160 POPULAR LECTURES AND ADDRESSES. 



places, notably the tide curve for Malta, taken 

 about ten years ago by Sir Cooper Key, and 

 observations on the Atlantic coasts and in many 

 other parts of the world, show something of 

 these phenomena ; a ripple or roughness on the 

 curve traced by the tide gauge, which, when 

 carefully looked to, indicates a variation not 

 regular but in some such period as twenty or 

 twenty-five minutes. It has been suggested that 

 they are caused by electric action ! Whenever 

 the cause of a thing is not known it is immediately 

 put down as electrical ! 



. I would like to explain to you the equilibrium 

 theory, and the kinetic theory, of the tides, but 

 I am afraid I must merely say there are such 

 things ; and that Laplace in his great work, his 

 Mecanique Celeste, first showed that the equi- 

 librium theory was utterly insufficient to account 

 for the phenomena, and gave the true principles 

 of the dynamic action on which they depend. 

 The resultant effect of the tide-generating force 

 is to cause the water to tend to become protube- 

 rant towards the moon and the sun and from 



