How does Silver keep Tom Morgan from killing Jim Hawkins?

Some of the pirates begin to speak against Jim, and Morgan springs up and draws his knife in an attempt to kill him, but Long John Silver stops the pirates and says the since he was elected Captain he will protect the boy because "I never seen a better boy." In response, the rest of the pirates leave the house and have a council outside. While they are gone, Silver tells Jim that he decided to save him only because he was courageous enough to stand up for him. Silver vows that he will protect Jim if he will be a witness and save Silver from hanging when they return to civilization. Jim agrees and the shake on they agreement.