THE OCEAN. 673 



Where the tide enters a large bay or channel by two passages, the 

 height varies according as the waves from the two directions are both 

 at high water when they come together, or not. At Batscham, in 

 Tonquin, two tidal waves (from the China and Indian seas respectively) 

 meet when it is high water with one and low with the other, and the 

 result is no perceptible tide. 



The tidal waters, owing to the translation character of the wave on 

 soundings, often become tidal currents along shores. On the open 

 shores the translation action is small, though perpetual ; but at the 

 entrance to bays, as at New York Bay, it is a strong tidal current. 

 Along southern Long Island (see map, p. 422), there is some west- 

 ward action from the movement toward New York Bay. In Long 

 Island Sound, the translation wave, entering by the east passage, trav- 

 els along the Sound westward, sweeping each coast as far as the rocky 

 intricate passage called Hell Gate (near where the Sound approaches 

 New York Island), and here it meets the wave coming from the west 

 through New York Bay. The two usually encounter one another 

 with the water at different heights, and the violent currents and whirl- 

 pools of the place are the consequences. Mr. J. E. Hilgard, of the 

 Coast Survey, states that if there were a partition across at Hell Gate 

 the waters would stand on one side sometimes five feet higher, and, at 

 others, five feet lower, than on the other ; and the difference, while 

 less than this from more or less perfect overlappings of the two tidal 

 waves, is often as much as a foot within the space of 100 feet These 

 are illustrations of some of the kinds of action going forward along all 

 continental borders. The tidal current may have the violence of a 

 river-torrent, when the entrance to bays is of a kind to temporarily 

 detain the waters, until the tide has so accumulated them that they 

 rush forward with increased velocity, owing to the depth from the ac- 

 cumulation, so that the hinder part of the wave overtakes the front 

 part, and all move in together. In the Bay of Fundy, the waters of 

 the incoming tide are raised so high above their natural elevation, 

 that, as they advance, they seem to be pouring down a slope, making 

 a turbid waterfall of majestic extent and power, without foam. 



Where the tide moves in all at once the phenomenon is called an 

 eagre or bore. The most perfect examples are afforded at the mouths 

 of the rivers Amazon, Hoogly (one of the mouths of the Ganges), and 

 Tsientang, in China. In the case of the last-mentioned river, the wave 

 plunges on like an advancing cataract, four or five miles in breadth 

 and thirty feet high, and thus passes up the stream, to a distance of 

 eighty miles, at a rate of twenty-five miles an hour. The change from 

 ebb to flood-tide is almost instantaneous. Among the Chusan Islands, 

 just south of the bay, the tidal currents run through the funnel-shaped 

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