Henry Gellibrand (1597–1637) was an English mathematician. He is known for his work on the Earth's magnetic field. He discovered that magnetic declination – the angle of dip of a compass needle – is not constant but changes over time. He announced this in 1635, relying on previous observations by others, which had not yet been correctly interpreted.
He also devised a method for measuring longitude, based on eclipses. The mathematical tables of Henry Briggs, consisting of logarithms of trigonometric functions, were published by Gellibrand in 1633 as Trigonometria Britannica.
- van Helden, Albert; Burr, Elizabeth (1995). "Gellibrand, Henry". The Galileo Project. Rice University. Retrieved 24 October 2011.
- Lloyd Arnold Brown, The Story of Maps (1979), p. 133.
- Michael Hoskin, The Cambridge Concise History of Astronomy (2003), p. 150.
- O'Connor, John J.; Robertson, Edmund F., "Henry Gellibrand", MacTutor History of Mathematics archive, University of St Andrews.
- Hunter, John Aubrey (2000). "Henry Gellibrand". Brief lives. Selected and edited with introduction, glossary and notes by John Buchanan-Brown. Foreword by Michael. Penguin Books. ISBN 978-0-14-043589-4.