SPINNING MOVEMENT. 



suggested magnetic fields or electric discharges 

 from the points of the vanes. 



The key to the explanation is found by 

 supporting the pivot-pin in some other holder 

 than the hand. Take a narrow strip of stiff 

 cardboard, and fix the pin near one end by 

 driving it through up to the head. Fix the 

 strip so as to project over the edge of a side- 

 board or other object by laying the edge of 

 a book on it, the pin pointing upwards at a 

 distance of two inches or so from the side- 

 board. Next place the spinner in position on 

 the pin-point and retire a little distance away. 

 In a still room, the spinner now fails to move. 

 Hold the hand just under it, and it begins to 

 revolve. Clearly the motive power comes from 

 the hand beneath. 



The fact is, that the hand is usually warmer 

 than the surrounding air. The temperature 

 of the blood deep beneath the surface of the 

 body is about 98 F. The air of a room is often 

 60, more or less. But the hands are always 

 cooler than the body-blood simply because 

 they are always losing heat in warming the 

 air. Heat makes things expand ; and so the 

 heat of the hands, passing to the air in contact 

 with them, causes it to expand. Expanded 

 air is less dense, and therefore less heavy. It 

 is consequently out-balanced and driven up- 

 wards by the heavier unwarmed air around 

 it, just as the hot, expanded, light air from 

 j '9 



