Vessel type	:	Brig
Built by	:	T. Crosby in Bangor
Country of origin	:	U.S.A.
Year	:	1856

From research I learned that the brig Mary Stewart was a 284-ton brig built by T. Crosby in Bangor, Maine in 1856 and was owned by T. Stewart of Bangor. The painting on the right shows what the Mary Stewart looked like when she was a brig. The photograph below shows her after she was re-rigged to a schooner around 1875-76.

A Capt. J. W. Dennison (spelled with 2 'n's, but the register could be wrong) was master of a brig MARY STEWART in 1858. Although spelled differently and the fact that more ships did exist bearing that same name, there is a fair change that it was this vessel on which the octant was used.

Historic details: Mystic Seaport, The museum of America and the Sea, Ms. W. Schnur
Photographs: The Mariners' Museum, Newport News, Virginia, USA.