280 Proceedings of the Koyal Society of Edinburgh. [Sess. 
(only one pivot is shown in the diagram) to a frame /, which is in turn 
pivoted at 'P 2 P 2 uprights u, n carried by a base b which is attached 
Fig. 12. 
rigidly to the floor of the fuselage of the aeroplane, with the pivots 
lying fore and aft. 
Contained within the case c is a small turbine wheel, and this is driven 
rapidly by means of high-speed 
air led through the pipe d from 
the outside of the gj^^roscope 
casing. This turbine, with re- 
duction gearing, serves to rotate 
the spindle S slowly in the 
direction of spin of the gyro- 
scope g. Mounted on the spindle 
S is an erector e, the construc- 
tion of which is illustrated in 
figs. 12 and 13. 
Contained within a shallow 
cylindrical box are two solid 
spherical steel balls These 
rest on a rigid plate li, and 
each is surrounded by a slot of 
peculiar shape formed in the plate i. As will be seen from fig. 13, each 
slot or hole consists of an outer part k and an inner part m connected 
together by a narrowed part, or neck, n. Each of the slots or holes 
