350. =Microscopes and Telescopes.=--What has been said of the action of the convex lens upon the visual angle will serve to explain the operation of the microscope. This instrument may be single or compound. The compound microscope has more than one lens, and is used to magnify very minute objects. Its operation may be seen by the diagram, Fig. 240. Rays from the object, E F, passing through the first lens, or object-glass, as it is called, form a magnified inverted image, G H, which is still more magnified by the eye-glass, C D. In the telescope we have also convex lenses, but they are arranged differently from those of the microscope, as the objects to be magnified are distant. [Illustration: Fig. 241.] 351. =Magic Lantern.=--This is an instrument by which pictures made upon slips of glass with coloring substances which allow the light to pass readily are thrown upon a screen magnified. It is a metallic lantern, A A, Fig. 241, with a concave reflector, _p q_, and two convex lenses, _m_ and _n_. At _c d_ is a space between the lenses into which the pictures are introduced. L is a strong light, which is in the focus both of the mirror and the lens _m_. The picture is therefore illuminated strongly by the rays reflected from the mirror and passed through the lens. The lens _n_ which is movable, is so adjusted as to throw a highly magnified image of the picture upon the screen. As the image is an inverted one the pictures must be inserted upside down, that the images on the screen may be upright. The _solar microscope_ is, in its essential parts, like the magic lantern, the sun being used as the illuminator. [Illustration: Fig. 242.] [Illustration: Fig. 243.]