A double T-Frame Octant, by Spencer Browning & Co., London, circa 1840, complete with all filters, sighting tubes and degree scale housed in a mahogany wedge-shaped case with paper label attached to interior lid 'G.B.H. Filbri Jr: {Amsterdam, Netherlands}, and trade label 'Thomas C. Sargent, Rotherhithe, London', includes two letters, including a response from the National maritime Museum, Greenwich, London, England, envelope dated 18 Nov 1966, the case 12.5 cm high, 28 cm wide