SECONDARY UNDULA-TIONS OF OCEANIC TIDES; 105 



profile travel with different velocities ; but his argument has 

 been proved unsastainable.'" Again, inferior tidal components, 

 known as compound tides or overtides, which become conspicuous 

 only in shallow basins, have been explained by the analogy of 

 combination tones in acoustics. f It seems to us, however, 

 the theory alone is not sufficient to account for the facts that 

 in some gulfs or bays the amplitudes of superior tides are often 

 comparable with those of the proper tidal components and also 

 that most pronounced compound tides are different for different 

 bays or gulfs. FerrelJ attempted to explain some irregularities 

 of oceanic tides by considering oceans as making stationary 

 oscillation as in the case of seiches in lake. Recently E. A. 

 Harris,'^ '=' according to a similar view, constructed a cotidal 

 chart of the world. In his theory, water on the globe is divided 

 into several distinct portions, each of which has the proper period 

 of its own stationary oscillation. This point have been subjected 

 to criticism, by Gr. H. Darwin. He applied his theory also to 

 the explanation of tidal plienomena in many bays and straits, 

 the standing oscillations of which are forced by tidal waves 

 incident on their mouths. He considered, however, exclusively 

 the forced oscillation with diurnal and the semidiurnal periods, 

 and has not considered those oscillations peculiar to each bay. 



Now according to our view, any bay or gulf, either small 

 or large, may be considered as a resonator which oscillates 

 with its own period, if it be excited by waves in the external 

 sea having the synclironizing component. If the proper period 

 of the bay happens to coincide nearly with one of the tidal 



*) McCowen, Phil. Mag. (5), 35, 1892. 



t) W. Thomson, Proc. Roy. Soc. 7. G. H. D.irwio, Brit. Ass. Rep. 188. 



I) Ferrel, Tidal Researches, Rep. Coast and Geodetic Survey, Washington, 1874. 



**) R. A. Harris, Manual of Tides. 



