SPINNING MOVEMENT. 



effect is much stronger, and so are the convec- 

 tion currents, which are commonly known, 

 under these circumstances, as draughts. So 

 powerfully can these causes act that 

 on the platforms of some large halls the 

 flame of a spirit-lamp on the table, instead 

 of burning upwards, is blown straight across 

 horizontally even when there is no open 

 window, door, or other aperture in the 

 neighbourhood. 



When we consider what striking air move- 

 ments we get in the convection currents due 

 to such moderate and limited causes, and com- 

 pare with them the tremendous power of the 

 sun's fierce heat over millions of square miles 

 in the tropics, and the huge areas of severe 

 cold round the poles, we have no reason to be 

 surprised at the force of the most terrible storms 

 of wind, which are only convection currents 

 on a grander scale. The action of the breezes 

 which drive ships and windmills is, both in 

 origin and in operation, exactly similar to the 

 small up-current from the hand which causes 

 the revolutions of the mysterious spinner. 



2. Solids defying Gravity : the Gyroscope. 



Of all the purely mechanical paradoxes, 

 the most surprising is the one which shows 

 a solid substance with a support under one 

 side only, and yet not falling down. 



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