In Chapter 8 of Lord of the Flies by William Golding, a meeting is called because the beast is near where the signal fire is located; in addition, there is a challenge for Ralph's authority by Jack. But, when he calls for a vote, the boys do not respond, looking uncomfortably at the ground instead. Jack announces that he is going off by himself, and runs away, tears stinging his cheeks.
Then, Piggy starts to chide Ralph, but decides against doing so. Instead, he tells Ralph,
We can do without Jack Merridew. But now we really got a beast,....we really need to stay close to the platform; there'll be less need of him and his hunting....
Ralph replies, "There's no help, Piggy. Nothing to be done." And, the boys sit in "depressed silence" for a while until Simon appears and suggests climbing the mountain.
The circle shivered with dread. Simon broke off and turned to Piggy who was looking at him with an expression of derisive incomprehension.
The circle represents the boys who sit in a circle at the meetings. They are frightened of the sight of what they think is the "beast" and do not want to venture up the mountain.
The figurative term for the use of the circle to represent the group of boys is called metonymy. Metonymy is another form of metaphor, very similar to synecdoche in which the person(s) or thing(s) cchosen for the metaphorical image is closely associated with the subject to which it is compared. (e.g. referring to a king or queen as "the crown.") In Chapter 8 the boys are referred to as the circle since they have assembled several times and sit in a circle. Also, as a group,their feelings of fear are in unison: They shiver all together--hence, "the circle shivered."