Navigable canals may perhaps be most conveniently treated under two classes, Barge or Boat Canals, now in many cases almost superseded by railways and Ship Canals, which- judging from the stupendous works of this class recently executed and now in contemplation, seem as yet far from having exhausted the important aids they are destined to afford to navigation.
After giving a historical notice of early canals, the following article contains a brief notice of Barge Canals ; a digest of general engineering principles applicable to the construction of all canals; an account of Ship Canals recently constructed; and a notice of Ship Canals which have been proposed and are ere long likely to be carried into execution for facilitating ocean navigation.
From the writings of Herodotus, Aristotle, Pliny, and other ancient historians, we learn that canals existed in Egypt before the Christian era; and there is reason to believe that at the same early period artificial inland navigation also existed in China. Almost nothing, however, save their existence has been recorded with reference to these very early works ; but soon after the commencement of the Christian era canals were introduced and gradually extended throughout Europe, particularly in Greece, Italy, Spain, Russia, Sweden, Holland, and France. Invention In speaking, however, of the earliest of these works, it is not to be supposed that they resembled the modern canals now constructed in our own and other countries. Early as inland navigation was introduced, it was not until the invention of canal-locks, by which boats could be transferred from one level to another, that inland navigation became generally applicable and useful, and it has been truly remarked " that to us, living in an age of steam-engines and daguerreotypes, it might appear strange that an invention so simple in itself as the canal-lock, and founded on properties of fluids little recondite, should have escaped the acuteness of Egypt, Greece, and Borne." Not only, however, had the invention escaped the notice of the ancients, but what is more striking, the several gradations made towards the attainment of that simple but valuable improvement appear to have been so gradual that, like many discoveries of importance, great doubts exist as to the person, and even the nation that was the first to introduce canal-locks. One class of writers attributes the discovery to the Dutch, and Messrs Telford and Nimmo, who wrote the article " Inland Navigation" in Brewster's Edinburgh Encyclopaedia, adopt the conclusion that locks were used in Holland nearly a century before their application in Italy ; while, on the other hand, the invention has been strongly and not unreasonably claimed for engineers of the Italian school, and in particular for Leonardo da Vinci, the celebrated engineer and painter. Without, however, entering into a discussion of this question, which it is now perhaps impossible to solve, we may safely state that during the 14th century the introduction or locks, whether of Dutch or Italian origin, gave a new character to inland navigation, and laid the basis of its rapid and successful extension. And here it may be proper to remark, that the early canals of China and Egypt, although destitute of locks, do not appear to have been on that account formed on a uniformly level line, unadapted to varying heights. It is very doubtful, indeed, if the use of locks has even yet been introduced into China, intersected as it is by many canals of great antiquity and extent, the imperial canal being about 1000 miles in length. " This canal appears to have been completed in 1289, and is said to extend for a distance of forty days' navigation, and is provided with many sluices, and when vessels arrive at these sluices they are hoisted by means of machinery, whatever be their size, and let down on the other side into the water." Nevertheless the invention of locks was, as has been stated, a most important step in the history of canals ; and that mode of surmounting elevations may be said to be almost universally adopted throughout Europe and America. Inclined planes and perpendicular lifts have, it is true, been employed in those countries, as will be noticed hereafter; but the instances of their application are undoubtedly rare. Languedoc But without tracing the gradual introduction of canals CanaL from country to country, we remark at once that we find the French at the end of the 17th century, in the reign of Louis XIV., forming the Languedoc Canal, designed by Riquet, between the Bay of Biscay and the Mediterranean, a gigantic work, which was finished in 1681. It is 148 miles in length, and the summit level is 600 feet above the sea, while the works on its line embrace upwards of one hundred locks and fifty aqueducts, an undertaking which is a lasting monument of the skill and enterprize of its projectors; and with this work as a model it seems strange that Britain should not, till nearly a century after its execution, have been engaged in vigorously following so laudable an example. This seems the more extraordinary, as the Romans in early times had executed works in England, which, whatever might have been their original use, whether for the purposes of navigation or drainage, were ultimately, and that even at an early period, converted into navigable canals. Of these works we particularly specify the Caer Dyke and Foss Dyke cuts in Lincoln-shire, which are by general consent admitted to have been of Roman origin. The former extends from Peter-borough to the River Witham near the city of Lincoln, a distance of about 40 miles; and the latter extends from Lincoln to the River Trent, near Torksey, a distance of 11 miles.
Foss Dyke. Of the Caer Dyke the name only now remains ; but the Foss Dyke, though of Roman origin, still exists, and as it is the oldest British canal, the reader may be interested to learn the following facts as to its history. Camden in his Britannia states that the Foss Dyke was a cut originally made by the Romans, probably for water supply or drainage, and that it was deepened and rendered in some measure navigable in the year 1121 by Henry I. In 1762 it was reported on by Smeaton and Grundy, who found the depth at that time to be about 2 feet 8 inches. They, however, discouraged the idea of deepening by excavation. They say they found " the bottom to be either a rotten peat earth, or else a running sand," and that though the deepening of the navigation is in " nature possible," yet it " cannot be effected without removing one of the banks in order to widen the same," which would not only turn out expensive, but would "occasion much loss of time and profit to the proprietor while the work is executing." Nothing followed on this report; but in 1782 Smeaton was again called in, and deepened the navigation to 3 feet 6 inches, not, however, by widening the canal or dredging, but by raising the water-level 10 inches. From that period nothing more was done to enlarge the water-way, or adapt it to increased traffic. Meantime the adjoining Witham navigation having been improved, the defects of old Foss became more apparent, and in 1838 Mr Vignoles was consulted, and made an elaborate report on alternative schemes for increasing the depth to 4 and 6 feet; nothing, however, was done till 1840, when Messrs Stevenson were employed to design works for assimilating the Foss Dyke as far as practicable, both as regards width and depth, to the navigable channel of the Witham. The depth was found to be 3 feet 10 inches, and its breadth in many places was insufficient to admit of two boats passing each other, and for their convenience occasional passing places had been provided. It wras resolved to increase the dimensions of the canal, and to repair the whole work. Accordingly it was widened to the minimum breadth of 45 feet, and deepened to the extent of 6 feet throughout. The entrance lock communicating with the River Trent at Torksey was renewed, and a pumping engine was erected for supplying water from the Trent during dry seasons, and thus that ancient canal, which is quoted by Telford and Nimmo as " the oldest artificial canal in Britain," was restored to a state of perfect efficiency, at a cost of £40,000, and now forms an important connecting link between the Trent and Witham navigations.
Notwithstanding the existence of this early work, how- Bridge-ever, and of some others in the country, particularly the water Sankey Brook navigation, opened in 1760, it cannot becaua8' doubted that the formation of the Bridgewater Canal in Lancashire, the Act for which was obtained in 1759, was the commencement of British Barge Canal Navigation, of which we propose first to treat, and that Francis, duke of Bridgewater, and Brindley the engineer, who were its projectors, were the first to give a practical impulse to a class of works which, under the guidance mainly of Smeaton, Watt, Jessop, Nimmo, Rennie, and Telford, has been very generally adopted throughout the country, and has un-doubtedly been of vast importance in promoting its com-mercial prosperity.
