an optical instrument, consisting of lenses, or mirrors, by means of which small objects appear larger than they do the naked eye. Single microscopes consist of lenses or mirrors; or if more lenses or mirrors be made use of, they only serve to throw light upon the object, and not contribute to enlarge the image of it. Double microscopes are those in which the image of an object is composed by means of more lenses or mirrors than one. For the principles on which the construction of microscopes depend, and the best methods of making them, see (the Index subjoined to) Optics.