Projection Apparatus (1917)

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Bausch & Lo m b Optical Comp any The flint prism, or bottle prism with carbon bi-sulphide, (equilateral 60°) is placed on an adjustable table in front of the projection lens. If then the axis of the projection apparatus is given the proper inclination toward the screen, the sequence of colored images of the slit, which forms the spectrum, will appear on the screen. For the projection of emission spectra, or for the projection of comple- mentary colors, we offer special accessories accommodated on an accessory optical bed, which may be attached to the regular optical bed. This equipment is partic- ularly effective, projecting an exceptionally bright and pure spectrum. These accessories are fully described and illustrated under Accessories (see index). General Construction There are several features to be noted in the general construction of our projection apparatus, which play an important part mechanically in achieving the high degree of efficiency sought. To obtain portability in our B and C types of construction, the standards are made of heavy sheet metal by special forming tools. This method greatly reduces the weight of the apparatus, and the standards equal castings in rigidity. When the first Balopticon was designed with optical bed of the lathe type, there was adopted a certain size of bed, height of standard, etc., which has been adhered to in all instruments of this type, namely the Model D, Universal and Convertible, and their accessories, so that the same fittings and optical centers are insured upon all. This policy has resulted in securing that standardization of apparatus and interchangeability of parts which .characterize our entire line of projection apparatus. When a Balopticon is equipped with optical bed, any stand- ard carrying accessories, or any piece of apparatus provided with the necessary clamp, can be adjusted along the bed and the simple act of clamping secures the accessory in accurate optical alignment. Our instruments are finished with a dull, black lacquer thoroughly baked in a high-temperature oven. This treatment produces a rich, black finish which is both serviceable and appropriate. Illuminants While a number of different illuminants may be utilized to supply the light for projection purposes, we confine our attentions almost entirely to the arc lamp and the new gas-filled, Mazda stereopticon lamp, where electricity is available, or to the acetylene burner, where electricity cannot be used. The arc lamp is a most satisfactory form of illuminant and Lamp tor some kinds of projection, such as the projection of micro- scopical slides, of the spectrum and complementary colors— wherever, in fact, a very concentrated, homogeneous spot of light is required, it is the only light source we recommend. 15