314 James Elliot on certain 



it comes directly under the body of the top, as before." This 

 theory may, at first sight, seem plausible, but is liable to three 

 fatal objections. First, — an inclined cylinder, rolling upon 

 one end, never would roll towards the centre, but, on the 

 contrary, would continually deviate further from it, unless 

 its upper extremity were supported. Second, — the cause 

 would cease, and the top would immediately fall, whenever 

 any small hollow confined its point to one spot, as frequently 

 happens. And, third, — if the standing of the top depended 

 upon the thickness of the point, the finer the point 'the more 

 difficult it would be to keep up the top; and, if the peg could 

 be ground to a mathematical point, the top would invariably 

 and instantly fall. It is needless to say that such a conclu- 

 sion is contrary to common observation, which shows us that, 

 in mathematical language, the tendency to fall is no func- 

 tion of the fineness of the point. 



In comparing the motions of the top with those of the 

 earth, I thought that I perceived the true reason of the top's 

 standing, viz., that the tendency to fall is converted by the 

 rotation into the conical motion of the axis which I have be- 

 fore described. But, to render this clear, let us commence 

 with the common form of the top in which the centre of gra- 

 vity is above the centre of motion, and let us suppose, for the 

 sake of simplicity, the top to consist of a single circular plate, 

 or, if we choose, we may take a top of any form, and suppose 

 its whole mass to be concentrated in a single circular sec- 

 tion perpendicular to the axis, and the whole weight of 

 that section to be again collected into one circumference, 

 as a hoop around an axis. Further, suppose such a top al- 

 ready inclined to one side, as in the following diagram, CP 

 being the axis, AB the circular sec- 

 tion, or rather the circumference, just 

 described, and the arrow pointing out 

 the direction of rotation. The top 

 will then have a tendency to turn 

 over towards that side which is low- 

 est, in doing which, the lowest point, 

 B, of the circumference, would, of 

 course, fall ; while the highest point, 



