THE TIDES. 279 



The real motion will be that of the solid portion of the earth that 

 moves from Avest to east, and underneatli these waves, though these 

 waves do also acquire, by means of friction, n, part of this motion ; yet 

 the centrifugal and centripetal forces are so much superior as to mas- 

 ter the effect of this friction. This fri(;tional force carries also these 

 tide-waves so far eastward that they occur always several hours east 

 of the meridian ; tliat is, several hours q/i5er noon, and several hours 

 after midnight. 



It is a known fact that the waters of the tides rush up the rivers 

 and small bays on the east coasts of all countries with great violence, 

 but not up those on the west coasts. The reason of tliis is very evi- 

 dent. The west coasts turn away from the tide-waves ; while the east 

 coasts, moving with a velocity of nearly 1,000 miles an hour, in rota- 

 tion, within all parts of the tropics, dash violently eastward against 

 these waves. For this reason the waters, by resistance or inertia, a/j- 

 pear to be driven violently westward up the streams and bays, while 

 it is the mouths of these channels ploughing with violence into the 

 tide-waves themselves. 



It has been stated in this article that gravity is greater at that 

 part of the earth's surface turned away from sun and moon than any- 

 where else. It may be asked, "How then can centrifugal force drive 

 out the water above the usual level when its weight is increased?" 

 Tliis force acts in a line tangent to the earth's orbit, which tangent 

 line, being perpendicular to the radius vector at perihelion and aphe- 

 lion, and at all other points in the earth's orbit very nearly so, may 

 be said to be at right angles with a line extending from this point of 

 tangency through the centre of tlie earth to the centre of the sun. 

 Therefore, the attractive power of the sun acts on matter, at the part 

 of the earth most remote from it, in the direction of the radius vector ; 

 and centrifugal force acts on this same matter in a direction at right 

 angles with the radius vector. Now, as was first demonstrated by 

 Galileo, the motion of a body, produced by one force, is not destroyed 

 by another force acting on this same body at right angles with it. 

 The result of these two combined forces is only a change in the direc- 

 tion of motion. But, as has already been shown, centrifugal is always 

 in excess of centripetal force at the place of the earth now under con- 

 sideration. Hence this tide-wave at this side. 



I conclude by saying that the great motions of the waters of the 

 mighty deep are most assuredly the grandest ocular demonstrations 

 of the rotation of the earth upon her axis, and of her revolution around 

 the sun, that can be witnessed by the eyes of man. 



