Richard Dunthorne
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Richard Dunthorne (1711 – 3 March 1775) was an English
astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...
and surveyor, who worked in
Cambridge Cambridge ( ) is a university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cambridge bec ...
as astronomical and scientific assistant to
Roger Long Roger Long (1680 – 16 December 1770) was an English astronomer, and Master of Pembroke College, Cambridge between 1733 and 1770. Roger Long was the son of Thomas Long of Croxton, Norfolk. He was educated at Norwich School and later admitted ...
(master of
Pembroke Hall Pembroke College (officially "The Master, Fellows and Scholars of the College or Hall of Valence-Mary") is a constituent college of the University of Cambridge, England. The college is the third-oldest college of the university and has over 700 ...
and Lowndean Professor of Astronomy and Geometry), Library of St John's College, Cambridge, 2008; and Philosophical Transactions (Abridgement Series) (1809). and also concurrently for many years as surveyor to the Bedford Level Corporation.


Life and work

There are short biographical notes of Dunthorne, one in the Philosophical Transactions (Abridgement Series, published 1809) (unsigned), Philosophical Transactions (Abridgement Series) (1809). another in the 'Dictionary of National Biography' (vol.16), and a third by W T Lynn. Dunthorne was born in humble circumstances in
Ramsey, Cambridgeshire Ramsey is a market town and civil parish in the Huntingdonshire district of Cambridgeshire, England. The town is about north of Huntingdon. Ramsey parish includes the settlements of Ramsey Forty Foot, Ramsey Heights, Ramsey Mereside, Ramsey Ho ...
, where he attended the free grammar school. There he attracted the notice of
Roger Long Roger Long (1680 – 16 December 1770) was an English astronomer, and Master of Pembroke College, Cambridge between 1733 and 1770. Roger Long was the son of Thomas Long of Croxton, Norfolk. He was educated at Norwich School and later admitted ...
(later Master of Pembroke Hall, Cambridge), whose protégé Dunthorne became. Dunthorne moved to Cambridge where Long first appointed him as a "footboy", and where he received some further education (though this does not seem to have been regular university education). Dunthorne then "managed" a preparatory school in Coggeshall, Essex, and later returned to Cambridge where Long obtained for him an appointment as a "butler" at Pembroke Hall, an office that Dunthorne retained for the rest of his life. Here Dunthorne's main activity seems to have been in assisting Long in astronomical and scientific work. Dunthorne also held an appointment for some years, concurrently with his work with Long, as superintendent of works of the
Bedford Level Bedford is a market town in Bedfordshire, England. At the 2011 Census, the population of the Bedford built-up area (including Biddenham and Kempston) was 106,940, making it the second-largest settlement in Bedfordshire, behind Luton, whilst th ...
Corporation, responsible for water management in
the Fens The Fens, also known as the , in eastern England are a naturally marshy region supporting a rich ecology and numerous species. Most of the fens were drained centuries ago, resulting in a flat, dry, low-lying agricultural region supported by a ...
; he began this work several years" before 1761, continuing into the 1770s. In this role, Dunthorne was concerned in a survey of the
fen A fen is a type of peat-accumulating wetland fed by mineral-rich ground or surface water. It is one of the main types of wetlands along with marshes, swamps, and bogs. Bogs and fens, both peat-forming ecosystems, are also known as mires ...
s in Cambridgeshire, and he also supervised construction of locks near Chesterton on the
River Cam The River Cam () is the main river flowing through Cambridge in eastern England. After leaving Cambridge, it flows north and east before joining the River Great Ouse to the south of Ely, at Pope's Corner. The total distance from Cambridge to ...
. Dunthorne's association with Long remained lifelong, and in the end Dunthorne acted as executor of Long's will.


