308 MR. THOMAS CARRICK ON THE 



the action of the sun and moon on the principal ocean-areas 

 of the globe. 



In 1848, however, he virtually abandoned this hypothesis; 

 for, in his Bakerian Lecture on the tides of the Pacific, he 

 not only expressed grave doubts whether such a supposi- 

 tion rightly represents the mode in which ocean-surfaces 

 obey the action of the sun and moon, but he even ventured 

 upon a new hypothesis, in which the phenomena were at- 

 tempted to be explained on the supposition of stationary 

 undulations corresponding in period with the period of the 

 moon's apparent revolution. 



On this supposition an ocean would be divided into two 

 equal portions, by a middle line running from north to 

 south, forming an axis of no tide, the undulations giving 

 simultaneous high water on the eastern shores and simul- 

 taneous low water on the western shores at the same time 

 — the northerly and southerly shores being occupied by re- 

 volving waves, giving progressive hours along those coasts 

 only. 



This method of viewing tidal phenomena was doubtless 

 partly suggested by the consideration that, in direct opposi- 

 tion to the requirements of existing theories, the height of 

 tides at mid-ocean islands is everywhere found to be com- 

 paratively small. 



An hypothesis not very dissimilar to Dr. WhewelFs had 

 previously been broached by Captain (now Admiral) Fitzroy, 

 who referred the tides to oscillations or libratory motions 

 of the surface of the ocean from west to east and east to 

 west. But, independently of the difficulty of tracing such 

 motions to the action of the sun and moon, both these 

 kindred hypotheses lack the needful support of facts ; for 

 whereas they imply the existence of simultaneous high or 

 low water on the easterly and westerly shores of all con- 

 tinents, the east coast of Africa and part of the westerly 

 coast of the same continent alone show any decided approxi- 



