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 was the son of the physician Henry Gellibrand (1568–1615) and Mary Faversham. His four younger brothers were John, Edward, Thomas and Samuel. Samuel Gellibrand, became a prominent seventeenth century London bookseller.
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.
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- Henry Plomer (1907) A Dictionary of the Booksellers and Printers who Were at Work in England, Scotland and Ireland from 1641 to 1667
- Michael Hoskin, The Cambridge Concise History of Astronomy (2003), p. 150.
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- 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.