Nevil Maskelyne

Nevil Maskelyne (October 6th 1732 - February 9th 1811) was a British Astronome , royal astronomer of 1765 with 1811.

Astronomy

The solar eclipse of 1748 makes him a major impression; and after having finished its studies with the Trinity College with Cambridge it is given to be devoted to the Astronomie. It becomes intimate with James Bradley in 1755 and in 1761 it is delegated by the Royal Society to observe the Transit of Venus to Sainte-Hélène. During this voyage, it tries out also the method of the lunar Distance -- the angular variation of the position the the Moon at various time -- for measurements of Longitude S.

In 1765, it succeeds Nathaniel Bliss like royal astronomer, station which it occupies during 46 years until his death in 1811. Its first contribution is has Proposal for Discovering the Annual Parallax off Sirius ( a proposal for the determination of the Parallaxe of Sirius ) published in 1760 in the Philosphical transactions of Royal Society. In the same series of publication, appear its observations on the Venus transit of 1761 and 1769, the Marée S in Sainte-Hélène (1762), of the astronomical observations varied carried out on the same island and with the Barbados.

In 1763, it publishes British Mariner' S Guide ( Guide of the British sailors ). This guide included the suggestion to calculate in advance the lunar distance in a form accessible to the navigators to help them in calculations of longitude. This calculation is a central problem of sea transport at the 18th century. This proposal is born in the form of the Nautical Almanac whose first specimen, valid for the year 1767, appears in 1766. Continuous Nevil during the remainder of its life to supervise the edition of this almanac.

He convinces his government to annually publish his observations. With the assistance of only one assistant, work with the royal Observatoire of Greenwich methodically is organized and carried out. It introduces also several practical improvements such as the Mesure of time in tenth of a second and the replacement of several measuring instruments by more sophisticated versions.

Density of the Earth

See also: Experiment of Schiehallion

In 1772, it suggests with the Royal Society an experiment to determine the Densité of the Ground. Newton notes in its work that the gravity of with the presence of a mountainous mass must deviate a Plumbline but had concluded that measurements to be made asked for an inaccessible detail at the time. The French mathematician Pierre Bouguer makes a first attempt in 1749 but does not arrive at quantitative conclusions on the terrestrial density. Does Maskelyne then propose to measure the Altitude (?) different star S starting from two faces opposite from a mountain. The Schiehallion is selected. Measurement consists in determining the difference in angle between a plumbline and the altitude of a star and to deduce the Latitude from it from the point from observation. Same measurements are taken on the opposite face of the mountain, or the plumbline must be deviated in the other direction. These measurements are compared with measurements of latitude by Triangulation. The estimate of the density of the Montagne makes it possible to derive an estimate from the density of the Earth. The observations are made during several months by Maskelyne itself in 1774 and its results are published in 1775. The announced value is of 4,5 times that of the Eau. The current value accepted is appreciably higher: 5,5.

Geodesy

Maskelyne is also interested in the Géodésie, in particular in measurements of latitude in the Maryland and the Pennsylvania carried out by Charles Mason and Jeremiah Dixon between 1766 and 1768, then with the determination of the relative latitudes of Greenwich and Paris. French side, work is carried out by Jean-Dominique Cassini, Legendre and Méchain; British side, by the general Roy. This Triangulation is the beginning of the trigonometrical survey which will be extended to all the Great Britain the following years. Its observations are published in 4 volumes of 1776 with 1811.

Maskeline and Harrison

Maskelyne east depicts very negatively in the book of Dava Sobel. A long quarrel indeed opposed it to the Horloger John Harrison on the problem of the precise determination of longitude posed by the Longitude Act. While Harrison provides a method well and an instrument more precise than than proposed Maskelyne, the use of the lunar Distance is cheaper and will at sea remain preferred for the calculation of longitudes during the next century. Observations and calculations of Maskelyne being based on the Meridian of Greenwich which will be proposed and adopted like Méridien of reference in 1884.

Amongst other things honor it receives the Médaille Copley in 1755.

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