THE CONQUEST OF TIME AND SPACE 



lous to all of us, had we not all spun tops at an age when 

 the world was so full of wonders that we failed to marvel 

 at any of them. 



All these familiar things illustrate one of the principles 

 of gyroscopic action which Mr. Brennan has put to 

 account in developing his wonderful car — the fact, 

 namely, that every revolving body tends to maintain its 

 chief axis in a fixed direction, and resents — if I may be 

 permitted to use this expressive word — having that 

 direction changed. The same principle is illustrated 

 on a stupendous scale by our revolving earth, which 

 maintains the same tilt year after year as it whirls on its 

 great journey, notwithstanding the fact that the sun and 

 the moon are tugging constantly at its protuberant 

 equatorial region in a way that would quickly change its 

 direction if it were not spinning. 



But note, please, that whereas the whirling body 

 assumes a certain rigidity in space as regards the direc- 

 tion in which its axle points, the mere translation of the 

 body itself through space in any direction is not inter- 

 fered with in the least, provided the axle is kept parallel 

 with its original position. 



You may test this if you like in a very simple way. 

 Remove one of the wheels of your bicycle, and carry it 

 about the room, holding it by the axle while it is spinning 

 rapidly. You will discover that it requires no more 

 force to carry it when spinning than when at rest, pro- 

 vided you do not attempt to tip it from its plane of 

 rotation, but that if you do attempt so to tip it, the wheel 

 seems positively to resist, exerting a force of which it 

 did not show a trace when at rest. A large top, arranged 



[198] 



