412 ANNUAL OF SCIENTIFIC DISCOVERY. 



only docs so to cast a doubt on the matter. " Ephorus," he says, "who is 

 not very trustworthy, is often deceived, and often deceives. Thus he says 

 that comet on which the eyes of all men were fixed, because on its rising it 

 ushered in an immense event, namely, the swallowing up by the sea of 

 Helice and Buriu, was seen to set under the form of two stars, a thing 

 which no one else has mentioned before. For who can hare observed the 

 moment when the comet split into two parts? And how, if any one saw it 

 split asunder, does it happen that no one saw the junction of two bodies 

 to form it ? " 



This comet appeared, according to M. Humboldt, under the archonate of 

 Asteius, in the fourth year of the 101st Olympiad, two years before the bat- 

 tle of Leuctra, when the two towns of Achaia, mentioned by Seneca, were 

 washed away by the sea in consequence of an earthquake. Kepler has al- 

 ready confuted Seneca's criticisms in his work De Cornells, 1619, pages 49 

 and 50; but the separation of Biela's comet in two, sets the question at rest, 

 and shows that Ephorus spoke the truth ; but the comet of Asteius sepa- 

 rated suddenly and rapidly, since the separation was visible to the naked 

 eye, whereas that of Biela's comet has been effected very slowly. According 

 to M. Plantamour's measures and calculations, the distance of the two 

 nuclei, equal to that which exists between the earth and the moon, re- 

 mained nearly constant during the whole time of its appearance in 1846. 



According to M. Alexander, it would be necessary to go back five hundred 

 days in order to find the nuclei at one-tenth of that distance from each other, 

 and it was not until the lapse of seven years that the distance became ten 

 times greater. The two nuclei, in fact, follow the same route; there are but 

 very slight differences in the elements of their orbits ; they have the same 

 inclination, the same longitude of the node, with the exceptions of a few 

 seconds ; the same eccentricity, and the same orientation of the transverse 

 axis, so that the difference seems chiefly to bear on the diurnal motion, and 

 even there it is very slight. Hence the two comets have been moving to- 

 gether for years side by side, so to say, and at so short a distance from each 

 other that it was for a long time impossible to distinguish one from the other 

 with the naked eye. M. Faye hence concludes that the separation of Aste- 

 ius's comet .was owing to causes different from those operating on Biela's 

 comet. 



Secondary nuclei, he observes, are not unfrequently seen in a course of 

 formation in the principal nucleus of a comet, in the midst of the luminous 

 sectors which are successively developing themselves around it. MM. Donati 

 and Amici saw one in the dark space existing between two luminous aureo- 

 las of the large comet of 18-"8, and this phenomenon appears to be more 

 frequent even in telescopic comets. These secondary nuclei are in most 

 cases ultimately absorbed by the principal one when the intestine commo- 

 tions, caused by the neighborhood of the sun, have ceased; but during the 

 period of instability, the slightest cause might lead to the expulsion of one 

 of these nuclei, or, in other words, the formation of two comets out of one. 

 When the matter of the aureolas has been partially condensed into a nu- 

 cleus, the latter, having attained a certain degree of density, ceases to 

 form part of the principal nucleus, and then a small degree of force will 

 enable it to separate from the parent comet. 



M. Faye points to the tangential component of the solar repulsion acting 

 on the comet, as the probable force which produces that effect. When Biela's 

 comet, in its double state, again makes its appearance M. Faye confidently 



