118 ; On the Nature and Conflruétion 
at that time, to bring them to a focus fo as to throw light 
op the moon. 
The unenlightened part of the planet Venus has alfo been- 
feen by different perfons, and not having a fatellite, thofe 
regions that are turned from the fun cannot poffibly thine by 
a borrowed light; fo that this faint illumination muft denote 
fome phofphoric quality of the atmofphere of Venus. 
In the inftance of our large fpot on the fin, I conclude 
from appearances that I viewed the real body of the fun 
itfelf, of which we rarely fee more than its thining atmo-~ 
fphere. 
In the year 1783 I obferved a fine large fpot, and followed 
it up to the edge of the fun’s limb. Here I took notice that 
the fpot was plainly depreffed below the furface of the fun; 
and that. it had very broad fhelving fides. I alfo fufpected 
fome part, at leaft, of the fhelving fides to be elevated above 
the furface of the fun ; and obferved that, contrary to what 
ufually happens, the margin of that fide of the fpot which 
was fartheft from the limb was the broadeft. ‘ 
The luminous fhelving fide of a fpot may be explained by 
a gentle and gradual removal of the {hining fluid, which per- 
mits us to fee the globe of the fun. As. to the uncommon 
appearance of the broadeft margin being on that fide. of the 
fpot which was fartheft from the limb when the {pot came 
near the edge of it, we may furmife that the fun has inequa~ 
lities on its furface, which may poffibly be the caufe of it, 
For, when mountainous countries are expofed, if it fhould 
chance that the higheft partof the landfeape are fituated fo as 
to be near that fide of the margin, or penumbra of the fpot, 
which is towards the limb, it may partly intercept our view of 
it when the fpot is feen very obliquely. This would require 
elevations at leaft five or fix hundred milés high; but confider- 
ing the great attraction exerted by the fun upon bodies at its 
furface, and the flow revolution it has upon its axis, we may 
readily admit imequalities to that amount. From the centri- 
fugal force at the fun’s equator, and the weight of bodies at 
its furface, I compute that the power of throwing down a 
mountain by the exertion of the former, balanced by the_ 
fuperior 
