which connects two points with a single reach is preferable to one with two reaches. Indeed, a considerable increase in length is allowable to permit the canal to be constructed without a change of level. The reason for this is that transferring a boat from one level to another by locks or the other usual means is a slow operation, and, furthermore, locks are very expensive to construct compared with a similar length of the ordinary channel. The engineer carefully integrates these factors of time and cost and selects the route between the various points he wishes to connect which will give the minimum time of transit at the minimum cost. In deciding upon the cross section to be given to the channel, two things have to be considered, viz., its dimensions and its form. As regards dimensions, they are determined largely by the size of the vessels with which it is proposed to navigate the canal. The width must be at least sufficient to permit two vessels of the largest size to pass each other without fouling. Another influencing factor is that the resistance to traction is greater in a restricted waterway. Elaborate trials made in Germany on the DortImund and Ems Canal showed that while increase of water section diminished traction resistance and injury to the banks, increase of depth was more beneficial than increase of breadth.

It is generally assumed that a width of bottom equal to twice the beam of the largest vessel navigating the canal regularly is necessary in order to permit of two boats passing, and that the depth of water should be about 12 feet greater than the draft of these vessels, if good results are to be obtained, though this may vary from a few inches to 4 feet or more, as in the case of the Suez Canal, or even a greater amount, as in the Panama Canal. The form of the cross section is determined very largely by the material through which the channel is cut, and by the location of the channel under certain circumstances. The bottom of the channel is always made flat; in soft ground the sides are made sloping, the angle of slope depending upon the stability of the material, being quite steep in firm materials and quite flat in unstable materials; and in rock the sides are made vertical or nearly so. The attempt is always made, for the sake of economy of excavation, to approach as nearly to a rectangular cross section as the conditions will permit. When the canal passes through towns, the sides are made vertical to save space and provide quays, retaining walls being used in soft ground to form vertical sides.

Canal construction consists chiefly of open-cut excavation, but embankments, aqueducts, tunnels, culverts, bridges, and a variety of other construction work may be involved. The plant used and methods adopted in excavating canals depend very largely upon the size of the canal section and the material encountered. In rock the practice is the same everywhere, and consists in the use of power drills and explosives for breaking up the rock, and derricks, conveyers, and cars hauled by animal or mechanical power for removing it. In a boat canal of small section, the plant required is small and simple, but in large ship-canal sections very large and powerful machinery and elaborate power plants supplying compressed air and electricity are employed. In small canals soft-ground excavation was commonly performed by means of shovels and plows for loosening the material, and scrapers and carts for carrying it from the ex

cavation, but now power shovels are almost invariably used, as well as grading and excavating machines, the steam shovels loading into carts or cars hauled by horses or light locomotives. In ship canals of the largest section this plant is still further enlarged by the employment of special excavating and conveying machines and powerful dredges, both hydraulic and bucket or clamshell. Aqueducts are usually built in the form of masonry-arch bridges with the top formed into a channel for the water. Sometimes, however, masonry piers carry a wooden trough or, in later years, one of steel. In embankments the channel is formed by building up the sides and lining the bottom and slopes with concrete or a layer of clay or other impervious material. Tunnels for canals are built in the same manner as tunnels for other purposes. (See TUNNEL.) Culverts are provided for carrying streams underneath the canal and bridges for carrying highways and roadways over it. See BRIDGE; CABLEWAY; CRANE; DRILL; QUARRY.

Locks, Inclines, and Lifts. The usual methods of transferring vessels from one level or reach of a canal to another one are by locks, inclines, or lifts. Of these three devices, the lock is the one most extensively employed. A lock is a masonry chamber built at the junction of the two reaches, the bottom of which is a continuation of the bottom of the lower reach and the top of which is at the same level as the banks of the upper reach. Structurally this chamber consists of two parallel masonry side walls, closed near each end by a pair of folding gates or, more rarely, by sliding or lifting gates. When a vessel is passing from the lower reach to the upper reach through a lock, the sequence of operations is as follows: the lower gates being open and the water in the lock being at the same level as the water in the down reach, the vessel is floated into the lock chamber and the down gates are closed. By means of valves in the upper gates or culverts in the side walls or floor of the chamber, water from the upper reach is slowly admitted until the water levels in the chamber and in the upper reach are the same. The upper gates are then opened and the boat floated out into the upper reach to continue its journey. To lock a vessel from the upper reach to the lower reach, the operations described are merely reversed. The gates are usually made of wood or iron, and each leaf consists structurally of two vertical posts called the quoin post and the mitre post, connected by horizontal frames, which serve as a framework for carrying the water-tight boarding or plating. The quoin post has pivots at top and bottom which work in suitable fittings in the side wall, so that each gate leaf swings open and shuts like a door.

