In 1815 was constructed, on the octagonal tower of the east, the great copper cupola furnished with apertures for telescopes, the floor of which moves round, so that the astronomer in observation can follow the revolutions of the stars throughout the night. This revolving dome, the largest known in the scientific world, has a diameter of about thirteen metres. In its centre is the immense parallactic telescope of Bruner. It is nine metres long and thirty-eight centimetres in diameter. Mention must be made, in other parts of the edifice, beneath smaller cupolas, of hydrometers for measuring the rain, the equatorial telescope of Secrétan and Eychens, together with thermometers, regulators, telegraphic and registering apparatus, Gamby’s mural circle, micrometers, the great meridian circle, and the immense telescope, one of the four largest telescopes in the world, furnished with a mirror silvered by the Foucourt process and having a diameter of 120 centimetres. The Observatory avenue was the scene of a tragic event on the 7th of December, 1815, when, at daybreak, in front of the wall of a public dancing-place, known as the Closerie des Lilas, Marshal Ney, condemned to death by sentence of the Court of Peers, was shot. Marshal Ney, Duke of Elchingen and Prince of Moscow (or of “Moskowa,” the Moscow river), after gaining distinction in all Napoleon’s campaigns, found himself, under the Restoration, in 1814, charged with the duty of seizing his former chief, who had just disembarked from Elba, and bringing him as a prisoner to Paris. Though far from being an enthusiastic supporter of the Bourbons, Ney considered that after the arrangements of Vienna and the pacification of Europe, Napoleon had committed a serious offence in coming back to France. Marshal Soult, then Minister of War, sent him to the south of France, where he was to take measures against Napoleon from headquarters at Besançon. Before proceeding on his mission Ney had an audience of Louis XVIII., in the course of which, speaking of Napoleon, he promised to bring him back “in an iron cage.” Arriving at Besançon, Ney learned that the Count of Artois, brother of the king, had gone to Lyons, where he at once wrote to the count saying that as the small number of troops at Besançon did not require his presence in that town, he begged his royal highness to employ him near his person, and, if possible, as commander of the vanguard; desiring, as in all other circumstances, to give proofs of his zeal and fidelity. On the day following, M de Maillé, the count’s first gentleman of the chamber, went to inform the marshal of the prince’s departure from Lyons and of Bonaparte’s arrival at Grenoble. Ney thereupon decided to move his headquarters to Lons-le-Saunier, “resolved,” as he wrote to the Minister of War, “to attack the enemy on the first favourable occasion.” On reaching Lons-le-Saunier, he heard that Napoleon had entered Lyons, on