The Panama Canal

With the currents thus checked, the Chagres will lose all power to interfere with the navigation of the canal, although upon the bosom of its water will travel for a distance of 35 miles all the ships that pass through the big waterway from Gatun to Miraflores. This fresh water will serve a useful purpose besides carrying ships over the backbone of the continent. Barnacles lose their clinging power in fresh water, and when a ship passes up through the locks from sea level to lake level and from salt water to fresh, the barnacles that have clung to the sides and bottom of the vessel through many a thousand mile of "sky-hooting through the brine" will have their grip broken and they will drop off helplessly and fall to the bed of the lake, which, in the course of years, will become barnacle-paved. How many times in dry-dock this will save can only be surmised, but the ship that goes through the canal regularly will not have much bother with barnacles.

The engineer who worked out the details of the engineering examination of the dam in 1908 was Caleb M. Saville, who had had experience on some of the greatest dams in the world. In the first place, the whole foundation was honeycombed with test borings, and several shafts were sunk so that the engineers could go down and see for themselves exactly what was the nature of the material below. There are some problems in engineering where a decision is so close between safety and danger that none but an engineer can decide them. But Gatun Dam could speak for itself and in the layman's tongue.

After investigating the site and getting such conclusive evidence that the proverbial wayfaring man might understand it the engineers next conducted a series of experiments to determine whether or not the material of which they proposed to build the dam would be watertight. They wanted to make sure whether enough water would seep through to carry any of the dam material along with it. The maximum normal depth of the water is 85 feet. The material it would have to seep through is nearly a half mile thick. In order to determine how the water would behave they took some 3 feet of the material and put it in a strong iron cylinder with water above it and subjected it to a pressure equivalent to a head of 185 feet of water. Only an occasional drop came through. If only an occasional drop of clear water gets through 3 feet of material under a pressure of 185 feet of water, it does not require a great engineer to determine that there will not be any seepage through more than a thousand feet of the same material under a head of only 85 feet.

And that is only a sample of their seeking after the truth. When they had gone thus far it was then decided to build a little dam a few yards long identical in cross section with Gatun Dam. It was built on the scale of an inch to the foot, by the identical processes with which it was intended to build the big dam. The result only added confirmation to the other experiments. With a proportionate head of water against it, it behaved exactly as they had concluded the big dam would when completed. Every engineer who has read Saville's report pronounces it a masterpiece of engineering investigation. It proved conclusively that the site of the dam is stable, and the dam itself impervious to seepage. The engineers who visited the Isthmus at the time with President-elect Taft unanimously agreed that those investigations removed every trace of doubt.

The Gatun Dam covers about 288 acres. The material in it weighs nearly 30,000,000 tons. The pressure of the highest part of the dam on the foundations beneath amounts to many tons per square foot. The old bugaboo about earthquakes throwing it down is a danger that exists only in the minds of those who see ghosts. Some of the biggest earth dams in the world are located in California. The Contra Costa Water Company's dam at San Leandro is 120 feet high and not nearly so immense in its proportions as Gatun Dam, yet it weathered the San Francisco earthquake without difficulty. In Panama City there is an old flat arch that once was a part of a church. It looks as though one might throw it down with a golf stick, and yet it has stood there for several centuries. As a matter of fact, Panama is out of the line of earthquakes and volcanoes, but even if shocks much worse than those at San Francisco were to come, there is no reason to fear for the safety of the big structure.

The lack of knowledge of some of those who in years past criticized the Gatun Dam was illustrated by an amusing incident that occurred at a senatorial hearing on the Isthmus. Philander C. Knox, afterwards Secretary of State, was then a Senator and a member of the committee which went to the Isthmus. Another Senator in the party had grave doubts about the stability of Gatun Dam, and asked Colonel Goethals to explain how a dam could hold in check such an immense body of water. Colonel Goethals, in his usual lucid way, explained that it was because of that well-known principle of physics that the outward pressure of water is determined by its depth and not by its volume—that a column of water 10 feet high and a foot thick would have just as much outward pressure as a lake 200 square miles in extent and 10 feet deep. Still unconvinced, the Senator pressed his examination further. At this juncture Senator Knox, who is a past master at the art of answering a question with a question, interposed, and asked his colleague: "Senator, if your theory holds good, how is it that the dikes of Holland hold in check the Atlantic Ocean?"

