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SCIENCE PROGRESS 



When we remember that local conditions, such as rainfall, or 

 the amount of cloud, must also affect the yield of these crops, 

 it must be concluded that the correspondence between the 

 various productivities and the intensity of the Gulf Stream 

 drift, as represented by the surface-temperature of the sea, is 

 surprisingly close. Probably the growth of these crops is 

 determined to a great extent during the few months imme- 

 diately following the time of sowing. During this period the 

 upper layers of the ground are affected by the temperature of 



Fig. 6. — Correspondence between the average sea-temperature beneath the Sognefjord section, 

 the average air-temperature in Norway, and the yields of various harvests in Norway. 



(From Helland-Hansen and Nansen, loc. cit. p. 349.) 



the air in contact with it ; by the more or less rapid movement 

 of the latter; and by the amount of sunshine and cloud. But 

 these are just the factors which lead to the heating of the 

 surface layers of the sea. The warmer the air, the greater 

 the amount of solar radiation, and the less the amount of cloud- 

 covered sky, the warmer will be the surface layers of the sea 

 in comparison with those beneath. Now, if the temperature 

 of the stratum of sea immediately beneath the surface be com- 

 pared with that at 200 metres depth, we obtain a measure 

 of the intensity of the factors causing the heating-up of the 



