30* KELVIN 



at Dover the current begins to flow west through the whole 

 of the Channel. When it is mid-tide at Dover the tide is 

 flowing fastest in the Channel. This was first brought to 

 light by Admiral Beechey. 



I wish I had time to show the similar theory as to the 

 tides in the Irish Channel. The water runs up the English 

 Channel to Dover, and up the Irish Channel to fill up the 

 basin round the Isle of Man. Take the northern mouth of 

 the Irish Channel between the Mull of Cantire and the north- 

 east coast of Ireland. The water rushes in through the 

 straits between Cantire and Rathlin Island, to fill up the 

 Bay of Liverpool and the great area of water round the Isle 

 of Man. This tidal wave entering from the north, running 

 southward through the Channel, meets in the Liverpool 

 basin with the tidal stream coming from the south entrance, 

 and causes the time of high water at Liverpool to be within 

 half-an-hour of the time of no currents in the northern and 

 southern parts of the Channel. 



I would like to read you the late Astronomer-Royal's ap- 

 preciation of Laplace's splendid work on the tides. 



Airy says of Laplace: "If now, putting from our 

 thoughts the details of the investigation, we consider its 

 general plan and objects, we must allow it to be one of the 

 most splendid works of the greatest mathematician of the 

 past age. To appreciate this, the reader must consider, first, 

 the boldness of the writer, who, having a clear understand- 

 ing of the gross imperfections in the methods of his pred- 

 ecessors, had also the courage deliberately to take up the 

 problem on grounds fundamentally correct (however it 

 might be limited by suppositions afterwards introduced) ; 

 secondly, the general difficulty of treating the motion of 

 fluids ; thirdly, the peculiar difficulty of treating the motions 

 when the fluids cover an area which is not plane but con- 

 vex; and fourthly, the sagacity of perceiving that it was 

 necessary to consider the earth as a revolving body, and the 

 skill of correctly introducing this consideration. This last 

 point alone, in our opinion, gives a greater claim for reputa- 

 tion than the boasted explanation of the long inequality of 

 Jupiter and Saturn/' 



Tidal theory must be carried on along with tidal ob- 



