62 A TEXTBOOK OF OCEANOGRAPHY 



made quarterly, and the sea temperatures are recorded, not 

 only at the surface, but also at intermediate depths, by means 

 of the Pettersson-Nansen water-bottle. The daily routine 

 observations on surface temperature are made with "Kiel" 

 thermometers, which are regularly checked with a Richter 

 thermometer, which in turn had been compared with a standard 

 hydrogen thermometer at the Charlottenburg Institute. On 

 the quarterly cruises the deep-sea temperatures are observed 

 by a Nansen deep-sea thermometer in case the Pettersson- 

 Nansen water-bottle is used, or with a reversing thermometer 

 of Richter with the Ekman water-bottle. The surface tempera- 

 tures on the quarterly cruises (when a trained scientist is always 

 present) are registered on a Richter thermometer. By this 

 means records of a high degree of accuracy are obtained. 



In the shallower parts of the Irish Sea the water is 

 homothermous, except for small differences due to convection 

 currents set up by the chilling of the surface waters and lateral 

 shore drifts set up by winds. 



Warm Atlantic water of high salinity can be distinguished 

 flowing into the Irish Sea area. This is the so-called Gulf 

 Stream drift. The amount of this water is greatest in the 

 spring and least in the autumn, and its course up the Irish 

 Sea bears no relation to the deep channel between Ireland and 

 the Isle of Man and through the North Channel. This deep 

 channel is a submerged river valley, and is not due to marine 

 currents. 



The Gulf Stream pulsates, and the amount of Atlantic 

 water entering the Irish and North Seas varies from year to 

 year. When the drift is. at its maximum a current of water 

 flowing northward strikes St. David's Head, and a portion is 

 deflected southward (Fig. 10). 



The climate of the British Islands undoubtedly depends 

 to a certain extent on the strength of the Gulf Stream in any 

 particular year. 



W T hen the Gulf Stream drift is weak less water of high 

 salinity and temperature reaches our shores from the Atlantic, 



