40 



AQUEOUS AGENCIES. 



sity of the equatorial and polar seas would cause exchange or circulation 

 between these regions by means of north and south currents in all 

 longitudes, the equatorial currents being superficial because warm, and 

 the polar currents deep-seated because cold. It is obviously impossible, 

 however, that the principal exchange should be with the pole itself, 

 since this is but a point, but with the northern regions. Observation 

 shows that it is between the equator and the polar circle. In the case 

 we are now considering, the exchange, being in all longitudes, would 

 be scarcely, if at all, perceptible. 



Suppose, second, the earth be set a rotating : then the currents pass- 

 ing from either polar to the equatorial region would be deflected more 

 and more to the westward until, uniting at the equator, they would 

 there form a directly westward equatorial current running around the 

 earth. This westward-moving water would be constantly turning north- 

 ward and southward in all longitudes as a superficial current, and finally 

 eastward about the polar circle, to join again the deep-seated polar cur- 

 rent going to the equator ; thus forming a series ' of regular ellipses 

 lying over each other in strata, dipping eastward and outcropping 

 westward — as represented in Fig. 32. As the north and south currents 

 a a' and b V would take place in all longitudes, they would be scarcely, 

 if at all, perceptible ; but the east currents d d\ and the westward 

 equatorial current c c, where all these unite, would be decided. 



In the third place, introduce continents passing across the equator 

 from north to south, forming impassable barriers to the east and 



west currents c c and cl d. 

 Then many of the lines of 

 current a a a would be 

 crowded against the west- 

 ern shore of the ocean, 

 and of the lines b b b against 

 the eastern shore, forming 

 in each case by concentra- 

 tion very decided currents, 

 while in mid-ocean these 

 currents would be still im- 

 perceptible. Thus thepe?'- 

 ceptible currents of an ocean situated between continents would be rep- 

 resented by the figure (Fig. 33) taken from Dana. 



Besides the main currents above mentioned there would be minor 

 exchanges with the pole itself.* A portion of the eastward current d 

 and d' would turn north and southward, e e\ and circling around would 

 return toward the equator as a deep-seated current under «, hugging 



Fig. 32.— The strong lines a a a show superficial, 

 dotted lines bbb deep-seated currents. 



and the 



* Dana's Manual, p. 



