200 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
the right throws the weight more on the front wheels. The forces 
applied by the ground to the front wheels are diminished in the 
former case and increased in the latter. There is danger, therefore, 
of the steering power of the car being interfered with, if the corner 
is taken at too great a speed. 
As a final example, we take an aeroplane. Here the rotor of the 
engine and the propeller together form a compound gyrostat of con- 
siderable power. As the bearings are fore and aft, the action is simi- 
lar to that of the flywheel of the motor car. Turning horizontally 
in one direction gives rise to the gyrostatic couple tending to make 
the aeroplane dive, turning the opposite way sets up a couple which 
makes the aeroplane rear up in front. If the aeroplane is kept hori- 
zontal, such couples have to be balanced by stresses in the framework. 
These considerations show that sudden turning of aeroplanes should, 
if possible, be avoided. Maneuvers calling for such turning are 
_ accompanied by very considerable danger. No doubt aviators are 
aware of the existence of gyrostatic action, but there is considerable 
hhaziness in people’s minds as to its direction in the various possible 
cases. The peculiar properties of rotating bodies need not, of course, 
be understood theoretically by aviators, though it is well to know 
something about them. But the aviator, like a person walking or 
swimming, must know instinctively what to do in an emergency, and 
what motions must be avoided. The gyrostatic action he has to con- 
tend with lies hid, as it were, until he tries some new and violent 
maneuver; and then it brings him to grief. 
T now pass on to some special experiments which can be carried out 
with these motor gyrostats. First, take one or two old experiments,! 
which are more effectively performed with these fast-running instru- 
ments. Here is a skate attachment (fig. 4) on which I place the 
eyrostat after its speed has been adjusted to the moderate value of 
about 6,000 revolutions per minute. The plane of the flywheel is 
inclined to the vertical, and you see that the top does not fall down, 
but precesses round on the table. I increase the inclination and the 
precession becomes more rapid. Now J] attempt to hurry the preces- 
sion and the gyrostat stands up erect; I try to resist the precession 
and the gyrostat falls over. 
I mount the gyrostat with its wheel horizontal over a flexible sup- 
port, in the present case a universal joint (fig. 5). Without rotation 
the instrument would fall over at once; but you see that it stands 
stably erect when the flywheel is spinning, and has a precessional 
motion when disturbed from the upright position. 
Again, here is a two-stilt support. (Fig. 6.) One of the stilts is 
held by a long socket, at one side of the case, and may be regarded 
1See Thomson & Tait’s Natural Philosophy, sec. 345* et seq. 
