208 



BOOK VI. 



or by a horse or by water-power ; if by a man, the lower board of a large bellows is 

 fixed to the timbers above the conduit which projects out of the shaft, and so 

 placed that when the blast is blown through the conduit, its nozzle is 

 set in the conduit. When it is desired to suck out heavy or pestilential 

 vapours, the blow-hole of the bellows is fitted all round the mouth of the 

 conduit. Fixed to the upper bellows board is a lever which couples 

 with another running downward from a little axle, into which it is 

 mortised so that it may remain immovable ; the iron journals of this little 

 axle revolve in openings of upright posts ; and so when the workman pulls 

 down the lever the upper board of the bellows is raised, and at the same time 

 the flap of the blow-hole is dragged open by the force of the wind. If the 

 nozzle of the bellows is enclosed in the conduit it draws pure air into itself, 

 but if its blow-hole is fitted all round the mouth of the conduit it exhausts 

 the heavy and pestilential vapours out of the conduit and thus from the 

 shaft, even if it is one hundred and twenty feet deep. A stone placed on the 

 upper board of the bellows depresses it and then the flap of the blow-hole is 



A SMALLER PART OF SHAFT. B SQUARE CONDUIT. C BELLOWS. D LARGER PART 



OF SHAFT. 



