At this time it had become clear from mechanical considerations, more especially such as had been deduced by Newton, that, since the earth is a rotating body, her form cannot be that of a perfect sphere, but must be that of a spheroid, oblate or flattened at the poles. It would follow, from this, that the length of a degree must be greater near the poles than at the equator. The French Academy resolved to extend Picard's operation, by prolonging the measures in each direction, and making the result the basis of a more accurate map of France. Delays, however, took place, and it was not until 1718 that the measures, from Dunkirk on the north to the southern extremity of France, were completed. A discussion arose as to the interpretation of these measures, some affirming that they indicated a prolate, others an oblate spheroid; the former figure may be popularly represented by a lemon, the latter by an orange. To settle this, the French Government, aided by the Academy, sent out two expeditions to measure degrees of the meridian--one under the equator, the other as far north as possible; the former went to Peru, the latter to Swedish Lapland. Very great difficulties were encountered by both parties. The Lapland commission, however, completed its observations long before the Peruvian, which consumed not less than nine years. The results of the measures thus obtained confirmed the theoretical expectation of the oblate form. Since that time many extensive and exact repetitions of the observation have been made, among which may be mentioned those of the English in England and in India, and particularly that of the French on the occasion of the introduction of the metric system of weights and measures. It was begun by Delambre and Mechain, from Dunkirk to Barcelona, and thence extended, by Biot and Arago, to the island of Formentera near Minorea. Its length was nearly twelve and a half degrees. Besides this method of direct measurement, the figure of the earth may be determined from the observed number of oscillations made by a pendulum of invariable length in different latitudes. These, though they confirm the foregoing results, give a somewhat greater ellipticity to the earth than that found by the measurement of degrees. Pendulums vibrate more slowly the nearer they are to the equator. It follows, therefore, that they are there farther from the centre of the earth. From the most reliable measures that have been made, the dimensions of the earth may be thus stated: Greater or equatorial diameter..............7,925 miles. Less or polar diameter......................7,899 " Difference or polar compression............. 26 " Such was the result of the discussion respecting the figure and size of the earth. While it was yet undetermined, another controversy arose, fraught with even more serious consequences. This was the conflict respecting the earth's position with regard to the sun and the planetary bodies.