How does William Golding present ideas of power in the novel The Lord of the Flies?

There is an immediate establishment of power in Golding's
Lord of the Flies as the "fair boy," Ralph appears in Chapter One. 
This fair boy with his "golden body" is the natural leader, who commands merely by his
appearance. With Piggy's adulation and assistance in reasoning, along with the conch, a
symbol of parliamentary power, Ralph is chosen as the leader of all the boys, even over
the assertive, red-haired Jack Merridew.

However, with fire
as a symbol of great force, the most significant action that defines the reversal of
power from Ralph to Jack is the hunters' stealing of the fire in Chapter Eight. Alluding
to the mythological tale of Prometheus, who steals fire from the gods and gives it to
man, Golding allegorically symbolizes Jack's usurping of power over the
boys. 

Another symbol that designates power is the pig's
head, the lord of the flies. This symbol of Beelzebub indicates the supremacy of evil
over the boys.  For, when Simon stumbles upon it, he falls inside its mouth and passes
out. After he regains consciousness, Simon speaks with the lord of flies and,later,
tries futilely to articulate this experience, but is crushed by the evil, savage power
of Jack and the others. This power of the "beast" in the heart of man leads to the
deaths of Simon and Piggy and the reckless pursuit of
Ralph:

Ralph
stumbled, feeling no pain but panic, and the tribe, screaming now like the chief, began
to advance.  Another spear, a bent one that would not fly straight, went past his face
and one fell from on high where Roger was.  The twins lay hidden behind the tribe and
the anonymous devils' faces swarmed across the neck.  Ralph turned and ran....He saw the
headless body of the sow and jumped in time.....

The
yelling ceased, and Samneric lay looking up in quiet terror.  Roger advanced upon them
as one wielding a nameless
authority. 

This "nameless
authority" is the power of evil, the ultimate force on the island, one that has always
been present in the sadistic Roger and is now in the savage Jack and the other
hunters.