William Gascoigne (scientist)

William Gascoigne (1612 – 2 July 1644) was an English astronomer, mathematician and maker of scientific instruments from Middleton, Leeds who invented the micrometer. He was one of a group of astronomers in the north of England who followed the astronomy of Johannes Kepler which included, Jeremiah Horrocks and William Crabtree.

Gascoigne was born in Middleton, Leeds in 1611, the son of a minor country gentleman. His father was Henry Gascoigne, Esq., of Thorpe-on-the-Hill in the parish of Rothwell, near Leeds, Yorkshire. His mother was Margaret Jane, daughter of William Cartwright. Little is known of his early life. He claimed he was educated at the University of Oxford, although no record of this has been found.

In the late 1630s, Gascoigne, was working on a Keplerian optical arrangement when a thread from a spider’s web happened to become caught at exactly the combined optical focal points of the two lenses. When he looked through the arrangement Gascoigne saw the web bright and sharp within the field of view. He realized that he could more accurately point the telescope using the line as a guide, and went on to invent the telescopic sight by placing crossed wires at the focal point to define the centre of the field of view. He then added this arrangement to a sextant modelled on the instrument used by Tycho Brahe, although Tycho’s sextant was only a naked-eye instrument. Gascoigne's sextant was five feet in radius, and measured the distance between astronomical bodies to an unprecedented degree of accuracy. Gascoigne then realised that by introducing two points, whose separation could be adjusted using a screw, he could measure the size of the image enclosed by them. Using the known pitch of the screw, and knowing the focal length of the lens producing the image, he could work out the size of the object, such as the Moon or the planets, to a hitherto unattainable degree of accuracy.

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