According to Mr Smiles, the barge-canals laid out by Brindley, although not all executed by him, were :
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It is believed that the length of the inland boat naviga tions constructed in Britain exceeds 4700 miles, and the system has been extensively carried out both in Europe and America. Many of them were made at great cost through hills and over valleys. The Harecastle tunnel on the Grand Trunk Canal, made by Brindley, and afterwards doubled by Telford, is nearly a mile and a half in length, and the Pont-y-Cyssylte aqueduct, on the Ellesmere Canal, over the Dee, constructed by Telford at a cost of £47,000, has nineteen openings 45 feet span, and is elevated 126 feet above the river, the canal being carried across in a cast-iron trough.1
It must be obvious, that to construct a navigable channel through a country varying in level, and affording, perhaps, no great facilities for obtaining a supply of water, infers high engineering skill. Vast reservoirs must in some cases be formed for storing the water necessary to supply, during dry seasons, the loss by lockage, leakage, and evaporation. Feeders must be made to lead this water to the canal, hills must be pierced by tunnels, valleys must be crossed on lofty embankments, or spanned by spacious aqueducts, and, above all, the whole must be conceived and laid out with scrupulous regard to the all-important object of securing the works against injury from an overflow of water during floods, and a consequent inundation of the surrounding country. Moreover, the necessity of laying out the canal in level stretches, and surmounting elevations by means of locks or inclined planes, occurring at intervals, often occa-sions much difficulty and greatly restricts the resources of the engineer. Taking, then, all these circumstances into consideration, and bearing in mind that canals were the pioneers of railways, we think it may safely be affirmed that the canal engineers of former days had more serious physical difficulties to contend with than are experienced in carrying out the railways of modern times, if we except such works as the Britannia Bridge, the high-level bridge of Newcastle, the Boxhill tunnel, and some other kindred works. But, indeed, their mechanical difficulties were also greater, for the introduction of steam, and its wide-spread application to all engineering operations, afford facilities to the engineers of the present day which Smeaton at the Eddystone, Stevenson at the Bell Rock, and Rennie and Telford in their early navigation works, did not enjoy. The distinguished merits of the engineers who practised in the former and at the commencement of the present century, cannot indeed be over-estimated, and had it been within the scope of this article it would have been profitable and instructive to have described in detail some of the grand aqueducts and other works on the lines of our canals. For this reference is made to the articles AQUEDUCT, BRIDGE, TUNNEL, and RESERVOIR, all of which are more or less applicable to the formation of canals. We shall only therefore offer to the student the following sum-mary of engineering principles generally applicable to all cases.
A canal cannot be properly worked without a supply of supply. water calculated to last over the driest season of the year, and in that respect, except as to the quality of the water, demands all the care requisite in investigating the sources of water for supplying towns. If there be no nattiral lake in the district, available for supply and storage, the engineer must select situations suitable for artificial reservoirs, and the conditions to be attended to in selecting their positions are the same as those for water-works. They must com-mand a sufficient area of drainage to supply the loss by leakage, evaporation, and lockage, due to the length of canal, number and size of the locks, and probable amount of traffic. The capability of the district to afford this supply will depend on the area of the basin drained and the annual amount of rainfall. The offlets from the reservoirs must be at such an elevation as to convey water to the summit-level of the canal. The embankments for retaining the water must be erected on sites affording a favourable foundation, and, if possible, in situations where an embank-ment of small height and length may dam up a large amount of water. It is further necessary to consider whether the subsoil of the valley forming the reservoirs is throughout of so retentive a nature as to prevent leakage, and it is essential to provide, by means of waste weirs, for the discharge of floods. The Caledonian Canal, to be afterwards noticed, is in this respect very favourably situated, the whole supply being obtained from natural lochs. In other cases, such as the Union, Forth and Clyde, Crinan, Birmingham, and other canals, it was necessary to construct large reservoirs in which the water is stored in winter and led in feeders to points convenient for supplying the canal in summer. Where the canal communicates with the sea or a tidal river, and where the natural supply is small, as at the Foss Dyke already referred to, the water is raised by pumping engines. It will readily be seen, therefore, how important it is to reduce to a minimum the loss of water due to leakage from deficient workmanship, as well as to lockage of the traffic through the canal, and (while on this subject) it may be stated that the up con-sumes a greater amount of water than the down traffic, for an ascending boat on entering a lock displaces a volume of water equal to its submerged capacity; the water so displaced flows into the lower reach of the canal and the lower gates are closed, the boat is then raised, and on passing into the higher reach of the canal its displacement lost on entering is supplied by water withdrawn from, the higher reach. A descending boat, on the other hand, on entering a lock likewise displaces a volume of water equal to its submerged capacity, but the water in this case flows back into the higher reach of the canal, where it is retained when the gates are closed. Mr Fulton gives the consump-tion of 25-ton boats through locks of 8 feet lift as about 163 tons of water in ascending, and 103 in descending.2 Several proposals have been made for reducing the loss of water by side ponds to receive part of the water, but all such plans delay the traffic and have not come into general use.
FIG. 1.Section in retentive soil.
puddle was introduced, as shown in fig. 2. Professor Rankine says the depth of water and sectional area of water-way should be such as not to cause any material
The barge-canals constructed in this country are between Sectional 4 and 5 feet in depth. When the soil in which they were areas 01 made was retentive, they were formed as shown in the ^f*s cross-section, fig. 1. But when the soil was porous, clay
increase of the resistance to the motion of the boats beyond what it would encounter in open water, and gives the following rules as fulfilling these conditions :
Least breadth at bottom = 2 x greatest breadth of boat. Least depth of water := 1J foot + greatest draught of boat. Least area of water-way - 6x greatest midship section of boat.
In laying out a line of canal the engineer is more restricted than in forming the route of a road or railway, where gradients can be introduced to suit the undulating surface of the country. A canal, on the contrary, must follow rigidly the bases of hills and windings of valleys, to preserve a uniform level, accommodation being made for the road traffic by erecting suitable "fixed" and " movable " bridges. It is important, as already stated, to lay out the work in long level reaches, and to overcome elevations in cumulo by groups of looks at places where it can be most advantageously done. This leads to a saving of attendance and expense in working the canal, and causes fewer stoppages to the traffic. But to prevent waste of water the locks must be placed sufficiently far apart, say 100 yards, or an intervening pond or increased width of canal must be formed, so that a descending boat does not let off more water than the area below will receive without raising its surface so much as to lose the surplus water over the waste weirs. The mode of overcoming the difference of level between the various level reaches is, with few exceptions, by locks, which generally have a lift of 8 or 10 feet, though in some cases it is somewhat greater. The dimensions of the locks ought to be regulated by the traffic; but they should, in order to save water, be as nearly as possible the size of the craft to be passed through them, allowing from 6 inches to a foot of extra breadth and draught of water. The barge-canals in England have locks about 8 feet in breadth, and from 70 to 80 feet long, and their use in raising or lowering boats from the different reaches is so well known as not to require explanation; and for details as to the construction of the masonry of the chamber and walls, and the timber and iron work of the gates and sluices, reference is made to "Rankine's Engineer-ing." The water is generally admitted into and flows from each lock by sluices formed in the gates, and the passage of a boat occupies from three to six minutes, depending on the lift. Sir William Cubitt, on the Severn navigation, introduced the water through a culvert parallel to the side wall of the lock, and opening in the centre by means of a tunnel, which admits of 16,000 cubic feet of water flowing into or out of the lock in \\ minute; and in little more than that time loaded vessels can be passed through.
