The change from north to south
declination takes place every fourteen days, but these changes
do not necessarily take place at the change in the phases of
the moon. When the moon is south of the equator, she is nearer
to the Southern Ocean, where the tides are generated. The new
moon is nearest to the sun, and crosses the meridian at midday,
while the full moon crosses it at midnight.
The height of the afternoon tide varies from that of the
morning tide; sometimes one is the higher and sometimes the
other, according to the declination of the sun and moon. This
is called the "diurnal inequality." The average difference
between the night and morning tides is about 5 in on the east
coast and about 8in on the west coast. When there is a
considerable difference in the height of high water of two
consecutive tides, the ebb which follows the higher tide is
lower than that following the lower high water, and as a
general rule the higher the tide rises the lower it will fall.
The height of spring tides varies throughout the year, being at
a maximum when the sun is over the equator at the equinoxes and
at a minimum in June at the summer solstice when the sun is
furthest away from the equator. In the Southern Ocean high
water of spring tides occurs at mid-day on the meridian of
Greenwich and at midnight on the 180 meridian, and is later on
the coasts of other seas in proportion to the time taken for
the derivative waves to reach them, the tide being about three-
fourths of a day later at Land's End and one day and a half
later at the mouth of the Thames.
Pages:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25