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lutio7i round the circle by its point A (attached to the centre by a 

 hinge) its parts in the same time will make a revolution round the 

 centre of gravity C." The first and most obvious remark upon 

 this notable proposition is, that the latter part of it, all that is in 

 italics, is wholly untrue, and most directly contrary to the truth ; 

 and 1 cannot comprehend how any man in his right mind should 

 ever have been able to persuade himself that it is true, unless, 

 indeed, it were on Tertullian's principle of believing a thing he- 

 cause it is impossible I When a rod so situated revolves round 

 the centre of a circle, not only " its centre of gravity C," hut oho 

 all the other particles of its mass, "change their positions relatively 

 to other bodies ;" while, on the contrary, were it to rotate on its 

 axis C, whether that rotation be visible or invisible, " its parts 

 would not change their positions with regard to one another." 

 They would, on the contrary, preserve invariably the same re- 

 lations to each other, to the orbifs centre, and to their own 

 axis or centre of gravity, but would change their relations conti- 

 nually to everything else. This seems to me perfectly self-evident. 

 It must follow, at least, from what I have shown already; and the 

 only reason astronomers can give for maintaining such a propo- 

 sition is, that, if it were not true, their doctrine of the moon's 

 rotation would not be true either. The doctrine and the propo- 

 sition are thus perfectly consistent with each other, but their truth 

 is just as problematical, and, not to mince the matter, just as 

 false as the ancient doctrine which placed the earth in the centre 

 of the universe, and made the sun, moon, and stars, the whole 

 host of heaven, revolve about it. The proposition above quoted 

 has not even such appearance of truth ; for it is just as directly 

 contrary to appearance as to fact ; and no man in his senses 

 would ever have believed it, had he not first persuaded himself, 

 on other grounds, that it must be true, in spite of appearances. 

 In short, the proposition is not an induction from observed facts, 

 but only a deduction from an erroneous hypothesis, contradicted 

 by facts. 



The latter part of the proposition, " if the rod makes a com- 

 plete revolution round the circle by its point A {attached to the 

 centre by a hinge), its parts in the same time will make a revolu- 

 tion round the centre of gravity C," is just as utterly untrue and 

 contrary to fact as all the rest. Take two rods of equal length, 

 each attached by a hinge to the centre of the same circle, but on 

 opposite sides, so as to form together one diameter of the circle, 

 or, what would do as well or better, take a single rod of double 

 the length of the rod AB, and fixed by its middle upon a pivot 

 in the centre of a circle or orbit, whose circumference shall be 

 described by the middle part of each half of the rod. Call these 

 two centres of gravity C and c, and the two halves AB, with its axis 

 C, and DE with the axis c. These are virtually two distinct rods, 



