Projection Apparatus (1917)

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Bausch & Lomb Optical Co m p a n y chamber is a swinging mirror which catches in any one of three positions as may be required for the method of projection being employed. The mirror is operated by a lever, E, at either side. Upon the slide on top of the dark chamber a Delezenne polarizer, F, is mounted in a metal box, on the front of which the quarter-wave mica plates for rotating the polarized beam are located at G. The size of the beam of light avail- able with this accurately constructed Delezenne polarizer is very large and of exceptional brilliancy, excelling that obtained with any other than very large and expensive nicol prisms. It illuminates an ample field. The stage, H, for objects, the objective, I, and analyzer, J, are mounted on supports, which are adjustable along the horizontal bed. The stage is 95 mm in diameter, is revolvable and has centering screws. It may also be removed and a revolving mechanical stage, furnished at an extra cost, substituted. Between the polar- izer and the stage is the mounting, K, for a highly convergent lens, while a similar mounting, L, is provided on the front of the stage for a highly divergent lens which is supplied with an iris diaphragm for controlling the size of the transmitted beam. These lenses are used when projecting with convergent polarized light, as m work with interference figures. The mountings include quick acting screws, which en- able the operator to turn either or both lenses out of the optical axis, when parallel polarized light is desired, and to focus. The objective is of 4-inch focus and, with a nicol prism, approximately 12 mm, is held in a tube which slides in a main tube. This in turn is mounted with a standard rack and pinion adjustment, M, thus affording a wide range for focusing. The analyzer may be revolved. This polariscope, giving a large, clear field upon the screen, offers means for extensively demonstrating the properties of parallel and convergent polarized light, with rock sections, crystals, etc. For vertical work it is only necessary to slide the plate over until the vertical attachment is in line with the opening in the roof of the dark chamber. The sliding plate is moved by means of the handle, N, and a stop insures its being brought into exact alignment. The interior mirror of the dark chamber must also be low- ered to its first or 45° position, to direct a beam of light directly upwards. The vertical attachment consists of a plano-convex condenser, O, which is mounted in the sliding plate with the plane side up, and thus serves also for a stage, 4/4 inches in diameter, upon which the glass dishes, specimens, etc., to be projec- ted, are placed. At one corner of the sliding plate is a vertical rod, B, which carries the projection lens and mirror by which the beam of light is directed to the screen. When projecting opaque objects the vertical attachment is withdrawn from the path of the large projection lens by means of the sliding plate, and the supports carrying the body tube and revolving stage of the polariscope are hinged so that they, too, can be turned away from the path of light. When projecting lantern slides or microscopic specimens the interior mirror is raised to its third position to 118