344 Prof. A, D. Bache on Tidal Observations. 



an interesting part of Mr. Whewell's labors, the conclusions of 

 which are given in the same vokime of the Phil. Trans. 



In all ihese^cases. however, there are two tides in the course 

 of the day, so as to bring out the diurnal inequality by the com- 

 parison of the consecutive high or low water. The subject is 

 followed up in the eleventh series of tidal researches by Mr. 

 Whewell, and in the appendix, in which the diagrams of the 

 tides of Petropaulofskj in the Bay of Avatcha, Kanitschatka, ap- 

 proaching very nearly, at certain parts of the lunar month, to the 

 order of single day tides, is given, to prove that the diurnal in- 

 equality may be so large *'as to lead to the appearance of only 

 one tide in twenty-four (lunar) hours.'^ The equations of the 

 diurnal and semi-diurnal tide waves are given in this paper, and 

 the wave produced by certain cases of their interference is dis- 

 cussed. (Phil. Trans, for 1S40.) 



I do not pretend to give such notice of these important papers 

 as would be necessary in a formal communication. Unquestion- 

 ably the observations now under examination would have fur- 

 nished to Mr. Whewell only the means of trying ideas and con- 

 sequences flowing from those which have been already discussed 

 by him, yet the forms of discussion are original, and perhaps 

 new, and the conclusions present so much of novelty that they 

 remain to be fully put to the test by more elaborate discussion, 

 and by bringing the results at other places to bear upon the same 

 question. I am forced by the necessity for brevity to omit a ref- 

 erence to the learned, ingenious, and elaborate paper of Mr. Airy, 

 in the Phil. Trans, for 1848- 



The small rise and fall of the tides, amounting on the average 

 to but one foot, would seem to make it difficult to obtain the 

 law of the phenomena, even with the aid of the most careful 

 and truthful observations, the class to which those under discus- 

 sion have proved to belong. In regard both to time and height, 

 we may expect to be baffled by small irregularities, requiring 

 long continuance of observations and comparisons of means, to 

 get rid of. Thus far, few cases have occurred which do not ex- 

 hibit more striking coincidences than differences. 



1. To show the time of high or low water in such a w^ay that 

 the discussion miaht be readily o;enera1ized, the diagrams, of which 

 a specimen is before the Association, were made (PI. 3, or iNo- Ij; 

 the hours of the day are the prdinates, and the days of the month 

 the abscissa. The signs H and L show in their proper place the 

 hour of occurrence of high and low water for each day. The 

 time of the moon's superior transit is marked, and the periods of 

 greatest declination, and of crossing the equator. The result is 

 easily generalized, that there is ordinarily but one high and one 

 low water at Cat Island in twenty-four (lunar) hours, and that 

 when there are two tides they occur about the time of the moon's 



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