ks into the things of reality. HERSCHEL'S paper on _Saturn_,
in 1790, is an admirable example of this.

HERSCHEL'S observations on _Saturn_ began in 1772. From 1790 to 1808 he
published six memoirs on the figure, the ring, and the satellites of
this planet. The spheroidal shape of the ball was first discovered by
him, and we owe much of our certain knowledge of the constitution of the
rings to his work. The sixth and seventh satellites, _Mimas_ and
_Enceladus_, were discovered by him in 1789. The periods of rotation of
the ball and of the ring were also fixed. In his conclusions as to the
real figure of the rings, there is a degree of scientific caution which
is truly remarkable, and which to-day seems almost excessive.

In his paper of 1792, HERSCHEL shows that the most distant satellite of
_Saturn_--_Japetus_--turns once on its axis in each revolution about its
primary, just as our moon does. He says of this:

"I cannot help reflecting with some pleasure on the discovery of an
analogy which shows that a certain uniform plan is carried on among
the secondary planets of our solar system; and we may conjecture
that probably most of the satellites are governed by the same law;
especially if it be founded on such a construction of their figure
as makes them more ponderous towards their primary planets."

I believe the last suggestion to have been the first statement of the
possible arrangement of matter in satellites, which was afterwards so
forcibly maintained by HANSEN in his theory of the moon. HANSEN'S
researches show the consequences of such an arrangement, although they
do not prove its existence.

It should be recorded that the explanation which is to-day received of
the belts and bands upon _Jupiter_, is, I believe, first found in
HERSCHEL'S memoir on _Venus_ (1793). His memoir of 1797, on the
changeable brightness of the satellites of _Jupiter_, has already been
referred to. The times of the rotation of the satellites on their axes
was first determined by HERSCHEL from these observations, which also
contain accounts of the curious, and as yet unexplained, phenomena
attending their appearances on the disc of the planet.

HERSCHEL discovered in January, 1787, the two brighter satellites of
_Uranus_, now called _Oberon_ and _Titania_. They are among the faintest
objects in the solar system. A later discussion of all his observations
led him to the belief that there were four more, and he