178 A TEXTBOOK OF OCEANOGRAPHY 



like the Irish Sea, where the tidal currents are very strong, 

 long series of observations are necessary in order to determine 

 what current remains when tidal streams have been eliminated. 

 According to drift-bottle experiments there is a current 

 running east in the English Channel, but the International 

 investigations show that there are considerable differences 

 from year to year. There are pulsations of the Florida Current 

 which result in a very different influx of oceanic water into our 

 seas from year to year. The detailed description of the annual 

 variations in salinity and temperature in the British seas is 

 beyond the scope of this work, and reference should be made 

 to the numerous reports of the International Council for the 

 Exploration of the Seas. It may be remarked that these varia- 

 tions are accompanied by a change in the plankton. In 

 August, 1905, water of high salinity (over 36 per mille) entered 

 the English Channel, and at the same time large swarms of 

 pteropods, which are of oceanic habit, appeared in the Channel 

 and even in Plymouth Sound. 



The east-going current in the English Channel, after 

 allowing for the influence of the tidal streams, must be slight. 

 The coastal plankton predominates and rapidly overcomes the 

 introduced oceanic species, although there are notable excep- 

 tions, as in 1903, when the diatom Ceratium tripos rapidly 

 extended from the Lyme Regis-Guernsey line in May to 

 Dungeness in November. On the French coast the general 

 drift is to the east, and the coastal drift of sand and pebbles 

 confirms this. There may be at certain times of the year a 

 westerly drift in the northern part of the entrance to the 

 Channel, and there seems reason to believe that a certain 

 amount of water leaves the Channel here and flows west and 

 north-west round the Lizard and Land's End. Northerly 

 currents have been determined along the north coasts of Devon 

 and Cornwall, and Gough states that a planktonic Siphono- 

 phore (Muggicea atlantica) drifts across from the neighbour- 

 hood of Land's End towards the Smalls and thence to the Irish 

 coast, and then south and west to the Fastnet, 



