372 l'HILOSOI'HICAL TRANSACTIONS'. [ANNO 1783. 



not terminate all at once at the darkest shade, as in fact it does ? These few in- 

 congruities, which meet us as it were in the very threshold of the theory, are so 

 very palpable, that of themselves they raise unsurmountable doubts. For, gene- 

 rally speaking, the umbra immediately contiguous to the nucleus, instead of 

 being very dark, as it ought to be, from our seeing the immersed parts of the 

 opaque rock through a thin stratum of the igneous matter, is, on the contrary, 

 very nearly of the same splendour as the external surface. 



Concerning the nucleus, or that part of the opaque rock which stands above 

 the surface of the sun, M. de la Lande produces no optical arguments in support 

 of this 3d dimension or height. Neither does he say any thing particular as to 

 the degree of elevation above the surface. But from what has been already 

 hinted in the course of this paper, it appears, that if this were any thing sensible, 

 it ought to be discovered by phenomena very opposite to those which we have 

 found to be so general. Again, a flux and reflux of the igneous matter, so con- 

 siderable as sometimes to produce a great number of spots all over the middle 

 zone, might affect the apparent diameter of the sun, making that which passes 

 through his equator less than the polar one, by the retreat of the igneous matter 

 towards those regions where no spots ever appear. But as a difference of this kind 

 of nearly a thousandth part of the whole would be perceivable, as we learn from 

 M. de la Lande's own observations, compared with those of Mr. Short, in 

 Histoire Acad. 1760, p. 123, it would seem, that the theory had also this dif- 

 ficulty to combat. Further, when among spots very near each other, some are 

 observed to be increasing, while others are diminishing, how is it possible that 

 this can be the effect of such a supposed flux and reflux ? This last inconsistency 

 is mentioned by the author himself, who endeavours to avoid it, by making a 

 new demand on the general fund of hypothesis, deriving from thence such quali- 

 ties of the igneous matter as the case seems to require ; and such must be the 

 method of proceeding in all systems merely theoretical. 



But it is unnecessary to pursue at more length illusive speculations of this kind, 

 especially as we lie under a conviction, founded on fact, of the theory being 

 utterly erroneous. It hardly differs in any respect from that proposed by M. de 

 la Hire, and a little amended by the writer of the Histoire de L'Acad. for 1707, 

 p. 111. 



The writer of the Histoire de L'Acad. for 1719, p. 76, after reviewing the 

 merits of this theory, and comparing it with several phenomena of the spots 

 which had been observed for the 4 preceeding years, pronounces it unsatisfactory. 

 And indeed views, much of the same kind, were even entertained by some so 

 long ago as the days of Scheiner, as we find mentioned by that indefatigable 

 author in his Rosa Ursina, p. 746. 



