FOR THE ADVANCEMENT OF SCIENCE, 1857. 487 



or more additions to the number of the planetoids; and in one 

 year alone (1852), no fewer than eight of these bodies were disco- 

 vered. The last year has furnished its quota oifve; and in the 

 present, three more have been found, one by Mr. Pogson, of Oxford, 

 and the other two by M. Groldschmidt, of Paris. Their known 

 number is now forty-five. Their total mass, however, is very 

 small; the diameter of the largest being less than forty miles, 

 while that of the smallest, Atalanta, is little more than four. 



These discoveries have been facilitated by star-maps and star- 

 catalogues, the formation of which they have, on the other hand, 

 stimulated. Two very extensive works of this kind are now in 

 progress, the Star-catalogue of M. Chacornac, made at the Ob- 

 servatory of Marseilles, in course of publication by the French 

 Government ; and that of Mr. Cooper, made at his Observatory at 

 Markree, in Ireland, which is now being published by the help of 

 the parliamentary grant of the Eoyal Society. It is a remark- 

 able result of the latter labour, that no fewer than seventy-seven 

 stars, previously catalogued, are now missing. This, no doubt, is 

 to be ascribed, in part, to the errors of former observations ; but it 

 seems reasonable to suppose that, to some extent at least, it is the 

 result of changes actually in progress in the Sidereal Systems. 



The sudden appearance of a new fixed star in the heavens, it* 

 subsequent change of lustre, and its final disappearance, are 

 phenomena which have at all times attracted the attention of 

 astronomers. About twenty such have been observed. Arago has 

 given the history of the most remarkable, and discussed the various 

 hypotheses which have been proposed for their explanation. Of 

 these, the most plausible is that which attributes the phenomenon 

 to unequal brightness of the faces of the star, which are presented 

 successively to the earth by the star's rotation round its axis. On 

 this hypothesis the appearances should be periodic. M. Goldschmidt 

 has recently given support to this explanation, by rendering it 

 probable that the new star of 1609 is the same whose appearance 

 was recorded in the years 393, 798, and 1203 ; its period, in such 

 case, is 405 years. 



The greater part of the celestial phenomena are comprised in 

 movements of the heavenly bodies, and the configurations depend- 

 ing on them ; and they are for the most part reducible to the same 

 law of gravity which governs the planetary motions. But there 

 are appearances which indicate the operation of other forces, and 