Inclined planes and perpendicular lifts, which have the advantage of saving water, were adopted so long ago as 1789 on the Ketling Canal in Shropshire, and afterwards on the duke of Bridgewater's canal. Mr Douglas of New York constructed the Morris Canal in the United States with 23 inclined planes, having gradients of about 1 in 10, with an average lift of 58 feet. The boats weighed, when loaded, 50 tons, and after being grounded on a carriage, were raised by water-power up the inclines with great ease and expedition. The length of the Morris Canal, between the rivers Hudson and Delaware, is 101 miles, and the whole rise and fall is 1557 feet, of which 223 were overcome by locks, and the remaining 1334 by inclined planes. When first describing this work the author stated that the principal objection to the inclined planes for moving boats was the injury they were apt to sustain in supporting great weights while resting on the cradle. A slimly-built canal boat, 80 feet long, and loaded with 30 tons, could not be grounded on a smooth surface without straining her timbers, but this objection has to some extent been overcome on an inclined plane constructed by Mr Leslie and Mr Bateman on the Monkland Canal, where the boats are not wholly grounded on the carriage, but are transported in a caisson of boiler-plate containing 2 feet of water, and are thus water-borne. This inclined plane is wrought by two high-pressure steam-engines of 25 horse-power each. The height is 96 feet, and the gradient 1 in 10. The maximum weight raised is 80 tons, and the transit takes about ten minutes. The average number of boats passing over the incline is about 7500 per annum. Mr Green introduced
on the Great Western Canal a perpendicular lift of 46 feet.
Sir W. Cubitt also introduced three inclined planes, having gradients of 1 in 8, on the Chard Canal, Somersetshire.
One of these inclines overcomes a rise of 86 feet; and they are said to act very satisfactorily.
An essential adjunct to a canal is a sufficient number of waste-weirs to discharge surplus water accumulating during floods, which, if not provided with an exit, may overflow the tow-path, and cause a breach in the banks, stoppage of the traffic, and damage to adjoining lands. The numbe* and positions of these waste-weirs must depend on the nature of the country through which the canal passes. Wherever the canal crosses a stream a waste-weir should be formed in the aqueduct; but independently of this the engineer must consider at what points large influxes of water may be apprehended, and must at such places not only form waste-weirs of sufficient size to carry off the surplus, but form artificial courses for its discharge into the nearest streams. These waste-weirs are placed at the top water-level of the canal, so that when a flood occurs the water flows over them and thus relieves the banks. The want of these has occasioned overflows of canal banks, attended with very serious injury to the works, and lengthened suspension of the traffic ; and attention to this particular part of canal construction is of essential importance.
Stop-gates are necessary at short intervals of a few miles for the purpose of dividing the canal into isolated reaches, so that in the event of a breach the gates may be shut, and the discharge of wxater confined to the small reach inter-cepted between two of them, instead of extending through-out the whole line of canal. In broad canals these stop-gates may be formed like the gates of locks, two pairs of gates being made to shut in opposite directions. In small works they may be made of thick planks slipped into grooves formed at the narrow points of the canal under road bridges, or at contractions made at intermediate points to receive them. Self-acting stop-gates have been tried, but their success has not been such as to lead to their general introduction. When repairs have to be made stop-gates allow of the water being run off from a short reach, and afterwards restored with comparatively little interruption to the traffic. Their value in obviating serious accidents has been well exemplified in the author's own experience. The water during a flood flowed over the towing-path of the Union Canal connecting Edinburgh and Glasgow, and the uncontrolled current carried away the embankment and the soil on which it rested to the depth of 80 feet, as measured from the top water-level. The stop-gates were promptly applied, and the discharge confined to a short reach of a few miles, otherwise the injury (which was, even in its modified form, very considerable) would have been enor-mous, not only to the canal works but to the adjoining lands.
For the purpose of draining off the water to admit of repairs after the stop-gates have been closed, it is proper to introduce, at convenient situations, a series of exits called " offlets," which are pipes placed at the level of the bottom of the canal, and fitted with valves which can be opened when required. These offlets are generally formed at aqueducts or bridges crossing rivers, where the contents of the canal can be run off into the bed of the stream, the stop-gates on both sides being closed so as to isolate the part of the canal from which the water is withdrawn.
Drainage of Tow-Paths.
In executing the work, provision must be made for the proper drainage of the tow-path, which should be made highest at the side next the canal, and sloped with a gentle inclination towards the outside. The drainage of the tow-path should be carried to a sky drain, and at intervals passed below it into the canal, as shown in fig 3.
The preservation of the banks at the water-line is also a matter of importance. "Pitching" with stones and " facing" wdth brushwood are employed, and in the author's experience the latter, if well executed, forms an economical and effectual protection.
In forming the alveus or bed of the canal care must be taken, especially on embankments, and even in cuttings where the soil is porous, to provide against leakage by using puddle, as shown as fig 2. An all-important matter, as affecting the construction of the works, is the possibility of getting clay in the district, or such other soil as may be worked into puddle, on the good quality of which the sta-bility of the reservoir embankments and the imperviousness of the beds and banks of the canal mainly depend.
These are the only points of general application, in the construction of canals, to which reference can here be made; and in applying them to each case the engineer must be guided, first, by theoretical knowledge, to be acquired by a careful study of his profession; and, secondly, by that knowledge which can be gained only by expe-rience.
Mode of Conducting .....
Not a little has been written on the best mode of conducting traffic on canals, and the reader who wishes to study the subject fully is referred to the observations made by Mr Walker and Mr George Rennie in the Transactions of the Royal Society and of the Institution of Civil Engi-neers, and especially to the valuable researches on hydro-dynamics by Mr J. Scott Russell in the Transactions of the Royal Society of Edinburgh. Mr Russell while experi-menting on propelling boats at high speeds found that the primary wave of displacement produced by the motion of a boat moves with a velocity due to the depth of water in the canal, being the velocity that is due to gravity acting through a height equal to the depth of the centre of gravity of the cross-section of the channel below the surface of the fluid. The velocity is in no degree dejjendent on the form or velocity of the body which generates it, or on the breadth of the canal. A wave that had a velocity of 8 miles an hour was traced to a point where the channel became deeper, and its velocity was suddenly accelerated; the channel became alternately narrower and wider without producing any sensible effect, but when the wave once more reached that part of the channel which was of the original depth it resumed its original velocity. A fact of great practical value was established, that a boat, if raised by a sudden effort to the top of a primary wave, could be drawn along at 10 miles an hour with less fatigue to the horses than if drawn at the rate of 6 miles, while the waste was less severe on the banks of the canal. These investigations were made before the general establishment of railways, when swift canal travelling seemed a desirable attainment. But though boats propelled at high speed on canals have given place to railway carriages, yet the canal traffic at slow speeds must be conducted, and the cheapest means of effecting the " haulage" with the least danger to the banks is still an important inquiry, and has within the last few years afforded matter for some highly interesting papers arid statements in the Proceedings of the Institution of Civil Engineers. These are communications on the employment of steam-power on the Gloucester and Berkeley Canal, by G. W. B. Clegram j1 on the Grand Canal, Ireland, by Mr Healy f on the Forth and Clyde, by Mr J. Milne ;3 and on the Aire and Calder, by Mr W. H. Bartholomew, to all which reference is made.
Wasting of the Banks.
