The tide-generating force of one body on another is directly as the mass of the one body and inversely as the cube of the distance between them. Hence the moon is more effective in producing terrestrial tides than the sun.
The tidal wave directly produced by the moon in the open ocean is about 5 feet high, that produced by the sun is about 2 feet. Hence the average spring tide is to the average neap as about 7 to 3. The lunar tide varies between apogee and perigee from 4·3 to 5·9.
The solar tide varies between aphelion and perihelion from 1·9 to 2·1. Hence the highest spring tide is to the lowest neap as 5·9 + 2·1 is to 4·3 -2·1, or as 8 to 2·2.
The semi-synchronous oscillation of the Southern Ocean raises the magnitude of oceanic tides somewhat above these directly generated values.
Oceanic tides are true waves, not currents. Coast tides are currents. The momentum of the water, when the tidal wave breaks upon a continent and rushes up channels, raises coast tides to a much greater height—in some places up to 50 or 60 feet, or even more.
Early observed connections between moon and tides would be these:—
1st. Spring tides at new and full moon.
2nd. Average interval between tide and tide is half a lunar, not a solar, day—a lunar day being the interval between two successive returns of the moon to the meridian: 24 hours and 50 minutes.
3rd. The tides of a given place at new and full moon occur always at the same time of day whatever the season of the year.