and circumstances and expressions relative to glass mirrors must certainly have occurred. Though glass continued long to be held in high estimation, particularly at Rome; and though many kinds of glass-ware are mentioned in ancient authors, among costly pieces of furniture, mirrors are mentioned only among articles of silver plate. I am acquainted with no certain trace of glass mirrors from the time of Pliny to the thirteenth century; but after that period, at which they are spoken of in the clearest manner, we find them often mentioned in every century; and mirrors of metal at length entirely disappear. How the Sidonian mirrors were made, is not known; but if I may be allowed a conjecture, I am of opinion that they consisted of dark-coloured glass, which had a resemblance to the obsidian stone. Such is the usual progress of inventions. At those periods one had no other representation of glass mirrors than that afforded by natural glass or vitreous stones. When artists wished to make mirrors of glass, they would try to imitate the latter. After the invention of printing, people endeavoured to render printed books as like as possible to manuscripts; because they imagined that this invention was to be approved only so far as it enabled them to imitate these, without observing that it could far excel the art of writing. But the Sidonian glass mirrors were so much surpassed by the silver or brass ones, which perhaps were invented about the same time, that on this account they were never brought into use. Glass mirrors, perhaps, would have been invented sooner, had mankind employed at an earlier period glass-windows, which often, when they are shut on the outside so that no light can pass through them, reflect images in a much better manner than the best mirrors of metal. This observation, which may be made daily, would then, in all probability, have been sooner turned to advantage.