Physical Geography of the Great Oceans 89 



the shape of the continental elevations. The one dovetails 

 into the other. Again, in north polar regions we have a 

 detached oceanic area, while in south polar regions we have 

 a detached continental area. These are similarities of form, 

 and have to do with the earth as a solid. 



There is another class of similarities which are produced 

 by climate re-acting on the surface of the globe and producing 

 tin alterations on it. We find similar alterations of this 

 kind in corresponding localities. 



It may be well in a sentence or two to recall the charac- 

 teristics of intertropical climate. As the belt between the 

 tropics is the only region of the globe within which the sun 

 is ever vertical, and it is always vertical over some part of it, 

 it is the most highly heated part of the earth's surface. Acting 

 on the air, the earth, and the water, the sun's heat renders 

 them all specifically lighter, less dense. In the case of the 

 air and the water, the particles of which are mobile, it produces 

 disturbances of equilibrium, which are adjusted by the move- 

 ment of the particles producing in the air, winds, and in the 

 currents. Further, as the water is capable, under the 

 influence of heat, of changing from the liquid to the aeriform 

 . there is a continual exchange going on between the water 

 the air, producing on the one hand, rain, and on the other, 

 the less evident phenomenon of evaporation. All places on 

 the same parallel of latitude are situated similarly with regard 

 to the prime cause of climate, namely, radiation from the sun 

 and into space. But the sensible effect of the sun's rays dep 

 in a great measure on the nature of the substance whi< h tin -v 

 e, In passing through the atmosphere they hardly warm 

 all ; falling on the sea they warm the water moderate 1\ 

 and on the land they heat the ground intensely. Hence one 

 reason why distribution of sea and land modifies climate. 

 Another and secondary, but not less efficient cause, is th< 

 <-d by land masses to ocean currents, and in 

 >dified way to winds. The effect of tin sun's bestowing 

 greatest amount f hr.it in tin- equatorial region, is to 

 tin- nortl 'id sniith-rast trade winds \\hich blow 



latitudes towards tin .|n.it>r. -uttering a deflection 



