488 PHILOSOPHICAL TRANSACTIONS. [aNNO 1774. 



not distinguishable from any other part of the sun's surface. This is certain 

 from the accounts of all observers. 



Queries and Conjectures, lending to explain the above Properties of the Spots. 



When we consider that the solar spots^ some of whose properties have just 

 now been enumerated, are so many vast excavations in the luminous substance 

 of the sun, and that, wherever such excavations are found, we always discern 

 dark and obscure parts situated below; is it not reasonable to think, that the 

 great and stupendous body of the sun is made up of two kinds of matter, very 

 different in their qualities ; that by far the greater part is solid and dark ; and 

 that this immense and dark globe is encompassed with a thin covering of that 

 resplendent substance, from which the sun would seem to derive the whole of 

 his vivifying heat and energy? And will not this hypothesis help to account for 

 many phenomena of the spots in a satisfactory manner ? For if a portion of this 

 luminous covering were . by any means displaced, so as to expose to our view a 

 part of the internal dark globe, would not this give the appearance of a spot ? In 

 this case, would not that part of the dark globe, which is now laid bare, cor- 

 respond to the nucleus, and the sloping sides of the luminous matter to the 

 umbra ? And is not this consonant to that property of a spot mentioned in the 

 first article ; for would it not hence follow, that every spot, having a nucleus, 

 should also have an umbra surrounding that nucleus, a natural account being 

 at the same time suggested, for the boundary between the nucleus and umbra 

 being always distinctly defined, as mentioned in the 2d article. 



Though we may never have a competent notion of the nature and qualities of 

 this shining and resplendent substance, or of the means by which the excavations 

 in it are formed ; we however discover, in their production, the agency of some 

 mighty, though unknown cause, which is there often exerting itself. Though 

 we manifestly behold its effects, yet the mode of its operations may perhaps re- 

 main unsearchable. But if we were here to venture a conjecture, might we not 

 suppose, that the luminous matter is so disturbed, and the excavations in it oc- 

 casioned, by the working of some sort of elastic vapour, generated within the 

 dark globe? And might not this elastic principle, by its expansion, swell into 

 such a volume, as to reach up to the surface of the luminous matter, which 

 would thus be separated and laid aside in all directions ? And as there is no re- 

 gularity in the time of a spot's enlarging, compared to the time of its decreasing, 

 some enlarging quickly, and decreasing slowly, and vice versa, may we not 

 imagine, that this is owing to the duration and quantity of the elastic principle 

 now mentioned? and in general, may we not hence form some idea of the pro- 

 duction and subsequent enlargement of a spot, as mentioned in the 3d article ? 



But to proceed: as we know from experience, that the spots are of a transient 



