Not only was the time for the nearest approach of the comet computed, but its exact path among the stars was worked out with such accuracy that directions could be given as to the precise point toward which the telescope must be directed when the comet came within range of observation. On August 5, 1835, when M. Dumouchel, director of the observatory of the Roman College, turned his telescope in the direction indicated and looked through the tube, to his great delight he saw the comet as a faint and almost invisible stain of light on the deep blue of the heavens. Thus did science triumph in a most remarkable manner, the comet making its nearest approach within nine days of the predicted time. It appeared as a nearly circular misty object near to the predicted place, and began to develop a tail about the middle of September, which attained a length of about twenty-four degrees, or nearly five times the distance between the pointers, Alpha and Beta, in the constellation of Ursa Major. To the naked eye the head of the comet resembled a reddish star rather brighter than Antares in the constellation of the Scorpion. Bessel compared it to a blazing coal, and called attention to the peculiar fan-like haze of luminous matter forming the train, which seemed to sway to and fro like a pendulum across the radius vector, an imaginary line joining the sun and the nucleus of the comet. This oscillation took place during a period of four and three-fifths days. He came to the conclusion that a repulsive force about twice as powerful as the attractive force of gravity was responsible for the production of these remarkable effects, thus anticipating the theory according to which the very fine particles forming the train of a comet may be driven away from the direction of the sun by radiation pressure. Meanwhile Halley’s comet was passing through a remarkable series of transformations, first appearing as a nebula, then as a well-regulated comet with nucleus and train, next shining as a star, and finally dilating till it resembled a ball, then assuming paraboloidal form about May 5, 1836, after which it vanished as if melting into adjacent space through the excessive diffusion of its light. Moreover, it lost its tail previous to its arrival at perihelion on November 16, nor did it begin to recover its elongated shape until more than two months later.