Tides

The surface of the ocean rises and falls twice in every ‘lunar’ day, i.e. about 25 hours, and this rise and motion—ebbing fall appears along a coast to be a ‘horizontal’ tide-wave WAVES is auite different from that of a wind-wave (see below), for it affects the whole depth of the ocean equally, while even the most violent wind waves do not trouble the water at all at a depth of 50 feet. Every fortnight, i.e. after a new or a full moon, the tides rise much higher than in the alternate weeks after the first and last quarters of the moon and these high tides are called Spring T., the low; ones being called Neap. This shows that the moon’s influence is much greater than the sun’s. Of course, the whole attraction of the sun on the earth is enormously greater than that of the moon but the moon is so much nearer to the earth that; the difference between her attraction at its centre and on its surface is nearly three times as great as the difference of the sun’s. And it is ‘this difference' that causes the tides. Spring Tides are the result of both sun and moon pulling in the same direction, and Neap tides are the result of their pulling at right angles to each other.