The tide is like a wave. It is not very high, but wonderfully wide. It is so broad that a single tide-wave will reach half round the world. Out at sea it is impossible to tell whether it is high or low tide at any time. Near the shore the tides behave in a curious and often wonderful manner, and we can walk along the beaches and see how they work. One of the best places to do this is the vicinity of New York city.
South of this city is the harbor. Still farther south, past the Narrows, is the beautiful bay called New York Bay. Sandy Hook at the south and Coney Island at the north mark the broad entrance to this bay from the Atlantic Ocean. The Hudson River, that stretches far back into the country, runs along the west side of the city. On the east is the narrow and crooked arm of the sea called the East River. You know all this, and it may seem a trifle like a school-book, but your books never told you of half the wonders of this familiar place. The East River opens into Long Island Sound, and the Sound opens into the Atlantic at the farther end of Long Island. Thus it is possible for ships to start from New York and go to sea by the way of the harbor and bay, past Sandy Hook, or they may sail up the East River into the Sound, and reach the sea at Block Island, more than a hundred miles to the east of Sandy Hook.
In the same way the tide coming in from the sea may reach New York by the way of Long Island Sound and the East River, or by the way of Sandy Hook and the bay. Suppose it is low tide off Block Island, at the east end of Long Island (you should look on your map for all this). The tide begins to rise, and enters the Sound. In two hours the wave reaches Sand's Point, and begins to enter the East River. Now happens a curious thing. The Sound grows narrower, and the river is narrower still, and as all the water has to pass at the same time, it rises higher and runs faster. At Block Island the tide rises only two feet. At Hallet's Point, near the city, it rises more than seven feet. The quiet peaceful tide at Block Island becomes here a swiftly flowing stream that surges with foam and fury between the rough rocky banks, and making many a dangerous eddy and whirl-pool. It is no wonder the sailors used to call this place Hell Gate.
Let us look at this place a moment. The East River is open to the sea at each end. It is not like a real river, flowing down hill, and with a current constantly flowing in one direction. It has no current of its own, and were it not for the tides that surge backward and forward through the place twice every day, its waters would be dull and stagnant as any of the quiet lagoons behind the beaches that we have been studying. You can guess what would happen then. The place would soon fill up with mud and sand. Oysters and shell-fish would make it their home; sea-weeds and mosses would cover the bottom, and before long the river would be filled up, and Hell Gate would be closed. This wild turmoil of water just here, this swift-flowing current, keeps the place clear. The tides scour out the river-bed, and help keep it clean for the ships. There are more vessels passing through Hell Gate in a year than at any other place on this continent. If it were closed, our commerce would be sadly injured. Millions of dollars have been spent to make the channel clear, but it is the moon that keeps this great water gate open.
The same tide that first appears off Block Island, and travels through the Sound, also travels along the southern shore of Long Island, and reaches Sandy Hook. As the water grows more shallow, the tide piles up higher, and at Sandy Hook it is more than four feet high. It sweeps on into the bay, and past the Narrows into the harbor, growing higher at every step. It rushes past the Battery, and into the East River, and now it is a swift and powerful current. It rushes onward along both sides of Blackwell's Island, and at Hell Gate the two tides meet. This only increases the war and turmoil of the waters. One tide seems to be piled upon another, and the currents become more furious. In a very little while one or the other gives way. The current turns, and rushes as swiftly the other way. All this strange performance is the work of the moon and the sun.
Everywhere on the sea-coast all round the world the moon lends a hand to help the sea carve out the land. At Sandy Hook it also holds the key of the bay, and keeps the harbor open, that ships may pass out and come in. Were it not for the moon, Sandy Hook would creep slowly out over the shallow waters until it nearly reached Coney Island. The friendly tide comes sweeping in from the sea, and spreads far and wide over the bay. It fills miles and miles of bays and rivers with water, and then when the moon passes on, and the water can follow her no farther, it turns in a mighty flood, and scours and sweeps out all the channels. The outflowing tide is a big broom to brush away the sand and mud, and keep the front door of our port open to all the ships of the world. Did not the sea every day try to reach after the moon, perhaps there would be no tides. Were the tides to stop, our grand front gate would soon be shut, and our convenient back way into the Sound would be closed. It is in this way a great and wise Creator has commanded even the moon to lend a hand in controlling the sea and the land.
