370 THE ASTEE01DS 13ETWEEN MARS AND JUPITER. 



IV. — SIKONA AND CERES. 



Sirona. Cores. 



Distance 2. 7GG1 2. 7G73 



Period 10S0 d .3 1681 d .4 



Longitude of perihelion . 152° 53' 149° 38' 



Longitude of ascending node 04° 2C 80° 47' 



Eccentricity.. 0.1439 0.07(15 



Inclination 11° 35' 10° 37' 



V. — TJEDA AND GERDa. 



In the American Journal of Science for February, 1877, Dr. Peters, 

 the discoverer of these asteroids, calls attention to several striking 

 coincidences between the elements of their orbits. The mean distance, 

 inclination, and ascending node of the former are very nearly identical 

 wiili those of the latter. "The fact of two planets moving in the same 

 plane, with the same time of revolution, having also the line of apsides 

 in common,* but with a widely different eccentricity," as Dr. Peters 

 justly remarks, "is worthy of note." The results of further observa- 

 tions will be looked for with interest. 



CONCLUSION. 



13. When the nebular hypothesis was proposed by Laplace, but four 

 minor planets had been discovered. According to that hypothesis those 

 new members of the system had been formed by the breaking up of a 

 nebulous ring into fragments so small that no one had sufficient attrac- 

 tive force to unite the others about its center as a single spheroidal 

 mass. After the number of asteroids had been largely increased the 

 celebrated Plana regarded their phenomena as confirming, if not dem- 

 onstrating, Laplace's theory. " The double fact," he remarks, "of the 

 multitude of those bodies and of their circulation in the same direction 

 around the sun, is now too imposing to admit an explanation of their 

 origin and formation different from that developed by Laplace, in his 

 Systeme du Monde."t 



But the form and extent of the zone of the minor planets, as well as 

 the known facts in regard to Saturn's rings, seem to require a modifica- 

 tion of Laplace's theory. Throughout the greater part of the interval 

 between Mars and Jupiter an almost continuous succession either of 

 very narrow rings or of extremely small planetary masses appears to 

 have been abandoned at the solar equator. The entire cluster, distrib- 

 uted throughout a ring whose outer radius exceeds the inner by 100 



* The longitudes of their perihelia differ by nearly 180°. 



t Note sur la Formation probable de la Multitude des Astero'ides qui, eutre Mars et 

 Jupiter, eirculent autonr du Soleil. Par Jean Plana. Presentee le 2 Mars, 1856, a. 

 TAcaddruie Royale des Sciences de Turin. 



