TIDES 



By H. a. MARMER 



United States Coast and Geodetic Survey 



Plates 31, 32 



With regard to systematic tidal investigations at 

 the present time, it may be said that with but few 

 exceptions they are being carried on by govern- 

 mental agencies and not by educational or research 

 institutions. Furthermore, the governmental agen- 

 cies engaged in tidal work are carrying on this work 

 primarily as a necessary adjunct to other work. 

 For example, in the United States the tidal work is 

 centered almost exclusively in the Coast and 

 Geodetic Survey which carries on this work pri- 

 marily in connection with its hydrographic and 

 geodetic surveying operations. The three major 

 oceanographic research institutions in the United 

 States do not include tidal investigations in their 

 programs of study, although each of these cooperates 

 with the Coast and Geodetic Survey in maintaining 

 a tide station at its institution. 



This almost complete indifference on the part of 

 educational and research institutions to tides has 

 naturally acted to limit drastically the number of 

 students of tidal phenomena. Furthermore, the 

 governmental agencies engaged in tidal work are 

 necessarily interested in its technical rather than 

 in its scientific aspects. As a consequence, tidal 

 investigations in recent years have been largely 

 concerned with technical problems rather than 

 with scientific research. 



The status of tidal investigation at the present 

 time, so far as the observations are concerned, is 

 well pictured in the two maps shown here which 

 are generalized from a manuscript chart showing 

 the locations of tide stations given in Special Publi- 

 cation No. 31 of the International Hydrographic 

 Bureau, now in press. The red dots indicate tide 

 stations in operation in 1935, the blue dots the loca- 

 tion of tide stations at which observations have been 

 made previously. Because of the small scale of the 

 chart, red lines are used to indicate a number 

 of stations in operation along the particular coast, 

 while blue lines indicate the location of a number of 

 stations which were in operation in previous years. 



These maps do not attempt to show all places 

 where tide observations have been made, but rather 

 the places where systematic observations have been 

 carried on. Since the tide varies from day to day, 

 month to month, and year to year, it is obvious 

 that scattered observations of a few days or even 

 more can give nothing but quaUtative information 

 relating to the tide. Such scattered observations 

 on the range and time of the tide are not shown 

 on these maps as they do not furnish sufficiently 

 precise data and do not lend themselves readily to 

 the harmonic analysis, the results of which are of 

 primary importance in tidal research. In passing, 

 too, it may be noted that no attempt has been made 

 to indicate the locations in the Arctic and Antarctic 

 where tide observations have been made. 



A glance at these maps brings out immediately 

 two important facts. First, that along large 

 stretches of the coast there are no tidal observa- 

 tions available. And secondly, out in the open sea 

 observations are wholly wanting except for a few 

 islands. 



With regard to the continental coast, it may 

 reasonably be expected that such observations will 

 become available over the greater part of the world 

 in the not distant future in connection with the 

 hydrographic surveys and with the securing of tidal 

 data for tide tables. 



In the open sea the problem of securing tide 

 observations is a difficult one. While pressure gages 

 have been used in shallow depths, they do not lend 

 themselves for observations at considerable depths. 

 But advantage might be taken of the islands scat- 

 tered through the oceans. The cost of a tide gage 

 is relatively little and its operation is extremely 

 simple. After installation it can be maintained 

 in operation by a local resident. 



Tide observations in the tropical regions are 

 especially needed not only to bring out the local 

 tidal features and their relations to the tidal phe- 

 nomenon as a whole, but also in connection with the 



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