Henry Gregory was a mathematical

Mathematical instrument

A mathematical instrument is a tool or device used in the study or practice of mathematics.Most instruments are used within the field of geometry, including the ruler, dividers, protractor, set square, compass, ellipsograph and opisometer...

 and optical instrument maker. He was in business from c. 1750–1792 from premises in Francis Court, Clerkenwell

Clerkenwell

Clerkenwell is an area of central London in the London Borough of Islington. From 1900 to 1965 it was part of the Metropolitan Borough of Finsbury. The well after which it was named was rediscovered in 1924. The watchmaking and watch repairing trades were once of great importance...

, London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

 and an establishment known as "The Azimuth Compass" in Leadenhall Street

Leadenhall Street

Leadenhall Street is a street in the City of London, formerly part of the A11. It runs east from Cornhill to Aldgate, and west vice-versa. Aldgate Pump is at the junction with Aldgate...

, London. His company later became known as Gregory and Son.

Gregory manufactured navigational instruments, including quadrants

Quadrant (instrument)

A quadrant is an instrument that is used to measure angles up to 90°. It was originally proposed by Ptolemy as a better kind of astrolabe. Several different variations of the instrument were later produced by medieval Muslim astronomers.-Types of quadrants:...

 of the type invented by John Hadley

John Hadley

John Hadley was an English mathematician, inventor of the octant, a precursor to the sextant, around 1730.He was born in Bloomsbury, London, to Katherine FitzJames and George Hadley....

 and compasses

Compass

A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

. One of his azimuth compasses traveled with the explorer James Cook

James Cook

Captain James Cook, FRS, RN was a British explorer, navigator and cartographer who ultimately rose to the rank of captain in the Royal Navy...

 on his second voyage to the southern Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

in 1772–1775. An azimuth compass is a compass fitted with vertical sights, used to take the magnetic azimuth of a star or planet.