MECHANICAL PARADOXES. 



A very good gyroscope top to illustrate 

 this can be got for half-a-crown, and a fairly 

 good one for a shilling ; but any one who is 

 handy with a fretsaw or keyhole saw can make 

 a good substitute for himself. 



Take a flat piece of board without any 

 warp in it, and mark out a circle five, six, or 

 seven inches in diameter. Saw carefully round 

 this mark, bore a hole in the centre, and insert 



an axle projecting three or 

 four inches on one side and 

 two on the other. A wooden 

 penholder will make a very 

 good axle. The axle must 

 beset as truly perpendicular 

 to the wheel and as truly 

 central as possible. Near 

 the end of the axle, on its 

 longer projection, cut a deep 

 nick as at A, Fig. 6 ; and 

 take or make a wire ring which will only just 

 go over the axle. Push it on as far as the 

 nick, then squeeze it to an elliptical form, so 

 that it will not come off again, and finally 

 tie to it a string about as long as from the 

 ground to an upper window the longer the 

 better, so that there may be more time to watch 

 the effect. The apparatus is now ready. 



Wind up the string (a fine one, or strong 

 thread) on the axle, giving it a few turns over 

 itself at the beginning, to fix it for winding. 



24 



FIG. 6. HOME-MADE 

 GYROSCOPE. 



