230 PROCEEDINGS OF THE AMERICAN ACADEMY 



should have the numbers as he states them. Suppose then that the 

 length of the Mississippi River, measured on a meridian^ is only 

 fourteen hundred miles, and that the mouth is only about two and a 

 half miles more distant from the earth's centre than the source. The 

 question arises whether the flow of the river from north to south is 

 caused by the centrifugal force, or whether the criticism of Mr. Mann 

 upon this mechanical solution of the problem is sound. The critic 

 asks : ' Why then does not the mighty force which sends the Missis- 

 sippi up hill four miles send the Nile back to the Mountains of the 

 Moon ? ' And again he asks : ' Why does not the centrifugal motion 

 of the earth drive the waters of the Atlantic and Pacific Oceans to- 

 wards the equator, at the rate of ninety-six miles a day ? ' 



" Let us attend next to Mr. Mann's own explanation of the flow of the 

 Mississippi. After enlarging upon the protuberant matter at the earth's 

 equator, he continues : ' Now water, like every other material thing, 

 is attracted towards the centre of gravity. The centre of gravity is 

 that point about which all the parts are in equilibrio. Or, in popu- 

 lar language, water, like everything else, being attracted by matter, 

 is most attracted, other things being equal, by the greatest quantity. 

 The only philosophical idea we can have of up or doum is from 

 or towards the point of greatest attraction, that is, from or towards 

 the centre of gravity.' Elsewhere, this writer speaks of the earth 

 ' being an oblate spheroid, having the greatest quantity of matter, and 

 therefore the greatest attraction, under the equator.' Finally he 

 says : ' The whole truth is, that the waters of the Mississippi are 

 constantly tending to the common centre of attraction ; but, being pre- 

 vented from approaching that centre in a direct line, they approach 

 it indirectly, by moving forwards along the bed of the channel. They 

 are constantly approaching the centre of gravity, that is, they are con- 

 stantly descending.'' • 



" One error into which Mr. Mann .has fallen is that of supposing 

 that the attraction which the earth exerts at any particular point of its 

 surface is a local phenomenon, and not the resultant of the aggregate 

 attractions of every particle of matter in the earth. This error leads 

 him to a conclusion contradicted by the experiments and observations 

 of the last two centuries ; namely, that where there is the most matter, 

 there is also the most attraction, and that consequently the attraction 

 is stronger at the equator than it is at the poles. We might 

 ask Mr. Maun why this mighty force of attraction does not send the 



