310 Proceedings of the Eoyal Society of Edinburgh. [Sess. 
at the intersection of the pivot axes, or on the vertical passing through 
the intersection. Thus the system should be balanced up with the balls 
in position, each held in contact with its pusher. 
It is of the utmost importance that, before being set up on an aero- 
plane or other vehicle, the stabiliser should be adjusted by an expert, 
and that, once installed, the balance of the instrument should not be 
interfered with. 
The final balancing of the stabiliser is accomplished by placing small 
weights on four pins arranged as shown in fig. 33. These pins lie, as 
shown, in line with and order that the balancing weights 
may not alter the amount of 
gravity control, if any, with 
which the instrument is pro- 
vided, the pins are placed in 
the plane of the pivots. Once 
the adjustments are complete 
the weights may be fixed in 
position by passing split-pins 
through the pins or rods. 
The stabiliser should be 
adjusted as follows. The balls 
are fixed in their resting posi- 
tions (so that they are in 
contact with their pushers) 
and the gyroscope and erector 
set in motion. The pivoted 
system is then adjusted by 
hand so that its axis is vertical, and is then watched. In general, of 
course, the system drifts from the upright position owing to want of 
balance. Weights are now placed on the pins so as to eliminate drifts ; 
and when the pivoted system, so adjusted, retains the upright position 
undisturbed for a considerable interval of time, the operation is complete, 
and the instrument may be installed on the aeroplane. 
On no account should the above adjustments be carried out with the 
gyroscope at rest. Static balancing is of little value. When the gyroscope 
is spinning the vibration results in the pivot friction being enormously 
diminished. By arranging that the erector is slightly out of balance the 
pivoted system may be caused to rock to and fro on the pivots, through 
a very small angle, in the period of the erector, and this has the result 
of diminishing the pivot friction. In general, a stabiliser balanced up 
Fig. 33 . 
