How and why do the boys make fire?

In chapter 2, Ralph holds an assembly in which he addresses the top priorities that must be completed in order to be rescued from the uninhabited island. Ralph mentions that the boys must build a signal fire so that passing ships will be able to spot them from a distance. He also suggests that the signal fire should be built on top of the mountain to make it more visible to passing ships. All the boys agree that making a signal fire is top priority and race to collect dead wood from the nearby forest. However, once the boys have a massive collection of firewood, they have no way of starting the fire. Fortunately, Jack notices Piggy's glasses and realizes the boys can use the lenses to focus a ray from the sun, which will heat the dry wood and eventually create a spark. Ralph then takes Piggy's glasses, focuses a sun ray onto the wood, and lights the fire. Unfortunately, the pile is too large, and a massive flame is lifted into the air as the wind carries sparks to the surrounding forest. The boys accidentally start a forest fire, and a littlun disappears in the burning woods.