fluence of Saturn, and five hundred and eighteen days by the action of Jupiter;—he therefore fixed its perihelion passage for the 13th of April, 1759, stating, at the same time, that the result might be inaccurate by some thirty days either way, in consequence of being · pressed for time, and his having neglected certain small perturbations.

These results were presented to the Academy of Sciences on the 14th of November, 1758, and on the 25th of the following December, George Palitch, an amateur peasant astronomer, caught the first glimpse of the long expected wanderer, which, after an absence of three-quarters of a century, once more returned to crown with triumph the great English astronomer who first foretold its period, and the eminent French mathematicians who had actually computed its perihelion passage, to within nineteen days, in seventy-six years!

Here, then, was a new world added to the solar system, linked to the sun by the immutable law of gravitation; sweeping out into space to the amazing distance of 3,800,000,000 of miles; lost to the gaze of the most powerful telescope, and yet traced by the human mind through its vast and hidden career, with an accuracy and precision from which there was no escape. The very small error of nineteen days in Clairaut's computation strikes us with astonishment, when we remember the imperfect state of analytical science at that day, and the fact that two planets Uranus and Neptune, which have since been discovered, were then not even suspected to have any existence.

The magnificent display which had marked some U

of the early returns of Halley's comet, and which produced such consternation among all classes, the educated as well as the ignorant, were not presented during its appearance in 1758. This was owing, in part, to the unfavorable position of the earth in its orbit at the time of the comet's perihelion passage.The vast trains of light which are sometimes seen to accompany comets, are only displayed in their approach to the sun. They attain their greatest splendor while the comet is in the act of passing its perihelion, and as it recedes into space, the tail fades away, from two causes-an actual diminution from condensation, and an apparent decrease on account of increased distance.

As the comet, when near the sun, moves with increased velocity, it occupies, in general, only a short period in passing through the limits of distance from the sun within which any train of light is developed. It may happen that at one return of the same comet, the earth may occupy a point in her orbit, during its perihelion passage, which may be very near to the comet, and thus afford an opportunity of witnessing its appearance at a short distance; while, on the next return, the earth being at a remote part of its orbit while the comet is passing the sun, it may be seen only with great difficulty, or even become quite invisible. If, therefore, astronomers were obliged to depend upon a uniform physical appearance of comets at their successive returns, to determine their identity, there would scarcely be the slightest chance of ever recognizing even a single one among the many thousands which are sweeping through the regions of space

The interval from 1759 to 1835, when Halley's comet ought to make its next appearance, had wit nessed extraordinary changes in astronomy. The methods for computing planetary perturbations had been greatly improved; the planet Uranus had been added to the system, and more accurate masses of the larger planets, especially of Saturn, had been obtained. Twenty-five years before the close of the comet's period, its return commenced to interest astronomers, and prizes were offered by two academies for the most perfect theory of this remarkable body. Baron Damoiseau and M. Pontecoulant were the successful competitors for the two prizes, although several other astronomers undertook and completed the task of computing the planetary perturbations. Although the computers differed slightly in the time of the perihelion passage, the difference was due to the imperfection of the data employed, rather than to any defect in the methods of computation.

For the expected return in 1835, not only was the perihelion passage computed, but the exact route of the comet among the fixed stars was wrought out with surprising accuracy, and the precise point towards which the telescope must be directed at the time when the comet would first attain the limits of visibility. Strange and almost incredible as it must appear, guided by these predictions, M. Dumouchel, director of the observatory of the Roman College, on the evening of the 5th of August, 1835, fixed his telescope in the position indicated by computation, and, on placing his eye to the tube, lo! the comet appeared, as a faint and almost invisible stain cf light on the deep blue of the heavens.

Again did science triumph, in the most remarkable manner, and the computed orbit of the comet was followed by it with the most surprising accuracy.— The perihelion passage was predicted to within nine days of its actual occurrence, a most astonishing approximation to the truth, when it is remembered that this body, far as it penetrates into space, never, even at the remotest point of its orbit, escapes from the sensible influence of the planet Jupiter. Moreover, at that time, the new planet, Neptune, was unknown, and its influence over the comet could not be taken into account.

It is interesting to remark the confidence with which astronomers relied on Halley's comet for infor mation relative to those bodies, which inhabited the regions of space exterior to the known limits of the solar system. It was urged by every computer that the orbit of this comet would one day come to be so perfectly known, that the perturbations due to the recognized bodies of the solar system might be computed with such precision, that the residual perturbations might be pronounced to be the effect of unknown planets or comets circulating in the distant regions of space. This conjecture has been realized, although by different means, and a planet is now added to our system, which revolves in an orbit so vast as to circumscribe within its limits the entire sweep of the comet; and as the orbits of Neptune and Halley's comet are inclined under an angle of only 15° or 16°, a time will come when the perturbations experienced by the comet when at its aphelion, from Neptune's influence, may be so great that, but for the fortunate discovery of the cause, would have

falsified, in the most unaccountable manner, the predictions of the comet's return by future astronomers. During its late return, the finest telescopes in the world were employed in a critical examination of the physical condition of Halley's comet. Elaborate drawings have been made by M. Struve, the distinguished director of the Imperial Observatory at Pulkova, Russia, with the grand refracting telescope under his charge, and also by Sir John Herschel, at the Cape of Good Hope, with a twenty feet reflector of superior power. To these beautiful drawings reference will be made hereafter.

The most wonderful changes in the magnitude and figure of the comet were observed to take place from night to night, and almost perceptible from hour to hour under the eye of the observer. The nucleus was sometimes seen sharp and strongly condensed, with more or less nebulous light around it. Sometimes a luminous crescent became distinctly visible near the nucleus, giving to the comet a most extraordinary appearance. At one time M. Struve saw the comet attended by two delicately shaped appendages of light of a most graceful form, the one preceding, the other following the nucleus of the comet. At other times it was seen to be surrounded by a sort of semi-circular veil, which, extending backwards, was lost in a double train of light, which flung itself out to a vast distance from the body of the comet.

Leaving, for the present, the consideration of the physical constitution of these eccentric bodies, we proceed to the examination of a remarkable object which bears the name of Encke's comet, in consequence of the discovery by this learnod astronomer