Arc measures

In this context, by arcs is meant sections of lines of latitude or longitude, or sometimes lines oblique to the main lines, that have been accurately measured at some time in the past for use in determining the size and shape of the earth or as part of a national mapping framework.

A list of these, together with some of their attributes is being compiled by J R Smith.

The lines usually covered one or more degrees of latitude (or longitude) with some stretching for over 25 degrees. Among those of note are:

• The arc by Eratosthenes c 230 BC
• The arc by the Chinese 724 AD
• The arc by the Arabs 820 AD
• The first by triangulation - Snellius in Holland 1615
• The arc by Abbé La Caille in South Africa 1751
• The arc through India from north of Sri Lanka to the foothills of the Himalayas of 1800-1840
• The arc from near North Cape in Norway to the Black Sea of 1816-1855 (= the Struve arc)
• The arc along the border between Sweden and Finland of 1737
• The arc along the mountain summits of Ecuador (Peru in those days) of 1736-1744
• The arc through France 1795-1798 (for the determination of the metre)

From Geodaesia or the Art of Surveying. J Love. 1768. Courtesy Jan de Graeve.

Bibliography

See for example:

From Plane to Spheroid. Determining the figure of the Earth from 3000 BC to the 18^th century Lapland and Peruvian survey expeditions. J R Smith. 1986. Landmark Enterprises, California. ISBN 0-910845-29-8

A Calendar of Surveying. A P H Werner Australian Surveyor. Series of parts Sept. 1966-June 1968.

Colonel Sir George Everest, CB, FRS, (1790-1866) a celebration of the bicentenary of his birth. Royal Geographical Society, London 1990 ISBN 0-85406-478-8

Everest. The Man and the Mountain.  J R Smith. 1999 Whittles Publishing. ISBN 1-870325-72-9

Erdgestalt, Kosmologie und Weltanschauung. V Bialas. Konrad Wittwer. 1982 ISBN 3-87919-133-6