Henry Gellibrand

Henry Gellibrand (1597 to 1637) was an English mathematician known for his work on the Earth's magnetic field. He discovered that magnetic declination is not constant but changes over time, announcing this in 1635 on the basis of earlier observations by others that had not yet been correctly interpreted. He also devised a method for measuring longitude from eclipses. The mathematical tables of Henry Briggs, logarithms of trigonometric functions, were published by Gellibrand in 1633 as Trigonometria Britannica. He was professor at Gresham College, succeeding Edmund Gunter in 1626. The son of the physician Henry Gellibrand and Mary Faversham, he had four younger brothers, one of whom, Samuel Gellibrand, became a prominent seventeenth century London bookseller. He was buried at St Peter le Poer, a London church demolished in 1907.