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Bausch & Lomb Optical Company Condensing Systems The condensing lenses play an important part in the optical system of any projection apparatus, inasmuch as the uniformity of illumination and the size of the illuminated field are dependent on the purity of the glass they are made from (freedom from striae, bubbles, etc.) and on the correctness of their focal length. We furnish two different condensing systems, a double system, consisting of two plano-convex lenses with the convex sides facing each other, and a triple system composed of a meniscus and a plano-convex lens mounted in close proximity and another plano-convex lens mounted separately, as shown in the illustration. Both systems provide for the insertion of a water cooling cell between the plano-convex lenses, if desired. Sectional View of Triple Condensing System, Showing Light Rays Coming from Illuminant, L, Rendered Parallel by Rear Condensers, C, and Converged Again by Front Condenser, C', at L\ The two rear lenses of the triple system render the light parallel. This system permits a more universal application of the light, since by simply removing the front lens a parallel beam is obtained for any other form of projection which may require it, without necessitating the substitution of a special system. A difficulty encountered with all condensing systems is the liability of breakage, due to unequal expansion or contraction caused by sudden extreme changes in temperature. We have devised and patented a ventilated mount, which we believe to be the best safe- Our Ventilated Mount Patent Ventilated Condenser Mount. guard on the market against the breakage of lenses. The rear lens, which comes in closest proximity to the lamp, is one-half inch smaller in diameter than the front 19