BOOK VI. 



209 



closed. The bellows, by the first method, blows fresh air into the conduit 

 through its nozzle, and by the second method blows out through the nozzle 

 the hcav}' and pestilential vapours which have been collected. In this 

 latter case fresh air enters through the larger part of the shaft, and the miners 

 getting the benefit of it can sustain their toil. A certain smaller part of the 

 shaft which forms a kind of estuarj', requires to be partitioned off from the 

 other larger part by uninterrupted lagging, which reaches from the top of the 

 shaft to the bottom ; through this part the long but narrow conduit reaches 

 down nearly to the bottom of the shaft. 



When no shaft has been sunk to such depth as to meet a tunnel driven 

 far into a mountain, these machines should be built in such a manner that 

 the workman can move them about. Close by the drains of the tunnel 

 through which the water flows away, wooden pipes should be placed and 

 joined tightly together in such a manner that they can hold the air ; these 

 should reach from the mouth of the tunnel to its furthest end. At the mouth 

 of the tunnel the bellows should be so placed that through its nozzle it can 

 blow its accumulated blasts into the pipes or the conduit ; since one blast 



A — Tunnel. B — Pipe. C — Nozzle of double bellows. 



