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Bausch & Lomb Optical Company Model D Balopticon Figure 1—Model D Balopticon with Small Lamp House. The Model D Balopticon is constructed on what is known as the optical bed type of construction. An accurately milled bed of lathe type is supported by feet at either end, those at the front being provided with leveling screws. To this optical bed the lamp house containing the arc and the standards supporting the different accessories are attached by means of clamping blocks. These stand- ards may be adjusted along the bed to any position, and the act of clamping fixes them rigidly in optical alignment. Science teachers have been quick to appreciate the refinements and conveniences of this Balopticon, and its optical bed affords convenient accommodation for the many accessories used in science laboratories. The Model D is equipped with the triple condensing system and a water cooling cell, which makes it the most perfect outfit for lantern slide projection. A combination of two of these instruments, equipped with our iris dissolver, makes an excellent double dissolving outfit for auditorium use (see Figure 2). The lanterns are readily separated for use in class rooms and laboratories. Two styles of lamp house are offered. The large, light-tight housing meets the most rigid requirements of the Boards of Underwriters. It is particu- larly recommended where a part of the audience is seated back of the lantern and for use with arcs of high amperage. This lamp house is well adapted to double dissolving outfits. The small lamp house is illustrated in Figure 1. Specifications Base —Consists of cast iron supports of 6-in. spread, front and back, supporting optical bed iyi in. in height; front support provided with elevating screws. Optical Bed Of lathe type, carefully planed, accommodating supports for differ- ent parts which may be adjusted as desired and rigidly clamped; measures 19/2 in. in length and accommodates projection lenses up to 15-in. focus; two models (see DA 18 and DAL 18 below) are furnished with 25-in. optical bed accommodating projection lenses up to 22-in. focus. 38