Figure of speech. In one of the early paragraphs of
Aeolus, a sentence is followed by another one that
reverses the order of its elements: "Grossbooted draymen
rolled barrels dullthudding out of Prince's stores and bumped
them up on the brewery float. On the brewery float bumped
dullthudding barrels rolled by grossbooted draymen out of
Prince's stores." In rhetorical theory this kind of ABBA
structure is called chiasmus, or sometimes antimetabole.
It shows up again, somewhat disguised, later in
the chapter.
Chiasmus (kee-AZ-mus) comes from the Greek letter chi,
written X. Hence it means "crossing" or "diagonal
arrangement." Antimetabole (AN-tee-meh-TAB-uh-lee) is
compounded of anti- = in the opposite direction + metabole
= turning about. The device has proved highly effective in
oratory, as in the supposed Winson Churchill sentences
diagrammed here, or in the famous lines from John F. Kennedy's
inauguration speech: "Ask not what your country can do for
you––ask what you can do for your country." Richard Nordquist
(thoughtco.com) cites a less formal example of real
brilliance: "Your manuscript is both good and original, but
the part that is good is not original, and the part that is
original is not good."
Chiasmus excels at achieving such short, punchy effects by
balancing individual words against one another, but it also
can be deployed over much more complex syntactic structures.
Joyce performs the trick of turning a moderately long sentence
back on itself by changing "rolled" from an active to a
passive verb and "bumped" from a transitive to an
intransitive verb. As a result, the order of time is reversed,
somewhat as in Stephen's fantasy of a film
rolling backwards. The first sentence shows empty beer
barrels rolling out of a pub and bumping up onto a cart. The
second shows them bumping up onto a cart after having rolled
out of a pub.
Chiasmus, or antimetabole, is one form of the general
rhetorical principle of antithesis, as Quintilian points out.
