hole.

The only effect of gravitational perturbation and of collisions is
gradually to broaden out the whole ring, enlarging its outer and
diminishing its inner diameter. But if there were any frictional
resistance in the medium through which the rings spin, then other
effects would slowly occur, which ought to be looked for with interest.
So complete and intimate is the way Maxwell works out and describes the
whole circumstances of the motion of such an assemblage of particles,
and so cogent his argument as to the necessity that they must move
precisely so, and no otherwise, else the rings would not be stable, that
it was a Cambridge joke concerning him that he paid a visit to Saturn
one evening, and made his observations on the spot.

NOTES TO LECTURE XIV

The total number of stars in the heavens visible to a good eye is about
5,000. The total number at present seen by telescope is about
50,000,000. The number able to impress a photographic plate has not yet
been estimated; but it is enormously greater still. Of those which we
can see in these latitudes, about 14 are of the first magnitude, 48 of
the second, 152 of the third, 313 of the fourth, 854 of the fifth, and
2,010 of the sixth; total, 3,391.

The quickest-moving stars known are a double star of the sixth
magnitude, called 61 Cygni, and one of the seventh magnitude, called
Groombridge 1830. The velocity of the latter is 200 miles a second. The
nearest known stars are 61 Cygni and [alpha] Centauri. The distance
of these from us is about 400,000 times the distance of the sun. Their
parallax is accordingly half a second of arc. Sirius is more than a
million times further from us than our sun is, and twenty times as big;
many of the brightest stars are at more than double this distance. The
distance of Arcturus is too great to measure even now. Stellar parallax
was first securely detected in 1838, by Bessel, for 61 Cygni. Bessel was
born in 1784, and died in 1846, shortly before the discovery of Neptune.

The stars are suns, and are most likely surrounded by planets. One
planet belonging to Sirius has been discovered. It was predicted by
Bessel, its position calculated by Peters, and seen by Alvan Clark in
1862. Another predicted one, belonging to Procyon, has not yet been
seen.

A velocity of 5 miles a second could carry a projectile right round the
earth. A velocity of 7 miles a second would carry it away from the
earth, and round the sun. A veloci