lar tide is four tenths as great as the lunar. The
water doubtless obeys in a slight way the attraction of the other
celestial bodies, but the motions thus imparted are too small to be
discerned; they are lost in the great variety of influences which
affect all the matter on the earth.

Although the tides are due to the attraction of the solar bodies,
mainly to that of the moon, the mode in which the result is brought
about is somewhat complicated. It may briefly and somewhat
incompletely be stated as follows: Owing to the fact that the
attracting power of the earth is about eighty times greater than that
of the moon, the centre of gravity of the two bodies lies within the
earth. About this centre the spheres revolve, each in a way swinging
around the other. At this point there is no centrifugal motion arising
from the revolution of the pair of spheres, but on the side of the
earth opposite the moon, some six thousand miles away, the centrifugal
force is considerable, becoming constantly greater as we pass away
from the turning point. At the same time the attraction of the moon on
the water becomes less. Thus the tide opposite the satellite is
formed. On the side toward the moon the same centrifugal action
operates, though less effectively than in the other case, for the
reason that the turning point is nearer the surface; but this action
is re-enforced by the greater attraction of the moon, due to the fact
that the water is much nearer that body.

In the existing conditions of the earth, what we may call the normal
run of the tides is greatly interrupted. Only in the southern ocean
can the waters obey the lunar and solar attraction in anything like a
normal way. In that part of the earth two sets of tides are
discernible, the one and greater due to the moon, the other, much
smaller, to the sun. As these tides travel round at different rates,
the movements which they produce are sometimes added to each other
and sometimes subtracted--that is, at times they come together, while
again the elevation of one falls in the hollow of the other. Once
again supposing the earth to be all ocean covered, computation shows
that the tides in such a sea would be very broad waves, having,
indeed, a diameter of half the earth's circumference. Those produced
by the moon would have an altitude of about one foot, and those by the
sun of about three inches. The geological effects of these swayings
would be very slight; the water would pass