ATLANTIC COAST TIDES 505 



His study is important for its actual detection of oscillatory 

 slopes in the gulf, its notice of synchronism of tides and currents 

 in each of the two areas, and its frank abandonment of the pro- 

 gressive wave. 



A more satisfactory reason for the delay in the Gulf of Maine 

 tides may perhaps be found in the insistence on the east-west 

 direction of the ocean oscillation that originates the shore tides. 

 The deep entrance to the gulf is about 200 miles from shore on 

 a northwest-southeast line. An east-west cross-section on the 

 shelf in latitude 43° measures more than 400 miles, reaching 

 the steep descent from the shelf a Httle south of the Sable Island 

 bank. Supposing the earliest impulse to enter the Gulf of Maine 

 be that by the deep channel, this must be followed and aug- 

 mented by the progressive waves across the bench, and later by 

 those that have come across the shallower banks. Such an im- 

 pulse would need to be a bodily transfer of the water-mass ; ob- 

 served currents are not incompatible with the idea, a northward 

 deflection of all w r ater entering the gulf being brought about by 

 the gradient into the Bay of Fundy. 



It is interesting that true nodal oscillations have been detected 

 in the Bay of Fundy by Mr A. W. Duff.* He finds an oscilla- 

 tion of the waters between St John, N. B., and Digby Gut(?) in 

 three segments and a period of 42 minutes, according well with 

 the depth and width of the section and having the northwest- 

 southeast direction indicated by our cotidal wave-front. A sim- 

 ilar oscillation of much shorter period is noted in the mouth of 

 the St John river. The free oscillation period of the Gulf of 

 Maine, however, would be much less than the observed one of a 

 half lunar day. The only tenable conception of the Gulf of 

 Maine tides as oscillations with a node on the Sill requires that 

 the whole ocean from the Sill to Europe form the outer segment 

 to the gulf waters, and this, of course, requires the gulf times 

 to agree with general coast times. 



LONG ISLAND SOUND TIDES 



No application of Mr Mitchell's analysis to the tides of Long- 

 Island sound is possible, as the tide unquestionably enters on 

 the east; yet the tide is certainly more belated here than in the 

 Gulf of Maine, and shows a close analogy to the fluming observed 

 in the Bay of Fundy. What happens in the entrance to the 

 basin is better known here, since the passage is a narrow one, 



*Am. Journal of Science, 1897, p. 400. 



