National Geographic : 1898 Nov
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 accuracy. 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.