474 WHAT IS THE TIDE OF THE OPEN ATLANTIC? 



in half a lunar . . . day." Just as the hand that supports 

 a pendulum may maintain its motion by a gentle lateral move- 

 ment, so the moon's attraction may apply a periodic impulse to 

 a body of water deep and wide enough to oscillate in half a 

 lunar day, and thus make its oscillations perpetual. 



Admiral Fitzro}^,* in 1863, republished some suggestions of 

 his own of earlier date, that the North Atlantic tides (among 

 others) seemed better accounted for as an '' oscillation, as of 

 water in a basin ; or a libration, as a mass of jelly," than as a 

 progression of a southern tide wave. His argument points to 

 irregularities in any system of cotidals, the absence of signifi- 

 cant tide in the Plata estuary, opening fairly to the supposed 

 ocean tide, and the relation between times of high water on op- 

 posite shores. In the North Atlantic he found high water on 

 the American shore fairly synchronous with low water in Eu- 

 rope. In 1879 Mr Henry Mitchell t pointed out that high tide 

 is fairly synchronous from Newfoundland to Hatteras, omitting 

 the Gulf of Maine. Moreover, along this outer coast flood tide 

 current sets to southwest and ebb to northeast. These two facts 

 and the phenomena of the Gulf of Maine are more intelligible 

 . on the hypothesis of an oscillating North Atlantic than on any 

 other. The current would result from the northeast-southwest 

 trend of the coast, confining an ocean oscillating east and west, 

 a portion of the westward motion being resolved parallel to the 

 coast. 



THE STATIONARY WAVE IN THE NORTH ATLANTIC 



It has been noted above that Dr Whewell's data of 1836 showed 

 him that the American cotidals were imperfect. Though he did 

 not redraw the line, he stated that the xii-hour cotidal should 

 be nearer the coast, and Dr Bache + drew it closely contouring 

 from Nantucket to Hatteras and south. It is well established 

 now that, omitting the Gulf of Maine and other enclosed areas, 

 the tides are fairly synchronous from New Foundland to Florida. 

 The great Atlantic oscillation belongs to the deep basin. Across 

 the continental shelf, both east and west, the disturbance is trans- 

 mitted as a progressive wave, and of course delayed in trans- 

 mission. As a rough outline of the Atlantic basin, I have dotted 

 in figure 1 the portions less than 2,000 fathoms deep, not that 



* Weather Book, Appendix on Tides. 



f Ann. Report U. S. Coast and Geodetic Survey, p. 175. 



% Ann. Report U. S. Coast and Geodetic Survey, 1857. 



