300 THE BEDSHIEL KAIMS 



of iron the same amount. To convert one pound of water 

 into aqueous vapour (or to boil it all away) requires nearly- 

 one thousand (966) times as much heat as would raise 

 that pound one degree Fahrenheit. Hence, to convert 

 one pound (somewhat less than a pint) of sea-water into 

 aqueous vapour requires as much heat as would raise 

 five pounds of iron to 2000° F., which is its fusing 

 point. All this heat remains, as it were, locked up, for 

 a time, in the aqueous vapour, and from that it is slowly 

 given out to the air around as the vapour condenses 

 while drifting from its birth-place. Now, the prevalent 

 winds may transport this very important magazine of heat 

 considerable distances before the whole of it is chilled back 

 again into either rain or snow. So that vast quantities of 

 heat are transferred by the winds from the tropics to distant 

 shores, where it is again set free into the air when the 

 vapour is condensed. On the west coast of Britain the 

 quantity of heat brought to us by this means alone has 

 been computed to be equal to half that derived from the 

 sunheat itself. 



Now, it is well known that the same winds that bring 

 this immense store of heat to our shores also blow along 

 the warm surface-layers of the ocean water from the regions 

 where the evaporation has been most active ; and as the 

 water acquires heat, and also parts with it, very slowly, it 

 drifts many hundreds of miles before it has quite cooled 

 down. Indeed, although the Sun's heat is most powerful 

 in June, the sea is not at its hottest until August, and has 

 not cooled down to its lowest temperature again until 

 February. It used to be this warm surface-water that was 

 regarded as the chief factor in elevating the winter tempera- 

 ture of our climate to its present average. No doubt it is 

 important in that respect ; but so, also, is the other factor 

 mentioned. If, therefore, we understand that when the 

 term " Gulf Stream " is employed, it means the conjoined 

 action of both these factors, it will be more satisfactory than 

 the older way of regarding the term. 



Under present geographical conditions, the Gulf Stream is 

 brought close to our land, and the vapourous part of it is 

 usually pondense4 there Into rain, because our mountains are 



