through that narrow and shallow passage; hence the two floods meet in the Straits of Dover, which accounts for the miserable chop-sea so sadly prevalent in that unfortunate bit of water. The natural height of the tide seems to be from two to five feet, as shown in the midst of the broad Pacific. “But when dashing against the land, and forced into deep gulfs and estuaries,” to quote Professor Simon Newcomb, “the accumulating tide-waters sometimes reach a very great height. On the eastern coast of North America, which is directly in the path of the great Atlantic wave, the tide rises on an average from 9 to 12 feet. In the Bay of Fundy, which opens its bosom to receive the full wave, the tide, which at the entrance is 18 feet, rushes with great fury into that long and narrow channel, and swells to the enormous height of 60 feet, and even to 70 feet in the highest spring tides. In the Bristol Channel, on the coast of England, the spring tides rise to 40 feet, and swell to 50 in the English Channel at St. Malo on the coast of France.” To this cause is also due in some degree those great oceanic currents which form another striking fact in the history of the sea; but they are mainly due to temperature, wind, and the rotation of the earth. The drops that make up a body of water are the most restless things in the world; they are always sliding down the least slope, sinking out of the way of lighter substances, rising to let a heavier object pass beneath them, or moving hither and thither in an ever hopeful search of that levelness and quiet that we call equilibrium. Furthermore, when water is heated it becomes lighter. Should, therefore, a portion of the sea grow warmer than the remainder, it must and will rise to the surface; and whenever a portion becomes cooled, it must and will sink.