CHAPTER IV

If one who has never seen a lock canal is to get a proper idea of what part the locks play in the Panama Canal, he must follow attentively while we make an imaginary journey through the canal on a ship that has just come down from New York. Approaching the Atlantic entrance from the north, we pass the end of the great man-made peninsula, jutting out 11,000 feet into the bay known as Toro Point Breakwater. It was built to protect the entrance of the canal, the harbor, and anchorages from the violent storms that sweep down from the north over that region. Omitting our stops for the payment of tolls, the securing of supplies, etc., we steam directly in through a great ditch 500 feet wide and 41 feet deep, which simply permits the ocean to come inland 7 miles to Gatun. When we arrive there we find that our chance to go farther is at an end unless we have some means of getting up into the beautiful lake whose surface is 85 feet above us. Here is where the locks come to our rescue. They will not only give us one lift, but three.

When we approach the locks we find a great central pier jutting out into the sea-level channel. If our navigating officers know their duty they will run up alongside of this guide wall and tie up to it. If they do not they will run the ship's nose into a giant chain, with links made of 3-inch iron, that is guaranteed to bring a 1,000-ton ship, going at the rate of 5 knots per hour, to a dead standstill in 70 feet. When we are once safely alongside the guide wall, four quiet, but powerful locomotives, run by electricity, come out and take charge of our ship. Two of them get before it to pull us forward, and two behind it to hold us back. Then the great chain, which effectively would have barred us from going into the locks under our own steam, or from colliding with the lock gates, is let down and we begin to move into the first lock.

Starting at the sea-level channel, the first, second, and third gates are opened and our ship towed into the first lock. Then the second and third gates are closed again, and the lock filled with water, by gravity, raising the ship at the rate of about 2 feet a minute, although, if there is a great rush of business, it may be filled at the rate of 3 feet a minute. When the water in this lock reaches the level of the water in the lock above, gates four and five are opened, and we are towed in. Then gate four is closed again, and water is let into this lock until it reaches the level of the third one. Gates six, seven, and eight are next opened, and we are towed into the upper lock. Gates six and seven are now closed, and the water allowed to fill the third lock until we are up to the level of Gatun Lake. Then gates nine and ten are opened, the emergency dam is swung from athwart the channel, if it happens to be in that position, the fender chain like the one encountered when we entered the first lock, and like the ones which protect gates seven and eight, is let down, the towing engines turn us loose, and we resume our journey, with 32 miles of clear sailing, until we reach Pedro Miguel. Here, by a reverse process, we are dropped down 30¹⁄₃ feet. Then we go on to Miraflores, a mile and a half away, where we are lifted down 54²⁄₃ feet in two more lifts. This brings us back to sea level again, where we meet the waters of the Pacific, and steam out upon it through a channel 500 feet wide and 8 miles long.

Having learned something of the part the locks play in getting us across the Isthmus, by helping us up out of one ocean into Gatun Lake and then dropping down into the other ocean, it will be interesting to note something of the mechanism. A very good idea of how a lock looks may be gathered from the accompanying bird's-eye view of the model of Pedro Miguel Lock.

