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the French Government having been authorized by the Chambers to appropriate to that work a sum of 500,000 francs. The operation was entrusted to the members of the Geographical Service of the Army, under the direction of General Bassot. The Government of the Republic of Ecuador (on whose territory the arc of Bouguer is now comprised) having shown a disposition to favour the enterprise, two French officers, Captains Maurain and Lacombe, of the Geographical Service, were sent in 1899 to reconnoitre the country. They left Bordeaux at the end of May, and returned in January 1900, after having surveyed, in less than five months (July to November), an arc of 6°, between the Cerro de Pasto (1° 10' N. lat., Colombian territory) and the Cerro Ereo (4° 55' S. lat., Peruvian territory), thus lengthening by 1° towards the north and 2 southwardly the arc of Bouguer. In the southern part of the arc they could retain the old stations of the French academicians; in the northern part they had to rise above the former stations, found defective. The obstacles were formidable, for there the twin Cordilleras rise to peaks—some of them volcanoes—of from 5000 to 6000 metres in altitude, namely, Pichincha, Chimborazo, Cotopaxi, &c. MM. Maurain and Lacombe, with a zeal and persistence above all praise, traversed 3500 kilometres and effected about thirty ascents in one of the most difficult countries, investigated the sites of two new base-lines, and determined fifteen geodetical stations; they brought back topographical sketches and plans which give a clear idea of the work to be accomplished. In July 1900 an official report, presented by M. Poincare in the name of the Academy of Sciences, drew out the lines of the projected revision of the arc of Quito. The system implies a series of 57 triangles and is supported by three base-lines, each of about 8500 metres. The principal base will be situated towards the middle of the arc, near Riobamba, in 1° 30' S. lat., and 2500 metres above the sea-level; two bases of verification are to be established at both extremities : the one near Cumbal, in Colombia, the other between Quiroz and Sullana (Peru). For measuring the angles, 52 stations (28 from the old chain of Bouguer and La Condamine) will be established along both Cordilleras, their altitude being often of 4000 metres; the sides of the triangles will be of 30 to 40 kilometres. The mission will be divided into two parties, who will proceed in parallel lines, the one along the western range, the other along the eastern. As it would be hazardous to build up signals, always liable to be destroyed by the Indians, optic telegraphy will be resorted to, by means of heliostats, in order to maintain communication between the successive stations. The difference of longitude of the extremities will be a little less than 3°. In the southern part of the Gulf of Guayaquil the hills are near enough to the coast to make it possible to push on the triangulation to the sea, by connecting it with a point where an old lighthouse stands, and also, perhaps, with a point of Puna Island. The altitude of the principal base (Riobamba) will be obtained by a spirit-levelling, which will follow the line of the future Guayaquil-Quito railroad. The sea-level will be obtained by means of a “ medimaremetre ” placed at Playas, on the Pacific coast, distant about 70 kilometres from Guayaquil. The line of levelling from Playas to Riobamba will attain a development of 280 kilometres and rise to 2500 metres. For the other bases a geodetic levelling by zenith distances may suffice. The astronomical stations for the observation of the fundamental elements (latitude, longitude, azimuth) will be multiplied as much as possible, and likewise the stations for pendulum observations. The principal station will be at Quito, where a perfectly fitted observatory already stands, the direction of which has

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been entrusted to a French astronomer, M. Gonnessiat. The differences of longitude between Quito, Guayaquil, and several other astronomical stations will be determined with the help of the telegraph. It is estimated that this programme can be executed within four years by a party of five officers, namely, Commandant Bourgeois, head of the mission, Captains Lacombe, Maurain, Lallemand, and Lieutenant Perrier; the other members are a military physician, a mechanician, and sixteen corporals and privates. A vanguard mission, consisting of Captains Maurain and Lallemand, sailed in December 1900, and reached Guayaquil in January 1901. The rest of the personnel followed in April with the instruments. It is right to recall here that geodetical studies have recovered, in France, their former expansion under the vigorous impulse of Colonel (afterwards General) Perrier. When occupied with the triangulation of Algeria, Colonel Perrier had conceived the possibility of the geodetic junction of Algeria to Spain, over the Mediterranean; therefore the French meridian line, which was already connected with England, and was thus produced to the 60th parallel, could further be linked to the Spanish triangulation, cross thence into Algeria and extend to the Sahara, so as to form an arc of about 30° in length. But it became, then, urgent to proceed to a new measurement of the French arc, between Dunkirk and Perpignan. In 1869 Perrier was authorized by Marechal Niel to undertake that revision. He devoted himself to that work till the end of his career, closed by premature death in February 1888, at the very moment when the Depot de la Guerre had just been transformed into the Geographical Service of the Army, of which General Perrier was the first director. His work was continued by his assistant, Colonel (afterwards General) Bassot. The operations concerning the revision of the French arc (triangulation, remeasurement of the Perpignan base, measurement of a new base near Melun, which may replace the former, &c.) were completed only in 1896. Meanwhile the French geodesists had accomplished the junction of Algeria to Spain, with the help of the geodesists of the Madrid Institute under General Ibanez (1879), and measured the meridian line between * Algiers and El Aghouat (1881). They have since been busy in prolonging the meridians of El Aghouat and Biskra, so as to converge towards Wargla, through Gardaia and Tuggurt. A careful study of the deflections of the vertical has been commenced in the hills of the Algerian Sahel. In France the Geographical Service of the Army has been entrusted with the triangulations of the first, second, and third orders, to serve as a basis for the new majj of France.1 The Geographical Service has thus been led to undertake the revision of the whole triangulation of France, with methods and instruments of high precision. The parallel of Paris has been connected with the German net by the co-operation of German and French geodesists. The fundamental co-ordinates of the Pantheon have also been obtained anew, by connecting the Pantheon and the Paris Observatory with the five stations of Bry-sur-Marne, Morlu, Mont Yalerien, Chatillon, and Montsouris, where the observations of latitude and azimuth have been effected. The triangulation of Italy is finished and in connexion with the French net on north and south, where it is linked to Tunis. The geodetic junction of Malta to Sicily was executed in 1900 by M. Guarducci. The observations were made by night, by means of light signals. The distances of many of the stations reach to 200 kilometres. The probable error in closing the triangles does not exceed 1 See the work entitled La Carte de France, 1750-1898; ttude histonque, par le Colonel Berthaut, 2 vols. 4to, 1898-99.