A gate consists of two leaves, the swinging edges of which meet on the centre line of the chamber; but as each leaf is somewhat wider than half the width of the chamber, they do not form a straight diaphragm across the chamber when closed, but are shaped like a very flat letter V with its point projecting towards the upper level or reach. This construction gives greater strength to resist the pressure of the water. The height between the bottom of the down reach and the bottom of the upper reach is called the lift of the lock. The practicable height of lift in lock construction is limited, and where great differences in level have to be over

come, a series or flight of locks built end to end is employed.

Where a vessel passes through a lock from one level to another, a lockful of water is lost from the upper level to the lower level for each pair of boats passed. Where water is scarce and the total lift is large, therefore, resort is sometimes had to inclined planes up and down which the boats are transported in cradles or tanks running on wheels and hauled by cables or other power. Inclined planes for canals are of very early origin, being at one time quite extensively used for high lifts, and some of these old inclines on American canals are described in the following section, though these canals are now abandoned. In Europe they are still encountered, as the Grand Junction, England; at Ourcq, France; Shropshire, England; and Oberland, Germany.

A more important system of transferring canal boats from one level to another is the vertical lift or lift-lock system, which has been installed in a number of places and is proposed for several other places where very high and important differences of level occur. In the vertical liftlock system the boat is floated into a movable trough, the ends of which are closed by gates, while similar gates close the ends of the canal approaches. When the gates are closed behind the boat, the trough is raised or lowered, as the case may be, until it coincides with the other level of the canal, when the front gates are opened and the boat proceeds upon its way. The trough is raised and lowered by means of hydraulic or other power, aided sometimes by counterweights or flotation tanks. The first vertical lift on a large scale was that built at Anderton, England, on the Trent and Mersey Canal, in 1875, and operated for several years with hydraulic machinery until in 1908 the plunger and hydraulic appliances were removed and each tank was counterweighted separately and the machinery was operated by electricity; a second was built at Les Fontinettes, France, on the Neuffossé, in 1885; a third at La Louvière, Belgium, in 1888; and a fourth at Heinrichenberg, Germany, in 1895. In 1895 a lift lock was designed to replace the flight of locks at Lockport, N. Y., on the Erie Canal. In 1904 an hydraulic lift lock was built at Peterborough, Canada, on the Trent Canal, and in 1906 another at Kirkfield on the same canal. The Heinrichenberg lift lock on the Dortmund and Ems Canal in Germany has a tank 229.6 X 28.2 X 8.2 feet, with a lift of 52.45 feet.

Boat Canals. History.-Canals date from a period long anterior to the Christian era and were employed as means of navigation and communication by the Assyrians, Egyptians, Hindus, and Chinese. The royal canal of Babylon was built about 600 B.C. As an interesting instance of canal construction, previous to the fifteenth century, may be mentioned the Grand Canal of China, built in the thirteenth century to connect the Yangtze-kiang and Pei-ho. This canal is 650 miles long; is largely composed of canalized rivers; is about 5 to 6 feet deep, and has inclined planes up which the boats are hauled by capstans and made to slide down a paved track. The lock is said to have been invented in 1481 by two Italian engineers, but the merit of this invention is also claimed by Holland. The known facts are that canal locks were used in both Holland and Italy in the fifteenth century, and that by their development a wonderful impetus was given to canal construction, which had

