332 MR. THOMAS CARRICK ON THE 



that the apparently arbitrary position assigned to the 

 northern circle has nevertheless a definite relation to the 

 facts which it professes to group. 



In like manner the circle which surrounds northern 

 Scotland emerges on the west coast at Crinan at 5^ 11°^; 

 and here again^ as in the case of the American continent, 

 whilst the progression northwards along the west coast of 

 Scotland is regular, there is an abrupt break of several 

 hours to the south of Crinan, with a nearly simultaneous 

 tide at 'all the ports on the south-west and south of Scot- 

 land, the average time being about 11^ 20"^. 



Where the same circle emerges on the east coast of 

 Scotland, there is no break in time, but a nearly simul- 

 taneous hour southwards from the Frith of Forth to Holy 

 Isle. 



This tendency to a simultaneous hour of high water on 

 coasts affected by the close proximity of one or more land- 

 areas is a marked feature in tidal phenomena, contrasting 

 strongly with the orderly progression of the wave else- 

 where. 



And it is also worthy of note, that whereas 12 hours 

 suffice for the revolving wave round the coast of each of 

 the American continents, an equal time is occupied by the 

 wave of the middle island of New Zealand, and by the 

 wave of the group of the Fseroe Islands, thus indicating 

 that large and small areas alike are independent centres of 

 action, the velocity of the wave of each area being propor- 

 tionate to the entire extent of coast to be traversed. 



It is well known by those who have handled the data of 

 tidal hours, that, besides the facts which are selected to 

 illustrate systematic progression, every coast is more or 

 less overlaid with irregular tidal hours ; and this feature 

 has become more apparent in proportion as correct data 

 have been accumulated. 



To a large extent, the difficulty of accounting for these 



