166 Chacomac on the Volcanoes of the Sun. 



CHACORNAC ON THE VOLCANOES OF THE SUN. 



We have, in former numbers, made mention of M. Chacornac' s 

 solar observations at Ville-Urbanne, and of the theories which 

 he has been led to form, and we are now indebted to him for a 

 long paper on "The Structure and Origin of Solar Volcanoes." 

 In the present condition of the sun, in which the production 

 of spots is at a minimum, he informs us that the time is 

 favourable for the study of little spots which frequently appear 

 entirely destitute of a penumbra so long as their largest 

 dimensions do not exceed five or sis seconds of an arc,- but 

 which acquire one as they grow bigger. Referring to earlier 

 observations, M. Chacornac informs us that he has drawings 

 of 740 isolated spots not exceeding the dimensions just stated, 

 and all destitute of any certain traces of a penumbra ; while 

 other spots, in closer aggregation or united by fissures, usually 

 exhibit a portion of a penumbra generally corresponding with 

 that part of the spot which is darkest and most deeply ex- 

 cavated. In this category must not be comprehended simple 

 superficial fissures, which are themselves only isolated penumbra, 

 and which appear of different degrees of shade from the intensity 

 of certain nuclei to that of the general surface of the orb, or 

 about a sixtieth below the surface. These are only variations 

 in the level of the photosphere, and seem to occur in the most 

 external layers of the immense luminou.s envelope of the sun. 

 The causes which produce them appear to reside in the super- 

 ficial layers, as it is only changes in the layers which underlie 

 the photosphere that can give rise to such phenomena, and 

 this fact, taken in connection with the rapid changes of form 

 that are noticed on the solar surface, leads to the conclusion 

 that we have to do with an immense atmosphere enveloping a 

 central nucleus. 



The phenomenon which should occupy the foremost place 

 in any Irypothesis is without doubt the rapidity of the precipi- 

 tation of spots one in the other. Hence comes the relative 

 movements of groups in different latitudes, and the appearance 

 of fusion which characterises the formation of spots. All 

 astronomers, for example, might remark the regular form of 

 the great spot which entered the visible hemisphere during the 

 night of the 7th — 8th of last July, and the persistence of 

 this form, which was nearly circular and without diminution, all 

 the while the spot appeared, which was up to the 20th July 

 at 6 P.M. ; and they could also notice the irregularities of shape 

 and the rapid changes exhibited by a single group which, 

 occupied the centre of the disc on the day last named. 



The very rapid chauges in this last group, M. Chacornac 



