very peculiar.

Deimos, being only 10 miles in diameter and about 12,500 miles from the
surface of the planet, does not give rise to so many phenomena as the
nearer satellite: still they are very numerous.

It revolves round the planet in 30-1/4 hours, but appears to take
131-1/2 hours to do so, being above the horizon about 60 hours, and
below it nearly 72 hours. These are the times as seen from the equator;
but, as in the case of Phobos, the farther the place is from the equator
the shorter is the period that Deimos is seen above the horizon, until,
when latitude 82 deg. is reached in either hemisphere, it ceases to
become visible at all.

Our moon, being so very much more distant from our earth, could be seen
from both the poles.

Deimos also passes nearly twice through all its phases whilst it is
above the horizon, viz. during about 60 hours, and may be seen twice
full and twice new in that time.

Eclipses of Deimos by the planet and occultations of it by the other
satellite are very frequent. Being so small, it can never cause an
eclipse of the sun, but it transits the sun as a dark spot about one
hundred and twenty times during the Martian year.

This is really a very inadequate list of the phenomena connected with
the satellites, but it will be seen that the number is enormous
compared with the few eclipses of the sun or moon seen on the earth
during the course of one year. Certainly Mars is an astronomer's world!

Merna heard my statements respecting these movements and phenomena as I
explained them to my two friends; and when I had finished, he remarked,
"You seem to be fairly well posted in these matters, sir?"

"Yes," I said; "thanks to our astronomers, both professional and
amateur, all these things have been very carefully calculated; and, with
the exception of a few doubtful points, we probably know nearly as much
about them as the Martians themselves do."

M'Allister then turned to me and said, "Professor, you told us that the
two satellites of Mars revolved round the planet in a certain time, but
in each case you afterwards said they appeared to take a much longer
time to do so. I'm rather puzzled to understand how that can be."

"It's really a simple matter, M'Allister," I answered, "and I think I
can make it clear to you. While the satellite is making one revolution
round the planet the latter is turning on its axis in the same direction
as the satellite is moving, following it up in fact;