Chapter four has two different scenes that show interesting aspects of power on the island in Lord of the Flies. 

The first scene occurs as Roger follows Henry and begins to throw stones at him, missing on purpose.  This scene reveals the connection that Roger feels between violence and control.  Throwing the rocks at Henry, a much smaller boy than Roger, makes Roger feel powerful; it is the essence of bullying.  He exerts his control over Henry, and subsequently feels that power to harm him if he should choose to do so.  This scene with Roger suggests that power can come through control and the ability to use violence.

The second scene that informs the reader about power on the island occurs when Jack dons his hunter's mask for the first time, making him feel like "an awesome stranger" (63).  The mask, and the coverage it provides, makes Jack feel powerful and liberated.  The mask is compelling to Jack and the other boys, making them feel "liberated from shame and consciousness" (64).  In this scene, Jack derives power from hiding away his true appearance.  The mask enables him to be bolder, fiercer.  Later in the chapter when he makes his first kill, Jack feels the rush of authority that comes with the respect of the other boys at the hunt. 

Both Roger and Jack derive power from their ability to use violence in chapter four.  Their savage outlook will challenge the fledgling civilization and order on the island and ultimately overcome even Ralph's leadership in later chapters.