Up to this time the ship had been proceeding under her own steam and at about full speed. Now slowing down she gradually comes to a full stop alongside the central guide wall. Here will be waiting four electric locomotives, two on the central, two on the side wall. Made fast, bow and stern, the satellites start off with the ship in tow. It will take an hour and a half to pass the three locks at Gatun and arrangements will probably be made for passengers to leave the ship and walk by its side if desired, as it climbs the three steps to the waters of Gatun Lake 85 feet above. Probably the first thing the observant passenger will notice is that as the ship steams into the open lock the great gates which are to close behind her and hold the water which flows in from below, slowly lifting her to the lock above, are folded flush with the wall, a recess having been built to receive them. The chamber which the vessel has entered is 1000 feet long, if the full water capacity be employed, 110 feet wide and will raise the ship 28¹⁄₃ feet. If the ship is a comparatively small one the full length of the lock will not be used, as intermediate gates are provided which will permit the use of 400 or 600 feet of the lock as required--thus saving water, which means saving power, for the water that raises and lowers the ships also generates electric power which will be employed in several ways. Back of each pair of gates is a second pair of emergency gates folded back flush with the wall and only to be used in case of injury to the first pair. On the floor of the canal at the entrance to the lock lies a great chain, attached to machinery which, at the first sign of a ship’s becoming unmanageable, will raise it and bar the passage. Nearly all serious accidents which have occurred to locks have been due to vessels of which control has been lost, by some error in telegraphing from the bridge to the engine room. For this reason at Panama vessels once in the locks will be controlled wholly by the four locomotives on the lock walls which can check its momentum at the slightest sign of danger. Their own engines will be shut down. Finally at the upper entrance to the locks is an emergency dam built on the guide wall. It is evident that if an accident should happen to the gates of the upper lock the water on the upper level would rush with destructive force against the lower ones, perhaps sweeping away one after the other and wrecking the canal disastrously. To avert this the emergency dams are swung on a pivot, something like a drawbridge, athwart the lock and great plates let down one after the other, stayed by the perpendicular steel framework until the rush of the waters is checked. A caisson is then sunk against these plates, making the dam complete.