previously been confined to such countries as permitted canals of a single level or reach to be used. The first European country to take up the construction of navigation canals on a systematic plan and extensive scale was France. The Briare Canal, connecting the rivers Seine and Loire, was built from 1605 to 1642; the Orléans Canal was built in 1675, and the Languedoc Canal in 1666-81. For the time this last was an enormous work-the canal connecting the Bay of Biscay with the Mediterranean by an artificial waterway 148 miles long and 62 feet deep, with 119 locks having an aggre gate rise of 600 feet, and capable of floating vessels of 100 tons. In Russia a great system of canals connecting St. Petersburg with the Caspian Sea was developed during the eighteenth century; a canal connecting the North Sea and Baltic, 100 miles long, was finished in 1785. The Gotha Canal, 280 miles long, connecting Stockholm and Gothenburg, in Sweden, was completed in 1832; and the Danube and Main Canal, 108 miles long, was constructed 1836-46. France, however, was the continental country which devoted the greatest attention to canal construction. Notable among recent works is the Marseilles-Rhône Canal, begun in 1904 and to be finished about 1918. It will be 48 miles long (approx.), 82 feet wide, 8 feet 2 inches to 9 feet 10 inches deep, with locks 52% feet wide and 525 feet long, and will cost about $20,000,000. Barges of 600 tons can be accommodated. Under the Nerthe range will be a $10,000,000 tunnel 41⁄2 miles long, the greatest of its kind. Marseilles, gaining direct water communication with the interior of France and northern Europe, expects to become the chief clearing house for the North African trade. It will be declared a free port, like Hamburg, which has long depended greatly on a network of canals. France now has upward of 3000 miles of canal and 2000 miles of canalized rivers.

Germany has spent much effort in developing its canal systems recently, and it was estimated in 1912 that the Rhine and Weser Canal then under construction would have a traffic capacity of 17,000,000 tons annually. Standard forms and sizes of barges of 600 tons and 400 tons capacity have been adopted as most advantageous after elaborate experiments. The former are 213.25 feet in length, 26.25 feet in beam, and draw loaded 5.74 feet of water. The 400-ton barges were 180.44 feet in length, but with other dimensions the same. Lock systems to accommodate barges of this size were recommended where they did not exist. In Belgium there has been a marked tendency to increase the dimensions of existing canal systems, so that, for example, the lower portion of the canal from Charleroi to Brussels extending from Clabecq to the latter city may accommodate 1000-ton boats. The countries of continental Europe continue to manifest considerable activity in enlarging and extending their boat-canal systems, while Eng land and America have practically abandoned the development of their systems of navigable waterways. In Great Britain the boat canals have been criticized as being absolutely lacking in uniformity of management or design and dimensions and, generally speaking, being incapable of being worked by steam. Furthermore, the system of tolls has been unequal, and with the development of railways little thought has been given to the consistent evolution and increase of a natural canal system,

LOCK No. 2 AT WATERFORD, THE EASTERN TERMINUS OF THE ERIE CANAL. This is the first of a series of high lift locks located within about a mile and a half, with a combined total lift of 169 feet, the greatest flight of high lift locks in the world. Three locks of the older canal may be seen on the right.

The first canals in Great Britain are generally conceded to have been the Foss dike and Caes dike in Lincolnshire, 11 and 40 miles long respectively, the former of which is still navigable. These channels are stated to have been first excavated by the Romans and to have been enlarged in the twelfth century. It was not until the latter part of the eighteenth century, however, that canal building assumed importance in England through the energy and liberality of the Duke of Bridgewater and the skill of the engineer, James Brindley, the success of whose works stimulated others to engage in similar undertakings. The era of canal building, ushered in by the Duke of Bridgewater by the construction of the Bridgewater Canal in 1761, continued until 1834, when the last inland boat canal was built in Great Britain. It is interesting to note that from 1791 to 1794 speculation in canal shares became a mania in England and finally resulted in a financial crash and the ruin of many persons. At the end of 1834 there were about 3800 miles of canal in Great Britain, of which about 3000 miles were in England. The following may be mentioned as among the more notable of the British canals: Grand Canal, Dublin to Ballinasloe, Ireland, 164 miles long, 40 feet wide, 6 feet deep, built in 1765; Royal Canal, Dublin to Torinansburg, Ireland, built after the Grand Canal; Gloucester and Berkeley Canal, Sharpness to Gloucester, 17 miles; Caledonian Canal, crossing Scotland, 17 feet deep; Forth and Clyde Canal, 35 miles long and 10 feet deep; and the Crinan Canal across the peninsula of Kintyre, 12 feet deep. The depth of the great majority of British canals, however, varies from 32 feet to 5 feet, and many of these are now owned by the railways. Various schemes to increase the facilities for internal waterways have been considered by parliamentary and other commissions, but beyond reports and discussions little has resulted.

