It is humorously ironic how the boys have all gone and worked enthusiastically to gather firewood only for them to realize that they have no means to start a fire. The large pile of wood that they have all labored to put together stands like a monolith, but it is useless unless someone finds a method of setting it alight. Ralph and Jack are ashamed and look at each other in embarrassment. Jack starts to suggest rubbing two sticks together, something he has probably only seen others do or that he has heard about but obviously cannot do himself.
Ralph then shamefacedly asks if anyone has any matches. Roger suggests making a bow and spinning the arrow, using sound effects to illustrate. Piggy, who has been absent up till now, arrives on the scene and immediately draws attention. Ralph hopefully asks him if he has any matches, and Piggy remarks that they have gathered quite a big pile of firewood.
It is at this point that Jack points at Piggy's spectacles and suggests that they use them as burning glasses. Jack snatches the glasses from his face, and Ralph then maneuvers the lenses in different directions until he has the sun's rays centered on a piece of rotten wood. Because the sunlight is focused and therefore much stronger and more powerful than normal, it makes the wood smolder. Jack kneels and blows on the smoldering section, which makes a tiny flame appear. The flame soon spreads until the whole pile, which consists of extremely dry or rotten wood, is aflame.
The fire is meant to act as a signal to any passing ships. Ironically, though, since the wood burns so easily and cleanly, there is no smoke and therefore no signal. In addition, the fire soon runs out of control and destroys a large part of the forest.
Jack is the one who finds a solution to their problem, which suggests that he is not a fool and can make logical connections. This makes his savage behavior later in the novel quite ironic, since one would expect that a person who can rationalize as he does would be able to realize the folly of his actions, which he seemingly does not or refuses to do. Furthermore, Jack's actions also foreshadow what he does later in the novel when he once again snatches Piggy's glasses. In this incident, though, he needs the glasses for himself and his hunters and not for the entire group. It is also Jack who sends the spectacles flying, breaking one of the lenses, when he smacks Piggy on another occasion.