THE PLANET EROS. 641 



THE PLANET EEOS. 



By Professor SOLON I. BAILEY, 



HARVARD COLLEGE OBSERVATORY. 



EEOS is the name of a small planet discovered in 1898, by Witt, of 

 Berlin. It does not appear to be altogether certain that it really 

 belongs to the group of minor planets, usually known as planetoids or 

 asteroids. With the exception of Eros, all known asteroids move in 

 orbits whose mean distances are greater than that of Mars and less 

 than that of Jupiter. The mean distance from the sun of Mars is 141 

 million miles, and that of Jupiter is 483 million miles, while the dis- 

 tances of the asteroids vary in round numbers between 200 and 400 

 million miles. The mean distance of Eros, however, is only 135 million 

 miles, which is less than that of Mars. In spite of this very impor- 

 tant difference, Eros has been placed among the great band of as- 

 teroids, among whom he numbers 433. To belong to the celestial 

 400 is perhaps more of misfortune than of honor, for the number of 

 this plebeian band has already waxed so great that they have become 

 a care which threatens in the future to balance the benefits which they 

 bring to astronomy. Nevertheless, the history of this numerous fam- 

 ily is sufficiently full of interest, and throws light upon the way in 

 which we should regard them. 



In 1772, Bode announced the so-called law which bears his name. 

 The law may be stated as follows: If to a series of 4's, beginning at 

 the second, the numbers 3, 6, 12, 24, etc., be added, the resulting 

 numbers divided by 10 will approximately express the distance of the 

 planets from the sun in terms of the distance of our earth taken as 

 unity. The law gave fairly well the distances of all the planets known 

 at that time, except that it called for a planet between Mars and 

 Jupiter, where nothing was then known to exist. When, a few years 

 later, in 1784, Uranus was discovered and was found to conform closely 

 to the law, the impression was deepened that the missing member 

 of the solar system must somehow be supplied or explained, and an 

 association of astronomers was formed to hunt for it. At that time 

 the discovery of a small body, such as one of the asteroids, was no 

 easy matter, and the honor of finding the first did not fall to one of 

 the associates, but to Piazzi, a Sicilian astronomer, who discovered 

 it while making a star catalogue. It was perhaps fitting that a cen- 

 tury which was to be signalized by the discovery of some 450 new 

 but small worlds, where one had been sought, should be properly 



VOL. LVIII. — il 



