162 AN EMPIRICAL STUDY OF GYRATING BODIES. 



seen in the hands of the street toy venders on Broadway, 

 New York. Almost any pleasant day they may be found 

 exhibiting before an interested little crowd. All that is 

 needed for such exhibitions is a piece of smooth hard 

 cord eight or ten feet long, and a somewhat peculiar 

 gyroscope. On the ring in line with the axis are soldered 

 two small round projections, one at each end. One of 

 these is solid ; the other has a slot in it about the size 

 and shape of the slot in the head of a common wood- 

 screw. The solid end acts as the point of a gyroscope, 

 or top, and presents nothing peculiar. It is with the 

 other end that we have to do. The wheel is set in rapid 

 motion, and then the instrument is placed on the string 

 which has been fastened securely to an object sufficiently 

 distant to draw it taut, (fig. 36). The slot straddles the 

 string. The exhibitor raises the end next to him, and 

 the gyroscope moves securely down the incline. Then 

 he lowers the same end, and the instrument slides back. 



Why does it not fall off % 



Let fig. 37 represent a section of the wheel and its axle, 

 omitting the ring and the upper half of the shaft (we 

 thus get our tee-square again). The slit for the string is 

 seen at a, and just above, at d, is the pivot on which the 

 axle revolves with little friction. Suppose the tee to be 

 vertical. In a moment it begins to tilt, b, for example, 

 going up and c going down. As soon as this is done — 

 say in one-fiftieth of a second —suppose the tee to be in- 

 stantly reversed ; b will continue going up and c will 

 continue going down, and this means pushing the tee 

 back towards its first position. There will be a little loss 

 each time, but the principle is the same that we have 

 considered in case of the gyroscope and top. In reality, 

 a gyroscope thus placed is only a top in a frame, and is 

 subject to all the laws of a top, the frame merely keeps 

 it from slipping off the string. No farther explanation 

 is needed. 



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