What are the dramatic functions of each act in The Crucible?

This play consists of three acts, divided primarily by the
passing of time and the momentum of the witch trials in Salem.  Each act takes place in
one day, though what happens in the interim is explained; and each act is a mini-drama
of its own.

Act I depicts the source of the trouble, the
cause of the witch hunts.  Miller introduces us not only to each character but also to
the antecedent action (that which happened before the story began).  We understand the
environment which exists as well as the paranoia and suspicion which will soon breed
such despicable things. The conflicts become evident; the alliances begin to form; and
the battle lines (both spiritual and physical) are
drawn.

Act II takes place eight days later, once the trials
have begun.  The protagonist, John Proctor, has not been privvy to any of the action
going on in town, so others must inform him of the hysteria that has struck Salem.  In
this act we watch broken trust get painfully rebuilt and broken again; the motive of the
primary instigator, Abigail, is horribly confirmed; and our hope that this is just some
kind of ridiculous over-reaction evaporates in the face of alarming false accusations. 
The climax of this act happens in the courtroom, when John tells the truth but is not
believed, and his wife Elizabeth lies but is taken as truthful.  Despite the fact that
we all know the witch trials did end in a relatively short amount of time, there is
little hope that the characters we have developed relationships with will survive the
ordeal.

Act III is set in another season, probably several
months after Act II ends.  The hopelessness we feared has come to pass; and, though they
are still alive, the primary characters in the play are facing an imminent and
undeserved death.  Dramatically, the moment when Proctor denies his confession and cries
out "I have given you my soul; leave me my name!" is both awful and amazing.  This
reversal represents the hope, at last, that common sense may once again rule in Salem. 
And, even though at least twenty innocent people lost their lives in the hysteria, the
few we feel we know died as upright citizens and people of
faith.