Wolf, have accounted for the great majority of the discoveries. It was, however, becoming more and more a matter of question what advantage was to be gained by the continuance of the hunt, when a fresh fillip was given to interest by the discovery in 1898 of the anomalous asteroid named Eros. Hitherto no minor planet had been known to have the greater portion of its orbit within that of Mars, though several do cross the red planet's borders; but the mean distance of Eros from the sun proves to be about 135,000,000, while that of Mars is 141,000,000 miles. In addition, the orbit of the new planet is such that at intervals of sixty-seven years it comes within 15,000,000 miles of the earth, or in other words nearer to us than any other celestial body except the moon or a chance comet. It may thus come to afford a means of revising estimates of celestial distances. Eros presents another peculiarity. It has been found by E. von Oppolzer to be variable in a period of two hours thirty-eight minutes; and the theory has been put forward that the planet is double, consisting of two bodies which revolve almost in contact and mutually eclipse one another--in short, that Eros as a planet presents the same phenomenon which we shall find as a characteristic of that type of variable stars known as the Algol type. An explanation, in some respects more simple and satisfactory, is that the variation in light is caused by the different reflective power of various parts of its surface; but the question is still open. The best results for the sizes of the four asteroids first discovered are those of Barnard, from direct measurements with the Lick telescope in 1894. He found the diameter of Ceres to be 485 miles, that of Pallas 304, those of Vesta and Juno 243 and 118 miles respectively. There appears to be as great diversity in the reflective power of these original members of the group as in their diameters. Ceres is large and dull, and, in Miss Clerke's words, 'must be composed of rugged and sombre rock, unclothed probably by any vestige of air,' while Vesta has a surface which reflects light with four times the intensity of that of Ceres, and is, in fact, almost as brilliantly white as newly fallen snow. In the place of Olbers' discredited hypothesis of an exploded planet, has now been set the theory first suggested by Kirkwood, that instead of having in the asteroids the remnants of a world which has become defunct, we have the materials of one which was never allowed to form, the overwhelming power of Jupiter's attraction having exerted a disruptive influence over them while their formation was still only beginning.