150 THE THEORY OF THE BICYCLE. 
I will now set the wheel in rapid motion, much more 
rapid than any bicycle wheel cango. I place the instru- 
ment—its name in this particular form is gyrostat—I 
place it on a smooth, hard surface,—I have here a pane 
of glass,—and leave it to itself. 
At once it begins, as you see, to revolve around a ver- 
tical axis. If it leans little, it revolves slowly; if it 
leans much, it revolves faster. 
It retains its upright position, though I push it, or 
even strike it a violent blow. It resists with remarkable 
force. It fact it is scarcely possible to upset it even by 
the impact of a hammer, providing the blow be delivered 
on either S or T, and in a vertical plane. You may hang 
a weight of a pound or more on T or 8S, and although 
standing on only a knife-edge, the instrument will not 
fall over. The only effect, as you see, is to make it spin 
more rapidly around a line drawn perpendicular to the 
table at the point of contact. 
I now take it by the projecting wires, and attempt to 
make it move in a straight course, as a bicycle does when 
it spins along the road. Instantly it falls. The rotation 
of the wheel on its axis was not, in the slightest degree, 
interfered with; but the stability vanished the moment 
the rotation around the verticle axis ceased. Yet, you 
observe, the conditions are far more favorable to stability 
than in the bicycle, 7/ the latter’s stability is due to gy- 
100 
