1921-22.] Gyroscope and “Vertical” Problem on Aircraft. 281 
surrounds a solid spherical steel ball, and their function is to constrain the 
balls so to move relatively to the plate h, beneath the plate when the 
latter is inclined to the horizontal, that an integral erecting couple is 
applied to the gyroscope. 
The action will be clear from fig. 14. The erector e, it is to be under- 
stood, is revolving slowly in the direction of spin of the gyroscope g. We 
suppose the pivoted system inclined to the vertical about the axis P 2 P 2 ’ ^1^® 
erector being turned towards the observer. The direction of rotation of the 
gyroscope, and of the erector, is supposed clockwise, as seen from above. 
Since the spindle S is inclined to the vertical (about the pivots P 2 P 2 )’ 
each slot moves in a circular path which is inclined to the horizontal. 
Fig. 14. 
Fig. 14 (a) shows the plate i and the balls at an instant at which the slot 
Sj is at the crest of the slope. The slot is now at the lowest position 
of its path. The ball \ has rolled down the slope from to , and 
has rolled down from to k .^ . During the ensuing half turn of the 
erector the balls h-^ and remain within the inner and outer parts, respec- 
tively, of their containing slots. This is a consequence of the peculiar 
shape of the slots and of the rotation of the erector. The action will be 
clear from fig. 14 (6), which shows the plate and balls after the erector has 
advanced through a quarter turn. 
After the completion of the half turn of the erector, the ball moves 
from the inner to the outer part of , and similarly moves from the 
outer to the inner part of §2 • Thus, so long as the erector is inclined to 
the horizontal, each ball when moving uphill is situated at a greater 
distance from the centre of the plate i than when moving downhill, and, 
with the direction of the erector that of the gyroscope, this results in the 
