How do the boys start a fire in Chapter 2 of Lord of the Flies?

In Chapter 2 of Lord of the Flies,
most of the boys agree that they need to start a signal fire, but they are not sure how
to do so since no one has any matches.  Then, Jack gets the idea to use Piggy's glasses
as "burning glasses."  Though Piggy protests, the boys are successful in their
efforts:

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Ralph moved the lenses back and forth, this way
and that, till a glossy white image of the declining sun lay on a piece of rotten wood. 
Almost at once a thin trickle of smoke rose up and made him cough.  Jack knelt too and
blew gently, so that the smoke drifted away, thickening, and a tiny flame
appeared.

Eventually, the
fire gets out of control (Piggy says, "Now you been and set the whole island on fire.")
and the boy with the mulberry-colored birthmark goes missing. Even though he has the
conch, Piggy is unable to get the attention and respect that holding the shell is
supposed to bring.  (This is partly because the fire has caused chaos, and partly
because no one takes Piggy seriously.)  Panic ensues, as the little children watch the
flames and scream that they are afraid of "snakes."