About development of geodesy

Geodesy (“dividing the land” in Greek) is a science of the Earth, the establishment of the size and the shape of the parts of its surface.

The Eratosthenes schemes for establishing the diameter of the Earth.

In the Middle Ages the science of Greeks and Arabs was forgotten, only the great discoveries of the 16th century seafarers started the new attempts to establish the dimensions of the Earth. For establishing the size of the Earth it was necessary to know the length of one degree of the meridian arc.

The beginning of the 17th century may be considered the new era in the history of the measurement of the degree when the Dutch scientist Willebrord Snellius (born Snel van Royen) (1580–1626) began to use the triangulation method which in 1533 Gemma Frisius (1508–1555), also Dutch, had described. The triangulation method is based on the qualities of the triangles. In forming the net of triangles side by side, it is necessary to measure only some base lines and angles, the rest can be calculated. This method allows us to establish exactly the meridian arc, being thousands of kilometers long.

Triangulation, the drawing from the 16th century.

The next step was made by the French astronomer Jean Picard (1642–1727). In the years 1669–1670 he measured the arc between the towns Paris and Amiens commissioned by the French Academy of Sciences which was founded a little bit earlier. One degree of the meridian arc was measured as 57,060 toises or 111,212 km (the real length being 111,18 km).

When at the end of the 17th century Newton had created his gravitation theory, relying on it, it was possible to suppose that the Earth was evidently an even sphere. In the18th and 19th centuries it became especially important for astronomers, geodesists and other scientists to establish the exact shape and the size of the Earth. It became clear that the Earth has the shape of a sphere suppressed on the poles but it was necessary to determine the parameters of the mathematical model of the Earth – spheroid – more exact.

The expeditions organized by the French academy for the measurement of the degree to Peru led by Louis Godin (1704–1760) and to Lapland led by Pierre Louis Moreau de Maupertuis (1698–1759) in the 1730s established that the Earth is oblate at the poles and consequently the Newton’s gravitation theory held.

The 18th century French surveyor in Peru

Commissioned by the revolutionary legislative assembly in 1792 under the leadership of Jean-Baptiste Delambre (1749–1822) “The Great French Degree Measurement” was started with the purpose of establishing the exact length of the meter, the basic unit of the new unified system of measurement. It had to be the 1:40,000,000 part of the meridian passing through Paris. The work lasted until 1797 and 9 degrees 40 minutes were measured.

The honor for working out the theory of the geodetical and astronomical aspects of scientific degree measurement belongs to F. W. Bessel (1784–1846) who was the leader of degree measurement in Eastern Prussia and to C. F. Gauss (1777–1855) who was the leader of degree measurement in Hannover. Partially F. G. W. Struve (1793–1864) shares the merits. Bessel derived the most probable dimensions of the Earth ellipsoid in 1841.