466 WHAT IS THE TIDE OF THE OPEN ATLANTIC? 



fluctuations of pressure by means of'an electrical communica- 

 tion with the surface. 



All study of the tides must therefore proceed from the shores. 



SUBDIVISION OF AREA 



The tidal stations for our area fall naturally into two groups 

 as regards distribution in (1) the land-locked waters of the shore 

 itself and (2) the shallow waters bordering North America on 

 the east. Brief notes on the tides of the first area (estuarine) 

 have already been published in the September number of this 

 magazine. Certain water bodies of form not unlike the estuaries 

 there studied could not be included in that paper from the 

 anomalous character of their tides. These are the Bay of Fundy, 

 Vineyard sound, Buzzards ba}r, Narragansett bay , and Long Island 

 sound. For these waters and the general tidal phenomena of 

 the shallow offshore waters we get light from the consideration 

 of the tides in the open Atlantic, and we immediately see that 

 the older view of the ocean tides is in conflict with the facts now 

 widely observed. This was the view of the progressive wave 

 and the cotidal lines. Many difficulties are smoothed over by 

 limiting this conception to the shallower shore waters and sup- 

 posing the ocean basin to be the seat of a stationary wave with 

 vibration period adjusted to the motion of the moon. 



PROGRESSIVE AND STATIONARY WAVES 



A pebble dropped into still water' sends circling ripples in 

 every direction from the point of plunge. The rijDple is a little 

 wave that travels off till overcome by frictional resistances or 

 stopped by the shore. It is a progressive wave. To form it a 

 number of water particles in succession move up, forward, down, 

 and back, as ma}' be noted by floating sticks and straws. Such 

 a wave is produced at or off the mouths of estuaries and travels 

 up them. The velocity is supposed to be that acquired by a 

 body falling freely through one-half the depth of water.* 



If you lift one side of a basin or tub partly filled with water 

 and quickly lower it again, the water within oscillates as a whole 

 in a time dependent for any one vessel on the depth of water. 

 The water on opposite sides rises and falls, up at one side when 

 down on the other. Along a line across the center there is no 



* To make this available in rivers we need a formula for integrating the varying 

 depth and recognition of the effect of width. Now that the Delaware has been gauged, 

 such a study is possible. 



