OF ARTS AND SCIENCES. 231 



Nile back to the Mountains of the Moon. My own answer is, that this 

 excess of attraction at the equator does not exist, and therefore 

 neither carries the Mississippi towards its mouth, nor tends to carry 

 the Nile back from its mouth. To many, the assumption will seem 

 a plausible one, that the excess of matter at the equator should be ac- 

 companied with a redundancy of attraction there. They forget that 

 the whole earth attracts everywhere. And calculation proves that 

 the attraction of the whole earth upon a body at the surface is greater 

 the nearer this body is to the poles ; and for this obvious reason. The 

 excess of equatorial matter operates to the prejudice of equatorial 

 gravity, by keeping the rest of the earth at an unusually large dis- 

 tance. Moreover, it is of no importance to the flow of the Mississippi 

 whether the stronger attraction is at the equator or at the poles ; since 

 the flow of water is determined, not by the intensity of the gravity at 

 the place where the water is, or anywhere else, but by the direction 

 of this gravity in relation to the surface at that place. 



" Again, Mr. Mann speaks of the centre of gravity of the earth, and 

 says that the waters of the Mississippi are constantly approaching this 

 centre of gravity. But why is it that the Nile moves northward ? 

 Does that also approach constantly the same centre of gravity } The 

 whole argument from the centre of gravity of the earth is fallacious. 

 For the earth has no fixed centre of gravity. There is a new centre 

 of gravity to the earth for every new spot of surface which an attract- 

 ed body visits. Water could not flow in any direction without ap- 

 proaching some of these centres of gravhy, and deserting others. 

 And, in fact, the waters at the mouth of the Mississippi are farther 

 from the centre of gravity which belongs to the geographical situation 

 of the mouth, than the waters of the sources of the river are from the 

 centre of gravity which belongs to the position of these sources. In 

 the case of the Nile, exactly the reverse of this is true. 



" What, then, is the true mechanical principle which is applicable 

 to these cases ? It is this. The mutual attraction of the particles 

 of matter upon each other, which, if undisturbed, would mould a yield- 

 ing earth into the form of a perfect sphere, have been so modified by 

 the centrifugal force, resulting from the planet's rotation, as to make 

 the figure of an ellipsoid, in which the largest radius exceeds the 

 shortest by thirteen miles, the true figure of equilibrium. Cohesion 

 enables the solid land to hold out to a limited extent against these 

 moulding influences. But the free waters yield readily to their plas- 



