Reflecting Telescopes. The refracting astronomical telescope is formed of two convex lenses in a tube, and is the simplest form of telescope. In the Galillean telescope a concave eye-piece is used. Refracting telescopes for land objects are a compound form of the first-named, and are so constructed as, by the use of different qualities of glass, to prevent the decomposition of the light rays at the edges of the picture presented to the eye. When this is accomplished perfectly, such instruments are called achromatic (without colouring). Telescopes are not difficult to construct, and some of the finest have been made by amateur opticians.