In the United States the construction of the Erie Canal, begun in 1817, opened up the development of canal construction, which now aggregates upward of 4500 miles, located mostly in New York, Pennsylvania, Ohio, Illinois, Indiana, and Virginia. The first man who really saw the future of canal communication was George Washington, whose main efforts, how ever, were directed towards the connection of the Chesapeake and the Ohio River, but in 1808 Secretary Gallatin submitted a report recom mending an extensive system of waterways, on which, however, no action was taken. Canal building continued active in the United States until about 1837. After this date attention was turned chiefly to railway construction. Space is not available here to trace the development of the canal system of the United States in detail, but the essential facts respecting some of the more important enterprises will be given. In 1793 a canal was built around the rapids of the Connecticut River at South Hadley, Mass., and another, 3 miles long, was built around Turners Falls on the same stream in 1790-96. The canal at South Hadley is interesting as being the first canal built in America, and as having the two levels connected by an incline, up and down which the boats were raised and lowered in a tank or caisson filled with water and propelled by cables operated by water wheels.

The Erie Canal, connecting the Hudson River at Albany and Troy with Lake Erie at Buffalo,

is 363 miles in length. It was begun in 1817 and completed in 1825, at a cost of $7,602,000. Its construction was due chiefly to the foresight and energy of De Witt Clinton. The enterprise was undertaken and carried through by the State of New York, Clinton being Governor during nearly all the period of its progress. As its route lay chiefly through an uninhabited wilderness, it opened for settlement an immense territory. It was subsequently enlarged, until it was 70 feet broad at the surface and 56 feet at the bottom, with a depth of 7 feet. The canal was immensely successful, contributing largely to the growth of New York, Buffalo, and intermediate places, and serving for many years as the great artery of passenger as well as freight traffic between the northeastern sections of the United States and the newly settled States of what was then the West. Light packet boats, drawn by frequent relays of horses, which were made to proceed at a trot, made the trip from Albany to Buffalo in three and a half days. In 1896 it was estimated that the cost of construction and improvements had aggregated $52,540,800. An expenditure of $9,000,000 more for enlargement was authorized by popular vote in that year. Work was begun on this enlargement in the winter of 1896-97 and resumed again during the winter of 1897-98. In the spring of 1898 all of the $9,000,000 had been consumed and only a part of the projected deepening to 9 feet was completed. See ERIE CANAL.

New York State Barge Canal. In 1900, in response to a demand for increasing the capacity of the Erie Canal and other waterways of the State of New York, an investigation was set on foot to determine the cost and proper plan for its enlargement so that boats or barges of 1000 to 1200 tons could be used. By laws enacted in 1903 an appropriation of $101,000,000 was made to cover the cost of deepening and extending the canal system of the State. This involved the improvement of the Erie, Oswego, and Champlain canals, making a waterway 12 feet in depth and aggregating 431 miles, of which 27 miles was lake navigation, where Oneida, Onondaga, and Cross lakes were utilized. Fortythree per cent of the entire mileage was to have a minimum bottom width of 75 feet and the remainder not in lakes was to be constructed in canalized rivers and streams with a bottom width of channel ranging from 110 to 200 feet. If the full width of the locks that were constructed for the canal should be utilized, boats of 3000 tons could be accommodated, but for boats that could pass in the most restricted channels and be driven tandem or lifted together at one lockage a capacity of about 1600 tons as much as could be provided for. The economic value of the New York State Barge Canal during its construction was a matter of considerable dispute, but it presented many interesting engineering problems which will be found discussed under NEW YORK STATE BARGE CANAL (q.v.).

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The Illinois and Michigan Canal connects Lake Michigan and the navigable waters of the Illinois River, and allows the passage of vessels of limited size from the Gulf of Mexico to the Gulf of St. Lawrence by using also the Welland Canal, which forms a navigable channel from Lake Erie to Lake Ontario. In 1825 it was estimated that the canal, about 100 miles in length, would cost about $700,000, but nothing definite was attempted till 1836, when estimates