140 Mk. E. Hunt on certain Phenomena connected with 



first supposing the weight in the latter case to be gradually moved 

 nearer the point of support. As this change takes place, the line of action 

 of the upward pressure gradually approaches that of the reactionary 

 downward pressure on the point of support, until, on the weight reaching 

 the point of support, the two opposite pressures may be considered 

 either as coinciding in their lines of action, and so neutralizing each 

 other, or asvanisliing — the original weight being left acting on the point 

 of support, so that if that point of support were removed, it would make 

 the instrument fall. In fig. 7, my apparatus is represented as arranged 

 to show that the pressure of the weight actually does take effect on the 

 point of support. The ring a of the tly-wheel can turn about a hori- 

 zontal axis on pivots in the ring B, which last can turn about a vertical 

 axis on pivots in the bowed end c, of a lever D, set free to oscillate on 

 the point of a pillar E. A small weight f is fixed on the ring A, and a 

 thread G, attached to the lower pivot of the ring b, is made to catch the 

 side of the ring A, opposite to the point of attachment of the weight f. 

 When the thread G is thrown off, and the fly-wheel is not rotating, the 

 weight F falls down into the vertical hue, about which the ring b turns, 

 making the spindle of the fly-wheel vertical. In this position of the 

 weight F the lever D is balanced in a horizontal position by means of 

 the weight H. If now the weight f is kept up by means of the thread 

 G, the weight H will be over or underbalanced accordingly as by turn- 

 ing the ring B the weight f is placed nearer to or farther from the ful- 

 crum F, than the centre of the fly-wheel. If, however, the fly-wheel is 

 set spinning, the thread G may be thrown off, and the weight F will be 

 carried round horizontally by the precessional action, whilst the lever D 

 will remain horizontal, the weight H being balanced precisely as if the 

 weight F were acting at the centre of the fly-wheel. The thread G 

 prevents the ring a from tui'ning about its pivots in the ring B, just as 

 if these pivots were fixed ; if the precessional action did this in the same 

 waj', the leverage on the lever D, of the weight f, would vary as it 

 moved round ; but instead of this, it transfers the pressure to the centre 

 of the fly-wheel, where it has no tendency to turn the ring a about its 

 pivots, in the ring b. Again, the pi'essure of the weight f is not 

 diminished in amount during the precessional action, for the weight H 

 is balanced precisely as when the weight F hangs below the centre of 

 the fly-wheel, the latter not rotating. 



In the case of the sphere, if the axis of rotation is changed by an 

 impressed impulse, the rotatory velocity is changed also, — but Airy 

 demonstrates that when the axis changes continuously, in consequence 

 of a pressure acting continually on the pole of the actual axis, the 

 rotatory velocity does )iot change, — and this corresponds with the fact, 



