National Geographic : 1898 Dec
ATLANTIC COAST TIDES 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 430 measures more than 400 miles, reaching the steep descent from the shelf a little 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 water 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. 406.