It will be seen that there are two of them side by side—twin locks, they are called, making them like a double-track railway. The lock on the right is nearly filled for an upward passage. The ship will be seen in it, held in position by the four towing engines, which appear only as tiny specks hitched to hawsers from the stem and stern. Behind the ship are the downstream gates. They were first opened to admit the ship, and then closed to impound the water that flows up through the bottom of the lock. Ahead are the upstream gates, closed also until the water in the lock is brought up to the level of the water in the lake. Then the gates will be opened, the big chain fender will be dropped down, and the ship will be towed out into the lake and turned loose. On the side wall of the right lock there is a big bridge set on a pivot so that it can be swung around across the lock and girders let down from it to serve as a foundation upon which to lay a steel dam if anything happens to the locks or gates. On the other lock the bridge has been swung into position, and the steel girders let down. Great steel sheets will be let down on live roller bearings on these girders, and when all are in place they will form a watertight dam of steel. Between this bridge and the reader is a huge floating tank of steel, which may be used to dam all the water out of the locks when that is desired.

Referring to the next figure we see a cross section of the twin locks. The side walls are from 45 to 50 feet thick at the floor. At a point 24¹⁄₃ feet above the floor they begin to narrow by a series of 6-foot steps until they are 8 feet wide at the top. The middle wall is 60 feet wide all the way up, although at a point 42¹⁄₂ feet above the lock floor room is made for a filling of earth and for a three-story tunnel, the top story being used as a passageway for the operators, the second story as a conduit for electric wires, and the lower story as a drainage system.

In this figure D and G are the big 18-foot culverts through which water is admitted from the lake to the locks. Each of these three big culverts, which are nearly 7,000 feet long, is large enough to accommodate a modern express train, and is about the size of the Pennsylvania tubes under the Hudson and East Rivers. H represents the culverts extending across the lock from the big ones. Each of them is big enough to accommodate a two-horse wagon, and there are 14 in each lock. Every alternate one leads from the side wall culvert and the others from the center wall culvert. F represents the wells that lead up through the floor into the lock, each larger in diameter than a sugar barrel in girth. There are five wells on each cross culvert, or 70 in the floor of each lock.

The flow of the water into the locks and out again is controlled by great valves. The ones which control the great wall tunnels or culverts are called Stoney Gate valves, and operate something like giant windows in frames. They are mounted on roller bearings to make them work without friction. The others are ordinary cylindrical valves, but, having to close a culvert large enough to permit a two-horse team to be driven through it, they must be of great size. When a ship is passing from Gatun Lake down to the Atlantic Ocean, the water in the upper lock is brought up to the level of that in the lake, being admitted through the big wall culverts, whence it passes out through the 14 cross culverts and up into the locks through the 70 wells in the floor. Then the ship is towed in, the gates are shut behind it, the valves are closed against the water in the lake, the ones permitting the escape of this water into the lock below are opened, and it continues to flow out of the upper lock into the lower one until the water in the two has the same level. Then the gates between the two locks are opened, the ship is towed into the second one and the operation is repeated for the last lock in the same way.

The gates of the locks are an interesting feature. Their total weight is about 58,000 tons. There are 46 of them, each having two leaves. Their weight varies from 300 to 600 tons per leaf, dependent upon the varying height of the different gates. The lowest ones are 47 feet high and the highest ones 82 feet, their height depending upon the place where they are used. Some of these are known as intermediate gates, and are used for short ships, when it is desired to economize on both water and time. They divide each lock chamber into two smaller chambers of 350 and 550 feet, respectively. Perhaps 90 per cent of all the ships that pass Panama will not need to use the full length lock—1,000 feet. Duplicate gates will always be kept on the ground as a precaution against accident. Each leaf is 65 feet wide and 7 feet thick. The heaviest single piece of steel in each one of them is the lower sill, weighing 18 tons. It requires 6,000,000 rivets to put them together. In the lower part of each gate is a huge tank. When it is desired that the gate shall have buoyancy, as when operating it, this tank will be filled with air. When closed it is filled with water. The gates are opened and closed by a huge arm, or strut, one end of which is connected to the gate and the other to a huge wheel in the manner of the connecting rod to the driver of a locomotive. Leakage through the space between the gate and the miter sill on the floor of the lock is prevented by a seal which consists of heavy timbers with flaps of rubber 4 inches wide and half an inch thick. A special sealing device brings the edges of the two leaves of a gate together and holds them firmly while the gates are closed.

