C. B. WARRING. 115 



arms are instantly reversed, taking the position in tig. 7. 

 As the force necessary to reverse is at right angles to m 

 and b, it will neither increase nor diminish them. Con- 

 sequently A, when at the bottom, will continue to move 

 eastward, and B, which is now at the top, will continue 

 to move westward, each with unchanged velocity. 

 These motions tend 1,0 push A and B still, the first to 

 the right, and the other to the left, the effect of which is 

 to cause them to tend to go back to their first position— 

 a stress as it is called — and they would go back but for 

 reasons which I will try to explain. 



Although A and B are now reversed, their downward 

 motion, x o and z y, is not thereby affected, and gravity, 

 too, continues to operate ; hence, b and mhave two forces 

 to overcome before they can push the tee back to its start- 

 ing place. They are sufficient only for the one (o x and 

 z y) ; they just neutralize that. Hence, A and B continue 

 to fall, but without the acceleration of falling bodies, 

 for in these acceleration is due to the velocity of the pre- 

 vious instant being joined to that of the present. 1 



A pendulum, when it has reached the bottom of its 

 arc, has absolutely no downward motion — no downward 

 momentum — to overcome ; the whole energy from its fall 

 is permitted to spend itself in lifting the bob against 

 gravitation to the height from which it fell. 



But with the gyroscope the case is very different. 

 The whole energy of the fall is expended (after reversal) 

 in overcoming the downward momentum, leaving none 

 to act against the next instant's pull of gravity. 



It is as if a mass received successive impulses from 

 gravity, each of which carried it a small distance, and 

 then was neutralized by a counteracting force, which 

 was immediately followed by another equal impulse, 

 which in its turn was neutralized, and so on. The result 



1. There is an acceleration due to the change in the inclination of the axis, as will be 

 shown further on. 



99 