One great objection to high speeds on canals is the wasting of the banks by the displacement produced in propelling the vessel through the water. The wasting, indeed, takes place even with very low speeds, and as a matter of canal engineering it is necessary to notice it. To give an instance of the effect on the large scale:Mr Ure says that the river steamers on the Clyde, going at a speed of 8 to 9 miles per hour, produce a swell which commences to rise when the vessel is " 2 or 3 miles off,"a circumstance which was first noticed by Mr J. Scott Russell in 1837. The swell gradually increases as the steamer approaches, and at last becoming a wave of translation, it breaks on the river walls nearly abreast of the vessel, following her on her course along the river, as a violent breaking wave, measuring 8 or 10 feet from the hollow in the channel to the crest on the wall. A coating of heavy whinstone rock, from 2 to 3 feet thick, extending from low to high water-mark is found necessary to enable the banks to withstand it. Mr Ure also found that the action of passing steamers, though very destructive to the banks, was useful in stirring up the mud from the bottom, which was carried off by the currents to an extent which he estimates to be from 20 to 25 per cent, of the whole
whole quantity dredged from one particular part of the river where he carefully measured it. It will at once be apparent, that however inconvenient these wasting waves may be in a river, the waves in a canal, though smaller, are nevertheless a source of greater anxiety, acting as they do in a narrow artificial channel, formed at some places on high embankments, the failure of which would be attended with serious consequences.
The wasting on canals where the traffic is conducted at a moderate speed is found to extend not more than 18 inches to 2 feet, that is 1 foot above and below the water-line, and Mr Clegram states that he has found on the Gloucester Canal that a facing of stone filled into a recess cut in the banks formed a complete protection. Brushwood, as already noticed, is also an effectual remedy.
What has recently led to the consideration of the best means of protecting the banks of canals is the substitution of steam for horse power in working the traffic, which has been entirely successful. The first attempt at using steam-power on canals was made on the Forth and Clyde Canal with Symington's boat, in 1789. Various experiments were made to introduce tugs, but these were ultimately abandoned in favour of steam-lighters, which now in great numbers navigate the canal, and make passages to Leith, Greenock, and other trading ports on the Firths of Forth and Clyde.
This system, however, would not suit the trade of the steam-Gloucester Canal, which is chiefly frequented by sea-borne towing on vessels, and steam-towing has been introduced on that Gloucestei navigation. The following extracts from Mr Clegram'sCanal-paper5 seem generally applicable to all navigations where towing is to be adopted. He says the ship canal leads from the Severn at Gloucester to the Severn at Sharpness Point. It is 16-j- miles in length, and has a depth varying from 18 to 18 feet 6 inches, navigable by vessels of 700 tons register. Prior to the year 1860 all sea-going vessels passing through were towed by horses, the number of horses being regulated by a scale varying from 1 horse for a vessel of 40 tons to 9 horses for a vessel of 420 tons. The cost of this amounted generally to about one farthing per ton per mile on the register tonnage of the vessel. The speed varied from one mile to three miles per hour, according to the size of the vessel and the state of the weather.
In 1860 steam-tugs were placed upon the canal to do this work. They are iron boats, 65 feet long, 12 feet beam, and draw 6 feet 3 inches of water, fitted with high-pressure engines ; the diameters of the cylinders are 20 inches, stroke of 18 inches, pressure of the steam 32 lb on the inch, and the cost of each £3000. Nearly the whole of the sea-going craft are now towed by these tugs. The vessels range from 30 tons up to 700 tons register, with a draught of water from 6 to 16 feet. They are towed either singly or in a team, according to circumstances. Sometimes as many as thirteen loaded vessels of from 50 to 100 tons register have been towed by one tug at the rate of 3 to 3i miles an hour. The heaviest load drawn by any one tug has been 1690 tons of goods in three vessels. Their draught of water varied from 14 feet 6 inches to 15 feet 6 inches, and they were taken the whole length of the canal at the speed of 2 miles an hour. The smaller vessels are towed at a speed of 4 miles an hour, to which as a rule they are restricted.
The employment of steam for towing has been found very advantageous. The vessels rub less against the banks, the power being right ahead, and not on one side as with horses. The wear on the ropes used in tracking is reduced, the speed is increased, and vessels can be moved along the canal in weather which would have prevented horses doing the work. With a strong wind athwart the canal vessels cannot be tracked in train ; they must then be taken singly, or at most two at a time. When vessels are towed in train, as a rule the largest and heaviest draughted are placed first, and the hawser leading from the first vessel to the tug is taken from each side of the bow. With this arrangement, and a skilful management of the tug, the vessels can be kept fairly in the line of the canal.
The only disadvantage of this system, on a canal the sides of which are unprotected, is the additional wear caused by the run of water between the sides of the large vessels and the banks. Such vessels occupy a large part of the sectional area of the canal, and being taken along at a much greater speed than they were by horses the wash of water is more prejudicial. When the vessels or trains of vessels are heavy, and the tugs are working up to their full power and speed, the water thrown back by the action of the screw against the bow of the first vessel is thrown off by it to the banks on either side, and is the cause of considerable wash. This has been attempted to be remedied by placing the first vessel farther back from the tug; but in practice it is found that a distance of 40 to 50 feet is the farthest separation that can be allowed without sacrificing that hold between the two which prevents the vessel sheering from side to side. The first vessel being kept steadily in her course, the others follow without much difficulty.
The employment of tugs has afforded an unexpected facility for cleansing the canal from deposit of mud. Formerly it was difficult to remove this deposit from the slopes of the banks on which it collected, sometimes in-conveniently contracting the capacity of the canal. Since the vessels have been moved at greater speed and in trains this deposit has been entirely removed from the slopes to the bottom of the canal, whence it can readily be taken out by the dredger.
But though all efforts to improve barge-canals can never bring them to compete with railways in the quick con-veyance of passengers, it is surprising to find in how many places they still command an enormous traffic in goods and minerals, and thus act as a valuable relief to overburdened railways. This is specially the case in the manufacturing districts of England, where the Birmingham Grand Junction and other canals seem to carry on as brisk a trade as they did in days gone by when they had no competitors but the stage coach and the carrier's van.
These remarks, however, as to railway competition do Ship not apply to Ship-canals, which, undisturbed by competing caDa schemes, retain all the monopoly they ever possessed; and indeed, in the recent construction of the Suez and New Amsterdam canals, they have acquired an importance before unclaimed for works of that classan importance which entitles them to the highest consideration in any engineering treatise; for, apart from their structural interest to the engineer, their usefulness in affording a short and sheltered passage for sea-borne vessels has long been acknowledged and can hardly be over-estimated.
The Languedoc Canal already mentioned, by a short passage of 148 miles, saves a sea voyage of upwards of 2000 miles through the Straits of Gibraltar. By the Forth and Clyde Canal sea-borne vessels, not exceeding 8-§- feet draught of water, can pass from opposite coasts of Scotland, through the heart of the country, by 35 miles of inland navigation and avoid the dangers of the Pentland Firth; the Crinan Canal substitutes a short inland route of 9 miles for a sea voyage round the Mull of Kintyre of about 70 miles; and the last great canal between Suez and the Mediterranean effects a saving of 3750 miles on the route to India.
To most of the early ship canals that have been executed, the principles of construction already stated are generally applicablethe depth of water and dimensions of the locks and all other works being increased to suit the larger size of craft which use them, and therefore further notice of such details is not required. But having still to illustrate the larger class of works, we jjroceed to describe some of the largest of the ship-canals already constructed and projected, and in doing so, we shall consider ship-canals under the following three classes :
First, Canals which on their route from sea to sea Three traverse high districts, surmounting the elevation by locks classes of supplied by natural lakes or artificial reservoirs, such as the s^ cana''''* Languedoc in France, or the Caledonian Canal in Scotland;
Second, Canals in low-lying districts, which are carried on a uniform water-level from end to end, and are defended against the inroad of the sea at high water by double acting locks, which also retain the canal water at low tide, such as the canals of Holland and other low countries;
Third, Canals, of which the Suez is the only example yet made, without locks at either end, and communicating freely with the sea, from which it derives its water supply.