Remembering that these gates are nothing more than Brobdingnagian double doors which close in the shape of a flattened V, it follows that they must have hinges. And these hinges are worth going miles to see. That part which fastens to the wall of the lock weighs 36,752 pounds in the case of the operating gates, and 38,476 pounds in the protection gates. These latter are placed in pairs with the operating gates at all danger points—so that if one set of gates are rammed down, another pair will still be in position. The part of the hinge attached to the gate was made according to specifications which required that it should stand a strain of 40,000 pounds before stretching at all, and 70,000 pounds before breaking. Put into a huge testing machine, it actually stood a strain of 3,300,000 pounds before breaking—seven times as great as any stress it will ever be called upon to bear. The gates are all painted a lead gray, to match the ships of the American Navy. Those which come into contact with sea water will be treated with a barnacle-proof preparation.

Now that we have described the locks, we may go back and see them in course of construction. The first task was getting the lock building plant designed and built. At Gatun the plant consisted of a series of immense cableways, an electric railroad, and enormous concrete mixers. Great towers were erected on either side of the area excavated for the locks, with giant cables connecting them. These towers were 85 feet high, and were mounted on tracks like steam shovels, so that they could be moved forward as the work progressed. The cables connecting them were of 2¹⁄₂ lock steel wire covered with interlocking strands. They were guaranteed to carry 6 tons at a trip, 20 trips an hour, and to carry 60,000 loads before giving way. They actually did better than the specifications called for as far as endurance was concerned.

The sand for making the concrete for Gatun came from Nombre de Dios (Spanish for Name of God), and the gravel from Porto Bello. The sand and gravel were towed in great barges, first through the old French Canal, and later through the Atlantic entrance of the present canal. Great clamshell buckets on the Lidgerwood cableways would swoop down upon the barges, get 2 cubic yards of material at a mouthful, lift it up to the cable, carry it across to the storage piles and there dump it. In this way more than 2,000,000 wagon loads of sand and gravel were handled.

A special equipment was required to haul the sand, gravel, and cement from the storage piles to the concrete mixers. There were two circular railroads of 24-inch gauge, carrying little electric cars that ran without motormen. Each car was stopped, started, or reversed by a switch attached to the car. Their speed never varied more than 10 per cent whether they were going empty or loaded, up hill or down. When a car was going down hill its motor was reversed into a generator so that it helped make electricity to pull some other car up the hill. The cars ran into a little tunnel, where each was given its proper load of one part cement, three parts sand, and six parts gravel—2 cubic yards, in all—and was then hurried on to the big concrete mixers. These were so arranged in a series that it was not necessary to stop them to receive the sand, gravel, and cement, or to dump out the concrete.

On the emptying sides of the concrete mixers there were other little electric railway tracks. Here there were little trains of a motor and two cars each, with a motorman. The train, with two big 2-cubic-yard buckets, drew up alongside two concrete mixers. Without stopping their endless revolutions the mixers tilted and poured out their contents into the two buckets, 2 yards in each. Then the little train hurried away, stopping under a great cable. Across from above the lock walls came two empty buckets, carried on pulleys on the cableway. When they reached a point over the train they descended and were set on the cars, behind the full buckets. The full buckets were then attached to the lifting hooks, and were carried up to the cable and then across to the lock walls, where they were dumped and the concrete spread out by a force of men. Meanwhile the train hustled off with its two empty buckets, ready to be loaded again.

On the Pacific side the concrete handling plant was somewhat different. Instead of cableways there were great cantilever cranes built of structural steel. Some of these were in the shape of a giant T, while others looked like two T's fastened together. Here the clamshell dippers were run out on the arms of the cranes to the storage piles, where they picked up their loads of material. This was put in hoppers large enough to store material for 10 cubic yards. The sand and stone then passed through measuring hoppers and to the mixers with cement and water added. After it was mixed it was dumped into big buckets on little cars drawn by baby steam locomotives, which looked like overgrown toy engines. These little fellows reminded one of a lot of busy bees as they dashed about here and there with their loads of concrete, choo-chooing as majestically as the great dirt train engines which passed back and forth hard by. The cranes would take their filled buckets and leave empty ones in exchange, and this was kept up day in and day out until the locks were completed. When the plant was removed from Pedro Miguel to Miraflores, a large part of the concrete was handled directly from the mixers to the walls by the cranes without the intermediary locomotive service.

