THE TIDES III 



the rise of the tide occasionally attains remarkable dimensions. 

 Tlie best and most-quoted instance is that of the Bay of Fundy, 

 where at Cape Sable the rise is only 26 mètres, but in the 

 innermost reaches of Mines Basin spring-tides rise 15 to 16 

 mètres. 



In the British Isles the greatest rise of the tide is in the 

 Bristol Channel, where at Clevedon Pier on April 8, 1879, the 

 ascertained rise was i5-g mètres. 



Tide-Recordcrs or Water-Gauges. 



To elucidate the laws governing tidal movements it is 

 indispensable that careful records should be made of the rise 

 and fall of the tide in as many selected localities as possible. 

 The best form of instrument is the self-registering tide gauge, 

 of which there are several types. The principle is a simple 

 one. A float is connected by means of a bronze wire with a 

 self-recording pen or pencil which writes on a vertical cylinder 

 of paper. This paper revolves by means of clock-work, and 

 thus a curve is traced on the surface of the paper. This curve 

 is the tide for the selected locality. An inspection of a few 

 automatic tidal records gives one a good idea of the irregularity 

 of the tides. 



Tidal Théories. 



The first gênerai explanation of the phenomena of the 

 tides was given by Newton, though the connection between 

 the movements of the sun and moon and the rise and fall of 

 the tides had long previously been noted. Newton's theory 

 of gravitation was applied to account for the tides. He 

 supposed the océan to cover the whole earth, and to assume 

 at each instant a figure of equilibrium under the combined 

 gravitation influence of the earth, moon, and sun. 



There are four main tidal théories : 



1. The equilibrium theory (Newton). 



2. The dynamical theory of Laplace. 



3. The canal theory of Airy. 



4. The stationary wave theory of Harris. 



