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Lock Gates. The lock gates, each composed of two leaves, are 65 ft. wide, from 47 to 82 ft. high, 7 ft. thick and weigh from 90 to 730 tons. There are 92 leaves in all and their combined weight is 60,000 tons. They were carried in parts to the Isthmus and put together there. They are constructed to float like a ship. Each is a huge webbed steel box, the girders of which are covered with a steel sheathing. All portions of the interior are accessible, with water- tight compartments providing for the adjustment of the buoyancy so as to control within limits the dead load on the bearings, making the leaf practically float in the water. This watertight compartment is subdivided vertically into three sections, each independently watertight, so that if the shell should be broken in any way, or begin to leak, probably only one section would be affected. An air-shaft, 26 in. in diameter, runs from the bottom compartment up to the top of the gate, and this also is watertight where it passes through the upper half of the leaf. The girders are made with manholes through the webs, providing communication from the top to the bottom of the leaf, and are connected by several sets of vertical transverse diaphragms of solid plates, running from top to bottom of the leaf, thus making a cellular construction, and dividing'the spaces between the horizontal girders into small pockets, all of which are accessible through manholes. Each leaf rests at the bottom of its heel-post upon a hemispherical pivot of forged nickel steel, and is hinged at the top to the masonry of the lock wall. It swings free on the pivot like a door, without wheels or other support beneath it. Intermediate gates are used in all except one pair of locks, and are so placed as to divide the space into two chambers, one 600 and the other 400 ft. in length. This makes possible a saving of water and time in locking small vessels through, for about 95% of the vessels navigating the high seas are less than 600 ft. in length. The highest gates and the highest lock walls on the canal are those of the lower locks at Mira- flores, and these locks are the only ones which have no intermediate gates. The total lift from mean sea-level to the level of Miraflores lake, 54! ft., is divided equally between the upper and lower locks. The depth of water on the mitre sills is 40 feet. The locks are filled and emptied through the large and smaller culverts. The large cul- verts are controlled at points near the gates by large valves, and each of the small culverts feeds in both directions through the laterals, thus permitting the passage of water from one twin lock to another, effecting a saving of water if desired. The average time in filling and emptying a lock is about 15 minutes. The time to pass a vessel through all the locks is about two hours, one hour at each end of the canal. The time of passage of a vessel from ocean to ocean is from 8 to 10 hours, according to the ship's size and speed.

Passage of Locks. No vessel is permitted to enter or pass through the locks under its own power. On arrival at Gatun or Miraflores, it is tied up to the approach wall and turned over to the absolute control of the canal authorities. These place a representative of their own on the bridge and another in the engine-room. They then connect the towing locomotives, or " electric mules," with the ship. These locomotives operate on cog tracks on the lock walls, and proceed at the rate of 2 m. an hour. The number of locomotives varies with the size of the vessel. The usual number required is four: two ahead, one on each wall, imparting motion to the vessel; and two astern, one on each wall, to aid in keeping the vessel in a central position and to bring it to rest when entirely within the lock chamber. They are equipped with a slip drum, towing windlass and hawser, which permit the towing-line to be taken in or paid out without actual mo- tion of the locomotive on the track. The locomotives run on a level, except when in passing from one lock to another they climb heavy grades. Before a lock can be entered, a fender chain, stretched across the walls of the approach, must be passed. If all is proceeding properly, this chain is dropped into its groove to the bottom of the channel. If by any chance the ship is moving too rapidly for safety, the chain remains stretched and the vessel runs against it. The chain, which is operated by hydraulic machinery in the walls, then pays out slowly by automatic release until the vessel is brought to a stop. The chain, which weighs 24,098 lb., and is stronger than any previously made, is capable of stopping a lo,oop-ton ship running at 4 m. an hour within 73 ft., or less than the distance between the chain and the first gate. If the vessel by a remote possibility gets away from the towing locomotives and, breaking through the chain, rams the first gate, there is a second gate 50 ft. away, protecting the lock, which is certain to arrest further advance. When the leaves of this gate swing open, the vessel is towed in, and the gate is closed behind it. Then, from openings placed at regular intervals in the lock floor, water pours in, lifting the vessel to the level of the lock above. This inflow, coming equally from all points, does not move the ship from a stable position. The gates are never opened or closed with a head of water on either side of them. The process of lifting is repeated until the vessel reaches the lake level. At all times the vessel is in full view of the men who are controlling it and as safe as if tied to a wharf. The gates are opened and closed by a powerful machine invented by Edward Schildhauer, an electrical engineer in the employ of the Goethals Canal Commission. It consists of a crank gear or wheel moving through an arc of 197, placed hori- zontally in the lock wall. To the outer rim of the wheel is attached a strut or connecting-rod which is fastened to the top of a lock gate 17 ft. from the pintle or hinge. When the wheel turns in either direc- tion the gate leaf is opened or shut, the operation taking two minutes.