The Caledonian Canal in Scotland is as good a specimen of works of the first class as can be selected.
In 1773 James W'att was employed to survey the country between the Beauly at Inverness and Loch Eil at the mouth of the river Lochy, a distance of about 60 miles, with the view of forming a ship canal between the two seas, to save about 400 miles of coasting voyage by the North of Scotland through the stormy Pentland Firth. The district referred to, called the " Great Caledonian Glen," as will be seen from Plate XXXVI., embraces a chain of fresh-water lakes, which, in connection with the surrounding glens, have afforded an interesting field for the speculations of the geologist; and no doubt the first conception of a canal through the district owed its origin to the apparent facilities for inland navigation which the lakes afforded. In 1801 Telford was employed by Government to report, and the ultimate result of that report was the construction of the canal, which was opened in 1823.
The summit-level is at Laggan, between Loch Oich and Loch Lochy, whence the drainage flows to the Eastern and Western seas.
The district which discharges into the eastern outlet comprehends an area of about 700 square miles, chiefly of high mountainous country, intersected by streams and
lakes, which discharge themselves into Loch Oich, Loch Ness, and Loch Doughfour, and thence are conveyed into the Moray Firth by the Eiver Ness. Loch Oich, the summit-level of the canal, has an area of about 2 square miles, and the present standard level of its surface is understood to be 102 feet above the level of mean high water of neap tides in Beauly Firth. It receives the drainage of Loch Quoich and Loch Garry. The waters of Loch Oich are discharged through the Biver Oich into Loch Ness, which is about 24 miles in length, and has an area of about 30 square miles. Loch Ness receives the waters of the Tarff, the Foyers, and Glenmoriston, and the drainage of numerous other streams and lakes of less note. It discharges its waters through a comparatively narrow neck, called Bona Passage, into the small loch of Doughfour, whence they find an exit to the Beauly and Moray Firths by the Biver Ness, on which the town and harbour of Inverness are situated.
The drainage of the western district of the country, including Loch Arkegg, finds its way into Loch Lochy, which is about 10 miles long, and thence by the Puver Lochy to the Western Sea at Loch Eil.
The two locks in Loch Beauly at the northern entrance to the canal are each 170 feet long, 40 feet wide, and have a lift of about 8 feet. At Muirtown, a little further on, are four locks of 170 feet in length and 40 feet in width, having a rise of 32 feet, raising the canal to the level of Loch Ness, which it enters at Bona. The works westward of Loch Ness are an artificial canal with seven locks com-municating with Loch Oich. Between Lochs Oich and Lochy are two locks; at the south end of Loch Lochy is a regulating lock, and the canal is carried from this point on the level of Loch Lochy to Banavie, where it descends 64 feet by eight connected locks, forming what is called in the country " Neptune's Staircase ;" finally at Corpach the canal descends by two locks to the level of Loch Eil.
Of the whole distance, about 37^- miles are natural lake navigation, and the remaining 23 are artificial or canal navigation. The canals were made 120 feet in width at top-water level, 50 feet at bottom, and 20 feet in depth. In the course of inquiries as to the state of the canal, under a remit from the Admiralty, the author found that the shallows at Loch Oich and the cutting at the summit level originally contemplated had not been carried to the full depth, and an additional depth had been gained at that place by raising the level of Loch Oich; but still he was led to the conclusion that the standard depth of the canal cannot be regarded as more than 18 feet, giving access to vessels of 160 feet in length, 38 feet beam, and 17 feet draught of water.
In carrying out this remarkable work Telford had to deal with difficulties of no ordinary kind, in rendering available rugged Highland lakes, and surmounting the summit-level of the glen. The work, which cost about one million sterling, is a noble monument of his engineering skill. Canals of The canals of Holland are specimens of the second class North of works to which reference has been made, and of these a Holland. very remarkable one is the North Holland Canal, completed in 1825. It was designed by M. Blanken, who, instead of the high rugged Highland glens of Scotland, had to deal with the proverbial lowness of the country, and to protect his w7orks not from the assaults of mountain torrents but from encroachments of the waves, for there vessels are locked down from the sea into the canal. It extends from Amsterdam to the Helder, is 50 miles in length, and is formed of the cross-section shown in fig. 4. It enables vessels trading from Amsterdam to avoid the islands and sand-banks of the dangerous Zuider Zee, the passage through which in former times often occupied as many weeks as the transit through the canal now occupies hours.
FIG. 4.Cross-section of North Holland Canal.
But the North Holland Canal, which has long proved so Amster-useful to the commerce of the district, is destined soon to 'him Canal be superseded by the new Amsterdam Canal, a work of great magnitude, which it is proposed to describe as an illustration of ship-canals of the second class, from details furnished by Mr J. C. Hawkshaw, C.E.
The rapid increase in the trade of the ports to the south-ward and eastward of the Helder, effected by the construc-tion of railways throughout Europe, rendered it imperative for the merchants of Amsterdam to provide better com-munication with the North Sea than that afforded by the North Holland ship canal already noticed, or suffer its trade to pass to other ports more favourably situated for over-sea traffic.
In 1865 a company was formed for the purpose of con-structing a canal from Amsterdam, in nearly a direct line, to the North Sea, through Lake Y and Wyker Meer, a dis-tance of 16-^- miles. Sir John Hawkshaw and Mr Dirks were appointed the engineers to carry out the work, a plan and section of which are given in Plate XXXVI.
The harbour in which the canal terminates in the North Sea is formed by two piers built of concrete blocks founded on a deposit of rough basalt. The piers are each 5069 feet in length, and enclose an area of about 260 acres. About 140 acres of this area are to be dredged to a depth of 26 \ feet, the remainder is to be left at the present depth for the accommodation of small craft and fishing-boats.
From its commencement at the harbour the canal passes by a deep cutting through a broad belt of sand-hills which protect the whole of this part of the coast of Holland from the inroads of the sea. The cross-section of the canal at this place is shown in fig. 5. This cutting is about 3 miles
FIG. 5.Cross-section of Amsterdam Canal.
in length; the greatest depth of cutting from the surface to the bottom of the canal is 78 feet, and the amount of earth-work excavated is 6,213,000 cubic yards. On emerging from the sand-hills the canal passes by the village of Velsen, in the neighbourhood of which it is crossed by the railway from Haarlem to the Helder, and there enters the Wyker Meer, a large tract of tide-covered land. After traversing the Wyker Meer it passes by a cutting of 327,000 cubic yards through the promontory called Buitenhuizen, which sepa-rates that Meer from Lake Y, another large tide-covered area. The rest of its course lies through Lake Y as far as Amsterdam.
There are two sets of locks, one set at each end. The North Sea locks are at a distance of about three-quarters of a mile from the North Sea harbour. These locks, as shown in fig. 6, have three passages. The central or main one is 60 feet wide and 390 feet long, and will be furnished with J two pairs of gates at each end, pointing in opposite directions, and one pair in the centre. The northernmost side passage for barges is 30 feet long and 34 feet wide, with three pairs of gates; that to the south is 227 feet in length and 40 feet wide, with five pairs of gates.
FIG. 6.Plan of Locks on Amsterdam Canal.
In constructing the canal,which is (1876) now far advanced towards completion, the cuttings were first begun. The material proceeding from these cuttings was deposited so as to form two banks 443 feet apart, through the lakes on each side of the main canal, as shown by the hard lines on the plan, and also to form the banks of the branch canals on either side. The total length of these banks is 38-| miles. The nucleus of the bank is formed of sand with a coating of clay, and protected during its progress with fascines; and when the banks are far enough advanced, the deep channel for the canal is excavated by dredging. The cross-section of the canal and banks through these meers or lakes is shown in fig. 7.
