re not wanting for the surmise that probably moons to Mars
really existed. It was under the influence of this belief that an
attempt was made by Professor Asaph Hall at Washington to make a
determined search, and see if Mars might not be attended by satellites
large enough to be discoverable. The circumstances under which this
memorable inquiry was undertaken were eminently favourable for its
success. The orbit of Mars is one which possesses an exceptionally
high eccentricity; it consequently happens that the oppositions during
which the planet is to be observed vary very greatly in the facilities
they afford for a search like that contemplated by Professor Hall. It
is obviously advantageous that the planet should be situated as near
as possible to the earth, and in the opposition in 1877 the distance
was almost at the lowest point it is capable of attaining; but this
was not the only point in which Professor Hall was favoured; he had
the use of a telescope of magnificent proportions and of consummate
optical perfection. His observatory was also placed in Washington, so
that he had the advantage of a pure sky and of a much lower latitude
than any observatory in Great Britain is placed at. But the most
conspicuous advantage of all was the practised skill of the astronomer
himself, without which all these other advantages would have been but
of little avail. Great success rewarded his well-designed efforts; not
alone was one satellite discovered which revolved around the planet in
a period conformable with that of other similar cases, but a second
little satellite was found, which accomplished its revolution in a
wholly unexpected and unprecedented manner. The day of Mars himself,
that is, the period in which he can accomplish a rotation around his
axis, very closely approximates to our own day, being in fact half an
hour longer. This little satellite, the inner and more rapid of the
pair, requires for a single revolution a period of only seven hours
thirty-nine minutes, that is to say, the little body scampers more
than three times round its primary before the primary itself has
finished one of its leisurely rotations. Here was indeed a striking
fact, a unique fact in our system, which riveted the attention of
astronomers on this most beautiful discovery.

You will now see the bearing which the movement of the inner satellite
of Mars has on the doctrine of tidal evolution. As a legitimate
consequence of that doctrine, we