REFRACTING OPTICAL INSTRUMENTS. I. _The Magic Lantern._ No other optical instrument has ever caused so much wonderment and delight, from its origin to the present time, as this simple contrivance. For a long time its true value was overlooked, and only ridiculous or comic slides painted, but its educational importance is now being thoroughly appreciated, not only on account of the size of the diagrams that may be represented on the disc, but also from the fact that the attention of an audience is better secured in a room when the only object visible is the diagram under explanation. The lenses it contains are a "bull's eye" or plano-convex, nearest the light, and a double convex glass, for the purpose of focussing the picture which is inverted and placed between the two lenses. (Fig. 293.) [Illustration: Fig. 293. The magic lantern.] In many books full directions are given for painting the glass slides, but this is an art that requires very great practice and experience. A person may know how to draw and paint on paper or canvas, but it is quite a different thing where glass is concerned, and unless the juvenile artist has taken lessons from a regular painter on glass, his or her efforts are likely to be very unsatisfactory. In many popular works embracing the subject of optics, full directions are given on the mode of painting the slides for the magic lantern, or dissolving views; a new era, however, has dawned upon this mode of illustration, in the preparation of photographs on glass of the most lovely description, and now instead of exhibiting mere daubs of weak colouring, photographic pictures of singular perfection can be procured of Messrs. Negretti and Zambra, Holborn, who have turned their attention especially to this branch, and supply slides of all sizes. II. _The Dissolving Views._