Intelligence and Miscellaneous Articles. 159 



projected on to the umbra of a large spot, its superior brightness 

 usually prevents the cloudy stratum from being discerned at all, 

 even when the umbral portion only is included in the small field of 

 new. 



With respect to the highly interesting subject of the origin or 

 cause of the solar spots, I wish to direct special attention to the black 

 nucleus which in most of the large and symmetrical spots is found to 

 occupy some part of the umbra. I cannot but regret that, though 

 nearly twelve years have elapsed since I announced the frequent ex- 

 istence of such a black spot, and that it would be highly desirable to 

 restrict to it the term nucleus, yet I believe the distinction has never 

 been made by any other observer — the umbra having been univer- 

 sally, so far as I know, designated as the nucleus, and the existence 

 of the true black nucleus within it either forgotten or ignored. My 

 earnest desire that the distinction should be recognized and esta- 

 blished does not arise merely from the conviction that accuracy is 

 preferable to inaccuracy, and that where a decided difference really 

 exists it is desirable to express it by a difference of terms, though 

 I should imagine that such a ground would generally be deemed 

 sufficient of itself ; a still more cogent reason is found in the fact, 

 that the whole series of my observations for twelve years past has 

 led me to the conclusion that generally, if not universally, the exist- 

 ence or absence of the black nucleus is sufficient to determine, or at 

 least to throw much light upon, the origin of the spot, and that the 

 origin of those in which the nucleus exists is widely different from 

 the origin of those from which it is absent. To do justice, however, 

 to this view of the subject would unduly lengthen the present paper ; 

 and I therefore hope to be able, in a future communication, more 

 fully to lay before the Society the conclusions at which I have arrived. 

 — From the Monthly Notices of the Royal Astronomical Society , Decem- 

 ber 11, 1863. 



ON THE RAYS OF THE ULTKA-VIOLET SOLAR SPECTRUM. 

 NOTE BY M. MASCART. 



I have the honour to lay before the Academy a drawing of the 

 ultra-violet solar spectrum with most of the rays which it contains. 

 The method used to obtain it is the exact copy of that which serves 

 for the observation of the luminous spectrum. A collimator gonio- 

 meter was used, the two lenses of which are of quartz cut perpendi- 

 cularly to the optic axis, so that the rays traverse it only slightly 

 inclined in reference to this axis. The refracting prism is also of 

 quartz, cut parallel to the axis ; and I generally observed the extra- 

 ordinary spectrum, which is the most divergent. Such a system of 

 lenses is not achromatic ; but this does not prevent a pure spectrum 

 being obtained, and has no other effect than that of causing a consi- 

 derable change of position in passing from the less to the more refran- 

 gible rays. In the mounting of the eyepiece of the telescope is a cross 

 wire, and at the inner extremity of the eyepiece is a photographic 



