Ago rHILOSOPHICAL TRANSACTIONS. [aNNO 1.774 



imagine, that there may be the hke, or much greater, irregularities in the sur- 

 face of the sun ? 



Is not the property mentioned in the 8th article, namely, that the nucleus of 

 a spot vanishes sooner than the umbra, also agreeable to the present views ? 

 From this state of the phenomenon, we suppose that that part of the sun's dark 

 body, which had been uncovered and exposed to our view, when the spot first 

 broke out, is now again just overflowed by the gradual inundation of the lumi- 

 nous matter. But, after the nucleus thus disappears, may there not however, 

 in many cases, be still left a cavity in the luminous matter, large enough to be 

 perceived ? and will not this cavity, so long as it continues, give the appearance 

 of a small undivided umbra? and will not this umbra still be perceivable, till the 

 luminous matter, by continuing to flow in, has filled up the cavity ? after which, 

 will not the place of the umbra acquire the same lustre with the rest of the sun's 

 surface, and thus will . not all traces of the spot vanish from his body ? And do 

 not the particulars mentioned in the Qth, 10th, and 11th articles seem agreeable 

 to what is now said ? 



Both Scheiner and Hevelius seem to think, that spots sometimes alter their 

 place on the disc, not only by the sun's rotation round his axis, but also by a 

 motion, which they impute to the spots themselves. This Dr. W. could never 

 observe. It is very true, that when a number of small spots lie near one an- 

 other, there may be from time to time a change of their relative situation ; but 

 it is plain that this may proceed entirely from some of them increasing and 

 others diminishing irregularly. But what would further contribute towards form- 

 ing a judgment of this kind is, the apparent alteration of the relative place, which 

 must arise from the motion across the disc on a spherical surface. 



What has been advanced, in the course of the foregoing queries, may perhaps 

 be rendered still more probable, by considering the observations related in the 

 first part of this paper, concerning the changes which are made on the figure of 

 a spot, when another breaks out in its neighbourhood; and which seem to arise 

 from a disturbing force. For, from the cases there laid down, would it not 

 appear, that when a spot is breaking out,' the luminous matter is then forced, 

 in all directions, from the nucleus, and is affected much in the same manner, as 

 it would be, were it a fluid matter encompassing the sun's dark body ? As to the 

 particular nature and qualities of this luminous matter, we have been sometimes 

 apt to imagine, that it cannot well be any very ponderous fluid, but that it 

 rather must resemble, as to its consistence, a very dense and thick fog, that 

 broods on the surface of the sun's dark body. How far will this idea tend to 

 facilitate our conceptions of the various phenomena of the spots above described ? 



It has been gathered from many observations, that the time which the spots 



