observatory at Dantzic, and then with Cassini watching a comet at Paris. Upon the death of Flamstead, he succeeded to the office of astronomer royal, and though then in the sixty-fourth year of his age, he commenced the observation of the moon through a complete revolution of her nodes, involving a period of nineteen years, and lived to finish it, registering upward of two thousand observed lunar places. It was while journeying in France toward the close of 1680, that he observed the great comet of that year, on its return from proximity to the sun: and being aware of the conclusion of Newton, that such bodies describe very eccentric ellipses, his active mind began to study intently their phenomena, which resulted in a prophecy that has immortalized his name. After cataloguing and comparing a considerable number of comets, that of 1682 fortunately appeared. This he was led to regard as identical with those of 1456, 1531, and 1607, between which there is nearly the same interval. Hence he anticipated its return after the lapse of a similar period. “I dare venture,” said he, “to foretell that it will return again in 1758;” and, sanguine as to the result, he called upon posterity to notice that it was an Englishman who had hazarded the statement. This was a prediction announced in 1705, the accomplishment of which ranks with the greatest achievements of modern astronomy, and will perpetuate the fame of Halley to the remotest generations. He had been gathered to his grave in Lee church-yard seventeen years, when the celestial traveler re-appeared, at the time announced, to verify his words, illustrate his sagacity, and invest him with undying honor. [Illustration: =Halley’s Tomb.=] Bradley, the English Hipparchus, the model of observers, as he is styled by Laplace, became the third astronomer royal upon the death of Halley. He had previously effected one of his two great discoveries, the aberration of the stars, an optical illusion, arising from the combined movement of the earth in space, and the progressive transmission of light; a discovery of the highest importance, requiring the greatest precision of observation to detect. Ever since the doctrine of the earth’s translation in space had been received, astronomers had been anxious to find some parallax of the fixed stars, as a sensible confirmation of the fact. Although the whole diameter of the earth’s orbit is relatively insignificant, it is yet absolutely vast. Hence it was deemed no unreasonable expectation that some small apparent change of place in the heavens would be discerned in the case of the fixed stars, when viewed from the two extremities of the earth’s annual orbit—separated from each other by the mighty chasm of a hundred and ninety millions of miles.