eart of the earth have sent its pulses
as widely and rapidly on previous occasions.

The figure of the earth, even on the ocean, is irregular, in consequence
of the greater preponderance of land--and hence greater density--in the
northern hemisphere. These irregularities are often very perplexing
in making exact geodetic measurements. The tendency of matter to
fly from the centre by reason of revolution causes the equatorial
diameter to be twenty-six, miles longer than the polar one. By this
force the Mississippi River is enabled to run up a hill nearly
three miles high at a very rapid rate. Its mouth is that distance
farther from the centre of the earth than its source, when but
for this rotation both points would be equally distant.

If the water became more dense, or if the world were to revolve
faster, the oceans would rush to the equator, burying the tallest
mountains and leaving polar regions bare. If the water should become
lighter in an infinitesimal degree, or the world rotate more slowly,
the poles would be submerged and the equator become an arid waste.
No balance, turning to 1/1000 of a grain, is more delicate than
the poise of forces on the world. Laplace has given us proof that
the period of the earth's axial rotation has not changed 1/100
of a second of time in two thousand years.

[Page 146]
_Tides._

But there is an outside influence that is constantly acting upon
the earth, and to which it constantly responds. Two hundred and
forty thousand miles from the earth is the moon, having 1/81 the
mass of the world. Its attractive influence on the earth causes the
movable and nearer portions to hurry away from the more stable and
distant, and heap themselves up on that part of the earth nearest
the moon. Gravitation is inversely as the square of the distance;
hence the water on the surface of the earth is attracted more than
the body of the earth, some parts of which are eight thousand miles
farther off; hence the water rises on the side next the moon. But
the earth, as a whole, is nearer the moon than the water on the
opposite side, and being drawn more strongly, is taken away from
the water, leaving it heaped up also on the side opposite to the
moon.

A subsidiary cause of tides is found in the revolution of the earth
and moon about their common centre of gravity. Revolution about
an axis through the centre of a sphere enlarges the equator by
centrifugal force. Revolution about an axis touching the s