﻿314 WILCOCKS' REFLECTIONS ON THE 



it must be observed, that if they had been informed of the small amount of matter 

 contained in comets, the former would not have imagined that, by their falling upon 

 an extinguished sun, its glory could be restored; and the latter would not have 

 supposed that the plane of rotation of a sun could be changed by so insignificant an 

 object as a comet. 



Sir Wm. Herschel held the opinion that a cosmic cloud lay in the region between 

 Cassiopeia and the earth, and that the temporary star had been obscured by an 

 opaque portion of the cloud. 



The great La Place thus expresses himself on the subject of this star : 



" As to those stars which, appear almost suddenly with great brightness, and then 

 disappear, we may suspect with reason that great conflagrations, occasioned by extra- 

 ordinary causes, have taken place upon their surfaces. This suspicion is strengthened 

 by a change in their color, analogous to what occurs upon our own planet, in bodies 

 which, having become incandescent, subsequently undergo extinguishment."* 



Von Humboldt offers no theory of his own to account for the phenomena of the 

 star of 1572. He merely surmises, " that the apparition of new stars, as well as the 

 variations of the periodical stars, might be owing to an electro-magnetic process of 

 their photospheres. This may occur once or periodically. The electrical processes 

 of light on our earth manifest themselves either as thunderstorms in the regions of 

 the air, or as polar effluxes, and exhibit a certain periodicity."! 



Much as we venerate the name of the great, philosopher who suggested this analogy, 

 we must avow our inability to trace the similarity between the case of a star shining 

 uninteruptedly for seventeen months, and that of atmospheric electricity, a flash of 

 which, according to Sir Charles Wheatstone, does not last the one thousandth part of 

 a second. Nor do we see much resemblance between the light of a star visible at 

 noonday, and that of the polar effluxes, which requires that twilight should fade into 

 darkness ere their feeble flames can be perceived. 



Arago, like Yon Humboldt and Sir John Herschel, does not undertake to explain 

 the variations of this star by any special theory. He notices those offered by the 

 philosophers who had preceded him, and points out their fallacies. The only positive 

 opinion which he gives upon the subject is, that the star during the period of its 

 visibility must have undergone great physical changes.^ 



The doctrine of axial rotation, which has been adopted by many of those who 

 believed in the identity of the stars of 945, 1264 and 1572, to explain its periodicity, 

 brings with it these difficulties : 1st. That it is impossible to illuminate the surface of 

 a sphere in such a way, as that, by rotating at a uniform rate, it can be visible only 



*Systeme du Monde, p. 54. 

 fCosmos, vol. iii., chap. 4. 

 {Astronomic* Popnlaire, vol. i.. p. 425. 