The cost of the construction of the locks was estimated in 1908 at upward of $57,000,000. But economy in the handling of the material and efficiency on the part of the lock builders cut the actual cost far below that figure. On the Atlantic side about a dollar was saved on every yard of concrete laid—about $2,000,000. On the Pacific side more than twice as much was saved.

Before the locks could be built it became necessary to excavate down to bed rock. This required the removal of nearly 5,000,000 cubic yards of material at Gatun. Then extensive tests were made to make certain that the floor of the locks could be anchored safely to the rock. These tests demonstrated that by using the old steel rails that were left on the Isthmus by the French, the concrete and rock could be tied together so firmly as to defy the ravages of water and time. A huge apron of concrete was built out into Gatun Lake from the upper locks at that place, effectively preventing any water from getting between the rocks and the concrete lying upon them.

CHAPTER V

The first thing a ship encounters when it approaches the locks is the giant chain stretched across its path. That chain is made of links of 3 inches in diameter. When in normal position it is stretched across the locks, and the vessel which does not stop as soon as it should will ram its nose into the chain. There is a hydraulic paying-out arrangement at both ends of the chain, and when the pressure against it reaches a hundred gross tons the chain will begin to pay out and gradually bring the offending vessel to a stop. After a ship strikes the chain its momentum will be gradually reduced, its energy being absorbed by the chain mechanism. While the pressure at which the chain will begin to yield is fixed at 100 gross tons, the pressure required to break it is 262 tons. Thus the actual stress it can bear is two and a half times what it will be called upon to meet. The mechanism by which the paying-out of the chain is accomplished is exceedingly ingenious. The principle is practically the reverse of that of a hydraulic jack. The two ends of the 428-foot chain are attached to big plungers in the two walls of the locks. These plungers fit in large cylinders, which contain broad surfaces of water. They are connected with very small openings, which are kept closed until a pressure of 750 pounds to the square inch is exerted against them. By means of a resistance valve these openings are then made available, the water shooting out as through a nozzle under high pressure. This permits the chain plunger to rise gradually, while keeping the tension at 750 pounds to the inch, and the paying-out of the chain proceeds accordingly. Of course not all ships will strike the chain at the same speed, and in some cases the paying-out process will have to be more rapid than in others. This is provided for by the automatic enlargement of the hole through which the water is discharged, the size of the hole again becoming smaller as the tension of the chain decreases. This chain fender will stop the Olympic with full load, when going a mile and a half an hour, bringing it to a dead standstill within 70 feet, or it will stop an ordinary 10,000-ton ship in the same distance even if it have a speed of 5 miles. The function of the resistance valve is to prevent the chain from beginning to pay out until the stress against it goes up to 100 tons, and to regulate the paying-out so as to keep it constant at that point, so long as there is necessity for paying-out. Any pressure of less than a hundred tons will not put the paying-out mechanism into operation.

When a ship is to be put through the locks the chain will be let down into great grooves in the floor of the lock. There is a fixed plunger operating within a cylinder, which, in turn, operates within another cylinder, the resulting movement, by a system of pulleys, being made to pay out or pull in 4 feet of chain for every foot the plunger travels. The chain must be raised or lowered in one minute, and always will have to be lowered to permit the passage of a ship. The fender machines are situated in pits in the lock walls. These pits are likely to get filled with water from drippings, leakages, wave action, and drainage, so they are protected with automatic pumps. Float valves are lifted when the water rises in the pits. This automatically moves the switch controlling an electric motor, which starts a pump to working whenever the water gets within 1 inch of the top of the sump beneath the floor of the pit. Twenty-four of these chain fenders are required for the protection of the locks, and each requires two such tension machines.

