of the Sun and Fixed Stars. 119 
fuperior force of keeping it in its place of the latter, is near 
6+ times lefs on the fun than on our equatorial regions; and 
as an elevation fimilar to one of three miles on the earth 
would not be lefs than 334 miles on the fun, there can be 
no doubt but that a mountain much higher would ftand 
very firmly. The little denfity cf the folar body feems alfo 
to be in favour of the height of its mountains; for, ceteris 
paribus, denfe bodies will fooner come to their level than rare 
ones. The difference in the vanithing of the thelving fide, 
inftead of explaining it by mountains, may alfo, and perhaps | 
more fatisfactorily, be accounted for from the real difference of 
the extent, the arrangement, the height, and the intenfity of 
the fhining fluid, added to the occafional changes that may 
happen in thefe particulars during the time in which the fpot 
approaches to the edge of the difk. However, by admitting 
large mountains on the face of the fun, we hall account for 
the different opinions of two eminent aftronomers; one of 
whom believed the fpots depreffed below the fun, while the 
other believed them elevated above it. For it is not impof~ 
fible that fome of the folar mountams may be high enough 
occafionally to project above the fhining elaftic fluid, when, 
by fome agitation, or other caufe, it is not of the ufual 
height: and this opinion is much ftrengthened by the re- 
turn of fome remarkable {pots which erved Caffini to afcer- 
’ tain the period of the fun’s rotation. A very high country, 
or chain of mountains, may oftener become vifible, by the 
removal of the obftructing fluid, than the lower regions, on 
account of its not being fo deeply covered with it. 
In the year 1791 I examined a large fpot on the fun, and 
found it evidently deprefied below the level of the furface ; 
about the dark part was a broad margin, Yr plane, of confi- 
derable extent, lefs bright than the fun, and alfo lower than 
its furface. This plane feemed to rife, with fhelving fides, 
up to the place where it joined the level of the furface. 
In confirmation of thefe appearances, I carefully remarked 
that the difk of the fan was vifibly convex: and the reafon of 
my attention to this particular, was my being already long 
acquainted with a certain optical deception, tinat takes place 
now and then when we view the moon; which i is, that all 
the 
