1 54 Z)r. wilson’s Anfwer to the 
to fay any thing at all upon a point of this kind. The breadth: 
of the umbra is, as affumed in the computations, commonly 
‘about equal to that of the nucleus, though iometimes it varies 
more or lefs ;• but how far thefe relative dimenfions indicate 
depth or fhallownefs mil ft be expounded only by obfervation, 
and not by any vague or imperfect notions of tiie nature and 
conftitution of the fun. 
The mention of a pit or hollow or excavation fevers! 
thou hands of miles deep, reaching to that extent down through 
a luminous matter to darker regions, is ready to ftrike the ima- 
gination in a manner unfavourable to a jufb conception of the 
nature of the folarfpots as now defcribed. Upon firft thoughts 
it may look ft range, how the fidfes and bottom of iuch vaft: 
abyftes can remain fo very long in fight, whilft by the fun’s 
rotation they are made to prefent themfelves more and more 
obliquely to our view. But when it is considered, how ex- 
tremely inconfderable their greateft depth is, compared to the 
diameter of the fun, and how very wide and (helving they 
are, all difficulties of this fort will be entirely removed. 
Unlefs, however, we duly attend to thefe proportions, our 
notions upon the fubjed muft be very erroneous ; and it feem3 
the more neceffary to offer this caution, as this very thing is 
inaccurately reprefented in fig. 9. belonging to the Memoire 
under review, and in a way that may lead to miftakes. Inftead 
of exhibiting a fpot as depreffed below the furface of the fun 
one hundredth part of his femi-diameter, the fe&ion of it is 
there determined by two lines drawn from the circumference, 
and meeting in a point at the prodigious diftance of one- 
fifth of the femidiameter below. This author’s known 
dear and comprehenfive ideas of every thing relating to the 
fphere have doubtlefs led him to think, that any particular 
attention to exa&nefs was unneceflary in this reprefentation ; 
but 
