TOLLES'S LARGE MICROSCOPE. B.

This instrument is intended to meet the wants of the highest scientific investigation; to attain everything that the microscope can accomplish, without sparing the cost, and to permit the use of all the modern accessory apparatus. Like all of Tolles's' microscopes, it is constructed on the curved arm (Jackson ) model, which Dr. W. B. Carpenter, in his elaborate work on " The Microscope ," fourth edition, 1868, preferred over all other models; and in 1870, at a meeting of the Royal Microscopical Society, of London, still more emphatically approved in special communication, giving his reasons for thus in endorsing it. The instrument is eighteen inches high, weighs about fourteen lbs., thus giving a stability and freedom from tremor that cannot be obtained with stands of little weight. It is of simple construction, with fewer screws and pieces than any other first-class microscope. The curved arm is supported on a steel arbor between two strong brass pillars, made for durability, and not liable to get out of order, and provided with a method of compensation for wear. The arm is easily clamped and held in any position. and is readily removable. Has rack and pinion for coarse, and micrometer screw for fine adjustment for focus; graduated draw tube; sub-stage with rack and pinion, and centring screws for accessory apparatus; plain and concave mirrors, on double. jointed arm, Tolles's thin stage, admitting light of great obliquity, with rectangular movements by screw and rack and pinion, and rotation on the optical axis of about 325°,—all that is essentially necessary. Price, $225.

N. B. A newly devised mechanical stage, with rectangular movements throughout one inch of field, with rotation 360° in the optical axis. Price $200.

The above accessory is designed to attach to the bar holding the mirror while the other end has a fitting with a "Society Screw" which will hold an objective, but what is the function of this apparatus?

For a discussion of the life and work of Robert B. Tolles (1824-1883), see Three American Microscope Builders published by the American Optical Company 1945.