The tidal current at Havre is, moreover, accompanied by a further peculiarity. As was before said, the main flood title in the Channel runs in the offing with a direction from W. to E. until it strike, Cape Antifer ; there it divides, one portion or tidal current continuing to flow up tho Channel, the other running into the bay of the Seine from E. to IV., until it the jetty at the entrance to the port, which deflects it. a little, and causes the bulk of the current to run on until it meets the Cape du floe. A portion of the flood is there deflected, and turns back towards the mouth of the harbour, with a general S.E. by S. direction. A ship making this port at the flood tide, has thus to encounter no less than three tidal currents, flowing in different direc tions; and as all the shores swept by these currents are composed of rocks consisting of materials easily transportable by the water, there is a constant formation of shifting banks at the mouths of the Seine taking place at a short distance from the shore.
The effect of tidal currents upon the outline of a coast is one of the most important forms of their action. For instance, it will be found that all the bays exposed to the action of strongly defined floods open towards their line of advance; and it also generally is the case that the most violent storms blow in the same direction, that is to say, in the direction of the flood tide. In fact, the water is driven with the most violence upon the shores by the flood tides; and they are the great agents in removing and transporting the materials detached from the shores. In all works for coast defences it is important, therefore,
to oalettlete3 all the existing, and the probable future, effects of the tidal currents, observing always that they may depend in many cases on modifications of the outline of the coast lying far away from the locality considered. The advance of the flood tide on the eastern shore of England from the north to south is, for instance, an effect of the same circumstances which cause the flood tide on the weld coast of Ireland, and of Scotland, to flow from south to north ; and in the British Channel from west to cast. The direction of the bars at the mouths of rivers pouring into seas exposed to be crossed by tidal current,, it may be added, follow as a general rule the direction of a resultant between the lines of flow of the ebb from the river, and of the advancing flood.
The greatest amount of theoretical information on the subject of the laws of hydrodynamics affecting tidal currents, is to be found lit Venturoll, Sur la communication lateirale du mouvement dans l'eau ; ' ion Br&ontier and Emmy, Sur lea Ondes; ' iii Sganzin and Millard, Coors do Construction ; ' in the Nautical Magazine ; ' in Lubbock, Whewell, Airy, fie, On Tides,' in the Philosophical Transactions ; ' In Rennet's ' Investigation of Currents;' Young Tides,' in cycloptedia Itritannica,' fie., &e.