THE SMITHSONIAN INSTITUTION. ^ 13T 



LECTURES. 



No. in— THE ZONE OF SMALL PLANETS BETWEEN MARS AND JUPITER. 



BY PROFESSOR ELIAS LOOMIS, OF THE UNIVERSITY OF NEW YORK. 



Seventy-five years since, the only planets known to men of science 

 were the same which were known to the Chaldean shepherds thou- 

 sands of years ago. Between the orbit of Mars and that of Jupiter 

 there occurs an interval of no less than three hundred and fifty millions 

 of miles, in which no planet was known to exist before the commence- 

 ment of the present century. Nearly three centuries ago the immortal 

 Kepler had pointed out something like a regular progression in the dis- 

 tance of the ulanets as far as Mars, which was broken in the case of 

 Jupiter. Being unable to reconcile the actual slate of the planetary 

 system with any theory he could form i-especting it, he hazarded the 

 conjecture that a planet really existed between the orbits of Mars and 

 Jupiter, and that its smallness alone prevented it from being visible to 

 astronomers. But Kepler himself soon rejected this idea as improba- 

 ble, and it does not appear to have received any favor from the astrono- 

 mers of that time. 



An astronomer of Florence, by the name of Sizzi, took decided ground 

 against all such innovations of doctrine. He maintained that since 

 there are only seven apertures in the head — two eyes, two ears, twa 

 nostrils, and one mouth — and since there are only seven metals, and 

 seven days in the weeks, so there can be only seven planets. These 

 seven planets, according to the ancient systems of astronom}'', were 

 Saturn, Jupiter, Mars, the Sun, Venus, Mercury, and the Moon. 



In 1772, Professor Bode, of Berlin, first announced the lingular rela- 

 tion between the distances of the planets from the sun, which has since 

 been distinguished by the name of Bode's law. This law exhibited in 

 a striking fight the abrupt leap from Mars to Jupiter, and suggested 

 the probability of a planet revolving in the intermediate region. This 

 conjecture was rendered still more plausible by the discovery in 1781 

 of the planet Uranus, whose distance from the sun was found to con- 

 form nearly with the law of Bode. In Germany, especially, a strong 

 impression had been produced that a planet really existed bet^veen 

 Mars and Jupiter, and the Baron de Zach went so far as to compute 

 the orbit of the ideal planet, the elements of which he published in the 

 Berlin Almanac. In the year 1800, several astronomers, of whom the 

 Baron was one, formed an association, whose object was to effect the 

 discovery of the unseen body. For this purpose the zodiac was divided 

 into twenty-four zones, one of which was to be explored by each 

 astronomer. Soon after the formation of this society the planet waS' 

 discovered, but not by any of those astronomers w'ho were engaged ex- 

 pressly in searching tor it. Piazzi, the celebrated Itafian astronomer, 



