296 Proceedings of the Poyal Society of Edinburgh. [Sess. 
This method of shutting off the erector has the advantage that the 
necessity for using two motors is avoided ; the erector may, in fact, be 
driven by means of a wind turbine after the manner already described. 
With this addition to the erector it 
is necessary to take in current to the 
magneto ; and if in addition the 
stabiliser is to be used as a turn- 
indicator, five brushes in all are 
necessary. Hence the three rings 
^ 1 , 7*2 , ^3 shown in the experimental 
model illustrated above. 
In fig. 24 is shown a further form 
of erector. Two rotating ball systems 
are employed, one of which (a) rotates 
slowly in the direction of spin of the 
main gyroscope g (fig. 12), the other 
rapidl}^ in the opposite direction. A 
stabiliser fitted with this arrangement possesses the following properties. 
When the pivoted system is inclined to the vertical at an angle 0 greater 
than where is the angular speed of the ball-system (6), and 
is the distance of the centre of a ball from the centre of (h), both systems 
Fig. 23. 
function ; and if the ball-systems are identical but for their speeds, the 
pivoted system experiences no erecting couple. This follows from the fact 
that the magnitude of the integral couple due to the radial motion of the 
balls in the slots is independent of the erector speed, and that when the 
direction of the rotation of the erector is reversed the direction of the 
