h
we see to be due to great oceanic humps (great in area that is, though
small in height), let us proceed to ask what causes these humps; and if
it be the moon that does it, how does it do it?

The statement that the moon causes the tides sounds at first rather an
absurdity, and a mere popular superstition. Galileo chaffed Kepler for
believing it. Who it was that discovered the connection between moon and
tides we know not--probably it is a thing which has been several times
rediscovered by observant sailors or coast-dwellers--and it is certainly
a very ancient piece of information.

Probably the first connection observed was that about full moon and
about new moon the tides are extra high, being called spring tides,
whereas about half-moon the tides are much less, and are called neap
tides. The word spring in this connection has no reference to the season
of the year; except that both words probably represent the same idea of
energetic uprising or upspringing, while the word neap comes from nip,
and means pinched, scanty, nipped tide.

The next connection likely to be observed would be that the interval
between two day tides was not exactly a solar day of twenty-four hours,
but a lunar day of fifty minutes longer. For by reason of the moon's
monthly motion it lags behind the sun about fifty minutes a day, and the
tides do the same, and so perpetually occur later and later, about fifty
minutes a day later, or 12 hours and 25 minutes on the average between
tide and tide.

A third and still more striking connection was also discovered by some
of the ancient great navigators and philosophers--viz. that the time of
high water at a given place at full moon is always the same, or very
nearly so. In other words, the highest or spring tides always occur
nearly at the same time of day at a given place. For instance, at
Liverpool this time is noon and midnight. London is about two hours and
a half later. Each port has its own time for receiving a given tide, and
the time is called the "establishment" of the port. Look out a day when
the moon is full, and you will find the Liverpool high tide occurs at
half-past eleven, or close upon it. The same happens when the moon is
new. A day after full or new moon the spring tides rise to their
highest, and these extra high tides always occur in Liverpool at noon
and at midnight, whatever the season of the year. About the equinoxes
they are liable to be extraordinarily high. The extra l