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… … A — Smaller part of shaft . B — Square conduit . C — Bellows . D — Larger part OF SHAFT .
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