18th century Thomas Ripley 20'' octant

18th century Thomas Ripley 20'' mahogany and brass octant with plaque reading: ''Made by Thos Ripley at ye Hermitage Bridge, London, For I....Ian y1 1772'', in wood case. Lacking parts, loss to inlay on bottom, wear and splits from use. Case: 4-1/2''h, 21''l, 18''w. Note: This octant belonged to Captain John A. Burgess of the famous clipper ship David Crockett. Lot contains letters from Persis Pettis Hall, granddaughter of William Henry Pettis, who sailed with Captain John A. Burgess. Captain Burgess was William Henry Pettis's uncle. Literature: American Nautical Art and Antiques, by Jacqueline L. Kranz, illustration on page 121. Provenance: Estate of William Kranker, collector and dealer, Greenport, NY.