^J-^^._r-^390______ .J . ^
The formation of the banks through the Wyker Meer and Lake Y will enable about 12,000 acres of the shown on the plan, which is now occupied by these lakes, to be reclaimed. For the purpose of this reclamation, and also to provide for the drainage of the land on the margin of the lakes, including a large portion of what was formerly Haarlem Meer, pumps are provided by the company at various points on the main and branch canals. The Canal Company are bound to keep the surface-water of the canal about 1 foot 7 inches below average high-water level. In order to insure this level being maintained, three large pumps have been erected in connection with the locks hereafter to be described, on the dam between Amsterdam and the Zuider Zee. They consist of three Appold pumps, the largest of the kind yet made, the fans being 8 feet in diameter. Each pump is worked by a separate engine of 90 nominal horse-power. The maximum lift is 9 feet 9 inches, at which the three pumps are capable of discharging 1950 tons a minute; with the ordinary working lift of 3| feet they will discharge 2700 tons a minute.
Lake Y extends about 4A miles to the eastward of Amsterdam; and here it was necessary to form a dam with locks for the passage of vessels. The dam crosses Lake Y at a point about 2 miles to the eastward of Amsterdam, where it is contracted to 4265 feet in width. As it was necessary to construct these locks before completing the dam across Lake Y, a circular cofferdam 590 feet in diameter, consisting of two rows of piles 49 feet long, .was constructed in the tideway, and within this dam the locks were built. These locks have three main passages, each with five pairs of gates, and one smaller passage with three pairs of gates, arranged much in the same manner as the North Sea locks in fig. 6. The whole of the masonry and brickwork for these locks and sluiceways was founded on bearing-piles, upwards of 10,000 in number. The bottom where the cofferdam was placed consisted of mud, and some; difficulty was experienced in maintaining it till the work' was completed. The dam across Lake Y, as shown in section, fig. 8, consists of clay and sand, placed on and
FIG. 3.Section of Dam across Lake Y.
protected at the sides by large masses of wicker-work, which is afterwards covered with basalt in the manner usually adopted in Holland.
All the lock gates at both ends of the canal pointing seawards are of malleable iron; the gates pointing in-wards towards the canal are of wood. The necessity, for drainage purposes, of maintaining the surface water of the canal at the prescribed low level calls for a suffi-cient barrier being provided against the sea at both ends, as the sea-level will not unfrequently, at high water, be several feet above the level of the canal. This necessity, as well as the difference of level and periods of high water in the Zuider Zee and the North Sea, required a totally different design from the Suez Canal, to be afterwards described. The contract sum for the execution of the Amsterdam Canal is ¿£2,250,000, and it is expected that it will be ready for traffic in 1877.
Of the third class of works there is, as yet, only a single Suez Canal example in the Suez Canal, one of the most remarkable engineering works of modern times ; but though it is called a canal, it bears little resemblance to the works we have described under that name, for it has neither locks, gates, reservoirs, or pumping-engines, nor has it, indeed, anything in common with canals, except that it affords a short route for sea-borne ships. It is in fact, correctly speaking, an artificial strait or arm of the sea, connecting the Medi-terranean and the Red Sea, from both of which it derives its water-supply; and the fact that the two seas are nearly on the same level, and the rise of tide very small, allowed this construction to be adopted.
The idea of forming this connecting link between sea and sea is of very ancient origin, and its author is unknown. It is understood, however, that a water communication for small vessels between the two seas was formed as early as 600 years before the Christian era, and existed for a period of about 1400 years, after which it was allowed to fall into disuse. Baron De Tott in his Memoirs of the Turks and Tartars, written in 1785, after giving quotations from the historian Diodorus as to the existence of certain portions of the early work, and its having been abandoned in consequence of the supposed difference of level between the two seas, and threatened inundation of Egypt, says there still exist those early traces of work " qu'un léger travail rendrait navigable sans y employer d'écluses et sans menacer l'Égypte d'inondations." De Tott's opinion expressed in 1785 has certainly been carried out, but on a scale and at an expenditure of labour and money far beyond the conception of the French diplomatist. The idea of restoring this ancient communication on a scale suited to modern times is understood to be due to Napoleon I. who, about the close of the last century, obtained a report from M. Lepere, a French engineer, which however was followed by no result, and it remained for M. de Lesseps, in the present day, to realize what were thought the dreams of commercial speculators, by carrying out the long-desired passage between the two seas. But the post-ponement of the scheme unquestionably favoured the chances of its commercial success, for had the canal been completed even a few years earlier, comparatively few vessels would have been found to take advantage of it. Masters of sailing-vessels would not from choice have navi-gated the Mediterranean and encountered the passage through the canal and the tedious and difficult voyage of the Red Sea. They would undoubtedly have preferred to round the free seaway of the Cape of Good Hope, with all its ocean dangers and excitements, to threading their way through such an inland passage, involving risks of rocks and shoals, protracted calms and contrary winds. But the introduction of ocean-going screw-steamers was an entirely new feature in navigation. Being independent of wind for their propulsion, and being admirably fitted for navigating narrow straits and passages, their rapid and general adoption by all the leading shipping firms in the world afforded not only a plea, but a necessity for the short communication by the Mediterranean and Red Sea. It was indeed a great achievement to reduce the distance between Western Europe and India from 11,379 to 7628 miles, equal, according to Admiral Richards and Colonel Clarke, R.E., to a saving of thirty-six days on the voyage; and this is the great result effected by cutting the Suez Canal between the Mediterranean and the Red Sea.
Mr Bateman, C.E., who visited the canal as the representative of the Royal Society, communicated to that body a description of the works, in which he gives the following account of the early negotiations of M. Ferdinand Lesseps, who has the credit of having brought the work to a success-ful issue :
"The project" of M. Ferdinand Lesseps ''was to cut a great canal on the level of the two seas, by the nearest and most practicable route, which lay along the valley or depression containing Lake Menzaleh, Lake Ballah, Lake Timsah, and the Bitter Lakes. The character of this route was described in 1830 by General Chesney, R.A., who examined and drew up a report on the country between the Mediterranean and the Red Sea. At that time a difference of 30 feet between the two seas was still assumed, and all proposals for canals were laid out on that assump-tion. General Chesney summed up his report by stating, 'As to the executive part there is but one opinion; there are no serious difficulties ; not a single mountain intervenes, scarcely what deserves to be called a hillock; and in a country where labour can be had without limit, and at a rate infinitely below that of any other part of the world, the expense would be a moderate one for a single nation, and scarcely worth dividing among the great kingdoms of Europe, who would all be benefited by the measure.'
" M. Lesseps was well advised therefore in the route he selected, and (assuming the possibility of keeping open the canal) in the character of the project he proposed.
"From 1849 to 1854 he was occupied in maturing his project. In , the latter year Mahomet Said Pasha became Viceroy of Egpyt, and sent at once for M. Lesseps to consider with him the propriety of carrying out the work. The result of this interview was, that on the 30th of November a commission was signed at Cairo, charging M. Lesseps to constitute a company named ' The Universal Suez Canal Company.' In the following year, 1855, M.
Lesseps, acting for the Viceroy, invited a number of gentlemen, eminent as directors of public works, as engi-neers, and distinguished in other ways, to form an Inter-national Commission for the purpose of considering and reporting on the practicability of the scheme.
