OCEANIC CIRCULATION. 243 



much. If friction is so effective, then when the trade- 

 winds flag, as we have seen that they do, the ocean 

 currents ought to be brought to a standstill. More- 

 over, the submarine currents exist, and the wind theory 

 leaves them unexplained. The fact really is that Mr. 

 Croll's reasoning has no application to a system of fluid 

 circulation, where the advance of one part of the fluid 

 is always made room for, so to speak, by the removal 

 of that which it replaces. We might equally well 

 apply Mr. Croll's reasoning to prove that a river cannot 

 flow because of the friction along its banks, as to show 

 that ocean currents cannot flow within their liquid 

 banks. Indeed, many of the points in dispute in this 

 matter of oceanic circulation may be excellently illus- 

 trated by considering the case of a river. I propose to 

 draw this paper to a conclusion by setting forth such 

 an illustration. My readers will not fail to recognise 

 the opinions here severally parodied, so to speak, and 

 so to infer the theory which I regard as affording, 

 on the whole, the best explanation of the observed 

 relations. 



6 Shallow persons,' might one say, ' have launched 

 all sorts of stupidities upon the Mississippi Eiver. 

 Physical geographers have deluged the world with their 

 assumptions respecting it; theorists of all kinds have 

 floated their notions upon it. One says that it brings 

 down, past Baton Eouge and New Orleans, the drainage 

 of half the United States; others ascribe to it the 

 detritus around the delta of that great river which 

 flows into the Grulf of Mexico ; yet others consider that 



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