orm and much higher. We thus
see how futile it is, with our present knowledge, to dogmatise on the
existence or non-existence of life in other celestial orbs.

As to the canals Dr. Wallace puts forward a theory of his own. He
contends that after Mars had cooled to a state of solidity, a great
swarm of meteorites and small asteroids fell in upon it, with the result
that a thin molten layer was formed all over the planet. As this layer
cooled, the imprisoned gases escaped, producing vents or craterlets; and
as it attempted to contract further upon the solid interior, it split in
fissures radiating from points of weakness, such, for instance, as the
craterlets. And he goes on to suggest that the two tiny Martian
satellites, with which we shall deal next, are the last survivors of his
hypothetical swarm. Finally, with regard to the habitability of Mars,
Dr. Wallace not only denies it, but asserts that the planet is
"absolutely uninhabitable."

For a long time it was supposed that Mars did not possess any
satellites. In 1877, however, during that famous opposition in which
Schiaparelli first saw the canals, two tiny satellites were discovered
at the Washington Observatory by an American astronomer, Professor Asaph
Hall. These satellites are so minute, and so near to the planet, that
they can only be seen with very large telescopes; and even then the
bright disc of the planet must be shielded off. They have been
christened Phobos and Deimos (Fear and Dread); these being the names of
the two subordinate deities who, according to Homer, attended upon Mars,
the god of war.

It is impossible to measure the exact sizes of these satellites, as they
are too small to show any discs, but an estimate has been formed from
their brightness. The diameter of Phobos was at first thought to be six
miles, and that of Deimos, seven. As later estimates, however,
considerably exceed this, it will, perhaps, be not far from the truth to
state that they are each roughly about the size of the planetoid Eros.
Phobos revolves around Mars in about 7-1/2 hours, at a distance of about
only 4000 miles from the planet's surface, and Deimos in about 30 hours,
at a distance of about 12,000 miles. As Mars rotates on its axis in
about 24 hours, it will be seen that Phobos makes more than three
revolutions while the planet is rotating once--a very interesting
condition of things.

A strange foreshadowing of the discovery of the satellites of Mars will
be f