38 TRANSACTIONS OF THE [.TAN. 5, 



Before attempting an explanation, I ask that the following 

 principles be admitted : 



A body set in motion will continue in motion until something 

 stops it. This is a part of Newton's first law of motion. Its 

 best illustration for the present purpose is afforded by the pen- 

 dulum. When the latter reaches the bottom of its arc it does 

 not stop, but continues on its course up the opposite arc until 

 the continued action of gravitation has produced a counter- 

 force just equal to that caused by the fall, and then it stops. 

 Again gravity draws it down, and again it rises. And so it 

 goes on. Except for outside resistance, that from air and from 

 friction, it could never cease that up and down movement. In 

 the first part of its swing it accumulates energy, and in the 

 other part spends it. The work and the energy for each vibra- 

 tion are equal. 



Another principle equally important must also be remem- 

 bered. A body moving in any direction is not retarded 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, l)ut does nut affect 

 its velocity. 



If these two principles are clearly grasped, the explanation 

 of the Gyroscope is simple enough. 



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

 no other purpose than a convenience foi- 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 tlie Gyroscope for some 

 thing cheaper and more simple, but which will enable us to 

 show the working of the same principles. We will take a 

 common T-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 

 T-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 



