Isaac Dalby (1744 – 16 October 1824) was an English mathematician, surveyor and teacher. He was involved in the

Principal Triangulation of Great Britain The Principal Triangulation of Britain was the first high-precision triangulation survey of the whole of Great Britain and Ireland, carried out between 1791 and 1853 under the auspices of the Board of Ordnance. The aim of the survey was to estab ...

, the first high-precision

trigonometric Trigonometry () is a branch of mathematics concerned with relationships between angles and side lengths of triangles. In particular, the trigonometric functions relate the angles of a right triangle with ratios of its side lengths. The field ...

survey of Great Britain.

Life

Dalby was born in Gloucestershire in 1744. He attended a local school, and was expected to be a clothworker; but having taught himself mathematics, he secured the post of usher in a country school. After three years he opened his own school. The venture failed, and in 1772 he arrived in London, and obtained an appointment as teacher of arithmetic in Archbishop Tenison's School in

Lambeth Lambeth () is a district in South London, England, which today also gives its name to the (much larger) London Borough of Lambeth. Lambeth itself was an ancient parish in the county of Surrey. It is situated 1 mile (1.6 km) south of Charin ...

. Afterwards he was employed by

Topham Beauclerk Topham Beauclerk ( ; 22 December 1739 – 11 March 1780) was a celebrated English wit and a friend of Samuel Johnson and Horace Walpole. Early life Topham Beauclerk was born on 22 December 1739 in Pall Mall, London. He was the only son of Lord ...

in making astronomical observations, in a building which the latter had erected for the purpose; he was also librarian of Beauclerk's large library. This arrangement was broken up by the death of Beauclerk in 1780; in the following year Dalby was appointed mathematics master in a naval school at Chelsea, which later failed. In 1787 he was recommended by

Jesse Ramsden Jesse Ramsden Fellow of the Royal Society, FRS FRSE (6 October 1735 – 5 November 1800) was a British mathematician, astronomy, astronomical and scientific instrument maker. His reputation was built on the engraving and design of dividing engine ...

, the scientific instrument maker, to General

William Roy Major-General William Roy (4 May 17261 July 1790) was a Scottish military engineer, surveyor, and antiquarian. He was an innovator who applied new scientific discoveries and newly emerging technologies to the accurate geodetic mapping of Gr ...

, whom he assisted from 1787 to 1790 in the Anglo-French survey to connect the

Greenwich meridian The Greenwich meridian is a prime meridian, a geographical reference line that passes through the Royal Observatory, Greenwich, in London, England. From 1884 to 1974, the Greenwich meridian was the international standard prime meridian, ...

and the

Paris meridian The Paris meridian is a meridian line running through the Paris Observatory in Paris, France – now longitude 2°20′14.02500″ East. It was a long-standing rival to the Greenwich meridian as the prime meridian of the world. The "Paris meri ...

. He was engaged at a later period with Colonel Edward Williams and Captain

William Mudge William Mudge (1762–1820) was an English artillery officer and surveyor, born in Plymouth, an important figure in the work of the Ordnance Survey. Life William Mudge was a son of Dr. John Mudge of Plymouth, by his second wife, and grandson ...

to work on the trigonometrical survey of England and Wales. In 1799 he was appointed first professor of mathematics in the senior department of the Royal Military College, High Wycombe, which subsequently moved to

Farnham Farnham is a market town and civil parish in Surrey, England, around southwest of London. It is in the Borough of Waverley, close to the county border with Hampshire. The town is on the north branch of the River Wey, a tributary of the ...

in Surrey, and later became the

Royal Military College, Sandhurst The Royal Military College (RMC) was a United Kingdom, British military academy for training infantry and cavalry Officer (armed forces), officers of the British Army, British and British Indian Army, Indian Armies. It was founded in 1801 at Gre ...

. He held this post for twenty-one years, resigning it in 1820, when old age and infirmity had overtaken him. He was a contributor to '' The Ladies' Diary'', and was an original member of the

Linnean Society of London The Linnean Society of London is a learned society dedicated to the study and dissemination of information concerning natural history, evolution, and Taxonomy (biology), taxonomy. It possesses several important biological specimen, manuscript a ...

. Dalby died at Farnham on 16 October 1824, and was buried there at St Andrew's Church. His wife Lucy died in 1825.

Publications

He published: # ''Account of the late Reuben Burrow's Measurement of a Degree of Longitude and another of Latitude in Bengal'' (London, 1796) # ''Account of the Operations for accomplishing a Trigonometrical Survey of England and Wales, from the commencement in 1784 to the end in 1796'', in 3 volumes (London, 1799) # ''A Course of Mathematics designed for the use of the Officers and Cadets of the Royal Military College'', in 2 volumes (London, 1805) # ''The Longitude of Dunkirk and Paris from Greenwich, deduced from the Triangular Measurement in 1787–1788, supposing the Earth to be an Ellipsis'' (''

Philosophical Transactions of the Royal Society ''Philosophical Transactions of the Royal Society'' is a scientific journal published by the Royal Society. In its earliest days, it was a private venture of the Royal Society's secretary. It was established in 1665, making it the second journ ...

''. abr. xvii. 67, 1791)

References

Attribution * {{DEFAULTSORT:Dalby, Isaac 1744 births 1824 deaths 18th-century English mathematicians 19th-century English mathematicians English surveyors