(b. Bristol Township, Pennsylvania, 1704; d. Philadelphia, Pennsylvania, December 1749)
Godfrey’s major contribution was his invention of the double reflecting quadrant which became generally known as Hadley’s quadrant and is, essentially, the navigational sextant used today. It quickly replaced other instruments for measuring elevation.
Godfrey produced his instrument in October 1730 and had it tested in Delaware Bay and on a voyage to Jamaica. James Logan, the most learned man in Pennsylvania, sent a description of the device to the astronomer royal, Edmond Halley, but received no reply and was soon surprised to find in the Philosophical Transactions of the Royal Society an account of an almost identical instrument invented by John Hadley, a fellow of the Royal Society. Fearing that Godfrey had unjustly lost credit for his invention, Logan collected affidavits on the chronology of the invention, obtained reports from Jamaica, and wrote again to Halley as well as to several of his friends in the Royal Society. Godfrey, too, fowarded a presentation of his case. The society heard these papers and published Logan’s account in the next volume of Philosophical Transactions. Hadley clearly had the priority of publication, but Godfrey’s invention was solely his own in a day when identical independent inventions were not easily accepted.
Godfrey was an important member of a small intellectual circle in Philadelphia. A glazier by trade, he developed an impressive command of mathematics and, with the help of Logan and Logan’s extensive library, learned and used Latin. He was a founding member of Benjamin Franklin’s 1727 Junto and a director of the Library Company of Philadelphia from its establishment in 1731. The 1743 American Philosophical Society included Godfrey as its “Mathematician.”
Godfrey published almanacs from 1729 to 1736. He also contributed mathematical questions and answers, astronomical data, and general essays to the Pennsylvania Gazette and the Pennsylvania Journal. In 1740 he advertised instruction in navigation, astronomy, and mathematics. To fix the longitude of Philadelphia on his 1755 General Map of the Middle British Colonies, Lewis Evans used astronomical observations that he made with Godfrey.
Godfrey issued An Almanack for the Year 1730 (Philadelphia, 1729) and other annual almanacs until The Pennsylvania Almanack for 1737 (Philadelphia, 1736). He made occasional contributions to the Pennsylvania Gazette and the Pennsylvania Journal.
On the quadrant, the key writings are Godfrey’s letter to the Royal Society (9 Nov. 1732), in the Royal Society library (microfilm copy in American Philosophical Society Library), and James Logan, “An Account of Mr. T. Godfrey’s Improvement of Davis’s Quadrant,” in Philosophical Transactions of the Royal Society, 38 (1733–1734), 441–450. Both publications and other Logan letters appear also in American Magazine, I (1757–1758), 475–480, 529–534. Other related Logan correspondence is in the Royal Society library and in the Logan Papers of the Historical Society of Pennsylvania.
Nathan Spencer, “Essay of a Memorial of Thomas Godfrey, September 8, 1809,” MS., American Philosophical Society, is helpful. Frederick B. Tolles, James Logan and the Culture of Colonial Pennsylvania (Boston, 1957), pp. 202–204, is a brief but understanding account of Logan.