Lunar tables

Dunthorne published a book of astronomical tables in 1739 entitled ''Practical Astronomy of the Moon: or, new Tables... Exactly constructed from Sir Isaac Newton's Theory, as published by Dr Gregory in his Astronomy, London & Oxford, 1739''. These tables were modelled on
Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, Theology, theologian, and author (described in his time as a "natural philosophy, natural philosopher"), widely ...
's
lunar theory Lunar theory attempts to account for the motions of the Moon. There are many small variations (or perturbations) in the Moon's motion, and many attempts have been made to account for them. After centuries of being problematic, lunar motion can now ...
of 1702, to facilitate testing Newton's theory. In a 1746 letter to the keeper of Cambridge's Woodwardian Museum, Dunthorne wrote: "After I had compared a good Number of modern Observations made in different Situations of the Moon and of her Orbit in respect of the Sun, with the Newtonian Theory . . . I proceeded to examine the mean Motion of the Moon, of her Apogee, and Nodes, to see whether they were well represented by the Tables for any considerable Number of Years . . . " On the basis of his observations, Dunthorne proposed some adjustments of the numerical terms of the theory.


Acceleration of the Moon

Dunthorne is particularly remembered for his study of the phenomenon of the changing apparent speed of the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
in its
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
.
Edmond Halley Edmond (or Edmund) Halley (; – ) was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena in 1676–77, H ...
in about 1695 had already suggested on the basis of comparison between contemporary observations and on the other hand ancient records for the timing of ancient eclipses, that the Moon was very gradually accelerating in its orbit. (It was not yet known in Halley's or in Dunthorne's time that what is actually happening is a slowing-down of the Earth's rate of rotation – see Ephemeris time.) Dunthorne's computations, based in part on records of ancient accounts of eclipses, confirmed the apparent acceleration; and he was the first to quantify the effect, which he put at +10" (arcseconds/century^2) in terms of the difference of lunar longitude. Dunthorne's estimate is not far from those assessed later, e.g. in 1786 by de Lalande and still not very far away from the values from about 10" to nearly 13" being derived about a century later.


Astronomical publications and observations

Dunthorne published papers in the ''Philosophical Transactions'', including "On the motion of the Moon" (1746), "On the acceleration of the Moon" (1749), and the letter "Concerning comets" in 1751. He observed the transits of
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
in 1761 and 1769, and also published tables on the motion of
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousand ...
's satellites in 1762.


Work for the Nautical Almanac

On 18 July 1765 the
Board of Longitude The Commissioners for the Discovery of the Longitude at Sea, or more popularly Board of Longitude, was a British government body formed in 1714 to administer a scheme of prizes intended to encourage innovators to solve the problem of finding lon ...
(effectively led by
Nevil Maskelyne Nevil Maskelyne (; 6 October 1732 – 9 February 1811) was the fifth British Astronomer Royal. He held the office from 1765 to 1811. He was the first person to scientifically measure the mass of the planet Earth. He created the ''British Nau ...
) appointed Dunthorne as the first "Comparer of the Ephemeris and Corrector of the Proofs" for the (then still future) Nautical Almanac and Astronomical Ephemeris. The first issue appeared with data for the year 1767, breaking new ground in providing computational tools to enable mariners to use lunar observations to find their longitude at sea. Dunthorne worked as sole comparer for the first three issues, with data for 1767–69, and afterward continued as one of several comparers until the issue for 1776. Dunthorne also contributed a method for clearing nautical lunar observations of the effects of refraction and parallax, for the purpose of finding the longitude at sea, and Maskelyne included this in his 'Tables requisite to be used with the Nautical Ephemeris', an accessory volume published to accompany the Nautical Almanac. It is also reported that Dunthorne in 1772 received from the Board of Longitude a reward of £50 for this contribution towards shortening the tedious calculations involved in "clearing the lunar distance" (at the same time as a similar reward was given to the contributor of an alternative method for the same purpose, Israel Lyons, 1739–1775). Improvements were added and "Dunthorne's improved method" was included in an edition of 1802. In this area of celestial navigation, Dunthorne has been credited as the first to apply trigonometrical formulae for the general spherical triangle to the reduction of lunar distances and to give auxiliary tables for that purpose.


