[ 8 ] 
Regarding thefe circumftances as new, I began 
to conlider, what might be the caufe of them. 
• One of two things ieemed necefliirily to be the 
cafe ; either, that they were owing to fome phy- 
sical alteration or wafting of the fpot, and of that 
part of it where the deficiency of the umbra was 
obferved ; or ell’e, that they were owing to the 
nearer approach of the fpot to the limb, by the 
fun’s rotation on his axis. 
The laft of thefe two ideas had no fooner ftruck 
me, than I began to fufped, that the central part, 
or nucleus of this l'pot, was beneath the level of 
the fun’s Spherical furface ; and that the Shady 
zone or umbra, which Surrounded it, might be no- 
thing elle but the (helving fides of the luminous 
matter of the fun, reaching from his furface, in 
every direction, down to the nucleus : for, upon 
this- fuppofition, 1 perceived, that a juft account 
could be given of the changes, of the umbra and 
of the figure of the nucleus, above defenbed. 
The opinion therefore, which 1 ventured to form 
.from what I had fee n this day, was, that this fpot 
.might, probably, be a-vaft excavation in the lu- 
minous matter of the fun ; the nucleus, commonly 
So called, being the bottom, and the umbra the 
Shelving fides of the excavation : and, moreover, 
.that the umbra, next the center of the dife, although 
out of my view, did Still however exift, and was 
•rendered invisible by its prefent position only ; and 
further, that the Sudden alterations, now difeern- 
ible in the figure of the nucleus, were occafioned 
Jby Some part of it alfo being hid, by the inter- 
pofition 
