1918] on Gyrostats and Gyrostatic Action 63o 



overcome by the simple and effective device of makin<j: the flywheel 

 itself the rotor of a high-speed continuous-current electric motor. 

 The ordinary gramme-ring armature is well adapted for this. It 

 gives a wheel of great moment of inertia, or as I call it " spin 

 inertia " (that is, the matter of the wheel is distributed so as to be 

 on the whole as distant from the axis as possible), which can be run 

 at high speed for a long time without trouble of any kind from 

 bearings or contacts. 



For my first experiments the motor gyrostat is set up with the 

 axis of the flywheel horizontal, in this mounting, which consists, as 

 you see, of a fork perched on a pillar. Notice the possible motions, 

 the freedoms, I may call them, of the arrangement. The flywheel 

 can turn about its axle, the case can turn about the line of the pivots 

 which carry it in the fork, and the fork about a vertical axis provided 

 in the pillar. These three axles, which we shall number (1), (2), 

 (3), are mutually at right angles and meet at the centre of gravity of 

 the movable system or gyrostat proper. When thus set up the gyro- 

 stat is said to be freely mounted. 



With the flywheel at rest I push down on one side of the case, and 

 immediately turning takes place, as we should expect, about the axis 

 (2). Pushing down the other side of the case causes the instrument 

 to turn about the axis (2) in the opposite direction. I grasp the 

 fork in my hands and turn it about the axle (3) in either direction. 

 Nothing unexpected happens ; the gyrostat turns with the fork, its 

 axis remaining horizontal throughout. Again, I grasp the pillar in 

 my hands and turn it on the table, and you see that the friction of 

 the axle (3) is sufficient to cause the fork and gyrostat to move 

 round with the pillar. As before, the axis of the flywheel remains 

 horizontal. 



My assistant now causes a current of electricity to flow in the 

 coils which form part of the flywheel and in the coils which surround 

 the soft iron core of the magnet which is stationary wdthin the ring. 

 So far you can only tell that the flywheel is turning by the faint hum 

 which its motion sets up. But when I repeat the operations which I 

 have just performed on the non-rotating gyrostat, the behaviour of 

 the instrument is quite startlingly different. I push down on one 

 side of the case as before ; a resisting force is experienced, and the 

 gyrostat turns, not visibly about the axle (2), but about (3), the 

 vertical axis. So long as I maintain the tilting force so long does 

 the resistance and this turning about the vertical persist. I with- 

 draw the tilting force, and the turning motion ceases. 



Now I would direct attention to these rods with arrow heads, 

 which are screwed to the gyrostat case. This curved one shows the 

 direction in which the flywheel is spinning. The straight rods are 

 intended to represent the spin-momentum and the tilting action 

 respectively. Both are completely known when their amounts and 

 their planes are known. The spin-momentum is got by multiplying 



2 u 2 