No ship will be allowed to go through the canal except under the control of a canal pilot. He will certainly bring it to a stop at the approach wall. But if he does not, there is the chain fender. There is not a chance in a thousand for a collision with it, and not a chance in a hundred thousand that the ship will not be stopped when there is such a collision.

But if the pilot should fail to stop the ship, and it should collide with the fender chain, and then if the fender chain should fail to stop it, there would be the double gates at the head of the lock. There is not one chance in a hundred that a ship, checked as it inevitably would be by the fender chain, could ram down the first, or safety gate. But if it did, there would still be another set of gates some 70 feet away. The chances here might be one in a hundred of the second set being rammed down. From all this it will be seen that the chances of the second pair of gates being rammed is so remote as to be almost without the realm of possibility. But suppose all these precautions should fail, and suddenly the way should be opened for the water of Gatun Lake to rush through the locks at the destructive speed of 20 miles an hour? Even that day has been provided against by the construction of the big emergency dams. The emergency dams, like the fender chains, are designed only for protection, and have no other use in the operation of the locks. There will be six of these dams, one across each of the head locks at Gatun, Pedro Miguel, and Miraflores.

These emergency dams will be mounted on pivots on the side walls of the locks about 200 feet above the upper gates. When not in use they will rest on the side wall and parallel with it. When in use they will be swung across the locks, by electric machinery or by hand, and there rigidly wedged in. It will require two minutes to get them in position by electricity and 30 minutes by hand. There is a motor for driving the wedges which will hold the dam securely in position, and limit switches to prevent the dams being moved too far.

When a bridge is put into position across the lock, a series of wicket girders which are attached to the upstream side of the floor of the bridge are let down into the water, the connection between the bridge and one end of each girder being made by an elbow joint. The other end goes down into the water, its motion being controlled by a cable attached some distance from the free end of the girder and paid out or drawn in over an electrically operated drum. This free end passes down until it engages a big iron casting embedded in the concrete of the lock floor. This makes a sort of inclined railway at an angle of about 30 degrees from the perpendicular, over which huge steel plates are let down into the water. There are six of these girders, and they are all made of the finest nickel steel. When they are all in position, a row of six plates are let down, and they make the stream going through the locks several feet shallower. Then another row of plates is let down on these, and the stream becomes that much shallower. Another row of plates is added, and then another, until there is a solid sheet of steel plates resting on the six girders, and they make a complete steel dam which effectively arrests the mad impulse of the water in Gatun Lake to rush down into the sea. The plates are moved up and down by electrical machinery, and are mounted on roller-bearing wheels, so that the tremendous friction caused by their being pressed against the girders by the great force of the water may be overcome. That the emergency dams will be effective is shown by the experience at the "Soo" locks, on the canal connecting Lakes Superior and Huron. There, a vessel operating under its own power, rammed a lock gate. Although the emergency dam had grown so rusty by disuse that it could be operated only by hand, it was swung across the lock and effectively fulfilled its mission of checking the maddened flow of the water.

Another protective device for the locks is the big caisson gates that will be floated across the head and tail bays when it is desired to remove all the water from the locks for the purpose of permitting the lower guard gates to be examined, cleaned, painted, or repaired, and for allowing the sills of the emergency dams to be examined in the dry. The caisson gates are 112¹⁄₂ feet long, 36 feet beam, and have a light draft of 32 feet and a heavy draft of 61 feet. When one is floated into position to close the lock, water will be admitted to make it sink to the proper depth. Then its large centrifugal pumps, driven by electric motors, will pump the water out of the lock. When the work on the lock is completed these pumps will pump the water out of the caisson itself until it becomes buoyant enough to resume its light draft, after which it will be floated away.

The machinery for opening and closing the lock gates called for unusual care in its designing. The existing types of gate-operating machinery were all studied, and it was found that none of them could be depended on to prove satisfactory, so special machines had to be designed.

