410 
Proceedings of the Royal Society of Edinburgh. [Sess. 
factor is small in this case), results in the machine being brought into the 
vertical. To adapt the gyrostat to imitate the human rider the mass of 
the machine is made considerable, and the gyrostat is spun rapidly in a 
direction which coincides with that of the wheels of the bicycle when 
moving in the forward direction. When the machine tilts over to the left 
the gyrostat precesses round in azimuth, carrying with it the front wheel, 
and the precessional motion is such as to turn round the front wheel to the 
left ; if the machine tilts over to the right the gyrostat turns the front 
wheel to the right. The result is to give the machine stability. 
In a second mode of operating this form of bicycle the precessional 
motion of the gyrostat, brought about by the tilting of the machine, is 
automatically hurried. This is accomplished by giving considerable curve 
to the fork of the front wheel, with the result that the centre of gravity of 
that wheel lies considerably outside the line of the axis S. When so 
designed the front wheel is in unstable equilibrium when the bicycle is 
placed on the floor with the wheels in one vertical plane ; the centre of 
gravity of the front wheel is then at the highest point of the circle in which 
it is constrained to move about the axis S, and if the wheel is turned 
slightly in either direction about that axis it will fall over, carrying with it 
the gyrostat. Thus if the gyrostat is spinning and precessional motion 
occurs, such motion is automatically hurried. If now the gyrostat is spun 
rapidly, and the bicycle is put down on the floor and pushed in the forward 
direction, it runs in a path which is practically a straight line, and the 
balancing power is very surprising. With this second method of mounting 
the gyrostat the bicycle will balance either when in motion or when at rest. 
It is to be observed that, since the gyrostat is rigidly attached to the 
frame carrying the fork of the front wheel, the bicycle may be driven from 
the gyrostat. 
In fig. 4 is shown a second bicycle fitted with a gyrostatic rider. In 
this case the gyrostat is mounted on the bicycle in two horizontal pivots, 
carried as shown by a fork attached to the bicycle. The line of the pivots 
is perpendicular to the plane containing the wheels of the bicycle, which 
are locked in one plane in this type of machine. Further, the construction 
is such that when the axis of the gyrostat is vertical the line of the pivots 
carrying the gyrostat lies considerably below the centre of gravity of the 
gyrostat and its frame. The device is stable when run on a stretched wire. 
If the machine tilts over in either direction the gyrostat precesses so that 
its axis turns in a plane which is nearly vertical ; and since the centre of 
gravity of the gyrostat is above the line of the pivots, this precessional 
motion is hurried, with the result that the gyrostat regains the vertical 
