“The masonry of the Gatun locks was largely placed by cableways, having a span of 800 feet, covering the entire space to be occupied by the locks. The stone and sand for the concrete were obtained, respectively, 20 and 40 miles down the Caribbean coast, and were brought in barges up the old French Canal as closely as possible to the lock site, and were unloaded by cableways into large stock piles near the bank. The material, however, was still 3,500 feet away and 60 feet below the center of lock construction. This situation caused the adoption of a central mixing plant near the central portion of the locks, consisting of eight 2-yard mixers. An automatic, electric, loop-line railroad, each car carrying the material for a batch of concrete, was installed, passing under the cement shed, under the sand and stone piles; and over the mixers. The mixed concrete was delivered to the cableways requiring it by an electric line, the flat cars of which were handled by electric locomotives. Steel forms were used in constructing the walls of the locks”. A vital feature of the locks is, of course, getting the water into and out of them, and the method of operating the gigantic gates. The former is simple enough of explanation, though the _modus operandi_ will be entirely concealed when the locks are in operation. Through each of the side walls, and through the center walls which divide the pairs of locks, runs a tunnel 18 feet in diameter. To put it more graphically a tunnel large enough to take a mogul locomotive of the highest type. From this main tunnel smaller ones branch off to the floors of the locks that are to be served, and these smaller chutes are big enough for the passage of a farmer’s wagon with a span of horses. These smaller chutes extend under the floor of the lock and connect with it by valved openings, the valves being operated by electricity. There is no pumping of the water. Each lock is filled by the natural descent of the water from the lock above or from the lake. By the use of the great culvert in the central wall the water can be transferred from a lock on the west side of the flight to one on the east, or vice versa. Though it hardly seems necessary, every possible device for the conservation of the water supply has been provided. We will suppose a vessel from the Atlantic reaches Gatun and begins to climb to the lake above. The electric locomotives tow her into the first lock, which is filled just to the level of the Canal. The great gates close behind her. [Illustration: THE HEAVY WHEEL SHOWN IS THE “BULL WHEEL” By its revolution it thrusts or withdraws the arm at the right which moves the gate]