Benefactions in Cambridge

Dunthorne planned and funded the construction of an
observatory An observatory is a location used for observing terrestrial, marine, or celestial events. Astronomy, climatology/meteorology, geophysical, oceanography and volcanology are examples of disciplines for which observatories have been constructed. ...
in 1765. The observatory was situated on the Shrewsbury Gate of St. John's College. Dunthorne also gave astronomical instruments to the college.F J M Stratton (1949)
"The History of the Cambridge Observatories"
in ''Annals of the Solar Physics Observatory, Cambridge, Vol.1'' (Cambridge, 1949)
at page 2
The observatory remained in place until its closure in 1859. A contemporary, Rev. William Ludlam (in charge of the St John's College observatory from 1767), described Dunthorne as one "who without the benefit of an Academical education is arrived at such a perfection in many branches of learning, and particularly in Astronomy, as would do honour to the proudest Professor in any University . . . he joined to a consummate excellence in his profession a generosity without limit in the exercise of it."See also "The Eagle" (1888): "Founders and Benefactors of St Johns College", a
page 8
Dunthorne died at Cambridge. The crater Dunthorne on the Moon is named after him.


Dunthorne's publications

*Richard Dunthorne (1739), ''Practical Astronomy of the Moon: or, new Tables... Exactly constructed from Sir Isaac Newton's Theory, as published by Dr Gregory in his Astronomy'', London & Oxford, 1739. *Richard Dunthorne (1746)
"A Letter from Mr. Richard Dunthorne, to the Rev. Mr. Charles Mason, F. R. S. and Woodwardian Professor of Nat. Hist. at Cambridge, concerning the Moon's Motion"
''Philosophical Transactions'', Volume 44 (1746), pp.412–420.
*Richard Dunthorne (1749)
"A Letter from the Rev. Mr. Richard Dunthorne to the Reverend Mr. Richard Mason F. R. S. and Keeper of the Wood-Wardian Museum at Cambridge, concerning the Acceleration of the Moon"
''Philosophical Transactions'', Vol. 46 (1749–1750) No. 492, pp. 162–172.
-- also given in Philosophical Transactions (abridgements) (1809)
vol.9 (for 1744–49), pp. 669–675
as "On the Acceleration of the Moon, by the Rev. Richard Dunthorne".
*Richard Dunthorne (1751)
"A Letter from Mr. Rich. Dunthorne to the Rev. Dr. Long, F. R. S. Master of Pembroke-Hall in Cambridge, and Lowndes's Professor of Astronomy and Geometry in That University, concerning Comets"
Philosophical Transactions, Volume 47 (1751), pp. 281–288.
*Richard Dunthorne (1761)
"Elements of New Tables of the Motions of Jupiter's Satellites: In a Letter to the Reverend Charles Mason, D. D. Woodwardian Professor in the University of Cambridge, and F. R. S. from Mr. Richard Dunthorne"
Philosophical Transactions, Volume 52 (1761), pp. 105–107.


Notes and references


Other sources

* *Mary Croarken (2002)
"Providing Longitude for All"
Journal of Maritime Research (National Maritime Museum, Greenwich), September 2002.
*Library of St John's College, Cambridge, (online article) mentioning Dunthorne in connection with his astronomically-related gifts to the college 1764–5, including
regulator clock by John Shelton
*W T Lynn (1905)
"Richard Dunthorne"
''The Observatory'',vol.28 (1905), pp.215–6.
*Philosophical Transactions (Abridgement Series) (1809)
vol.9 (for 1744–49) pages 669–70
(unsigned) biographical note about Richard Dunthorne.
*Frédéric Marguet (Capitaine de Vaisseau) (1931), "Histoire générale de la navigation du XVe au XXe siècle", Paris 1931, chapter 7
at page 242
*
/cite> * ttp://curious.astro.cornell.edu/question.php?number=124 Curious About Astronomybr>"Right" Answers
* * Maskelyne, N. (1767), Nautical Almanac and Astronomical Ephemeris, editions for 1767 and 1768; (see especially Maskelyne'
Preface
acknowledging Dunthorne.
{{DEFAULTSORT:Dunthorne, Richard 18th-century British astronomers Amateur astronomers 1711 births 1775 deaths People from Ramsey, Cambridgeshire