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Bausch & Lo m b Optic a 1 Company The Universal Balopticon Figure 1 —Universal Balopticon ERA 15 in Position for Lantern Slide Projection. The Universal Balopticon has proved very popular wherever a combination apparatus of extreme rigidity and general adaptability is desired. The base instru- ment projects lantern slides and opaque objects, up to 6 inches square. It is widely used in the science departments of colleges and high schools, however, because of the attachments it readily accommodates for the efficient projection of a wide range of subjects : microscopical objects, large, transparent objects held in a horizontal plane, the spectrum and complementary colors and physical or chemical phenomena. These attachments may be added at any time and are so arranged that instant interchange is provided between the different kinds of projection, the interchange between lantern slides and opaque objects being accomplished by raising or lowering the lamp house as required. In audition to these possibilities, an attachment for the projection of moving pictures may be added upon special order. Lantern Slide Projection For work with lantern slides the lamp house remains in the horizontal position, as shown in Figure 1. The projection lens for lantern slides is mounted on top of the dark chamber with the slide carrier support and the third lens of the triple con- densing system. The first two lenses of this system are mounted in the front of the lamp house to collect the rays proceeding from the arc. In the dark chamber is a mirror in mounting so inclined as to reflect the light coming from the arc lamp up to a second mirror parallel to the first and mounted back of the projection lens on top of the dark chamber. The second mirror directs the light through the slide and projection lens to the screen. The position of the tnirror in the dark chamber is indicated by the exterior lever over the door, this lever being used to shift the mirror when it is desired to change to microscopical projection. 59