Prof. A. D. Bache on Tidal Observations. 343 



under my immediate direction, by Mr. G. W. Dean, Sub-Assis- 

 tant in the Coast Survey, and by Messrs. R. M. Bache, A. S. 

 Wadsurorth, Jr., and W. M. Johnson. 



I am indebted for the diagrams necessary to illustrate the con- 

 chisions already arrived at, to Messrs. Bache, Johnson, and Keyser. 



I present a part only of the labors of these gentlemen. The 

 whole of the hourly observations for the year have been thrown 

 m the form of curves, and numerous tables for examining and 

 verifying the different hypotheses have been made by them. 

 Though the subject was reached inductively, I do not propose to 

 present it strictly in that form. 



The work even now is far from being complete ; indeed we 

 have rather reached the true method of discussion, than have 

 completed the discussion ; and we may yet have to modify our 

 hypothesis, though I think not materially. I present it to tlie 

 Association as a work in ■progress. When the investigation for 

 this station is made complete, the application of the methods to 

 the other stations on the Gulf of Mexico will be in a degree 

 mechanical. 



_ It is curious that one among the earliest complete series of 

 tidal observations on record, is of tides ebbing and flowing but 

 once in twenty-four hours. The observations were made by Mr. 

 Francis Davenport, at Batsha, of the tides on the bar of Ton- 

 qpin, and communicated to Dr. Halley, who gave them, with a 

 diagram connecting the phenomena with the moon's motion in 

 the ecliptic, in the thirteenth volume of the Philosophical Trans- 

 actions for the year 1683. Newton explained these tides by his 

 lunar theory, but in a way, as appears to me, to leave it doubt- 

 ful whether he supposed the interference of two ordinary or six 

 hour tides to produce the phenomena. These tides have been 

 referred to since by almost every wrher of note, who has given 

 a general theory of the tides. 



The subject of the diurnal inequality of the tides has been so 

 ^mpletely and ingeniously discussed by Mr. Wliewell, Master of 

 Truiity, that it may be said emphatically to be his own. He 

 first pointed out the empirical law o^ variation of this inequality. 

 The first distinct attempt to trace the cause of apparent ebb and 

 flow once in twenty-four hours to the influence of the diurnal ir- 

 rp^gularity, is also, so far as I know, his. In discussing (Phil, 

 ^lans. for 1837, Part I,) the tides at Singapore, where the diur- 

 nal inequality is very larse, he was led to the conclusion, if car- 

 "■'ed a little further, "al a certain stage of it the alternate tides 

 Would vanish." To this effect he attributed the " single day tides 

 of King George's Sound, on the coast of New Holland, as observed 

 by Captain Fitz Roy," and gives the curves for a week's observ- 

 ations on the diagram accompanying his paj^rs. The progress 

 of the diurnal inequality wave along the coast of Europe forms 



