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THE WONDERS OF OPTICS.
observation than that given by the single bi-concave. This combination is commonly known as the astronomical eye-piece. It reverses the object looked at, but for astronomical purposes this defect is of no consequence.
Fig. 42.—The Astronomical Telescope.
The instrument shown in the above figure represents an astronomical telescope reduced to its simplest form.
Fixed parallel to the axis of the larger telescope is
