Fig. 112.—Attraction of the Moon
Causes the Tides.
Since the Earth revolves round its axis once in 24 hours these tidal waves go round the Earth and as there are two tidal waves each day there are two high tides and two low tides at every place on the ocean, but these are chiefly noticeable on the coasts. [Fig. 112] shows the position of the Moon and the Earth, while the wavy lines around the Earth represent the oceans.
Spring Tides and Neap Tides.—Not only does the Moon’s attraction cause the tides, but the Sun’s pull on the Earth also produces tides.
When the Sun and Moon are in a line with the Earth they pull together and the tides are raised very high and they fall very low, and these high and low tides are called spring tides.
Since we have either new Moon or full Moon, when the Sun, Earth and Moon are in a line, the spring tides occur at these times, or twice every month. [Figs. 113] and [114] show how the spring tides are formed.
Fig. 113.—How Spring Tides
Are Formed.
Fig. 114.—How Spring Tides
Are Formed.