Ceres, as far as we yet know, is the largest of the planetoids, and may be something more than four hundred miles in diameter. Juno is somewhere near the same size. Pallas is about two hundred miles in diameter, and Vesta about one hundred and eighteen. No doubt, these four were the first to be discovered, because they are the largest and so the easiest to be seen. At any rate, no others yet seen exceed them in size, and some of the more lately discovered are not more than fifteen or twenty miles in diameter. Many of those discovered by photography are doubtless even smaller than these, and are, perhaps, mere meteors in size. The combined mass of all those discovered up to this time is far smaller than that of any of the large planets, or even than that of our moon. Their mass cannot, of course, really be measured, because they are too small to have any perceptible gravitative effect on other bodies, and mass can only be determined by the influence of one body on another. But we do know that their aggregate mass, if it exceeded a certain limit, would show some disturbing effect on Mars; and, since it does not do this, we know that all of them taken together would make an extremely insignificant body. While the planetoids all revolve around the sun in the same manner and in the same direction as the planets do, yet they are very erratic in their courses, and do not all keep within the narrow limits of the zodiac through which--happily for our convenient observation--the larger bodies travel. The orbits of many of them are extremely elliptical, while some are almost circles; and their inclination to the ecliptic varies from almost nothing to nearly fifty degrees. If one could catch from one side a view of them all together, they would have much the appearance in space of a flock of swallows, the individuals darting this way and that, passing above and below one another in such intricate sweeps and sinuosities that it would be impossible to keep track of them separately. And yet time has brought these apparently tangled orbits into such nice adjustment that the little bodies can continue to cross and recross each other’s paths with no danger of interference from each other. Such collisions as there may have been occurred in the very beginning of their careers. Such of them as came into collision then traveled on together as one body until accommodation was made for all. One of the most wide-wandering of these tiny bodies has been named Eros, after the little god of love, more commonly known as Cupid. It has a particular interest for us, because of all the heavenly bodies it at times comes nearer to us than any except the moon and an occasional comet. At its nearest it is within fourteen million miles of the earth, which is more than ten million miles nearer than the closest approach of Venus, the nearest of the large planets.