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,
