From Carpenter's The Microscope and its Revelations, first American edition, 1855.

Mr. Charles A. Spencer of Canastota, New York, has manufactured a microscope of great excellence, the objectives of which will bear comparison with the best of foreign construction. His common angle of aperture for 1/4 inch objectives is 135°; for 1/8 inch, 170°, and for 1/12 and 1/16 inch, 176°. This. is believed to be the largest angle ever given to an object-glass, and for sharpness of definition and power of penetration, they are unexcelled by any of foreign make.

To Mr. Spencer is due the credit of having first resolved, with lenses of his own construction, the fine markings on the Navicular Spencerii and Grammatophora Subtilissima: these minute shells have since been adopted by microscopists as test-objects for the highest powers. The Navicula Spencerii, will exhibit one set of lines with Mr. Spencer's 1/4 th-inch object-glass: both sets with the 1/8 th-inch. The Glrammatophora Subtilissima is a good test for a 1/12 th or 1/16 th.

Of several microscopes made by Mr. Spencer, two or three only will be here noticed. His first-class or best instrument is mounted on trunnions, and embraces all the acknowledged improvements, in form and stage, whereby the greatest steadiness and freedom from tremor are secured. The price of this instrument with all the accessories and a full set of object-glasses will approach $350 (Fig, 426)