WATER AS A MECHANICAL AGENT. 



211 



England, the maximum height is 18 feet, and within it, at the mouth of 

 the Severn, 45 to 50 feet. In Long Island Sound (Fig. 189), which is 

 about 100 miles long, the tide outside, at Block Island, is but 2 feet ; but 

 inside, at New London, it is 3 feet ; at the mouth of the Connecticut, 4 ; 

 at New Haven, 6; at Bridgeport, 7; and off Hewlett's Point, near Hell 

 Gate, where it meets the inflowing tide of New York Bay, 7^ feet. The 

 map shows further, by the cotidal lines over the Sound, that the time of 

 the passage from Block Island to Hewlett's Point is about 4^ hours ; and 

 that, at the fourth hour, it is high tide almost simultaneously along the 

 whole inside coast. The height of the tide is depressed somewhat by 

 high atmospheric pressure, but the amount of depression is not yet pre- 

 cisely ascertained. 



189. 



Long Island Sound, ^ j 







Long Island, 



and the 

 Atlantic Border 



o 



X 



Depths along Bathjmetric ^\ \ \ ^ 



lines in fathoms; Cotidal v\ f _^ "^^ '^^ '•£^ 



lines m Long Island Soun \ tt—s y 



the under-water Channe ^ \ 



of Hudson River, from v / ^ 



When the tide enters straits by two passages, progress in eitlier direction 

 depends on depth and obstructions, and leads to meeting at different heights. 

 At Batscham, in Tong-king, the waves, coming from the China and India seas, 

 meet bringing opposite but nearly equal changes in the water level, and the 

 result is almost no perceptible tide. The tidal wave of New York Bay meets 

 that of the Sound at varying heights, causing violent currents at Hell Grate ; 



