always on our sky, never rising, never setting, never undergoing any change except from New Earth to Last Quarter! Would not it be fun to trace the shape of our great Oceans and Continents, and to say: 'there is the Mediterranean! there is China! there is the gulf of Mexico! there is the white line of the Rocky Mountains where old Marston is watching for us with his big telescope!' Then we should see every line, and brightness, and shadow fade away by degrees, as she came nearer and nearer to the Sun, until at last she sat completely lost in his dazzling rays! But—by the way—Barbican, are there any eclipses in the Moon?"
"O yes; solar eclipses" replied Barbican, "must always occur whenever the centres of the three heavenly bodies are in the same line, the Earth occupying the middle place. However, such eclipses must always be annular, as the Earth, projected like a screen on the solar disc, allows 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?"
"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 original idea!" said Barbican with a smile.
"My ideas generally are of that category," observed Ardan with an affectation of dry pomposity.
"Not this time, however, friend Michael," observed M'Nicholl.
"Oh! I'm a plagiarist, am I?" asked the Frenchman, pretending to be irritated.
"Well, something very like it," observed M'Nicholl quietly. "Apollonius Rhodius, as I read one evening in the Philadelphia Library, speaks of the Arcadians of Greece having a tradition that their
"O yes; solar eclipses" replied Barbican, "must always occur whenever the centres of the three heavenly bodies are in the same line, the Earth occupying the middle place. However, such eclipses must always be annular, as the Earth, projected like a screen on the solar disc, allows 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?"
"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 original idea!" said Barbican with a smile.
"My ideas generally are of that category," observed Ardan with an affectation of dry pomposity.
"Not this time, however, friend Michael," observed M'Nicholl.
"Oh! I'm a plagiarist, am I?" asked the Frenchman, pretending to be irritated.
"Well, something very like it," observed M'Nicholl quietly. "Apollonius Rhodius, as I read one evening in the Philadelphia Library, speaks of the Arcadians of Greece having a tradition that their
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