Mechanical Illustrations of the Planetary Motions. 333 



ring be displaced in the least, it will have a tendency to ap- 

 proach the planet on that side on which it is nearest to it ; 

 but that very tendency will produce its own remedy, by giv- 

 ing rise to another and a very peculiar movement, which I 

 am now about to explain. 



In considering the theory of the top, it appeared to me, 

 that, if the top were in the form of a ring, and if an attrac- 

 tive force within it, such as a magnet, were substituted for 

 the downward force of gravitation the ring would avoid fall- 

 ing in towards the centre of attraction by an evasive move- 

 ment, similar to that by which a top avoids a fall, and simi- 

 lar also to that by which, as we have already seen, the iron 

 disc avoids contact with the magnet above or below it, — that, 

 in fact, the tendency towards the centre would be converted 

 into a slow eccentric revolution of the centre of the ring 

 round the centre of attraction, entirely different from the 

 rotation of the ring itself, exactly in the same manner as the 

 tendency of the top to fall is converted into a slow conical 

 motion of the axis. Thus, in the following diagram, let RR 

 be the ring, C its centre, and P 

 the centre of the attracting power, 

 eccentrically placed with regard 

 to the ring, the nearest point of 

 the ring being A. That point A, 

 is then acted upon by two inde- 

 pendent forces, — that of the ro- 

 tation, carrying it forward from 

 A to B, and that of the attracting 

 power, drawing it from B towards 

 P, and is consequently brought to a point D between B and 

 P, while the centre of the ring passes, in consequence, into 

 the position C. The same movement continued brings the 

 nearest point successively into the position D, E, F, &c, and 

 carries the centre round the curve CC. 



It is only with a certain velocity of rotation, however, that 

 the curve CC will be part of a circle. If the velocity is less 

 than that, the point D will be nearer than A to P, and the 

 ring will become more and more eccentric, till it is brought 

 into collision with the attracting object, corresponding ex- 



NEW SERIES. — VOL. I. NO. IT. APRIL 1855. Z 



