method he measured the distance between Alkmaar and Bergen-op-Zoom, using thirty-three triangles. He obtained nearly the same results with Fernel as to the circumference of the earth. Since that time similar work has been going on almost uninterruptedly. In 1669 Picard measured the meridian Amiens—Malvoisine, and from it estimated the circumference of the earth to be 20,541,500 toises or fathoms. Picard's figures were used by Newton in the studies which led to the discovery of the universal law of gravitation. At this point in the investigations the question arose whether the earth is a perfect sphere or a spheroid. In order to solve this problem two expeditions were fitted out, the one to operate in Peru, the other in Lapland. Both occupied several years, completing their labors about 1740. The results obtained settled for all time the relation of the polar to the equatorial axis. Geodetic surveys are, however, still in progress. The most extensive of the older projects was completed by Arago and Biot in 1808, based on the labors of Mechain and Delambre. The meridian measured was that between Dunkirk and Formentera, an island near the Mediterranean coast of Spain. This arc extended over twelve degrees and twenty-two minutes. The principal object of this survey was to establish a fixed unit of linear measure for the meter, which was to be the one ten-millionth part of the earth's meridian quadrant. This is the so-called métre des Archives, a platinum rod deposited in Paris. Although it is now known that it is not strictly correct there is no probability that it will ever be changed, as it has become the foundation of the metric system. In 1861 general Baeyer proposed the measurement of the meridian Christiania-Palermo. The work was to be carried out by the European governments conjointly. The proposal led to a general conference of savants in Berlin in 1862. A permanent commission was organized under the presidency of General Baeyer. Another conference was held in Berlin in 1867, all the governments of Europe, except Turkey, having in the interval promised cooperation. Since then meetings of the commission have been held every two or three years, their object being the continuation and revision of the French measurements to Algiers, a complete triangulation of the Mediterranean Sea, the measurement of a parallel through Central Africa from Cape Town to Upper Egypt, and to take such other observations as usually fall within the scope of a geodetic survey. For many years the United States government has been engaged in measuring the ninety-eighth parallel which extends from the southern point of Texas to the Canadian border. Strange as it may seem in view of what they accomplished in several directions,
- The Prussian general Baeyer, who died in 1885 at the age of ninety-one, probably devoted more years to geodesy than any other man of modern times. He began his practical studies in 1816 and published his last work in 1881. He cooperated with Bessel in many of his measurements and astronomical observations.