154 ELEMENTS OF SCIENCE 



temperature, as we have seen there are in the air. 

 From the two extremely cold regions of the globe the 

 Arctic and Antarctic regions cold ocean currents 

 extend, in variously modified ways, towards the equator, 

 while warm currents diverge north and south from the 

 equatorial region towards the poles. 



As every one is aware, there is a diurnal ebb and flow 

 of the ocean which is known as " the tides," but their 

 consideration will be deferred* till some words have 

 been said about the celestial bodies, as otherwise they 

 could not be understood. 



The distribution of the earth's dry land has great 

 effect on these currents and on the climates of the world 

 generally. The greatly preponderating mass of dry 

 land is situated north of the equator, and is divisible 

 into two unequal sections (i) one consisting of the 

 continent of America, and the other (2) of the con- 

 tinents of Europe and Asia, with Africa. The latter 

 section may be regarded as one great whole because, 

 though Africa, but for the Isthmus of Suez, would be 

 an island, the Mediterranean and Red Seas, which 

 divide it from Europe and Asia, are very insignificant 

 tracts of water compared with the great oceans, and 

 each of these is bounded at its outlet by a very narrow 

 strait. These two great sections descend southwards in 

 three prolongations, dividing the earth's immense marine 

 envelope of salt water into three oceans. The American, 

 or New World, section, after becoming extremely 

 narrowed towards the Isthmus of Panama, rapidly 

 spreads out again into an enormous mass of land ex- 

 tending east and west, and then gradually narrows to Cape 

 Horn, which reaches southwards to the 56 of south 



* Seeposf, p. 182, 



