the orbit in which it may be moving.
Its mean distance from the sun is 141,500,000 miles, its greatest
distance over 154,000,000, and at its nearest approach to the sun, or
'perihelion,' as it is called, its distance is only 129,500,000 miles.
Mars travels in its orbit at a mean rate of 15 miles a second.

"As its orbit is also eccentrically placed in relation to the earth's
orbit, it follows that its nearest distance from us in any particular
years may vary greatly. The nearest possible approach it can make in
regard to the earth is a little under 35,000,000 miles; when at the
opposite point of its orbit its nearest approach is about 62,000,000
miles from the earth. As the years of Mars and the earth differ greatly
in length, and the two planets move at different speeds, the very
favourable oppositions can only occur about once every forty-five years;
though a comparatively near opposition occurs about every fifteen years.
Such a close approach we have just witnessed, and it will be fifteen
years before Mars is again so near to the earth!

[Illustration: _CHART: showing the Orbits of the Earth and Mars, and
the relative positions of the two Planets, during the years 1909-10.
Mars passed over the dotted portion of its Orbit in the year 1910._

_The Outer Circle is the Orbit of Mars, and the inner Circle is the
Orbit of the Earth. The Seasonal points on both Orbits show the Seasons
in the Northern hemisphere. In the Southern hemisphere the Seasons are
reversed, "Summer" occurring at the point marked "Winter," and "Spring"
at the point marked "Autumn," &c. &c._

_The dotted downward line on the left-hand side shows the course taken
by the "Areonal", which left the Earth on the 3rd of August and
arrived at Mars on the 24th of September. * Shows the point reached
when John wished to turn back; and the lower dotted line, the
alternative course then suggested._

_The long dotted line running upwards to the Spring Equinox of the Earth
shows the course taken on the homeward Voyage._

_Drawn by M. Wicks._

Plate VII]

"The Martian year is equal to 687 of our days, but as the Martian days
are slightly longer than ours, this really represents 668 Martian days.

"The entire surface of Mars contains an area of about 56,000,000 square
miles, which is about one-fourth of the area of the earth's surface.

"Its gravity is only three-eighths of the earth's gravity, thus
everything upon Mars would weigh proportionately lighter