feet the first second, at the surface of Menippe it would fall about one-fourth of an inch. A person might leap from its surface to a height of several hundred feet, in which case he could not return in much less than an hour. "But of such speculations," Sir John Herschel remarks, "there is no end." The number of these planetules between the orbits of Mars and Jupiter in all probability can never be known. It was estimated by Leverrier that the quantity of matter contained in the group could not be greater than one-fourth of the earth's mass. But this would be equal to five thousand planets, each as large as Vesta, to seventy-two millions as large as Menippe, or to four thousand millions of five miles in diameter. In short, the existence of an indefinite number too small for detection by the most powerful glasses is by no means improbable. The more we study this wonderful section of the solar system, the more mystery seems to envelop its origin and constitution. 6. The Orbits of the Asteroids. The form, magnitude, and position of a planet's orbit are determined by the following elements: 1. The semi-axis major, or mean distance, denoted by the symbol _a_. 2. The eccentricity, _e_. 3. The longitude of the perihelion, _π_. 4. The longitude of the ascending node, ☊. 5. The inclination, or the angle contained between the plane of the orbit and that of the ecliptic, _i_. And in order to compute a planet's place in its orbit for any given time we must also know 6. Its period, _P_, and 7. Its mean longitude, _l_, at a given epoch. These elements, except the last, are given for all the asteroids, so far as known, in Table II. In column first the number denoting the order of discovery is attached to each name. TABLE II. _Elements of the Asteroids._