WAVE OF HIGH WATER. 331 



In the northern island the progression is also in the re- 

 quired direction, but is much overlaid with irregular hours_, 

 arising out of the reactions of the middle island. 



It thus appears that, whilst no land- area exists in which 

 the conditions essential to a perfect revolving wave attain 

 to more than a very moderate degree of fulfilment, and 

 although every existing area is more or less subject to the 

 perturbing effects of adjacent areas, yet nevertheless, when- 

 ever any systematic progression of the hour of high water 

 can be distinctly traced, the wave of high water in the 

 northern hemisphere everywhere tends to revolve round 

 the coasts of land- areas in the direction of the motion of 

 the hands of a watch, and in the southern hemisphere 

 against the direction of the motion of the hands of a 

 watch. 



It may not be out of place to note some facts which 

 strikingly confirm the method of reducing continents, &c., 

 to circular areas of apparently arbitrary position and extent. 

 . The circle which encloses the North American continent 

 emerges, on the coast of the Pacific, at the Mexican port of 

 San Bias, and that which surrounds the main portion of 

 South America emerges on the same ocean at Panama. 

 Betv/een these two points there is a slight progressive in- 

 crease in the tidal hours, which range from 8^ 42"* at 

 Panama to 9^ 46"* at Acapulco; and then there is the 

 curious fact, that between the closely adjacent ports of 

 Acapulco and San Bias there is an abrupt break of several 

 hours in time, as under — 



li. in. 



Acapulco 9 46 



San Bias 4 41 



although, as has already been shown, the progression 

 northwards from San Bias along the west coast of North 

 America is unusually regular, thus showing conclusively 



