Enclosed by the Rue d’Enfer, the Rue du Faubourg Saint-Jacques, and the Boulevard Arago stands the Observatory, one of the most celebrated scientific establishments of Paris and of the world. It was founded by order of Louis XIV. Colbert took the work in hand, Claude Perrault designed it, and Cassini inaugurated it in the name of Science. The building, begun in 1667 and finished in 1672, still preserves its original design. With its square tower in front, on the side of the avenue, and its side wings in the form of octagonal pavilions, the Observatory would resemble some country house if its cupolas and the other appendages which surmount the terraces on its Italian roof did not indicate its scientific object. The four sides of this rectangular construction correspond exactly to the four cardinal points. The principal façade, to which, from the Luxemburg Gardens, leads the broad avenue, looks directly to the north. The posterior façade, on the Boulevard side, has a southern aspect. The left side, dominating the Faubourg Saint-Jacques, receives the rising sun, while the setting sun casts its rays on the right side, which runs in a line with the Rue d’Enfer. The latitude of the southern façade is taken, in the official geography and cosmography of France, for the latitude of Paris, so that the Paris meridian cuts the building into two equal parts. Neither wood nor iron has been employed in the construction, which is entirely of stone. The Observatory, a state establishment under the control of the Ministry of Public Instruction, is governed by a director, who has attached to him titular astronomers, eight adjunct astronomers, and five assistant astronomers. The administration is in the hands of the director, aided by a council, who, moreover, superintends the scientific surveys, and is charged with the correspondence and the publication of reports. The meridian of Paris, traced in a great hall on the second storey, divides the edifice into two parts by a line which, prolonged north and south, would reach, in one direction, Dunkirk on the North Sea, in the other Callioure on the Mediterranean. These two lines, which intersect one another at the central point of the façade, served as basis for the numerous triangles upon which were drawn up, in the last century, the map of France, known as the map of Cassini, and in the middle of the present century the map known as the “staff map,” begun under the direction of General Pelet. The east wing contains the chambers of observation and the instruments belonging to them; the west wing an amphitheatre capable of holding 8,000 persons. It was here that the illustrious Arago delivered his lectures.