A great wheel, resembling a drive wheel of a locomotive, except that a little over half of the rim is cog-geared, is mounted in a horizontal position on a big plate, planted firmly in the concrete of the wall and bolted there with huge bolts 11 feet long and 2¹⁄₄ inches in diameter. This plate weighs over 13,000 pounds, and the wheel, cast in two pieces, weighs 34,000 pounds. As the weight of the rim of the wheel on the eight spokes probably would tax their strength too much when the wheel is under stress, this is obviated by four bearing wheels, perpendicular to the big wheel, which support the rim. Between the crank pin and the point of attachment on the gate leaf there is a long arm, or strut, designed to bear an operating strain of nearly a hundred tons. The wheel will be revolved by a motor geared to the cogged part of the rim.

An ingenious arrangement of electric switches is that used to protect the gate-moving machines from harm. The big connecting rod between the master wheel and the gate leaf is attached to the gate leaf by a nest of springs capable of sustaining a pressure of 184,000 pounds, in addition to the fixed pressure of 60,000 pounds. Should any obstruction interfere with the closing of the gate and threaten a dangerous pressure on the connecting rod, the springs, as soon as they reach their full compression, establish an electrical contact and thus stop the motor. Likewise, should any obstruction come against the gate as the connecting rod is pulling it open, the springs again permit the establishment of an electrical contact and stop the motor. All of these precautions are entirely independent of and supplemental to the limit switches, which cut off the power from the gate-moving machine should the strain reach the danger line. These big machines move the huge gate leaves without the slightest noise or vibration. Such a machine is required for each of the 92 leaves used in the 46 gates with which the locks are equipped. The operator can open or close one of these big gates in two minutes.

The control of the water in the culverts of the locks is taken care of by an ingeniously designed series of valves. The big wall culverts, 18 feet in diameter, are divided into two sections at the points where the valves are installed, by the construction of a perpendicular pier. This makes two openings 8 by 18 feet. The big gates of steel are placed in frames to close these openings just as a window sash is placed in its frame. They are mounted on roller bearings, so as to overcome the friction caused by the pressure of water against the valve gates. They must be mounted so that there is not more than a fourth of an inch play in any direction. The big wall culvert gates will weigh about 10 tons each, and must be capable of operating under a head of more than 60 feet of water. They will be raised and lowered by electricity.

The electric locomotives which will be used to tow ships through the locks are one of the interesting features of the equipment. There will be 40 of them on the 3 sets of locks. The average ship will require four of them, two at the bow and two at the stern, to draw it through the locks. They will run on tracks on the lock walls, and will have two sets of wheels. One set will be cogged, and will be used when the locomotives are engaged in towing. The other set will be pressed into service when they are running light. When a vessel is in one lock waiting for the water to be equalized with that in the next one and the gates opened to permit passage, the forward locomotives will run free up the incline to the lock wall above, paying out hawser as they go. When they get to the next higher level they are ready to exert their maximum pull. Each locomotive consists of three parts: two motors hitched together, and the tandem may be operated from either end. The third part is a big winding drum around which the great hawsers are wound. This towing windlass permits the line to be paid out or pulled in and the distance between the ship and the locomotives varied at will. The locomotive may thus exert its pull or relax it while standing still on the track, a provision especially valuable in bringing ships to rest. In the main, however, the pull of the locomotive is exercised by its running on the semi-suppressed rack track anchored in the coping of the lock walls. Each flight of locks will be provided with two towing tracks, one on the side and one on the center wall. Each wall will be equipped with a return track of ordinary rails, so that when a set of locomotives has finished towing a ship through the locks they can be switched over from these tracks and hustled back for another job. When they reach the inclines from one lock to the next above the rack track will be pressed into service again until they reach the next level stretch.

