52 Dr. Herschel on the Nature and Construction 
side of the margin, or penumbra of the spot, which is towards 
the limb, it may partly intercept our view of it, when the spot 
is seen very obliquely. This would require elevations at least 
five or six hundred miles high ; but considering the great at- 
traction exerted by the sun upon bodies at its surface, and the 
slow revolution it has upon its axis, we may readily admit ine- 
qualities to that amount. From the centrifugal force at the 
sun's equator, and the weight of bodies at its surface, I com- 
pute that the power of throwing down a mountain by the exer- 
tion of the former, balanced by the superior force of keeping 
it in its situation of the latter, is near six and a half times less 
on the sun than on our equatorial regions ; and as an elevation 
similar to one of three miles on the earth would not be less 
than 334 miles on the sun, there can be no doubt but that a 
mountain much higher would stand very firmly. The little 
density of the solar body seems also to be in favour of the 
height of its mountains ; for, c ceteris paribus, dense bodies will 
sooner come to their level than rare ones. The difference in 
the vanishing of the shelving side, instead of explaining it by 
mountains, may also, and perhaps more satisfactorily, be ac- 
counted for from the real difference of the extent, the arrange- 
ment, the height, and the intensity of the shining fluid, added 
to the occasional changes that may happen in these particulars, 
during the time in which the spot approaches to the edge of 
the disc. However, by admitting large mountains on the sur- 
face of the sun, we shall account for the different opinions of 
two eminent astronomers ; one of whom believed the spots 
depressed below the sun, while the other supposed them ele- 
vated above it. For it is not improbable that some of the solar 
mountains may be high enough occasionally to project above 
