This passer-by was led to believe, not without a certain emotion, that a modification had been effected in this mysterious cause, when he saw one of the carriages begin to move; but it was merely a coachman who, afraid of his horses' catching cold, started them now and again on a brisk walk, all the more impressive because the rubber-tired wheels gave the sound of their hooves a background of silence from which it stood out more distinct and more explicit.