THE TIDES. (APP. D.} 209 



APPENDIX D. 



SKETCH OF PROPOSED PLAN OF PROCEDURE IN 

 TIDAL OBSERVATION AND ANALYSIS. 



{Circular issued by Sir William Thomson in December, 1867, 

 to the members of the Committee, appoi?ited, on his sug- 

 gestion, by the British Association in 1867 u For the 

 Purpose of Promoting the Extension, Improvement, and 

 Harmonic Analysis, of Tidal Observations."} 



[Brit is k Association Report, Norwich, 1868, p. 490.] 



i. The chief, it may be almost said the only, 

 practical conclusion deducible from, or at least 

 hitherto deduced from, the dynamical theory is, 

 that the height of the water at any place may be 

 expressed as the sum of a certain number of simple 

 harmonic functions 1 of the time, of which the 

 periods are known, being the periods of certain 

 components of the sun's and moon's motions. 2 

 Any such harmonic term will be called a tidal con- 

 stituent, or sometimes, for brevity, a tide. The 

 expression for it in ordinary analytical notation is 

 A cos nt + B sin nt ; or R cos (nt e), if A = R 



1 See Thomson's and Tail's Natural Philosophy > 53, 54. 



2 See Laplace, Mecanique Celeste, liv. iv. 16. Airy's Tides and 

 Waves, 585. 



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