210 IlEPORT ON THE SURFACE DRIFT OF THE ENGLISH CHANNEL 



determine the existence of such occasional currents by applying to the 

 data provided by drift-bottles a method of analysis to be described 

 below. 



The possibility of a permanent westward current through the 

 Channel from the North Sea is precluded by the results of Fulton's 

 experiments, which were briefly suunuarised in Mr. Allen's letter at the 

 commencement of this report. 



A second cause of surface currents independent of local winds is to 

 be found in the tides. The tidal stream in the Channel runs with a 

 velocity which in different parts varies from about half a mile to about 

 three miles an hour. There is no need to sum up here the peculiarities 

 of the Channel tides, but as the courses of the flood and ebb streams 

 are approximately parallel over the greater part of the Channel, it does 

 not appear that the course of drift-bottles would be materially affected 

 by them in the long run, except in certain well-defined regions of the 

 Channel. These are principally the two orifices of the Channel, to- 

 gether with Lyme Bay, the neighbourhood of the Solent and Spit Head, 

 and the Gulf of St. Malo. 



At the western entrance to the Channel the West Channel tidal 

 stream runs in opposite directions to the oceanic tidal stream, and where 

 the two streams meet the tides are rotary, with scarcely any interval 

 of slack water. Off Mounts Bay the ebb, or west-going stream, runs 

 longer and stronger than the flood, or east-going stream, so that a vessel 

 leaving Mounts Bay at half ebb counts upon a nine hours' tide to carry 

 her up the Bristol Chanuel. This preponderance of the westward 

 current is due partly to the meeting of the two tidal streams referred 

 to, and partly to the indraught into the Bristol Channel during flood 

 tide. The effect of the tidal currents in this neighbourhood is clearly 

 seen in the case of two of our batches of drift-bottles, nos. XXX. and 

 XL., as will be shown below. 



The conditions in the Straits of Dover are similar in principle, though 

 more complicated in detail. Here the West and East Channel streams 

 meet at high water and separate at low water, and there is the phenom- 

 enon of an "intermediate tide," which is found running along the 

 shore at high and low water when the main streams are at rest. The 

 Strait of Dover thus never has slack water throughout its extent at 

 any one time, and, as stated in the Channel Pilot, " if a vessel having 

 come up Channel with the last of the West Channel stream running 

 E. enters the intermediate tide running E. off Hastings, she will have 

 a continuation of it for four hours longer, and, if sailing eight knots, 

 will carry it to the N. Foreland." 



On the other hand, at the commencement of flood in the southern 

 portion of the Straits, owing to a simultaneous set of the intermediate 



