THE CONQUEST OF TIME AND SPACE 



This seems rather weird behavior, but if you will 

 note the direction of the arrow on the wheel you will see 

 a certain method in it. It will appear that in each case 

 the force you apply has been carried round a corner, as 

 it were, by the whirHng disc, and made to act at right 

 angles to the direction of its application. This change 

 of direction of a force applied is strictly comparable to 

 the change effected by the familiar device known as a 

 pulley. With that device, to be sure, a pull instead of 

 a push is used, but this is a distinction without a differ- 

 ence, for pushing and pulling are only opposite views of 

 the same thing. 



Possibly this suggested explanation of the action of 

 the gyrostat may not seem very satisfactory, but the 

 facts are perfectly clear, and if you will bear them stead- 

 ily in mind you will readily be able to understand the 

 Brennan gyroscope, as you otherwise cannot possibly 

 hope to do. You have only to recall that pushing down 

 at A causes motion (called "precession") to the left, 

 and pushing up at ^ , motion to the right ; and that in 

 order to make A either rise or fall, you must "accelerate 

 precession" by pushing to the left or to the right, re- 

 spectively. But you must understand further, that 

 when, through the application of any of these disturbing 

 forces, you have forced the axis O A into a new position, 

 it will tend to maintain that new position, having no 

 propensity whatever to return to its original position. 

 It is quite as stably in equilibrium with its axis pointing 

 upward as when in the position shown in the diagram. 

 One position is quite like another to it; but having 

 accepted a position it resents any change whatsoever. 



[206] 



