Many other discrepancies occur, but from the mean of the five principal measurements of arcs in Peru, India, France, England, and Lapland, Mr. Ivory has deduced that the figure which most nearly follows this law is an ellipsoid of revolution whose equatorial radius is 3962·824 miles, and the polar radius 3949·585 miles. The difference, or 13·239 miles, divided by the equatorial radius, is 1/299 nearly[3] (N. 128). This fraction is called the compression of the earth, and does not differ much from that given by the lunar inequalities. Since the preceding quantities were determined, arcs of the meridian have been measured in various parts of the globe, of which the most extensive are the Russian arc of 25° 20ʹ between the Glacial Sea and the Danube, conducted under the superintendence of M. Struve, and the Indian arc extended to 21° 21ʹ, by Colonel Everest. The compression deduced by Bessel from the sum of ten arcs is 298-3/4, the equatorial radius 3962·802, and the polar 3949·554 miles, whilst Mr. Airy arrives at an almost identical result (3962·824, 3949·585, and 298-83/100) from a consideration of all the arcs, measured up to 1831, including the great Indian and Russian ones. If we assume the earth to be a sphere, the length of a degree of the meridian is 69-14/100 English miles. Therefore 360 degrees, or the whole equatorial circumference of the globe, is 24,899 English miles. Eratosthenes, who died 194 years before the Christian era, was the first to give an approximate value of the earth’s circumference, by the measurement of an arc between Alexandria and Syene.