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rection contrary to the natural movement of the parts of its mass 

 under the influence of the forward-moving power. 



All that I have now said may be demonstrated mechanically 

 by the simplest means, and in the simplest manner, no more 

 costly or more complicated apparatus being required than a 

 common bottle-cork, with a long-tailed string tied round its 

 middle, and a pin with which to fix it to the centre of a circle, 

 and to serve as an axis or pivot of revolution and rotation. But 

 I shall use an instrument of somewhat more complexity, though 

 still within the reach of every one who wishes to try the experi- 

 ment. But first let us consider the diagram fig. 2, where E 

 and M are two circles of equal dimensions. Suppose E to 

 remain fixed and immovable while M revolves about it from 

 west to east. As M revolves, its several points, 2, 3, 4, 5, 6, 7, 

 8, 1, will present themselves successively in that order to E's 

 corresponding points; but, in doing so, M will necessarily turn 

 round once on its axis, and all the points in succession will pass 

 the radius-vector, or straight line that connects the centres of the 

 two circles, and of course revolves with M round E's centre point 

 Let M revolve a second time, with the same point of its circum- 

 ference No. 1, always in contact with E.'s circumference, and in 

 one with the radius- vector. It will revolve without giving the 

 smallest token of rotation, yet say astronomers, M in this case 

 has turned once round on its own axis, though that has been 

 rendered impossible by its adherence to the radius-vector. In 

 the first revolution also it turned once^ and no more than once, 

 why should the one invisible and imperceptible rotation which 

 they ascribe to the moon, produce such different results from 

 those of the visible, real, and undeniable single rotation of 

 M, as shown in the diagram, and of every other body similarly 

 situated, or revolving in an orbit ? Let M revolve a third time, 

 turning its points from east to west, or what is the same thing, 

 preserving the perfect parallelism of all its parts to the two sides 

 of the paper, it will present its points successively to E's points 

 in the reverse order, 8, 7, 6, 5, 4, 3, 2, 1, to E's, 1, 2, 3, 4, 5, 

 6, 7, 8, and each of them in its turn will pass the radius- 

 vector once. In this case it is said to revolve in its orbit, 

 without turning round on its axis; yet has it shown every requisite 

 token of rotation" and carried its several points in succession to 

 an always increasing angular distance from the orbit's centre, 

 till each of them has become the outermost point of its circumfe- 

 rence, and from that extreme distance of 180*, as shown by its 

 position below E, returned by the other side of the axis to its 

 first position, just as if M. had turned round on its axis all at 

 once, without moving forward in its orbit How can these 

 points get to the outside of the circumference, unless the body 



