arth and every particle of the earth. It was seen
how the fluid particles which form the oceans on the earth were enabled
to obey the attraction in a way that the solid parts could not. When the
moon is overhead it tends to draw the water up, as it were, into a heap
underneath, and thus to give rise to the high tide. The water on the
opposite side of the earth is also affected in a way that might not be
at first anticipated. The moon attracts the solid body of the earth with
greater intensity than it attracts the water at the other side which
lies more distant from it. The earth is thus drawn away from the water,
and there is therefore a tendency to a high tide as well on the side of
the earth away from the moon as on that towards the moon. The low tides
occupy the intermediate positions.

The sun also excites tides on the earth; but owing to the great distance
of the sun, the difference between its attraction on the sea and on the
solid interior of the earth is not so appreciable. The solar tides are
thus smaller than the lunar tides. When the two conspire, they cause a
spring tide; when the solar and lunar tides are opposed, we have the
neap tide.

There are, however, a multitude of circumstances to be taken into
account when we attempt to apply this general reasoning to the
conditions of a particular case. Owing to local peculiarities the tides
vary enormously at the different parts of the coast. In a confined area
like the Mediterranean Sea, the tides have only a comparatively small
range, varying at different places from one foot to a few feet. In
mid-ocean also the tidal rise and fall is not large, amounting, for
instance, to a range of three feet at St. Helena. Near the great
continental masses the tides become very much modified by the coasts. We
find at London a tide of eighteen or nineteen feet; but the most
remarkable tides in the British Islands are those in the Bristol
Channel, where, at Chepstow or Cardiff, there is a rise and fall during
spring tides to the height of thirty-seven or thirty-eight feet, and at
neap tides to a height of twenty-eight or twenty-nine. These tides are
surpassed in magnitude at other parts of the world. The greatest of all
tides are those in the Bay of Fundy, at some parts of which the rise and
fall at spring tides is not less than fifty feet.

The rising and falling of the tide is necessarily attended with the
formation of currents. Such currents are, indeed, well known, and i