26 



vector, which never does, and never can, turn round about the 

 revolving axis. 



The plummet being removed, and a long loose cord attached 

 to the same point of the cylindrical disk, and having its other 

 end fixed to the primary centre of the circle, make the rod re- 

 volve, and it will complete its revolution without aflPecting the 

 cord, without drawing it round the cylinder, showing unequivo- 

 cally that there has been no rotation there. Now, detach the 

 rod from the primary centre, and make it revolve, preserving its 

 parallelism with the line NS, so that its inner point A will 

 now describe exactly the same orbit for itself as that described 

 by the plummet When it completes its revolution in this 

 parallel fashion, strange to say, though it has revolved, as astro- 

 nomers allege and profess to believe, without turning round on 

 its own axis, it will nevertheless have drawn the cord round 

 about the fixed cylinder which has been revolving with it, also 

 without rotating on its axis, as alleged. But how can the 

 cord get round the cylinder if the cylinder has not rotated on 

 its own axis? And if the diameter of the cylinder were to 

 be made as large as the rod itself, then the cord would be drawn 

 round both the points of the revolving rod, notwithstanding its 

 pretended avoidance of rotation by preserving its parallelism. 

 And that the movement which has occasioned the drawing of the 

 cord round the cylinder has been exclusively on the part of the 

 rod itself, will be evident from the fact that the cord's movement 

 begins at the end attached to the moving rod, and is afi'ected 

 through its whole length, and at its central end only, when the 

 cylinder's rotation has drawn it all away from the centre ; and, 

 moreover, by the fact that when the rod was not loose, and con- 

 sequently did not move away from the centre, the cord remained 

 entirely unaffected by the pivot's revolution, showing that there 

 was no motion in the opposite direction, on the part of the pri- 

 mary centre and the radius- vector ; and if there was no such 

 opposite motion in that case, there could be just as little when 

 the rod was loosed, and it and the cylinder left at liberty to turn 

 away from the centre. 



To meet such arguments and illustrations as these, astrono- 

 mers and mechanicians have nothing better to oflTer than the 

 following notable proposition. " Let AB (Fig. 4) represent an 

 inflexible rod of no weight supported by a hinge at the point A, 

 in the centre of a circle, in such a manner that it may turn or 

 revolve freely round that centre. When it so revolves, its motion 

 may be divided into two ; one progressive, by which its centre of 

 gravity C changes its relative position to other bodies, and the 

 other rotatory round that centre, by which its parts change their 

 positions with regard to one another. If it make a complete revo- 



