The Stanhope lenses are now sold at such a cheap rate, and are so useful as simple portable microscopes, that it is hardly worth while to detail any plan by which a cheap single-lens magnifier may be obtained. Eloquent vendors of cheap microscopes are to be found in the streets, who make their instrument of a pill-box perforated with a pin-hole, in which a globule of glass fixed with Canada balsam is placed; and the spherical form of the drop affords the magnifying power: or a thin platinum wire may be bent into a small circular loop, and into this may be placed a splinter of flint-glass; if the flame of a spirit-lamp is urged upon the loop of platinum wire and glass by the blowpipe until it melts, a small double-convex lens may be obtained, which will answer very well as a magnifying-glass. Practice makes perfect, and after two or three trials, a good single lens may be obtained, which can be mounted between two small pieces of lead, brass, or cardboard, properly fixed together, with holes through them just large enough to retain the edge of the tiny lens. A prism can be made of two small pieces of window-glass stuck together with a lump of soft beeswax, and if a few drops of water are placed in the angle, they are retained by capillary attraction. The prism is used by holding it against a large pin-hole or small slit in a bit of card, and directing them towards the sky, when the beautiful colours of the spectrum will be apparent if the card and prism are brought close to the eye.