X NOTES BY THE EDITOR 



cribed in part to the errors of former observations ; but it seems rea- 

 sonable to suppose that, to some extent at least, it is the result of 

 changes actually in progress in the Sidereal System. The sudden ap- 

 pearance of a new fixed star in the heavens, its 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 offered 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 appearance should be periodic. M. Goldschmidt 

 has recently given support to this explanation, by rendering it proba- 

 ble that the new star of 1609 is the same whose appearance was re- 

 corded in the years 393, 798, and 1203. Its period in such case is 

 405J years. 



The greater part of the celestial phenomena are comprised in the 

 movements of the heavenly bodies and the configuration depending on 

 them; and they are for the most part reducible to the same law of 

 gravity which governs the planetary motions. But there are appear- 

 ances which indicate the operation of other forces, and which, there- 

 fore, demand the attention of the physicist although, from their na- 

 ture, they must probably long remain subjects of speculation. Of these, 

 the spiriform nebulas, discovered by Lord Rosse, indicate changes in 

 the more distant regions of the universe, to which there is nothing en- 

 tirely analogous in our own system. These appearances are accounted 

 for, by an able anonymous writer, by the action of gravitating forces 

 combined with the efi'ects of a resisting medium the resistance being 

 supposed to bear a sensible proportion to the gravitating action. The 

 constitution of the central "body of our own system presents a nearer 

 and more interesting subject of speculation. Towards the close of the 

 last century many hypotheses were advanced regarding the nature and 

 constitution of the sun, all of which agreed in considering it to be an 

 opaque body, surrounded at some distance by a luminous envelop. But 

 the only certain fact which has been added to science in this de- 

 partment is the proof given by Arago that the light of the sun ema- 

 nated (not from an incandescent solid, but) from a gaseous atmosphere, 

 the light of incandescent solid bodies being polarized by refraction, 

 while the light of the sun, and that emitted by gaseous bodies, is un- 

 polarized. According to the observations of Schwabe, which have 

 been continued without intermission for more than thirty years, the 

 magnitude of the solar surface obscured by spots increases and de- 

 creases periodically, the length of the period being eleven years and 

 forty days. This remarkable fact, and the relation which it appears to 



