Thomas Godfrey




NA/Mid-Atlantic region


Anglo-American Atlantic World (1641-1750)








Glazier, mathematician, and astronomer.

Godfrey's fame rests on his invention of the octant. Although his circumstances rendered him remote from maritime problems, he is traditionally claimed to have been given to intemperance and to frequenting waterfront taverns. From discussions with seamen he met there, he became familiar with navigational problems. One day while working at Stenton, he observed the double reflection from a piece of glass that had fallen and realized that by means of reflection, it would be possible to draw the image of the sun down to the horizon. Accordingly, he designed an instrument for observing the altitude of the sun or a star from a moving ship at sea, by means of which it was possible to establish the ship's latitude. According to surviving documents, in late October 1730 Godfrey borrowed a backstaff from his acquaintance George Steward, mate on the sloop Trueman, and temporarily attached several pieces of wood and mirror to create a new instrument, which tested successfully. He had a working model made from his design by a fellow worker at the state house, house carpenter Edmund Woolley. The instrument, taken to sea by Steward and the Trueman's shipmaster John Cox, was tested successfully on voyages to Jamaica in November and December and to St. John's, Newfoundland, in February 1731. Godfrey's reflecting quadrant--or octant, as it was later named--was commercially produced and sold in New York during the next few years by Godfrey's acquaintance, mathematical instrument-maker Anthony Lamb.

Logan, greatly impressed with the invention, in 1732 reported it to Edmund Halley, president of the Royal Society of London. At about the same time, however, the society's vice president, John Hadley, announced his claim to the same invention. He demonstrated his instrument before the society and had it patented. Logan's letter was received but not acknowledged, and later that year Godfrey addressed a letter to the society on his own behalf. Godfrey's letter and Logan's earlier letter were read before the society on 31 January 1733 and recorded in its Minutes but not otherwise acknowledged. Godfrey's report to the Royal Society of improvements he had made in another navigational instrument, the mariner's bow, was published in its Philosophical Transactions but not his description of his octant. His invention, however, is now acknowledged to have been made independently, almost simultaneously with Hadley's invention, or possibly slightly before it.

Record ID: 302