190 Mr. J. Croll on Ocean- currents in relation to the 



weak. Suppose now the northern hemisphere to be the cold one. 

 The north-east trade-winds of this hemisphere will far exceed 

 in strength the south-east trade-winds of the southern hemi- 

 sphere. The median line between the trades will consequently 

 lie to a very considerable distance to the south of the equator. 

 We have a good example of this at the present day. The dif- 

 ference of temperature between the two hemispheres at present 

 is but trifling to what it would be in the case under considera- 

 tion ; yet we find that the south-east trades of the Atlantic blow 

 with greater force than the north-east trades, and the result is 

 that the south-east trades sometimes extend to 10° or 15° 

 N. lat., whereas the north-east trades seldom blow south of the 

 equator. The effect of the northern trades blowing across the 

 equator to a great distance will be to impel the warm water of 

 the tropics over into the Southern Ocean. But this is not all; 

 not only would the median line of the trades be shifted south- 

 wards, but the great equatorial currents of the globe would also 

 be shifted southwards. 



Let us now consider how this would affect the Gulf- stream. 

 The South-American continent is shaped somewhat in the form 

 of a triangle, with one of its angular corners, called Cape St. 

 Roque, pointing eastwards. The equatorial current of the 

 Atlantic impinges against this corner ; but as the greater por- 

 tion of the current lies a little to the north of the corner, it flows 

 westward into the Gulf of Mexico and forms the Gulf-stream. 

 A considerable portion of the water, however, strikes the laud 

 to the south of the Cape and is deflected along the shores of 

 Brazil into the Southern Ocean, forming what is known as the 

 Brazilian current. 



Now it is perfectly obvious that the shifting of the equatorial 

 current of the Atlantic only a few degrees to the south of its 

 present position — a thing which would certainly take place under 

 the conditions which we have been detailing — would turn the 

 entire current into the Brazilian branch, and instead of flowing 

 chiefly into the Gulf of Mexico as at present, it would all flow 

 into the Southern Ocean, and the Gulf-stream would conse- 

 quently be stopped. The stoppage of the Gulf-stream, com- 

 bined with all those causes which we have just been considering, 

 would place Europe under a glacial condition, while at the same 

 time the temperature of the Southern Ocean would, in conse- 

 quence of the enormous quantity of warm water received, have its 

 temperature (already high from other causes) raised enormously. 



And what holds true in regard to the currents of the Atlantic 

 holds also true, though perhaps not to the same extent, of the 

 currents of the Pacific. 



But there is still another cause which must be noticed : — A 



