200 REMARKS ON THE SMALL PLANETS. 



II. 



Struck by the large interval which separates Mars from Jupiter, 

 Kepler had been led, by theoretical considerations, to interpose be- 

 tween those two bodies an unknown planet : ^^ inter Martem et Jovem 

 inteiyosiii 2)lcinefam, {mysiermm cosmograpMcmn.y But of his own 

 accord he afterwards renounced this hypothesis, which had been un- 

 favorably received by learned cotemporaries. An astronomer of 

 Florence, named Sizzi, protested, with particular earnestness, against 

 such a doctrine. "There are," said he, ''but seven openings in 

 the head, two eyes, two ears, two nostrils, and the mouth; there are 

 but seven metals, and but seven days in the week ; there are, there- 

 fore, but seven planets." These, in the system of Ptolemy, were 

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



The idea of Kepler was revived in the second half of the 18th cen- 

 tury. Lambert, Titius, and Bode successively called the attention of 

 astronomers to the void which seemed to exist between Mars and Ju- 

 piter; Bode especially attached extreme importance to the celebrated 

 law which bears his name, although, by his own acknowledgment, 

 that law was due to Titius. In seeking a numerical relation between 

 the distances of the planets from the sun, Titius had conceived the 

 idea of the following series, in which each term, proceeding from the 

 third, is double that which precedes : 



0, 3, 6, 12, 24, 48, 96. 

 Bv adding 4 to each of these terms, we obtain a new series : 



4, 7, 10, 16, 28, 52, 100. 

 In this series, 4 representing the distance of Mercury, 7 would repre- 

 sent the distance of Venus, 10 that of the earth, 16 that of Mars, 52 

 that of Jupiter, 100 the distance of Saturn; but the number 28 re- 

 presented nothing and seemed properly to correspond to the distance 

 of the Sun from an unknown planet. This hypothesis enlisted new 

 partisans, especially in Germany, when, in 1781, the discovery of 

 Uranus lent unexpected confirmation for the law of Bode. The 

 Baron de Zach went so far as to publish in advance, in the Almanack 

 of Berlin, the elements of the supposed planet, and he organized 

 an association of astronomers for the search after that object. The 

 zodiac was distributed into twenty-four zones, each of which was 

 assigned to the special examination of one of the members of the 

 society. The discovery was indeed not long in being made, but it 

 proceeded from another quarter. 



Piazzi, an astronomer at Palermo, had been for ten years occupied 

 with the correction of the catalogue of Wollaston. A false indication 

 in this catalogue called the attention of the observer to a certain re- 

 gion of the heavens and led him to examine minutely the most imper- 

 ceptible stars. One of these, whose position had been determined 

 the 1st of January, 1801, was found to be sensibly displaced the fol- 

 lowing day, and still more so on successive nights. Piazzi at first 

 took it for a comet, and followed its course till the IXth of February, 

 on which day his observations were interrupted by bad weather and 



