[W]hile the vast assembly, as if with one impulse, shrank from the centres of the rooms to the walls, he made his way uninterruptedly, but with the same solemn and measured step which had distinguished him from the first, through the blue chamber to the purple—through the purple to the green—through the green to the orange—through this again to the white—and even thence to the violet, ere a decided movement had been made to arrest him. What is the effect of parallelism in this excerpt?