Empty elements used as milestones

digested. Its long trunk, as seen slanting down from
out of the building across the wharf and into the ship,
is a mere wooden pipe; but this pipe is divided within.
It has two departments; and as the grain-bearing 
troughs pass up the one on a pliable band, they pass
empty down the other. The system therefore is that
of an ordinary dredging machine; only that corn, and
not mud is taken away, and that the buckets or 
troughs are hidden from sight. Below, within the
stomach of the poor bark, three or four labourers are
at work, helping to feed the elevator. They shovel
the corn up towards its maw, so that at every swallow
he should take in all that he can hold...
...The transit of the bushels 
of corn from the larger vessel to the smaller will have
taken less than a minute, and the cost of that transit
will have been—a farthing.

Advanced Markup Concepts, slide 11 of 15