TIDAL OBSERVATIONS. 277 



exceedingly iutercsting, and demoustrates the very rapid formation of overtides 

 in channels where the rise and fall is great in comparison with the depth at 

 low water. The results for Liverpool (Report 1872) are the means of seven 

 years' reductions, and for Helbre Island of ten years'. The value of the main 

 tides are approximately equal at both places, the solar and lunar semidiurnal 

 tides at Helbre Island being only about one and two per cent, respectively 

 less than the corresponding tides at St. George's landing-stage at Liverpool. 



S. M. MS. 

 Liverpool. Helbre Island. Liverpool. Helbre Island. Liverpool. Helbre Island, 



ft. ft. ft. ft. ft. ft. 



R-j 3'i6o5 3-1283 10-0259 9-8178 



Ej -0570 -0302 -6984 -4862 -4082 -2818 



Eg -1982 -0720 



E^ -0689 -0103 



The results for Kurrachee form a continuation of the three years' results 

 included in the Report for 1872. The previous results are given, quoted 

 below from the Report of 1872, along with the new results for the sake of 

 comparison. The results for the whole five years thus now given together 

 agree very fairly with one another, and form a very vahiable set of tidal com- 

 ponents for this portion of the Indian Ocean. 



Through the kindness of Professors Peirce and Hilgard, of the United- States 

 Coast Survey, two years' tidal observations taken at San Diego on the coast 

 of California, and one year's observations taken at Fort Clinch, Eernandina, 

 Florida, have been placed at the disposal of the Committee. The harmonic 

 analysis has been completed for these observations, and the results are given 

 below. The Committee are also indebted to the United-States Coast Survey 

 for the observations at Fort Point, California, and Cat Island, Gulf of Mexico, 

 of which the harmonic reductions were published in the Report for 1872. 

 These results also are repeated in the present Report, as well as those for 

 Kurrachee, for the sake of comparison. 



The agreement of results for the two years for Sau Diego is exceptionally 

 good throughout. There is a remarkable disproportion between the values 

 of the smaller and larger elHptic semidiurnal tides (R,, of L and N). The 

 eqnihbrium-theoretical proportion between these components is about as 1 to 

 7, but the proportion here is (mean of two years) about as 1 to 35. The 

 smaller component is exceptionally small. 



The retardation of phase of spring-tides (0-030 day) is less than that de- 

 termined for Fort Point, San Francisco Bay, and is the smallest value vet 

 found for any port. 



One of the chief points of interest in the results for Fort Clinch is the re- 

 markable disproportion between the mean solar and the mean lunar semi- 

 diurnal tides, which is as 1 to 6 very nearly. The equilibrium-theoretical 

 proportion being about as 1 to 2-1. This is very nearly fulfilled between the 

 solar and lunar diurnal tides (R^ of P and 0). The time of the coincidence 

 of phase of the P and dcclinational diurnal tides is here negative. This 

 is the first instance yet found of the coincidence happening hefore the times of 

 I^ew and Full Moon. 



Among the most interesting results found by the reduction of the tides 

 of these two places, is that at San Diego the proportion between the two 

 chief tides is nearly identical with what the equilibrium-thoory gives, namely, 

 about 2-1 to 1, while (as said above) the proportion between them at Fort 

 Clinch is about as 6 to 1, or the ratio of the solar tide to the hiiiar tide is 

 only one third of the value which the equilibrium theory assigns to it. 



