136 AN EMPIRICAL STUDY OF GYRATING BODIES. 



occurs, and the centre of gravity actually ascends till it 

 is vertically over the point of support. 



There are two cases of this kind varying in some im- 

 portant respects. I take that first whose explanation is 

 least difficult. 



I place before me any unbalanced gyroscope, fig. 16, 

 with axis horizontal and wheel in rapid motion. The ar- 

 rows bb, show the direction of the rotation of the wheel, 

 and S that of the gyration. I take a book, or something- 

 similar, and I bear down with some force on the upper 

 side of the wheel. The reaction from the friction will 

 send the gyroscope to the right ; that is, it accelerates 

 the horizontal movement ; and this, by the first of our 

 four laws, makes the instrument rise. With judicious 

 management, it is easy to start from any position, even 

 from one much below the horizontal, and make it rise to 

 a vertical. 



In place of a book, I find it much better to use a circle 

 of book-board ten or twelve inches in diameter. A loop 

 of tape tacked to the back enables me to hold it firmly. 

 When used, its centre should be approximately over 

 the supporting point. The experiment is novel and 

 pretty, and, with reasonable skill, never fails. The same 

 result may be produced by pressing the finger on the 

 upper side of the axle. If touched on the under side, 

 the friction acts against the horizontal movement, and 

 the instrument drops, as it ought, according to the 

 second of the four laws. 



The experiment is an interesting one. The axle seems 

 to be attached to and to follow the finger. 1 



In all these instances we have a fixed point of resist- 

 ance outside of the gyroscope and its standard ; and 

 consequently the problems presented are of no great 

 difficulty. It is no more than the case of the man in the 



1 For this last experiment, the balanced gyroscope is much the best, as it is easy to regu- 

 late its movements. With the other the gyration is so rapid that the experiment is very 

 difficult. 



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