Henry Gellibrand was an English

English people

The English are a nation and ethnic group native to England, who speak English. The English identity is of early mediaeval origin, when they were known in Old English as the Anglecynn. England is now a country of the United Kingdom, and the majority of English people in England are British Citizens...

 mathematician

Mathematician

A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

. He is known for his work on the Earth's magnetic field

Earth's magnetic field

Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...

. He discovered that magnetic declination

Magnetic declination

Magnetic declination is the angle between magnetic north and true north. The declination is positive when the magnetic north is east of true north. The term magnetic variation is a synonym, and is more often used in navigation...

 – 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

Longitude

Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

, based on eclipse

Eclipse

An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...

s. The mathematical tables of Henry Briggs

Henry Briggs

Henry Briggs may refer to:*Henry Briggs *Henry Briggs , *Henry Shaw Briggs , Union general in the American Civil War...

, consisting of logarithm

Logarithm

The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the power 3: More generally, if x = by, then y is the logarithm of x to base b, and is written...

s of trigonometric function

Trigonometric function

In mathematics, the trigonometric functions are functions of an angle. They are used to relate the angles of a triangle to the lengths of the sides of a triangle...

s, were published by Gellibrand in 1633 as Trigonometria Britannica.

He was Professor at Gresham College

Gresham College

Gresham College is an institution of higher learning located at Barnard's Inn Hall off Holborn in central London, England. It was founded in 1597 under the will of Sir Thomas Gresham and today it hosts over 140 free public lectures every year within the City of London.-History:Sir Thomas Gresham,...

, succeeding Edward Gunter in 1626. He was buried in St Peter Le Poer

St Peter Le Poer

St Peter le Poer was a church on the west side of Broad Street in the City of London. The church, often spelt "St Peter le Poor" was in existence by the end of the twelfth century...

.