Measurement of longitude In 1760 the
Royal Society appointed Maskelyne as an astronomer on one of their expeditions to observe the 1761
transit of Venus. He and the mathematician
Robert Waddington were sent to the island of
Saint Helena in the
South Atlantic. This was an important observation since accurate measurements would allow the accurate calculation of Earth's distance from the Sun, which would in turn allow the actual rather than the relative scale of the
Solar System to be calculated. This would allow, it was argued, the production of more accurate astronomical tables, in particular those predicting the motion of the Moon. Bad weather prevented observation of the transit, but Maskelyne used his journey to trial a method of determining
longitude using the position of the moon, which became known as the
lunar distance method. He returned to England, resuming his position as
curate at
Chipping Barnet in 1761, and began work on a book, publishing the lunar-distance method of longitude calculation and providing tables to facilitate its use in 1763 in ''The British Mariner's Guide'', which included the suggestion that to facilitate the finding of
longitude at sea, lunar distances should be calculated beforehand for each year and published in a form accessible to navigators. On 26 February 1765 he had been appointed Astronomer Royal The Board of Longitude therefore decided that rewards should be given to Harrison (£10,000), Mayer (£3000, posthumously) and others involved in helping to develop the lunar-distance method. Harrison was told that a further reward of £10,000 would be forthcoming if he could demonstrate the replicability of his watch. Although Harrison and his son later accused Maskelyne of bias against the timekeeping method, charges repeated by authors such as
Dava Sobel and
Rupert Gould, Maskelyne never submitted a method or an idea of his own for consideration by the Board of Longitude. He was to play a significant role in having
marine timekeepers, as well as the lunar-distance method, developed, tested and used on board voyages of exploration.
Measurement of latitude Maskelyne took a great interest in various
geodetical operations, including the measurement of the length of a degree of latitude in
Maryland and
Pennsylvania,
Schiehallion experiment In 1772 Maskelyne proposed to the
Royal Society what was to become known as the
Schiehallion experiment (named after the Scottish mountain on which it was performed), for the determination of the
Earth's density using a
plumb line. He was not the first to suggest this,
Pierre Bouguer and
Charles-Marie de la Condamine having attempted the same experiment in 1738 in the
Andes. Maskelyne performed his experiment in 1774 on
Schiehallion in
Perthshire, Scotland, the mountain being chosen due to its regular conical shape which permitted a reasonably accurate determination of its volume. The apparent difference of
latitude between two stations on opposite sides of the mountain were compared with the real difference of latitude obtained by
triangulation. From Maskelyne's observations
Charles Hutton deduced a density for the earth 4.5 times that of water (the modern value is 5.515). ==Other work==