Henry Gellibrand

Henry Gellibrand, who lived from 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 previous observations by others that had not yet been correctly interpreted. He was the son of the physician Henry Gellibrand and of Mary Faversham, and his younger brother Samuel became a prominent seventeenth-century London bookseller. He devised a method of measuring longitude from eclipses and in 1633 published the mathematical tables of Henry Briggs, logarithms of trigonometric functions, as the Trigonometria Britannica. He was professor at Gresham College, succeeding Edmund Gunter in 1626.