" The Commission met in Egypt in December 1855 and January 1856, and made a careful examination of the harbours in the two seas, and of the intervening desert, and arrived at the conclusion that a ship canal was practicable between the Gulf of Pelusium in the Mediterranean and the Red Sea near Suez. They differed, however, as to the mode in which such a canal should be constructed. The three English engineering members of the Commission were of opinion that a ship canal, having its surface raised 25 feet above the sea-level, and communicating with the Bay of Pelusium at one end and the Red Sea at the other, by means of locks, and supplied with water from the Nile, was the best mode of construction. The foreign members, on the contrary, held that a canal having its bottom 27 feet below sea-level, from sea to sea, without any lock, and with harbours at each end, was the best system,the harbours to be formed by piers and dredging out to deep water.
" The Commission met at Paris in June 1856, when the views of the English engineers were rejected, and the report to the Viceroy recommended the system which has since been carried out.
" Two years from the date of this report were spent in conferences and preliminary steps before M. Lesseps obtained the necessary funds for carrying out the works. About half the capital was subscribed on the Continent, by far the larger portion being taken in France, and the other half was found by the Viceroy. Further time was necessarily lost in preparation, and it was not till near the close of 1860 that the work was actually commenced.
" The original concession granted extraordinary privileges to the Company. It included or contemplated the forma-tion of a ' sweet water' canal for the use of the workmen engaged, and the Company were to become proprietors of all the land which could be irrigated by means of this canal. One of the conditions of the concession also was that the Viceroy should procure forced labour for the execution of the work, and soon after the commencement of operations, and for some time, the number of workmen so engaged amounted to from 25,000 to 30,000. The work thus commenced steadily proceeded until 1862, when the late Viceroy, during his visit to this country at the time of the International Exhibition, requested Sir John Hawkshaw to visit the canal and report on the condition of the works and the practicability of its being successfully completed and maintained. His Highness's instructions were that Sir John Hawkshaw should make an examination of the works quite independently of the French company and their engineers, and report the results at which he arrived."
We quote these results as given in Sir John Hawkshaw's report, because they show the nature of the difficulties that had been raised and the soundness of the advice which Sir John gaveadvice which undoubtedly greatly contributed to the successful completion of the work.
The following are given by Sir John as the objections to the work :
"1. That the canal will become a stagnant ditch.
" 2. That the canal will silt up, or that the moving sands of the Desert will fill it up.
'o 3. That the Bitter Lakes through which the canal is to pass will be filled up with salt.
"4. That the navigation of the Red Sea is dangerous and diffi-cult.
"5. That shipping will not approach Port Said, because of the difficulties that will he met with, and the danger of that port on a lee shore.
"6. That it will be. difficult, if not impracticable, to keep open the Mediterranean entrance to the canal,"
Having analysed each of these objections, and fully weighed the arguments on which they were based, he came to the following conclusions as to the practicability of construction and maintenance:
" 1st, As regards the engineering construction, there are no works on the canal presenting on their face any unusual difficulty of execution, and there are no contingencies that I can conceive likely to arise that would introduce difficulties insurmountable by engineer-ing skill.
'' Idly, As regards the maintenance of the canal, I am of opinion that no obstacles would be met with that w:ould prevent the work, when completed, being maintained with ease and efficiency, and without the necessity of incurring any extraordinary or unusual yearly expenditure."
" Said Pasha died between the period of Sir John Hawkshaw's examination of the country and the date of his report. He was succeeded by his brother, Ismail, the present Viceroy or Khedive, who, alarmed at the largeness and uncertainty of the grants to the Canal Company, of the proprietorship of land which could be irrigated by the sweet water canal, and anxious to retire from the obligation of finding forced labour for the construction of the works, refused to ratify or agree to the concessions granted by his brother. The whole question was then referred to the arbitration of the late Emperor of the French, who kindly undertook the task, and awarded the sum of £3,800,000 to be paid by the Viceroy to the Canal Company as indemnifica-tion for the loss they would sustain by the withdrawal of forced or native labour, for the retrocession of large grants of land, and for the abandonment of other privileges attached to the original act of concession. This money was applied to the prosecution of the works.
" The withdrawal of native labour involved very important changes in the mode of conducting the works, and occasioned at the time considerable delay. Mechanical appliances for the removal of the material, and European skilled labour, had to be substituted ; these had to be recruited from different parts of Europe, and great difficulty was experienced in procuring them. The accessory canals had to be widened for the conveyance of larger dredging-machines, and additional dwellings had to be provided for the accommodation of European labourers. Ultimately all difficulties were overcome, and the work proceeded."
After the works had been nearly completed, the Lords of the Admiralty instructed Admiral Richards, the hydro-grapher, and Lieutenant-Colonel Clarke, R. E., to visit Egypt, and report as to the condition of the canal. These officers accordingly made a most minute survey of the canal and its terminal harbours, and issued a most interesting report, from the information contained in which the plan of the canal, Plate XXXVI., has been mainly constructed. From this plan it will be seen that the canal extends from Port Said on the Mediterranean to Suez on the Red Sea, and that, as shown by the section, it traverses a compara-tively flat country. This route has been selected so as to take advantage of certain valleys or depressions which are called lakes, but were in fact, previous to the construction of the canal, low-lying tracts of country, at some places below the level of the Mediterranean and Red Seas. These valleys were found to be coated with a deep deposit of salt, and are described as having had all the appearance of being covered with snow, bearing evidence of their having been at one period overflowed by the sea. As will be seen from the plan, Lake Menzaleh is next to the Mediterranean, Lake Timsah about half-way across the isthmus, and the Bitter Lakes next to the Red Sea. Lake Timsah, which is about 5 miles long, and the Bitter Lakes, about 23, were quite dry before the cutting of the canal, and the water which has converted them into large inland lakes was supplied from the Red Sea and Mediterranean. The water began to flow from the Mediterranean in February 1809, and from the Red Sea in July, and by the beginning of October of the same year these vast tracts of country, which had formerly been parched and arid valleys, were converted into great lakes navigated by vessels of the largest class. It will be seen from the section that the surface of the ground is generally very low, the chief cuttings being at Serapeum and El Guisr, where the sandy dunes attain an elevation of about 50 to 60 feet. The channel through the lakes was excavated partly by hand labour and partly by dredging, and for a considerable portion the level of the valleys was so low as to afford sufficient depth without excavation. The material excavated appears to have been almost entirely alluvial, and easily removed ; the only rock was met with at El Guisr, where soft gypsum occurred, removable to a considerable extent by dredging, so that the canal works presented no physical difficulty.
The whole length of the navigation is 88 geographical miles. Of this distance 66 miles are actual canal, formed by cuttings, 14 miles are made by dredging through the lakes, and 8 miles required no works, the natural depth being equal to that of the canal. Throughout its whole length the canal was intended to have a navigable depth of 26 feet for a width of 72 feet at the bottom, and to have a width at the top varying according to the character of the cuttings. At those places where the cuttings are deep, the slopes were designed to be 2 to 1, with a surface width at the water-line of about 197 feet, as shown in fig. 9, which
K 7a 1'V >j
FIG. 9.Cross-section of Suez Canal at El Guisr.
is a cross-section at El Guisr; in the less elevated por-tions of the land, where the stuff is softer, the slopes are increased, giving a surface width of 325 feet. It will be understood that in the lakes the canal consists of a navigable channel of sufficient depth and breadth to admit the traffic, the surface of the water extending on either side to the edge of the lake. Fig. 10 shows a cross-section at Lake
<72 _* »_
FIG. 10.Cross-section at Menzaleh.
