Thatcher's Calculating Instrument, patd. by Edwin Thatcher November 1st. 1881, no. 1740, serial no. 773, with inner sliding cylinder, outer rotating "envelope" with printed scales divided by W.F. Stanley, London, 1882, lacquered brass fittings, and mahogany base wd. 21 1/2 in., in mahogany case with label of Keuffel & Esser Co., Manufacturers of Mathematical & Surveying Instruments, 127 Fulton St. & 42 Ann St., New York.