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Bausch & Lomb Optical Comp any Aspheric Condenser for Micro-Projection In microscopical projection the spherical correction of the condensing lenses used in connection with the illuminant is one of the principal points to be considered. We would for this reason call particular attention to the fact that we have designed for this work an aspheric condenser of 60 mm (2)4 inches) diameter, which is corrected for spherical aberration by grinding to non-spherical curves. By means of this correction an image of the arc is formed practically in one plane, so that a much greater percentage of the light collected from the arc may be utilized by the substage condenser than is possible with the regular spherical condensers. The focus of this aspheric lens is such that it takes in a cone of light from the arc lamp of about 60° and forms a large image of the arc, so that the full aperture of the substage condenser can be utilized. The results obtained with this condenser in all kinds of work with the micro- scope are so highly satisfactory that no doubt some of those who already have our Large Photomicrographic Camera or Combined Drawing and Photomicrographic Apparatus will wish to replace their condenser with this new form. We are therefore supplying it in mounts to fit these equipments as well. The aspheric condenser should not be used with an arc consuming more than five amperes of current. Illuminants Hand-feed Arc Lamp This lamp is carefully constructed, with screws and gears cut so as to prevent binding even after being thoroughly heated. The carbons can be fed independently or simultaneously. A wide range of adjustment is provided for by ac- curate centering screws, and all adjusting and feeding screws are carefully insulated. Either direct or alternating current can be used, although the former is desirable as it gives greater illumination, is quieter in operation and more easily and accurately controlled. A rheostat must always be used with this lamp to regulate the current. 102