72 GYROSCOPE. 



air and from friction — it could never cease that up and 

 down movement. In the first part of its swing it ac- 

 cumulates energy, and in the other part spends it. The 

 work and the energy for each vibration are equal. 



Another principle equally important must also be re- 

 membered. A body moving in any direction is not re- 

 tarded by a force, exerted at right angles to its direction. 

 The pendulum illustrates this also. The rod which 

 holds up the weight pulls at right angles to the direction 

 of the latter, but does not affect its velocity. 



If these two principles are clearly grasped, the ex- 

 planation of the Gyroscope is simple enough. 



We will suppose the ring to be laid aside, since it 

 serves no other purpose than a convenience for holding 

 the disk, and that the disk (or wheel) is cut away until 

 only a narrow strip is left, like two arms extending in 

 opposite directions from the axle. No one who has a 

 Gyroscope will wish to treat it in this manner, and as to 

 conceiving such a thing most people find it too difficult ; 

 we will therefore change the Gyroscope for something- 

 cheaper and more simple, but which will enable us to 

 show the working of the same principles. We will take 

 a common tee-square, or if we have none, we will nail a 

 small strip of wood, say one inch square and ten inches 

 long, at its middle on the end of another similar strip. 

 This will make a tee-square sufficient for our purpose. 

 Now hold the stem of the square in the left hand close 

 to the end, and make the cross-piece vertical. Hold the 

 left hand still, and let the cross-piece move up or down. 

 Evidently, it will describe part of a circle. If it is held 

 so that the cross is just in front of a plumb line — so that 

 both can be viewed at once — it will be seen that the 

 upper end of the cross moves away from the plumb to 

 the right, while the lower moves away from it also, but 

 to the left. If, while the left hand remained stationary, 

 the cross had been allowed to drop freely, the top and 



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