[AS.] The rising and falling of the sea, caused by the moon's action. Owing to gravity, the moon exerts an attraction on every part of the earth, whether liquid or solid, but only the liquid parts which constitute the ocean are free to yield to the attractive force. When the moon is overhead, the water is drawn outwards and heaped up on the side of the earth next the moon. The projecting portions of the water under the moon, on both sides of the earth, represent the positions of high tides, while the low tides occupy the intermediate positions, and we experience what is called high or low water, according as the higher or lower part of the wave reaches our shores. The sun as well as the moon produces tides; but owing to its greater distance, the effect produced by the sun is small in comparison with the attraction of the moon. When the sun and the moon act together we have spring tides; when in opposition we have neap tides. When the tide rushes up a narrow channel, it rises to an unusual height. In the Bay of Fundy the rise and fall is not less than fifty feet, and in the Bristol channel there is a rise of about thirty-eight feet at spring tides. In the Mediterranean the tides have only a small range, varying from one to two feet.