The vessel, then, in order to gain the level of Gatun Lake from the Atlantic entrance, has to pass through a flight of three successive locks. The maximum lift is 32 feet, or about four feet higher than at any other locks now in use. All the locks along the Panama Canal are duplicated--that is, there are two parallel sets with a common centre-wall--so that two ships could be simultaneously put through both flights in the same or in opposite directions. This "double-tracking" is in itself one of the many precautions taken against accidents at the locks. There are no locks in the world where these precautions are so minute and numerous. It is all of course in the interests of the owners to inspire the maximum of confidence in maritime circles. Complete efficiency in the operation of the canal, absolute safety for the vessels and cargoes entrusted for ten or twelve hours to its keeping, are the elementary conditions of success. Each lock through which the vessel passes is equipped with two pairs of mitre gates--that is, double swinging doors--the biggest lock-gates in the world; but in all cases the uppermost locks have a second pair of gates, so that if some unruly vessel were to ram open one set of gates there would still be another set ready to receive it. But even this is not all. Heavy chains are stretched across the channel with the ends attached to hydraulic paying-out machinery. These chains and their attachments are capable of bringing to a dead stop a vessel of 10,000 tons moving at the rate of five miles an hour. And still the precautionary devices are not exhausted. Let us suppose that all these barriers were broken down, though such a disaster is almost beyond the bounds of things possible. At the head of each flight of locks there are provided great cantilever swing-bridges which can be thrown across the channel in case of accident. From these bridges a series of nickel-steel wicket girders could be let down. The lower ends of these girders would drop into a sort of sill at the bottom of the rushing waters. The girders would then act as small perpendicular runways, down which large steel sheets on rollers would be let down, gradually damming back the escaping waters.