[IV.143] The presence of a ghost was believed to make lights burn blue or dimly. So in Richard III, V, iii, 180, when the ghosts appear to Richard, he says: "The lights burn blue. It is now dead midnight. Cold fearful drops stand on my trembling flesh."
[IV.144] this monstrous apparition. "Above all, the ghost that appeared unto Brutus shewed plainly that the gods were offended with the murder of Cæsar. The vision was thus: Brutus ... thought he heard a noise at his tent-door, and, looking towards the light of the lamp that waxed very dim, he saw a horrible vision of a man, of a wonderful greatness and dreadful look, which at the first made him marvellously afraid. But when he saw that it did no hurt, but stood at his bedside and said nothing; at length he asked him what he was. The image answered him: 'I am thy ill angel, Brutus, and thou shalt see me by the city of Philippes.' Then Brutus replied again, and said, 'Well, I shall see thee then.' Therewithal the spirit presently vanished from him."—Plutarch, Julius Cæsar.
[IV.145] stare: stand on end. 'To be stiff, rigid, fixed' is the primary idea. Cf. The Tempest, I, ii, 213; Hamlet, I, v, 16-20.
[IV.146] [Exit Ghost] Ff omit.
[IV.147] This strongly, though quietly, marks the Ghost as subjective; as soon as Brutus recovers his firmness, the illusion is broken. The order of things is highly judicious here, in bringing the "horrible vision" upon Brutus just after he has heard of Portia's shocking death. With that great sorrow weighing upon him, he might well see ghosts. The thickening of calamities upon him, growing out of the assassination of Cæsar, naturally awakens remorse.
[IV.148] false: out of tune. A charming touch in this boy study.
[IV.149] [To Varro] Globe Camb | Ff omit.
[IV.150] ll. 304, 308 Varro, Claudius | Both Ff.
[IV.151] commend me to: greet from me, remember me kindly to.
[IV.152] set on: cause to advance.