held possession of a thousand acres at Acharnae. Of
the whole of Greece, as it then appeared to me from above, being about
the size of four fingers, I think Attica was in proportion a mere speck.
So that I wondered on what condition it was left to these rich men to be
proud."[14]

[Footnote 14: Ikaromenippus; or, Above the Clouds. Prof. D.C. Brown's
translation.]

Such scenes as Lucian beheld, in imagination, upon the earth while
looking from the moon, many would fain behold, with telescopic aid,
upon the moon while looking from the earth. Galileo believed that the
details of the lunar surface revealed by his telescope closely resembled
in their nature the features of the earth's surface, and for a long
time, as the telescope continued to be improved, observers were
impressed with the belief that the moon possessed not only mountains and
plains, but seas and oceans also.

It was the discovery that the moon has no perceptible atmosphere that
first seriously undermined the theory of its habitability. Yet, as was
remarked in the introductory chapter, there has of late been some change
of view concerning a lunar atmosphere; but the change has been not so
much in the ascertained facts as in the way of looking at those facts.

But before we discuss this matter, it will be well to state what is
known beyond peradventure about the moon.

Its mean distance from the earth is usually called, for the sake of a
round number, 240,000 miles, but more accurately stated it is 238,840
miles. This is variable to the extent of more than 31,000 miles, on
account of the eccentricity of its orbit, and the eccentricity itself is
variable, in consequence of the perturbing attractions of the earth and
the sun, so that the distance of the moon from the earth is continually
changing. It may be as far away as 253,000 miles and as near as 221,600
miles.

Although the orbit of the moon is generally represented, for
convenience, as an ellipse about the earth, it is, in reality, a varying
curve, having the sun for its real focus, and always concave toward the
latter. This is a fact that can be more readily explained with the aid
of a diagram.

[Illustration: THE MOON'S PATH WITH RESPECT TO THE SUN AND THE EARTH.]

In the accompanying cut, when the earth is at _A_ the moon is between it
and the sun, in the phase called new moon. At this point the earth's
orbit about the sun is more curved than the moon's, and the earth is
moving relatively fas