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B a u s c h & L o m b Optical Co m p a n y project lantern slides and opaque objects only to the Department of Biology, requiring the microscope and vertical attachments, and the Departments of Physics and Chemistry, where projection with polarized light and the projection of the spectrum is desired in addition to that of opaque objects and lantern slides. This system of manufacture will also be appreciated by those who wish to add attach- ments from time to time as need arises, or who are unable for lack of funds to purchase a complete outfit at once. In our constant endeavor to perfect our apparatus we have introduced several new features and refinements in the latest model of the Convertible Balopticon. Chief among these are:—■ 1. Lever with quick acting cam for arresting the object holder at any point between base of instrument and bottom of dark chamber (see Figure 3). 2 . Two doors on right side of dark chamber, giving an opening the size of the entire side of the chamber for placing large objects, such as anatomical specimens, in position. 3. Set of reflectors for projecting anatomical specimens in vertical museum jars. 4. New design of carbon holder on arc lamp, making better electrical contact and keeping carbons in accurate alignment. The magnetic coils with which we equip this lamp have proved in practice to be very effic- ient in reducing the “blowing” of the arc and make the light much easier to control on high amperages. We also desire to lay emphasis upon two other features which, while not new with this model of the Convertible, are nevertheless lacking in other projection machines now on the market. These are: 1. All adjustments are made from the outside of the apparatus, and 2. All objects of ordinary size, such as books, etc., can be placed upon the object holder without opening the doors of the dark chamber. Lantern Slide Projection For work with lantern slides the lamp house remains in its horizontal position as shown in Figure 1, and the beam of light follows an uninterrupted path, as indicated by the dash lines in Figure 2. The accessories for lantern slide pro- jection are carried on the optical bed directly in front of the dark chamber and consist of a plano-convex condensing lens—which completes the triple condensing system and forms an image of the arc at the diaphragm plane of the projection lens—a double, quick changing slide carrier in support, a front standard carrying a projection lens and a bellows connecting front standard with slide carrier support to prevent light from escaping into the room. This apparatus requires no reflectors for lantern slide projection; consequently, maximum illumination is attained. This feature is of special importance where autochrome plates are to be projected, since these require all the illumination Possible. Autochrome slides are coming more and more into use, especially in medical school work, and many makers of these plates find it advantageous to make them 69