which appeared during the Year 181G. 183 



In regard to the spots which appeared on the sun during the 

 last year (1816) it may be remarked, that two which passed 

 over the disk in September were the largest which occurred. 

 Their situation and form are given in No. I, (Plate 111.) as they 

 were seen on tbe 16th of the above month. Thev were each sur- 

 rounded by an umbra, and preserved nearly the same relative 

 position, with respect to each other, during their progress over 

 the disk ; their course being parallel with and near to the sun's 

 equator. The larger of the two occupied about l-25th part of 

 the sun's diameter. 



As these maculae were very distinctly marked with an opaque 

 centre, encompassed by an imibra and of considerable magni-- 

 tude, they afforded a good opportunity of comparing their ap- 

 pearance with the theory about forty years since advanced by 

 Dr. Wilson the astronomer of Glasgow. He conceived these 

 maculae to consist of vast cavities in the substance of the sun ; 

 that the dark nucleus in the middle was tJie bottom or deep part 

 of the cavity; and that the nebulous circle or umbra was pro^ 

 duced by light faintly reflected from the sloping sides for some 

 depth below the orifice. In support of this theory the Doctor 

 o!)served, that when a spot accompanied by an umbra entered 

 the limb of the sun, the dark nucleus always appeared close to 

 that side of the umbra which was nearest the sun's centre; ,but 

 as the spot advanced towards the middle of tlie disk, the breadth 

 of the umbra gradually enlarged, till the nucleus seemed uni- 

 formly surrounded l)y it. Having passed the centre, the breadlh 

 of the umbra began to contract, on that side next the middle of 

 the sun, till it reached the opposite limb, in which situation the 

 nucleus seemed to touch the edi.;e of the umbra as before, pre- 

 senting tlirough its course, in a reversed order, the same grada- 

 tion exiiibited while advancing towards the centre. 



The appearances, however, which attended the spots in Sep- 

 tember last, did not correspond with the phenomena observed 

 by Dr. Wilson. The writer of this, bearmg in mind the above 

 theory, could not discover that the nucleus ever touched the 

 edge of the umbra; nor did the nebulous circle contract, as the 

 spots receded from the one limb, or approached the other in their 

 passage, further t'lan might be attributed to the ol)lique posi- 

 tion of objects placed on the surface. The cloudy weather pre- 

 vented any observation bring taken till the spots liad arrived at 

 a quarter of the sun's diameter, at which time the nucleus of 



revive, iiniduiiisly, !in (jid tlii.ii!:li liiirin ess ]■ kc. He de^i^ns <mi1v to show 

 that the opimorii ciitcrt:iitncl liy tire at |)hili)s(.|)hers ulun make deep and 

 lasting; iiiipressioiis iiii i!)c ptdilic, whciiier (if seriuiib 'ii- light iiiidcncy ; for 

 iiri other reason than that such opiiiiuiis liave been prDinulgated by men 

 eiiiineiitly j^reat. 



M 4 each 



