THE EARTH. 



moral impossibility. It may, however, be asked how they could have been 

 entertained by the world for so long a succession of ages. The answer is, that 

 so long as the rotation, of the universe round the earth was admitted, mankind 

 was ignorant of its vast dimensions and of the comparative insignificance of ( 

 the earth, with which every person of ordinary education is now more or less < 

 familiar. The discovery of this has been reserved for modern times, and con- ( 

 sequently the absurdity of the supposition that the earth is at rest and the 

 universe revolving daily round it was not apparent, as it now is. 



The first demonstration which we have to offer of the motion of the earth 

 upon its axis, is what is called, in the language of schools, a disjunctive syllo- 

 gism. 



1. Either the earth must tiirn diurnally on its axis, or the universe must * 

 turn diuraally round it. 



2. But it is absurd to suppose that the whole universe should turn diurnally 

 round the earth. 



Condus-ion. The earth must therefore turn diurnally on its axis. 

 Although this negative demonstration be sufficiently conclusive to satisfy 

 the understanding, it has always been considered desirable that we should 

 obtain some positive and direct evidence that the earth really has this diurnal 

 motion. Now, an experiment has been suggested and actually executed, by 

 which a mechanical effect produced by the diurnal motion is actually exhib- 

 ited. Let us suppose a lofty tower erected on the surface of the earth ; the 

 top of the tower would, of course, be more distant than its base from the centre 

 of the earth ; consequently it is evident that if the earth had a diurnal motion, 

 the top of the tower, in virtue of that motion, would describe a greater circle 

 than the bottom, and consequently would move from west to east with a greater 

 velocity. Let us suppose, then, a heavy body, such as a leaden bullet, held 

 on the top of the tower ; that body would participate in the velocity from west 

 to east which the top of the tower has by the earth's diurnal motion. If the 

 bullet were then disengaged and allowed to fall to the base of the tower, it 

 i would still retain the velocity which it had at the top of the tower, and in fact 

 | it would have a downward motion and an eastward motion at the same time. 

 . In virtue of the downward motion, it would fall to the ground at the base of 

 | the tower ; but in virtue of the eastward motion, it would fall as far to the east- 

 i ward as the top of the tower would have moved more than the bottom in the 

 \ time of its fall. 



i Now it must be remembered that the motion of the base of the tower east- 

 \ ward by the diurnal motion of the earth is less than that of the top of the tower, 

 1 and consequently in the time the ball would take to fall from the top of the 

 | tower to the ground, the base of the tower would not be as far eastward as the 

 1 top would move ; and consequently the ball ought to be expected to fall east- 

 ! ward of the foot of the tower at a distance equal to the difference between the 

 1 space through which the top and the base would have moved in the time of 

 the fall. 



But if the tower and the earth on which it was built had not this diurnal 

 \ motion, but were at rest, then the ball ought to fall exactly at the foot of the 

 1 tower, or vertically under the point from which it was disengaged. Thus, 

 I then, we have a positive experiment, the result of which, if rightly executed 

 1 and accurately observed, must discover to us the fact of the earth's motion, if 

 1 such motion existed. 



The experiment has been inaae ; ihe question has been asked ; nature has 

 I been submitted to cross-examination by science : and the secret has been 

 | extorted from her. The ball has fallen, not at the point vert^'illy un- 

 , er the place where it was disengaged, but eastward of that place to the ex- 



