described it as the transference of motion without the
transference of matter; of form without the substance; of force
without the agent.

The action produced by the sun and moon jointly is practically
the resultant of the effects which each would produce
separately, and as the net tide-producing effect of the moon is
to raise a crest of water 1.4 ft above the trough, and that of
the sun is 0.6 ft (being in the proportion of I to 0.445), when
the two forces are acting in conjunction a wave 1.4 + 0.6 = 2
ft high is produced in the Southern Ocean, and when acting in
opposition a wave 1.4 - 0.6 = 0.8 ft high is formed. As the
derivative wave, consisting of the large mass of water set in
motion by the comparatively small rise and fall of the primary
wave, is propagated through the branch oceans, it is affected
by many circumstances, such as the continual variation in width
between the opposite shores, the alterations in the depth of
the channels, and the irregularity of the coast line. When
obstruction occurs, as, for example, in the Bristol Channel,
where there is a gradually rising bed with a converging
channel, the velocity, and/or the amount of rise and fall of
the derivative wave is increased to an enormous extent; in
other places where the oceans widen out, the rise and/or
velocity is diminished, and similarly where a narrow channel
occurs between two pieces of land an increase in the velocity
of the wave will take place, forming a race in that locality.

Although the laws governing the production of tides are well
understood, the irregularities in the depths of the oceans and
the outlines of the coast, the geographical distribution of the