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342 Prof. A. D. Bache on Tidal Observations. 



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I hope, in the progress of the Survey along this part of our 

 coast, to develop the subject of these tides, full of importance to 

 the navigatofj and of interest to the man of science. These 

 tides, with special exceptions, ebb and flow but once in twenty- 

 four hours. « 



The tide gauge was of the kind known as the box gauge, with 

 a float and staft', graduated into feet and decimals of a foot. It 

 was placed in the harbor of Cat Island, near the light-house, at 

 the extremity of a temporary wharf. 



The harbor, as the Coast Survey chart which I now present to 

 the meeting shows, turns its widest and deepest opening to the 

 East. 



Apparent time was given by a mark, and the observations were 

 made at mean solar time by applying the equation. The time 

 was of less consequence than ordinary in these observations, 

 from the small rise and fall of the tide, which prevented small 

 differences of time from being noticeable by differences of rise 



and fall. Slight inequalities, caused chiefly by wind, were also 



found to aff^ect the observations so materially that it was not 

 deemed advisable to observe, oftener than once the hour; and 

 after attempting to determine the epoch of high and low water 

 by more frequent observations, it was decided that errors would 

 probably be introduced by aiming at a degree of precision which 

 the phenomena themselves did not present. 



The observations were made day and night, hourly, for a year, 

 with exceedingly rare omissions, and, as the discussion has shown, 

 with a degree of faithfuhiess which merits very great praise. 

 The observers were Messrs. Gustavus Wurdeman and R. T. Bas- 

 sett, attached to the Coast Survey. 



The general opinion of nautical men on the subject of these 

 tides is, that they mainly depend upon the action of the wind; 

 and the very regular effect which may be shown to result from a 

 discussion of the tides in reference to the local action by the 

 wind, lends plausibility to this generalization, which neverthe- 

 less is unfounded. # 



The causes are of a much more general character, and such as 

 usually influence the tides, so modified as to be difl&cult to bring 

 out; phenomena which are only accessory in the ordinary dis- 

 cussions assuming here the chief and overruling part. 



The regular tabulation of the observations was made by Lieu- 

 tenant Comd'g. C. P. Patterson, who did not fail to perceive that 

 the ordinary methods of discussion of the tides were inapplica- 

 ble. His removal from the Survey on other professional service 

 has devolved upon me the labor of discussing the resi^Its. 



Their importance, interest, and novelty, so far as our coast and 

 their striking peculiarities are concerned, have justified me in 

 giving much time to the discussion, which has been carried on 



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