r
surface?"

"It does reach her, in one sense," replied Barbican, "but it does not in
another. Remember the great refraction of the solar rays that must be
produced by the Earth's atmosphere. It is easy to show that this
refraction prevents the Sun from ever being totally invisible. See
here!" he continued, pulling out his tablets, "Let _a_ represent the
horizontal parallax, and _b_ the half of the Sun's apparent diameter--"

"Ouch!" cried the Frenchman, making a wry face, "here comes Mr. _x_
square riding to the mischief on a pair of double zeros again! Talk
English, or Yankee, or Dutch, or Greek, and I'm your man! Even a little
Arabic I can digest! But hang me, if I can endure your Algebra!"

"Well then, talking Yankee," replied Barbican with a smile, "the mean
distance of the Moon from the Earth being sixty terrestrial radii, the
length of the conic shadow, in consequence of atmospheric refraction, is
reduced to less than forty-two radii. Consequently, at the moment of an
eclipse, the Moon is far beyond the reach of the real shadow, so that
she can see not only the border rays of the Sun, but even those
proceeding from his very centre."

"Oh then," cried Ardan with a loud laugh, "we have an eclipse of the Sun
at the moment when the Sun is quite visible! Isn't that very like a
bull, Mr. Philosopher Barbican?"

"Yet it is perfectly true notwithstanding," answered Barbican. "At such
a moment the Sun is not eclipsed, because we can see him: and then again
he is eclipsed because we see him only by means of a few of his rays,
and even these have lost nearly all their brightness in their passage
through the terrestrial atmosphere!"

"Barbican is right, friend Michael," observed the Captain slowly: "the
same phenomenon occurs on earth every morning at sunrise, when
refraction shows us

'_the Sun new ris'n
Looking through the horizontal misty air,
Shorn of his beams._'"

"He must be right," said Ardan, who, to do him justice, though quick at
seeing a reason, was quicker to acknowledge its justice: "yes, he must
be right, because I begin to understand at last very clearly what he
really meant. However, we can judge for ourselves when we get
there.--But, apropos of nothing, tell me, Barbican, what do you think of
the Moon being an ancient comet, which had come so far within the sphere
of the Earth's attraction as to be kept there and turned into a
satellite?"

"Well, that _is_ an