Large 18th C. mariner's quadrant with limbs of ebony, scales of ivory, and brass furniture. The arc is divided to 95 degrees and is signed in script "SBR" denoting the prolific makers, Spencer, Browning & Rust, of London. This characteristically large instrument has a flat brass index arm measuring over 18 inches long. Note the early form thumb screw stop, ivory vernier scale marked from 0 to 20 arc minutes, backsight, and triple sun shades indicative of manufactory soon after 1780. (Private Collection. Ex. West Sea Co.)