C. B. WAKKIXG. 147 



mine whether this is in accordance with the facts. I 

 placed a fine point on my top, and set it spinning on a 

 plate of glass well blackened with smoke. The point 

 traced a clear line through the lampblack, and I was 

 thus able to see its path, the position of the axis, and of 

 the center of gravity. The result is shown in fig. 29. 

 In no case, save when the axis was vertical, did the 

 center of the top's gyration correspond with the projec- 

 tion of the center of gravity. The radius of the small 

 circle was often twenty or thirty, or even fifty times less 

 than the distance from its center to the foot of the per- 

 pendicular let fall from the center of gravity. In all 

 cases, except when the axis was vertical, it leaned as in 

 fig. 29 ; that is, the point of support and the projection 

 of the center of gravity were always on opposite sides of 

 the center of the circle described by the former. 



If the rotation of the toj) were absolutely without 

 friction, it would, as General Barnard says, revolve 

 around a perpendicular passing through its center of 

 gravity. But, in fact, there is resistance at both ends,— 

 that of the air, which is very small 1 , and that of the fric- 

 tion of the point on the glass, which is relatively large. 

 If the friction is such that the point cannot move at all, as 

 sometimes, when the point bores a little into the 

 glass, the gyrating center is at that point. When the 

 friction allows a little movement then this center is near 

 the point of the top, and so situated that the distance 

 from the point to the projection of the center of gravity 

 is divided by it into two parts, which are to each other 

 inversely as the friction at the point, and the resistance 

 of the air. 



The important thing just now, for our purpose, is that 

 the top and its point are on opposite sides of the center 

 of that circle, and consequently move in opposite 



1 The resistance here spoken of is not the friction of the air on the surface of the top. 

 but that which opposes the gy.ation. and as this is very slow, the resistance is very small. 



131 



