BOOK VI 



207 



sort is made of boards of the same width, but shorter, to which are bound 

 long thin blades of poplar or some other flexible wood ; the third sort has 

 boards like the last, to which are bound double and triple rows of goose 

 feathers. This last is less used than the second, which in turn is less used 

 than the first. The boards of the fan are mortised into the quadrangular 

 parts of the barrel axle. 



A— First kind of fan. B— Second kind of fan. C— Third kind of 

 FAN. D— Quadrangular part of axle. E— Round part of same. 



F — Crank. 



Blowing machines of the third genus, which are no less varied and of no 

 fewer forms than those of the second genus, are made with bellows, for by its 

 blasts the shafts and tunnels are not only furnished with air through conduits 

 or pipes, but they can also be cleared by suction of their heavy and pestilential 

 vapours. In the latter case, when the bellows is opened it draws the 

 vapours from the conduits through its blow-hole and sucks these vapours 

 into itself ; in the former case, when it is compressed, it drives the air through 

 its nozzle into the conduits or pipes. They are compressed either by a man. 



