more than half of the Sun to be still visible."

"How is that?" asked M'Nicholl, "no total eclipses in the Moon? Surely
the cone of the Earth's shadow must extend far enough to envelop her
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?"