WHAT IS THE TIDE OF THE OPEN ATLANTIC?* 

 By Mark S. W. Jefferson 



The writer has sought to collect the known facts of the tides 

 of Atlantic North America and study them in relation to the 

 geography. 



At the present date the mathematical theory of the tides has 

 reached a considerable degree of perfection. The theory of geo- 

 graphic influences can hardly be said to have been formulated. 

 Analysis has succeeded in predicting the tides of tomorrow from 

 those of yesterday, but no description of shore configuration and 

 submerged topography will yet enable the mathematician to 

 predict the time and height of the tide at an unknown port. 

 Give him a series of observations at that place, and he will learn 

 from them the local constants and compute the future tides with 

 accurac}\ This is indeed the only end he has had in view, and 

 it is of great practical importance. The results now accumu- 

 lated are sufficiently accurate and numerous to deserve compar- 

 ative study. Furthermore, much light is shed upon this study 

 by the hints that analysts have dropped by the way, if a layman 

 may venture to interpret them. But for Ferrel's "Treatise on 

 Tides " the present paper could not have been written. Most 

 readers would find the mathematical work veiled in mystery, 

 and not all mathematicians condescend to draw aside the veil. 

 Diurnal inequality, for instance, affects low water little or none 

 and high water much. A, mathematician states that harmonic 

 analysis shows it must be so, and we may get what enlighten- 

 ment from it we can. 



In such a study one is immediately struck by the twofold 

 aspect of the problem : 



(1) The tides of theory reside in the deep ocean. 



(2) The tides of observation belong to the margins of the land. 

 Data given for tides in the open ocean refer merely to the 



shores of oceanic islands, and it should be borne in mind that 

 tides on the ocean do not admit of measurement by any means 

 as yet at our command, though it is not inconceivable that a 

 gauge might be lowered to the ocean floor which should record 



* Extract from Thesis in research course in Geography at Harvard University. 

 32 465 



