|From George H. Darwin's article "Tides," Encyclopaedia
Britannica, IX Ed.,Chicago, 1890. Note that in this graph, time
increases to the left. Larger image.| Tides. This figure shows
the tidal record for two weeks (January 1-14, 1884) at Bombay.
The tide was recorded on a cylindrical sheet that turned once
every 24 hours. Each daily curve is labelled with its date. Some
obvious features: |The yearly travel of the Earth around the
sun, the monthly travel of the Moon around the Earth, and the
daily rotation of the Earth on its axis are the three main
rythms that govern the tides. (It is impossible to draw the Sun-
Earth-Moon system to scale. To scale, the Sun is a basketball in
the center of a football field, the Earth is the eraser on a
pencil held on the sidelines, and the Moon is the tip of a
straightened-out paper clip stuck in the eraser.)| In fact the
"tidal force" depends on the gradient of the gravitational
field. Because (in the case of the lunar tide) what creates the
bulge in the Earth's oceans on the