Europe. The artists of Bohemia, also, came to be held in considerable reputation. 30. The art was first practised in England, in the year 1557, when a manufactory was erected at Crutched Friars, in the city of London, and shortly afterwards, another at the Savoy, in the Strand. In these establishments, however, were made little else than common window glass, and coarse bottles, all the finer articles being still imported from Venice. In 1673, the celebrated Duke of Buckingham brought workmen from Italy, and established a manufactory for casting plate glass for mirrors and coach windows. The art, in all its branches, is now extensively practised in great perfection, not only in Great Britain, but in many of the other kingdoms of Europe. 31. Before the commencement of the late war with England, very little, if any, glass was manufactured in the United States, except the most common window glass, and the most ordinary kinds of hollow ware. Apothecaries' vials and bottles, as well as every other variety of the better kinds of glass wares, had been imported from Europe, and chiefly from England. 32. Our necessities, created by the event just mentioned, produced several manufactories, which, however, did not soon become flourishing, owing, at first, to inexperience, and, after the peace, to excessive importations. But adequate protection having been extended to this branch of our national industry, by the tariff of 1828, it is now in a highly prosperous condition--so much so, that importations of glass ware have nearly ceased. [Illustration: OPTICIAN.] THE OPTICIAN. 1. The word optician is applicable to persons who are particularly skilled in the science of vision, but especially to those who devote their attention to the manufacture of optical instruments, such as the spectacles, the camera obscura, the magic lantern, the telescope, the microscope, and the quadrant. 2. Light is an emanation from the sun and other luminous bodies, and is that substance which renders opaque bodies visible to the eye. It diverges in a direct line, unless interrupted by some obstacle, and its motion has been estimated at _two hundred thousand miles_ in a second. 3. A _ray of light_ is the motion of a single particle: and a parcel of rays passing from a single point, is called _a pencil of rays_. _Parallel rays_ are such as always move at the same distance from each other. Rays which continually approach each other, are said to _converge_; and when they continually recede from each other, they are said to _diverge_. The point at which converging rays meet is called the _focus_.