in a few minutes, its diameter was measured, and its magnitude computed. It is not my intention to follow, critically, the history of this wonderful discovery, yet there are some facts so remarkable that it would be wrong to pass them in silence. From the moment the planet was detected in Berlin, it has been observed by all the best instruments in the world, with a view of ascer taining how accurately theory had assigned the elements of its orbit. In consequence of its very slow motion, it became a matter of the utmost importance to obtain, if possible, some remote observation made by an astronomer who might have entered the place of the planet in his catalogue as a fixed star. Mr. Adams, of England, led the way in the computation of the elements of the orbit of the new planet, from actual observation, and was followed by many other computers, among them our countryman S. C. Walker, then of the Washington Observatory. Having obtained an approximate orbit, Mr. Walker computed backwards the places of the new planet for more than fifty years, and then examined the late catalogues, in the hope of finding its place on some of them as a fixed star. Among recent catalogues there was no success, but in an examination of Lalande's catalogue, he found an observation on a star of the eighth magnitude, made May the 10th, 1795, which was so near the place which his computation assigned the planet at the same date, that he was led to sus pect that this star might indeed prove to be the new planet. In case his conjecture were true, on turning the telescope to the place occupied by the star, it would be found blank, as its planetary motion would have removed it very far from the place which it oc cupied more than fifty years before. The experiment having been made, no star could be found, and strong evidence was thus presented that Mr. Walker had actually found an observation of the new planet, giving its position in 1795; but in consequence of the great discrepancy between the period of M. Leverrier and that which would result from a reliance on this observation of the new planet Neptune, Mr. Walker's discovery was at first received with great hesitation. A greater doubt was thrown over the matter from. the fact that Lalande had marked the observation as uncertain, and it was only by reference to the original manuscripts preserved in the Royal Observatory of Paris that the doubts could be removed. The discovery of Mr. Walker was subsequently made by Mr. Petersen, of Altona, and the results of these astronomers reached Paris on the same day. A committee was at once appointed to examine the original manuscript of Lalande, when a most remarkable discovery was made. This astronomer had ob served a star of the eighth magnitude on the evening of the 8th of May, 1795, and on the evening of the 10th, not finding the star as laid down, but observing one of the same magnitude very near the former place, he rejects the observation of the 8th of May as inaccurate, and enters the observation of the 10th, marking it doubtful. On close examination, this star proves to be the planet Neptune, and by this discovery we are placed in possession of observations which render it possible to determine the elliptic elements of the new planet with great precision. These differ so greatly from those announced by Leverrier and Adams previous to the discovery, that Prof. Pierce, of Cambridge, Mass., pronounces it impossible so to extend fairly the limits of Leverrier's analysis as to embrace the planet Neptune; and that, although its mass, as determined from the elongations of its satellite, renders it possible to account for all the perturbations of Uranus by its action, in the most surprising manner, yet, in the opinion of Prof. Pierce, it is not the planet to which geometrical analysis directed the telescope. Leverrier rejects absolutely the result reached by the American geometer, and claims Neptune to be the planet of his theory, in the strictest and most legitimate sense. Time and observation will settle the differences of these distinguished geometers, and truth being the grand object of all research, its discovery will be hailed with equal enthusiasm by both of the disputants. In any event, the profound analytic research of Leverrier is an ever-during monument to his genius, and his name is forever associated with the most wonderful discovery that ever marked the career of astronomical science. T2 LECTURE VIII. THE COMETARY WORLDS. THE Wonderful characteristics which mark the flight of comets through space; the suddenness with which they blaze forth; their exceeding velocity, and their terrific appearance; their eccentric motions, sweeping towards the sun from all regions and in all directions, have rendered these bodies objects of terror and dread in all ages of the world. While the planets pursue an undeviating course round the sun, in orbits nearly circular, and almost coincident with the plane of the earth's orbit, all revolving harmoniously in the same direction, the comets perform their revolutions in orbits of every possible eccentricity, confined to n. particular plane, and moving indifferently in accordance with, or opposed to, the general motion of the planets. They come up from below the plane of the ecliptic, or plunge downwards towards the sun from above, sweep swiftly round this their great centre, and with incredible velocity wing their flight far into the fathomless regions of space, in some cases never again to reäppear to human vision. In the early ages of the world, superstition regarded these wandering fiery worlds with awe, and looked upon them as omens of pestilence and war; and indeed, even in modern times, no eye can look fiery train spread out for millions of miles athwart upon the |