Henry GellibrandBorn 17 Nov 1597; died 16 Feb 1636 at age 38.English astronomer and mathematician who co-discovered (with John Marr) the geomagnetic secular variation. This refers to the magentic declination of the earth's magnetic field, the angle between magnetic north and true north, changing on a long-term time scale over years. He detected the direction of a compass needle in London had changed by seven degrees over a period of a half-century.He became professor of astronomy at Gresham College, London on 2 Jan 1627. His navigation textbooks helped improve English navigation at the time.Usingmanuscripts left unfinished whenhis friend Henry Briggsdied (1630), he completed volume two of Briggs'sTrigonometrica Britannica, in 1633.GellibrandpublishedA Discourse Mathematicall on the Variation of the Magneticall Needle, in 1635. He died the following year, at age 39.«[Image: Title page of Gellibrand's Discourse (1635).] |
