make up a world even one-hundredth as large as the earth would take hundreds of thousands of such worlds.
On the night of August 13, 1898, Herr Witt made a photograph of the region near β Aquarii, with an exposure of two hours. He wished to obtain an observation of a known asteroid which had not been observed for nine years, and which his calculations assigned to that region. When developed and examined on the following day, the plate not only showed the object desired, and also a second known asteroid, but a faint and long trail of some unknown object. From its rapid motion it was at first thought to be a comet, but an examination on the following night with a visual telescope revealed its true nature. As soon as the well-known computer of minor planet orbits, Herr Berberich, had computed its approximate orbit, the astonishing nature of the new planet became apparent. Of all the previously known members of the solar system, with the obvious exception of our moon, Venus and Mars approach nearest to the earth. Venus is distant from us at the most favorable times about twenty-five million miles, and Mars thirty-five million miles. Eros, however, approaches the earth at the most favorable oppositions within less than fourteen million miles, so that he is our nearest celestial neighbor. This leads to a solution, under better conditions perhaps than ever before granted, of that fundamental problem in astronomy, the distance of the sun, or, in other words, the determination of the solar parallax. In order to determine the orbit and position of a planet, certain quantities must be found, based upon at least three observations of the planet's place in the sky. It is, however, highly desirable to have more than three observations of the planet's position and to have them widely separated in time.
The following elements for Eros were computed by Dr. S. C. Chandler, and were based on the observations of 1898, combined with those of the Harvard photographs made in the years 1893, 1894 and 1896:
EPOCH 1898, AUGUST 31.5, GREENWICH MEAN TIME.
| Mean Anomaly | 221° | 35' | 45. | "6 | |
| Perihelion Distance of Ascending Node | 177 | 37 | 56. | 0 | 1898.0 |
| Longitude of Ascending Node | 303 | 31 | 57. | 1 | |
| Inclination of Orbit to Ecliptic | 10 | 50 | 11. | 8 | |
| Angle whose Sin is the Eccentricity | 12 | 52 | 9. | 8 | |
| Mean Daily Motion | 2015. | "2326 | |||
| Logarithm of Semi-major Axis | 0.1637876 | ||||
| Period of Revolution around Sun | 643d | .10 |
Later observations will doubtless slightly modify these results, but they are sufficiently precise for our purpose. These elements were published in December, 1898, and well illustrate the enormous photographic resources which at the present time are in the possession of the Harvard Observatory. Twenty years ago, the present Director,
