If the other allowed him to go on ahead, and did not yet arrest him, it was, in all appearance, in the hope of seeing him arrive at some significative rendezvous and some group worth capturing. This delicate operation is called tracking. What renders this conjecture highly probable, is the fact that the buttoned-up man, perceiving from the slope an empty fiacre passing, made a sign to the driver; the driver understood, evidently perceived with whom he had to deal, turned round, and began following the two men along the quay. This was not perceived by the ragged, shambling fellow in front. The hackney coach rolled along under the trees of the Champs Élysées, and over the parapet could be seen the bust of the driver, whip in hand. One of the secret instructions of the police to the agents is, "Always have a hackney coach at hand in case of need." While each of these men manœuvred with irreproachable strategy, they approached an incline in the quay, which allowed drivers coming from Passy to water their horses in the river. This incline has since been suppressed for the sake of symmetry,--horses die of thirst, but the eye is gratified. It was probable that the man in the blouse would ascend by this incline in order to try to escape in the Champs Élysées, a place adorned with trees, but, in return, much frequented by police agents, where the other could easily procure assistance. This point of the quay is a very little distance from the house brought from Moret to Paris in 1824 by Colonel Brack, and called the house of Francis I. A guard is at hand there. To the great surprise of his watcher, the tracked man did not turn up the road to the watering-place, but continued to advance along the bank parallel with the quay. His position was evidently becoming critical, for unless he threw himself into the Seine, what could he do?