Here again one meets the familiar safeguard against accident. Some engineer of one of these towing locomotives might sometime overload it, so the power of doing so has been taken out of his hands. On the windlass or drum that holds the towing hawser there is a friction coupling. If the engineer should attempt to overload his engine, or if for any other reason there should suddenly come upon the locomotive a greater strain than it could bear, or upon the track, or upon the hawser, the friction clutch would let loose at its appointed tension of 25,000 pounds, and all danger would be averted.

When the locomotives are towing a ship from the walls it is natural that there should be a side pull on the hawser. This is overcome by wheels that run against the side of the track and are mounted horizontally. All of the towing tracks extend out on the approach walls of the locks so that the locomotives can get out far enough to take charge of a ship before it gets close enough to do the locks any damage.

From the foregoing it will be seen that a great deal of electric current will be required in the operation of the locks. This will be generated at a big station at Gatun, with a smaller one at Miraflores, and they will be connected. The overflow water will be used for generating the required current, and in addition to the operation of the lock machinery it will operate the spillway gates, furnish the necessary lighting current, and eventually it may furnish the power for an electrified Panama Railroad.

In passing a ship through the canal it will be necessary to open and close 23 lock gates, of an aggregate weight of more than 25,000 tons, to lower and raise 12 fender chains, each weighing 24,000 pounds, and to shut and open dozens of great valves, each of which weighs tons. All these operations at each set of locks will be controlled by one man, at a central switchboard. In addition to these operations there is the towing apparatus. The arrangement at Gatun is typical; there 4 fender chains must be operated, 6 pairs of miter gates, and 46 valves. In all not less than 98 motors will be set in motion twice, and sometimes this number may be increased to 143. Some of them are more than half a mile away from the operator, and half of them are nearly a quarter of a mile away.

The operator in his control house will be high enough to have an uninterrupted view of the whole flight of locks over which he has command. His control board will consist of a representation of the locks his switches control. On his model he will see the rise and fall of the fender chains as he operates them, the movement of the big lock gates as they swing open or shut, the opening and closing of the valves which regulate the water in the culverts, and the rise and fall of the water in the locks.

A system of interlocked levers will prevent him from doing the wrong thing in handling his switches. Before he can open the valves at one end of a lock he must close those at the other end. Before he can open the lock gates, the valves in the culverts must be set so that no harm can result. Before he can start to open a lock gate, he must first have released the miter-forcing machine that latches the gates. Before he can close the gates protected by a fender chain, he must first have thrown the switch to bring the fender chain back to its protecting position, and he can not throw the switch to lower the chain until he first has provided for the opening of the gate it protects. All of this interlocking system makes it next to impossible to err, and taking into consideration the additional safeguard of limit switches, which automatically cut off the power when anything goes wrong, it will be seen that the personal equation is all but removed from the situation.

CHAPTER VI

Now stretches a man-made canyon across the backbone of the continent; now lies a channel for ships through the barrier; now is found what Columbus sought in vain—the gate through the west to the east. Men call it Culebra Cut.

Nine miles long, its average depth is 120 feet. At places its sides tower nearly 500 feet above its channel bottom, which is nowhere narrower than 300 feet.

It is the greatest single trophy of the triumph of man over the terrestrial arrangement of his world. Compared to it, the scooping out of the sand levels of Suez seems but child's play—the tunnels of Hoosac and Simplon but the sport of boys. It is majestic. It is awful. It is the Canal.

When estimates for digging the canal were made, it was calculated that 53,000,000 cubic yards of material would have to be removed from the cut, and that under the most favorable conditions it would require eight and a half years to complete the work. But at that time no one had the remotest idea of the actual difficulties that would beset the canal builders; no one dreamed of the avalanches of material that would slide into the cut.

One can in no way get a better idea of the meaning of the slides and breaks in Culebra Cut than to refer to the accompanying figure. There it will be seen that whereas it was originally planned that the top width of the cut at one point should be 670 feet, it has grown wider, because of slides and breaks, to as much as 1,800 feet at one place. In all, some 25,000,000 cubic yards of material which should have remained outside the canal prism slipped into it and had to be removed by the steam shovels.