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HISTORY OF PHYSICAL ASTRONOMY.

we except the coincidence of its mean distance with that of Ceres , was theinclination of its orbit to the ecliptic, which amounted to the very consider-able angle of 34° 39'. In consequence of the various peculiarities of thetwo new bodies, Sir William Herschel proposed to denominate them aste-roids, instead of planets, and this appellation is frequently applied to themas well as to the other bodies which have since been discovered revolvingin the same region.

An examination of the relative magnitudes of the planetary orbits hadsuggested the existence of an unknown planet, revolving between the orbitsof Mars and Jupiter . Instead of one planet, however, two were found, con-forming in this respect to the requirements of analogy. Considering thissingular fact, in connexion with the extreme minuteness of the two bodies,and the other circumstances by which they were distinguished from themore ancient planets, Olbers was led to suspect that they might possiblybe the fragments of a larger planet, which had once been revolving inthe same region, and at an anterior epoch had been shattered to pieces bythe energy of some unknown cause. Pursuing this ingenious conception,he was led to conclude that there might be many more similar fragmentswhich had not yet been discovered. He also inferred that the eccentricitiesand inclinations of their orbits might be very different, but that the meandistances would be nearly equal, and, as they all had a common origin, thattheir orbits would have two common points of intersection, situate in op-posite regions of the heavens, through which every fragment would neces-sarily pass in the course of each revolution. He proposed, therefore, tosearch carefully every month the north-western part of the constellationVirgo, and the western part of the constellation of the Whale, being the twoopposite regions in which the orbits of the two bodies already discoveredwere found to intersect each other. Meanwhile the discovery of a thirdplanet tended in a strong degree to confirm the truth of his hypothesis,and to encourage him in his arduous undertaking. In consequence of theextreme smallness of Ceres and Pallas, they are liable to be confoundedwith the telescopic stars, which lie near their paths, and consequentlywhen any time is allowed to elapse without their being observed, it be-comes a difficult matter to recognise them again. With the view of facili-tating this object, M. Harding, one of the astronomers attached to theObservatory of Lilienthal, had undertaken to construct a series of charts,whereon were laid down the positions of all the small stars which appearnear the geocentric paths of the two planets. On the 2nd September,1804, while engaged in exploring the heavens for this purpose, he per-ceived a small star in the constellation Pisces, very near to that partof the constellation of the Whale, through which Olbers had asserted thatthe fragments of the shattered planet would be sure to pass. On the 4thof September he repeated his observation, and found that the star hadchanged its place. The observations of the succeeding evenings esta-blished, beyond all doubt, that the star was in reality a new planet. Theelements of its orbit were calculated by Gauss, who found, as in the caseof the other two planets recently discovered, that it revolved between theorbits of Mars and Jupiter . The mean distance was 2-670, consequentlyit almost coincided with the mean distances of Ceres and Pallas. Theeccentricity amounted to 0-2543, and therefore surpassed that of any othermember of the planetary system. Harding conferred on the planet theappellation of Juno, with a sceptre surmounted by a star'for the symbolof designation. Like Ceres and Pallas, it is remarkable for its extreme