The second genus of blowing machine is made with fans, and is likewise
varied and of many forms, for the fans are either fitted to a windlass barrel
or to an axle. If to an axle, they are either contained in a hollow drum,
which is made of two wheels and a number of boards joining them together,
or else in a box-shaped casing. The drum is stationary and closed on the
sides, except for round holes of such size that the axle may turn in them ;
it has two square blow-holes, of which the upper one receives the air, while
the lower one empties into the conduit through which the air is led down the
shaft. The ends of the axle, which project on each side of the drum, are
supported by forked posts or hollowed beams plated with thick iron ; one
end of the axle has a crank, while in the other end are fixed four rods with
thick heavy ends, so that they weight the axle, and when turned, make it
