De Maupertuis The degree measurements by de Maupertuis in the Tornionlaakso Valley 1736-1737
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The Enlightenment
 The theory
The results
Later research


The theory

To settle the dispute of the shape of the earth two sets of measurements were needed in the 18th century. First the length of the arch on the ground had to be measured and secondly the corresponding central angle of this arch had to be defined.

The measurement of the length of the arch is made by measuring by degrees where triangular measurement on the ground is used. The central angle is measured with the help of stellar determination of the position. Supposing the earth is all round at the Equator and the arctic circle, the central angle of a certain size is equivalent to a distance of a similar length on the ground. If the earth is flattened by its poles the distance is longer at the arctic circle. If the earth is stretched by its poles the distance is longer at the Equator.

The Dimensions of the Earth

The dimensions of the earth, radius a of the equator circle and flattening ratio f of the meridian ellipse can be determined by measuring by degrees of two meridian arches. The figure shows that the arch corresponding to a central angle of the same size is longer at the poles than at the Equator areas. (Kakkuri, The Dimensions of the Earth, p. 160)

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