MECHANICAL PARADOXES. 



But without such special and violent inter- 

 ference, making your observations in a room 

 in which, so far as you could previously tell, 

 the air was everywhere absolutely still, you 

 are surprised to find at every point evidences 

 of a distinct draught upwards. Apparently 

 the air is rising bodily through the floor, at 

 every part of it, floating upwards in the whole 

 extent of the room, and going away through 

 the solid substance of the plaster all over the 

 ceiling 1 



Or is there some other mysterious agency 

 at work to keep the spinner revolving ? The 

 author had one made of thin sheet aluminium, 

 with four larger vanes instead of eight smaller 

 ones. Each vane had its outline cut in such 

 a way as to resemble a bird with wings and 

 tail outspread, and attached to the centre by 

 the central end of the inner wing. The obliquity 

 of the vanes, instead of being obvious, as in 

 the paper spinner previously described, was 

 disguised as an artistic set of the wings and 

 tails to imitate the natural attitude of birds 

 in some of the movements of flight. This, 

 on being tried, behaved in the same way as 

 the paper spinner. In every part of a room 

 where the air was expected to be calm and 

 still, it kept slowly revolving. Investigators 

 of the phenomenon were much puzzled. Civil 

 engineers and other scientific men were un- 

 able to give a satisfactory explanation. Some 



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