ence.

The eclipses of the Moon are less important, less interesting, than the
eclipses of the Sun. Yet their aspect must not be neglected on this
account, and it may be said to vary for each eclipse.

Generally speaking, our satellite does not disappear entirely in the
Earth's cone of shadow; the solar rays are refracted round our globe by
our atmosphere, and curving inward, illumine the lunar globe with a rosy
tint that reminds one of the sunset. Sometimes, indeed, this refraction
does not occur, owing doubtless to lack of transparency in the
atmosphere, and the Moon becomes invisible. This happened recently, on
April 11, 1903.

For any spot, eclipses of the Moon are incomparably more frequent than
eclipses of the Sun, because the cone of lunar shadow that produces the
solar eclipses is not very broad at its contact with the surface of the
globe (10, 20, 30, 50, 100 kilometers, according to the distance of the
Moon), whereas all the countries of the Earth for which the Moon is
above the horizon at the hour of the lunar eclipse are able to see it.
It is at all times a remarkable spectacle that uplifts our thoughts to
the Heavens, and I strongly advise my readers on no account to forego
it.

CHAPTER XI

ON METHODS

HOW CELESTIAL DISTANCES ARE DETERMINED, AND HOW THE SUN IS WEIGHED

I will not do my readers the injustice to suppose that they will be
alarmed at the title of this Lesson, and that they do not employ some
"method" in their own lives. I even assume that if they have been good
enough to take me on faith when I have spoken of the distances of the
Sun and Moon, and Stars, or of the weight of bodies at the surface of
Mars, they retain some curiosity as to how the astronomers solve these
problems. Hence it will be as interesting as it is useful to complete
the preceding statements by a brief summary of the methods employed for
acquiring these bold conclusions.

The Sun seems to touch the Earth when it disappears in the purple mists
of twilight: an immense abyss separates us from it. The stars go hand in
hand down the constellated sky; and yet one can not think of their
inconceivable distance without a shiver.

Our neighbor, Moon, floats in space, a stone's throw from us: but
without calculation we should never know the distance, which remains an
impassable desert to us.

The best educated persons sometimes find it difficult to admit that
these distances of Sun and Moon are better determined an