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A plano-convex lens is compose of a plane and convex surfaces, has a positive focal length.It is used for the changing between point light source and parallel beam.It is mean when the light through ...

A double-convex lens is compose of two convex surfaces, has a positive focal length. Normally Bi-Convex lenses are most suitable where the object and image are on opposite sides of the lens, and are ...

IN the latest edition of Carpenter on the microscope at p. 119 occurs the following, evidently from the pen of the late Dr. Dallinger:—“There is in the British Museum a remarkable piece of rock ...