1921-22.] Gyroscope and “Vertical” Problem on Aircraft. 311 
with the gyroscope at rest will be found to be, in reality, considerably 
out of balance. 
It has been shown that, under the conditions which prevail on aircraft, 
a gyroscopic pendulum, if it is to be capable of remaining undisturbed, 
within the limits required, in the presence of the horizontal accelerations 
which accompany curved flight, must possess a very great precessional 
period. For this reason the bombsight, camera, artificial horizon, or other 
instrument stabilised, should be so constructed that any adjustments 
which have to be made should be capable of being carried out without 
altering the position of the centre of gravity of the pivoted system. In 
the case of cameras in which plates are changed, or films rolled from one 
spool on to another, it is difficult to arrange that this condition shall 
be precisely fulfilled. In such cases the form of the invention shown 
in fig. 34 is employed. Rigidly attached to the pivoted system is an 
auxiliary gyroscope g' with its axis perpendicular to that of the main 
gyroscope g. Thus when the pivoted system is upright the axis of g is 
horizontal. Further, the pivoted system is so mounted on the frame /that 
