XXII INTRODUCTION. Part Secon^, so tnat customers looking for the most beauti¬ ful effects, without being restricted to a specific programme, will do well to consult these choice selected lists. Plain slides are now more frequently called for than those colored and mounted in wood, not only because they are cheaper, but because they are really quite in the fashion. Most of the plain or glass slides in market are in one or other of three shapes, viz. : 1. Views of interest in America, produced by Ameri¬ can photographers, are mostly made on quarter plate B. P. C. glass (best polished crown glass, three and a quarter by four and a quarter inches). This gives to the sides of the three-inch pictures a margin of fully half an inch for labels and for handling. The Woodbury and the Scientific Sciopticon Slides are also of the same size and shape. 2. The French slides are but four inches wide, the quar¬ ter of an inch being taken from the picture, and they are of thin glass. They are extensively used, and the best of them are doubtless the best in the market. 3. The English slides have also a smaller picture, with just margin enough all round for binding, making the whole three and a quarter inches square. They are apt to fail of covering the full opening in the slide carrier ; the name has to be stuck on the edge, and there are twice as many ways of getting it on to the screen in a wrong position. The Scientific Sciopticon slides are the most uniformly good for their purpose, and are put at the low price of thirty cents each, or twenty-five cents each by the set, to insure their being introduced so extensively as to be manu¬ factured to advantage. French slides are here reduced to sixty cents each, and the most of others to fifty cents.