The existence of these canals has been doubted. Mr. Lowell has now
devoted years to the subject, has drawn them over and over again, and
has photographed them; and accepts the explanation that they are
artificial, and that vegetation grows on their banks. Thus is revived
the old controversy between Whewell and Brewster as to the
habitability of the planets. The new arguments are not yet generally
accepted. Lowell believes he has, with the spectroscope, proved the
existence of water on Mars.

One of the most unexpected and interesting of all telescopic
discoveries took place in the opposition of 1877, when Mars was
unusually near to the earth. The Washington Observatory had acquired
the fine 26-inch refractor, and Asaph Hall searched for satellites,
concealing the planet's disc to avoid the glare. On August 11th he had
a suspicion of a satellite. This was confirmed on the 16th, and on the
following night a second one was added. They are exceedingly faint,
and can be seen only by the most powerful telescopes, and only at the
times of opposition. Their diameters are estimated at six or seven
miles. It was soon found that the first, Deimos, completes its orbit
in 30h. 18m. But the other, Phobos, at first was a puzzle, owing to
its incredible velocity being unsuspected. Later it was found that the
period of revolution was only 7h. 39m. 22s. Since the Martian day is
twenty-four and a half hours, this leads to remarkable results.
Obviously the easterly motion of the satellite overwhelms the diurnal
rotation of the planet, and Phobos must appear to the inhabitants, if
they exist, to rise in the west and set in the east, showing two or
even three full moons in a day, so that, sufficiently well for the
ordinary purposes of life, the hour of the day can be told by its
phases.