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Bausch & Lomb Optical Company Balopticon for Large Opaque Objects Designed for the direct projection of opaque objects and illustrative material on a much larger scale than ever before attempted, this unique Balopticon has proved entirely practical in operation and presents many new possibilities. Pro- jecting, as it does, opaque objects measuring 20 inches square, the instrument affords excellent opportunities for projecting on the screen large anatomical speci- mens, charts, etc. Not only is this Balopticon of service to the medical school, but in the Departments of Science, Engineering, etc., it is a valuable aid in projecting experi- ments, blue prints, working models or mechanical parts, etc. All subjects are clearly shown in their natural form and coloring in greatly enlarged images, which permit fine distinctions and details to be seen by a large audience. Model LR was originally designed for the National Cash Register Company, which is using four of these instruments in educating its salesmen. A section of a cash register is placed in the Balopticon and shown on the screen in actual oper- ation, while large advertisements and placards are also projected for purposes of comparison and discussion. The 400 square inches of projected area are brilliantly illuminated to the edges by two arc lamps carried in large, light-tight lamp houses. A 6-inch con- densing lens is carried before each lamp in a sliding mount operated from without, so that a smaller, more brilliant area can be projected by sliding these condensers into position. The illuminants are, however, sufficiently powerful to obviate the need for condensers with ordinary subjects, yet are not so close as to heat the speci- men unduly. Their position also results in complete elimination of all shadows. The projection lens is a high grade photographic, anastigmat lens, a Bausch & Lomb Tessar Ic of 19M-inch focus and 4^ie-inch diameter, which has unusual covering power for its speed—F:4.5. A mirror of a very high grade, measuring 17/4 x 9/4 inches and silvered on the first surface, directs the light toward the screen and also causes objects, illustrations and printed matter to appear in their true position. Focusing is accomplished by bringing the object into range of the lens. The large object table is adjustable vertically by means of a heavily constructed worm wheel and pinion actuating a rack. Objects of any thickness up to 9 inches can be accommodated, a dark velvet curtain preventing the light from escaping when the carrier is lowered. This unique instrument is naturally one of unusually large proportions for a projection lantern. The massive iron base has a spread of 54 x 24 inches, being provided with both castors and leveling screws. The height of the stand to the top of the mirror is approximately 80 inches. 87