The crank gear, constructed of cast steel, is 19 ft. 2 in. in diameter and weighs approximately 35,000 pounds. It is connected with an electric motor, and a small electric switch sets it in motion. Every operation in the passage of a vessel through the lock, except the movements of the towing locomotives, is controlled by a single man so placed in a building at the top of the centre wall as to command an unobstructed view of every part of the locks. He has before him a control board table about t> ft. long and 5 j ft. wide which is a com- plete model of the locks in duplicate with switches and indicators in the same relative positions the machines they control occupy in the lock walls. Standing by this board the operator throws the electric switches, and in response to his action he sees in the model the fender chains rise and fall, the gates open and close, the water rise and fall in the locks, and knows the exact position of the vessel at every stage of its progress. Each gate, each valve for letting in the water to the. culverts, each fender chain, is operated by a separate motor mounted near the machinery in chambers in the lock wall. In each machinery chamber there is a starting panel containing contractors by which current is applied to the motor, and these panels in turn are controlled from a main unit in the central control-house. Some of the machinery chambers at Gatun are 2, 700 ft. distant from the point of control, 90% of them are within 2,000 ft., and 50% within 1,200 feet.

Thf Canal Voyage. The length of the canal from shore-line to shore-line is about 40 m. and from deep water in the Atlantic to deep water in the Pacific about 50 miles. The canal does not, as is gener- ally supposed, cross the Isthmus from E. to W. It runs due S. from its entrance in Limon Hay, through the Gatun locks to a point in the widest portion of Gatun lake, a distance of about 1 1 J m. ; it then turns sharply toward the E. and follows a course generally south- eastern till it reaches the Bay of Panama. Its terminus near Panama is about 22\ m. E. of its terminus near Colon. In passing from the Atlantic to the Pacific a vessel enters the approach channel in Limon Bay, which has a bottom width of 500 ft. and extends to Gatun a distance of seven miles. At Gatun it enters a series of three locks in flight which lift it 85 feet. It then enters upon Gatun lake, the water- bridge of the Isthmus. The lake covers an area of 164 sq. m. with a ilc'plh varying from 45 to 87 ft., and contains 183,000,000,000 cub. ft. of water. It has a channel varying from 500 to 1,000 ft. in width, for a distance of about 24 m. to Bas Obispo, where the Cut passage begins. Through the lake a vessel may steam at full speed. The channel through the Cut, a distance of about nine m., has a bottom width of 300 ft. and a depth of 45 ft., and extends to the locks at Pedro Miguej, the Pacific end of the water-bridge. At Pedro Miguel the is lowered in the single Iock3oj ft. to a small lake, at an eleva- tion of 54! ft. above sea-level, through which the vessel passes, ij m. to the two locks at Miraflores. These drop it to sea-level, and through an approach passage 8} m. long, with a bottom width of 500 ft., it passes into the Pacific. The Cut has eight angles and at these the channel is widened sufficiently to allow a i,ooo-ft. vessel to make the turn. The smallest angle is 70 36' and the largest 30. In the whole canal there are 22 angles, the total curvature being 600 51'. The sharpest curve is 67 10'. The canal is lighted from end to end by electricity and gas. There are concrete lighthouses for range lights on the" hillsides, and beacons in the Cut, in which electricity is used. The channel through Gatun lake is marked with floating buoys lighted with compressed acetylene dissolved in acetone. The most powerful electric lights are those of the approach channels which are visible for from 12 to 18 nautical miles. The beacons and gas-buoy lights have about 850 candle-power. White lights are used throughout; and in order to eliminate the possibility of confusing the lights with one another, and with the lights on shore, all range-lights, beacons and buoys have individual characteristics, formed, by flashes and com- binations of flashes of light and dark intervals. The electric lights on the locks are suspended from brackets on concrete columns about 34 ft. high and are clustered under concrete hoods in such a way as to light the lock chambers and not penetrate along the axis of the canal.

Breakwaters. Long breakwaters have been constructed near the approach channels in both oceans. One in Limon Bay, or Colon harbour, called the West Breakwater, extends into the bay from Toro Point at an angle of 42 53' northward from a base-line drawn from Toro Point to Colon light, and is 11,526 ft. in length, 15 ft. wide at the top and 10 ft. above mean sea-level. A second, also in Limon Bay, known as the East Breakwater, is without land connex- ion, is about one m. in length and runs in an easterly direction at nearly a right-angle with the canal channel. It has a lighthouse on the channel end. The purpose of the West Breakwater is to protect the harbour against " northers," very severe gales which are likely to blow from Oct. to January. The purpose of the East Breakwater is to prevent silting in the canal channel. The breakwater at the Pacific entrance extends from Balboa to Naos Is., a distance of about 17,000 ft., or a little more than three miles. It lies from 900 to 2,700 ft. E. of, and for the greater part of the distance nearly parallel to. the axis of the canal prism, varies from 20 to 40 ft. in height above mean sea-level, and is from 50 to 3,000 ft. wide at the top. It was constructed for a twofold purpose; first, to divert cross-currents that would carry soft material from the shallow harbour of Panama into the canal channel; second, to furnish rail connexion between the islands and the mainland.

Permanent Canal Buildings. All permanent canal buildings, for civil or military use, are of concrete, replacing the temporary struc-