April io, 19 13] 



NATURE 



151 



steers to starboard ; when I turn the nose to starboard 

 the rudder steers the craft to port. 



The case of the pedestal gyrostat is provided with a 

 hook at one extremity of the axis (see Fig. 3). The 

 effect of hanging a weight on this hook is to apply 

 a couple tending to cause turning about the axis (2) — 

 that is, which would produce such turning if the fly- 

 wheel were not spinning. But the wheel is spinning, 

 and the visible actual turning" is about the axis (3). 

 Observe also that the wheel is rotating comparatively 

 slowly, and that the precessional motion is gruat. I 

 increase the speed of the flywheel and the gyrostat pro- 

 cesses more slowly. I replace the weight by a larger 

 one, and for the same spin the precessional motion is 

 greatly increased. Thus for a given applied couple the 

 faster the spin the slower the precessional motion, 

 and for a given spin the greater the couple the faster 

 the precessional motion. 



Now while the weight is in position and the gyrostat 

 precessing about the axle (3) I attempt to hurry the 

 precessional motion, and immediately the gyrostat 

 turns about the axis (2) so as to rise against gravity. 

 I try to delay the precession, and again the gyrostat 

 turns about the axis (2), but now so as to descend 

 under gravity. 



Without being aware of it people are constantly- 

 meeting with examples of gyrostatic action in daily 

 life. A child expert in trundling a hoop causes it to 

 turn its path to the right or left, by striking it a 

 blow at the top with the hoop stick, the effect of which 

 the ordinary person would suppose, if he thought 

 about it, should be to make the hoop to fall over to 

 the right or the left. A bicyclist riding without hold- 

 ing the handles leans over to the right if he wants 

 to steer the bicycle to the right, and to the left if he 

 wants to steer to the left. And if he feels himself 

 falling over to right or left he turns the handles in- 

 stinctively so as to turn the bicycle to that side, when 

 the machine resumes the upright position. In the 

 bicycle, however, the spin of the wheels is not the 

 most important action to be taken account of. 



The gyrostatic action in the bicycle is much more 

 marked in a motor machine, for in that a massive 

 flywheel rotates in the same direction as the wheels. 

 As the bicycle turns a corner it is constrained to 

 precess, and a couple is needed to produce this pre- 

 cession of the rotating parts quite apart from that 

 required to turn the rest of the machine. This the 

 rider applies by leaning over to the inside of the turn, 

 and leans over more than he would have to do if the 

 flywheel were not there or were not rotating. 



Good examples of gyrostatic action are given by 

 paddle and turbine steamers. A paddle steamer is 

 steadier in a cross-sea than a screw steamer of the 

 same size. This is due in part to the gyrostatic action 

 of the paddle-wheels, which, but for their com- 

 paratively slow speed of rotation, would form 

 a compound gyrostat of considerable power. 

 For this gyrostat the spin-momentum may 

 be conveniently represented by a line drawn 

 from the steamer towards the port-side. A 

 couple tending to tilt the steamer over to starboard 

 is represented by a line drawn towards the bow, and 

 a couple tending to tilt the steamer to port by a 

 line drawn towards the stern. Hence, if the steamer 

 heels over to starboard, her bow, in consequence of 

 gyrostatic action, precesses to starboard, but the star- 

 board wheel, becoming somewhat more deeply im- 

 mersed, uses more power and exerts a turning influ- 

 ence to port. Thus the steersman has less difficulty 

 in keeping the vessel on a straight course. 



But if the vessel be turned by the rudder, say to port, 

 the vessel will by gyrostatic action be slightly heeled 

 over to starboard, and the starboard wheel, being 



NO. 2267. VOL. qi] 



more deeply immersed, will assist the turning action 

 of the rudder. 



Though the gyrostatic actiqn of the wheels is not 

 very great, calculation shows that it is enough to 

 produce an appreciable variation in the immersion of 

 the wheels. 



The gyrostatic action of the flywheel in a motor-car 

 is of some practical interest. The flywheel is placed 

 with its plane athwart the car — that is, with the axis, 

 so to speak, fore and aft. It rotates in the clockwise 

 direction as viewed by an observer behind the car. 

 The effect of turning a corner to the left gives a 

 gyrostatic couple, throwing the weight of the car 

 more on the bade wheels; turning to the right throws 

 the weight more on the front wheels. The forces 

 applied bv 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 considerable power. As the 

 bearings are fore and aft, the action is similar to 

 that of the flywheel of the motor-car. Turning hori- 

 zontally in one direction gives rise to a gyrostatic 

 couple tending to make the aeroplane dive, turning the 



Fig. 4. — Motor-gyrostat balancing on a skate. 



opposite way sets up a couple which makes the aero- 

 plane 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. Manoeuvres 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 haziness 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 contend with lies hid, as it were, until he 

 tries some new and violent manoeuvre ; and then it 

 brings him to grief. 



I now pass on to some special experiments which 

 can be carried out with these motor-gyrostats. First 



