VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 3/] 



pies assumed in part 2, or the conclusions drawn from them ; in short, those 

 who will call that part a theory, and who think it a bad one, may, if they please, 

 mend it, or contrive a new and a better one of their own. But so long as they 

 cannot, by irrefragable optical arguments, set aside the induction laid down in 

 part 1, we must demand of them, so to fabricate their theories as to account for 

 the various circumstances of the spots, considered as things which possess 3 di- 

 mensions, viz. length, breadth, and depth, or, in other words, as excavations in 

 the luminous matter of the sun. This fact is the only one, says Dr. W., I am 

 solicitous to maintain, or to contend for ; and for a very good reason, because I 

 consider it as actually demonstrated by competent observations. As such, to in- 

 dulge for a moment in a figure, it would be a pity not to rescue it from being 

 drawn into the eddy of some treacherous theory, the nature of all which is to 

 sweep into their vortex, and finally to precipitate to the bottom, every thing 

 which obstructs their impetuous career. Sir Isaac Newton, perceiving too well 

 this proneness to system, has laid down his 4th rule of philosophising, that 

 arguments of induction may not be evaded by hypothesis. It will become us 

 therefore, in all things, and in the present subject in particular, to have respect 

 to so excellent a precept. In speaking hereafter of the solar spots, let us separate 

 what things claim to be heard as matters of fact from what- rest on the sandy 

 foundations of mere theory, and no longer confound them together. 



It remains now only to make a (ew strictures on M. de laLande's theory of the 

 solar spots, humbly submitting them to the consideration of the reader. The 

 import of it is, " that the spots as phenomena arise from dark bodies like rocks, 

 which by an alternate flux and reflux of the liquid igneous matter of the sun some- 

 times raise their heads above the general surface. That part of the opaque rock, 

 which at any time thus stands above, gives the appearance of the nucleus, while 

 those parts, which in each lie only a little under the igneous matter, appear to 

 us as the surrounding umbra." 



In the first place it may be remarked, " that the whole proceeds on mere 

 supposition." This indeed the author himself very readily acknowledges. Though, 

 therefore, it could not be disputed by arguments derived from observation, yet 

 conjecture of any kind, if equally plausible, might fitly be employed to set aside 

 its credit. Now all observers, and all good representations of the spots, bear 

 testimony to the exterior boundary of the umbra being always well defined, and 

 to the umbra itself being less and less shady the nearer it comes to the nucleus. 

 Now it may be asked, how this could possibly be, according to M. de la Lande's 

 theory? If the umbra be occasioned by our seeing parts of the opaque rock, which 

 lie a little under the surface of the igneous matter, should it not always be darkest 

 next the nucleus, and from the nucleus outward should it not wax more and 

 more bright, and at last lose itself in the general lustre of the sun's surface, and 



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