"Sailin' upside down? Indeed, sorr, an' ye can't make me believe that, for shure I'm shtandin' on me feet like yourself, head uppermost."
"Well, whether you believe it or not, we are sailing upside down, just as ships going to Australia sail upside down as compared with ships sailing the North Atlantic. But the point of gravity is this: Here we are surrounded on all sides by the shell of the earth, which attracts equally in all directions. Hence all objects in the interior world have no weight as regards whatever thickness of the earth's shell surrounds them. You see, weight is caused by an object having the world on one side of it. Thus both the world and the object attract each other according to the density and distance apart. What we call a pound weight is a mass of matter attracted by the earth on its surface with a force equal to the weight of sixteen ounces. A pound weight on the surface of the earth weighs sixteen ounces, and all the mighty volume of our planet, with all its mountains, continents and seas, weighs only sixteen ounces on the surface of a pound weight. The earth may still weigh many millions of tons as regards the sun, but as regards a pound weight it only weighs sixteen ounces."
"That is an illustration of Flathootly's mental calibre," said Captain Wallace. "He only believes what his brain can accommodate in the way of knowledge."
"God bless the captain," said Flathootly, "I'm shure his brain is as big as mine any day in the week."
"Now," continued the astronomer, "it seems to me that the substances of the earth, rocks, metals, and water, have, under the influence of centrifugal gravity, massed themselves very thickly at the equator or point of greatest motion, and stretch toward the poles in a gradually-lessening mass until the polar gulfs are reached. Thus the earth's shell resembles a musk-melon with the inside cleaned out."
"It makes me mouth wather to think of it," said Flathootly.
"Now, listen," said the astronomer; "we are also under the influence of the earth's centrifugal motion, and wherever we are on the interior surface we swing round our circle of latitude in twenty-four hours, and thus men, ship, and ocean are held up against the interior vault like a boy being able to hold water in a vertical position at the bottom of the pail he swings round him at the end of a cord."
"Don't you think, professor," I inquired, "we will become heavier as we approach the region of greatest motion under the equator?"
"I don't think so," he replied, "for the ocean around the poles has naturally gravitated to the internal as well as to the external equator, to restore the equilibrium of gravity. The reason why a man does not weigh less on the external equator than at the poles, although flying around at the rate of a thousand miles an hour, is that the deeper ocean, that is, the extra twenty-six miles that the earth is thicker on the equator, counter balances by its attraction the loss of weight due to the rapid centrifugal motion, and so preserves in all objects on the earth a uniform weight."
"The whole thing," said Flathootly, "is as clear as mud. I'm glad to know, sorr, I haven't lost me entire constitution at all evints, an' if I can only carry home what weight I've got lift I'll make a fortune in a dime museum."