. Elementary physical geography;. due to the loss of one of the oil bags, and as soon as anotherwas put out and kept supplied with oil no more waves came on board. The force with which waves strike an opposing surfaceis very great. On the coast of Scotland, measurementsshow that calm-weather waves may strike with a force ofsix hundred pounds per square foot; the momentum of theheaviest storm waves is about ten times as great. Notwithstanding their tremendous energy, waves aresuperficial. The effects of calm-weather waves do notextend more than a few fathoms; the fiercest storm wavesdo not reac
. Elementary physical geography;. due to the loss of one of the oil bags, and as soon as anotherwas put out and kept supplied with oil no more waves came on board. The force with which waves strike an opposing surfaceis very great. On the coast of Scotland, measurementsshow that calm-weather waves may strike with a force ofsix hundred pounds per square foot; the momentum of theheaviest storm waves is about ten times as great. Notwithstanding their tremendous energy, waves aresuperficial. The effects of calm-weather waves do notextend more than a few fathoms; the fiercest storm wavesdo not reach more than two hundred feet below the surface. WAVES, TIDES, AND CURRENTS 201 Tides.—The alternate rise and fall of the sea twice a day-is familiar to everyone who has visited the sea shore. Forsix hours the level of the water gradually rises, spreadsover the shore and fills the river estuaries. For a few mo-ments, the water is stationary; during the next six hoursit falls—ever repeating, never ceasing its oscillations. Nei-. THE TIDE WAVE: MOON IN CONJUNCTION ther the high nor the low water level varies much at anyone place. As the level rises and the water flows in uponthe shore, the tide is flood; as it recedes it is ebb; its highestlevel is high water, and its lowest, low water. During thefew minutes at the turn of the tide it is slack water. This movement of the water is practically a wave severalthousand miles broad. Both the sun and the moon at-
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