Menzaleh. The deep channel through the lakes is marked by iron beacons on either side, 250 feet apart, and the Admiralty reporters state that " in practice it is found more difficult to keep in the centre while passing through these beacons, than it is when between the embankments." Al every 5 or 6 miles there is a passing-place, to enable large vessels to moor for the night, or to bring-up in order to allow others to pass, all these movements being regulated by telegraph from Port Said, Ismailia, or Suez. Perhaps the most interesting question to the engineer is the action of the tide in the narrow channel between the two seas, and the observations made on this subject are given in the following quotation from the Admiralty report :
" The tidal observations which we were able to make were necessarily somewhat imperfect from want of time, but they were made at that period of the moon's age when their effect would be greatest; the results show that in the southern portion of the canal, between Suez and Great Bitter Lake, the tidal influence from the Red Sea is felt, there being a regular flow and ebb,the flood running in for about seven hours, and the ebb running out for five hours ; at the Suez entrance, the rise at springs, unless effected by strong winds, is between 5 and 6 feet; about half way from Suez to the Small Bitter Lake, a distance of 6 miles, it is under 2 feet; at the south end of the Small Bitter Lake, a few inches only; while at the south end of the Great Lake there is scarcely any perceptible tidal influence. We were informed by the authorities at Ismailia, that since the Great Lake has been filled, the level of Lake Tinisah- which was filled from trie Mediterranean in April 1867, has risen 12 centi-metres, or about 4 inches, and that its waters are continually run-ning at a slow rate into the Mediterranean; certainly this statement agreed with what we ourselves remarked, for we always found a current running northward from Lake Timsah at the rate of from half a mile to a mile an hour. Limited, however, as these tidal ob-servations were, they were taken with great care, and appear suffi-cient to show that, except at the Suez end, the tides will not ma-terially affect the passage of vessels ; at that end, therefore, large vessels must regulate their time of passing ; indeed, the greatest difficulty which will be experienced will be not from the tides, but from the prevailing north-east wind in the canal, which will make close steerage difficult in going from north to south."
It thus appears that the tidal column of 5 feet range in the Red Sea is reduced to 2 feet at the distance of 6 miles, and is practically annihilated by the wide expanse of the Bitter Lakes. But it would be highly interesting to have this conclusion confirmed by further systematic tidal obser-vations.
In executing this strange work of the desert, and converting dry sands into navigable lakes, it is stated that there have been about eighty millions of cubic yards of material excavated, and at one time sixty dredging-machines and nearly 30,000 labourers were employed. For their use a supply of fresh water was conveyed from the Nile at Cairo, and distributed along the whole length of the canal, a work which of itself was one of no small magnitude.
The cost of the whole undertaking, including the harbours, is stated to have been about £20,000,000. The terminal harbours are important adjuncts of this great work. That on the Mediterranean is Port Said, which is formed by two breakwaters constructed of concrete blocks, the western one 6940 feet in length and the eastern 6020 feet, enclosing an area of about 450 acres, with an average depth of only 13 or 14 feet, excepting in the channel leading to the canal, where the depth is 25 to 28 feet. The entrance to the canal at Suez is also protected by a breakwater, and in connection with the harbour at this place there are two large basins and a dry dock.
The canal may be regarded as a highway for steamers of 400 feet in length and 50 feet beam. A delay of three days is calculated on for the passage across from Port Said to Suez.
It is satisfactory to learn from the report of Commander Wharton, of H.M.S. " Shearwater," " that the canal retains its depth of water. That report states that " comparing generally the depth of the canal in 1873 and 1875 it seems that it is in about the same condition, with perhaps a slight balance in favour of increased depth now; while its average minimum may be stated at 26 feet, there are yet consider-able tracts where 25 feet and even as little as 24 feet will be passed over." The survey of Lieutenant Millard, also reported to the Admiralty in 1875, shows that at the entrance to Port Said harbour the 27, 30, and 33 feet contour lines were seaward of those obtained before, proving that some shallowing of the water at the entrance has taken place.
The use made of the canal may be judged of from the following table of the traffic passing through since its commencement :
== TABLE ==
The tonnage has thus been quadrupled in five years ; and the best means of enlargingthe canal to accommodate increas-ing trade must soon become an important question for its owners.
Such works as the ship canals we have been describing entirely revolutionize ocean navigation, and consequently demand the zealous attention of all nations whose interests they seem to affect. Of this zealous watchfulness the interest taken by the Powers of Europe in the distribution of the property in the Suez Canal may be cited as an example. But notwithstanding the difficulties, legal and-political, which the execution of such works are almost sure to create by severing continents before united, and connecting seas before separated by thousands of miles of exposed navigation, we may safely conclude that wherever the perils and delays of ocean sailing can be lessened by forming canals these valuable helps to navigation will at all hazards be carried out. Viewing then the subject prospec-tively, we offer no apology for noticing two important short sea passages which, though still unexecuted, will doubtless in some form be eventually carried out.
One of these canals is designed to obviate the navigation Proposed of the dangerous strait between Ceylon and the mainland Paumuen of India, which is shallow and narrow, and in some states caEa1, of the wind has a violent current, so that it can only be navigated by vessels of' small draught. Ships of the larger class have to circumnavigate Ceylon in making their passages to the eastern section of Hindustan. The importance of avoiding this detour round Ceylon of 350 miles of exposed navigation in the direct Suez route to Calcutta and Madras will be readily acknowledged, and the execution of the work cannot long be delayed.
The strait to which we allude is the Paumben passage leading from the Gulf of Manaar on the west to Palk Bay on the east, as shown in fig. 11, and many attempts have been made by blasting to clear away the rocky obstructions that at present render its navigation dangerous. But in order to provide a safe passage of the strait between Ceylon and India for the ships which now navigate the Suez Canal, nothing will suffice but a canal affording the same depth and width, though very much shorter in length than its great pioneer in shortening ocean sailing ; and accordingly surveys have been made and schemes have been proposed to effect this important improvement. Mr George Robertson, Civil Engineer, when inspecting the harbours of India, was asked by the British Government to visit the locality and report on these schemes ; and from his Report on Indian Harbours we find that the site he selected as most suit-able is through the island of Ramaseram, about a mile east from Paumben lighthouse. The distance across from sea to sea is about 2 miles, the ground being a flat sandy plain, raised on an average about 7 feet above high water, and from the borings that have been made it is not expected that much rock will be found in the course of the canal. In order to assimilate it to the Suez Canal the navigable depth should if possible be about 26 feet. On the north side the distance from high water mark to 30 feet at low water is, according to a chart by the Surveyor-General at Colombo, upwards of a mile; on the south side the distance to the same depth is still greater, so that very considerable works of dredging will be necessary in forming and afterwards maintaining the entrances to the canal. The south end of the canal is under shelter of a coral reef, but the north end may perhaps require to be protected by break-waters. The cost of cutting the canal has been named at £440,000.
The other scheme to which we referred has a far higher Atlantic importance, its object being to separate the continents of 3ncl Pacific North and South America, and to give a free navigation cani between the Atlantic and the Pacific Oceans, by overcoming the physical difficulties presented by the climate and the geological formation of the Isthmus that separates the two seas, to which has to be added the problem of making and maintaining a deep-water channel from the ocean to the entrances to the canal
This bold scheme, first proposed in the 16th century, has at various intervals been the subject of many deputa-tions and much correspondence between the American and European powers; and more recently, in 1845, when Louis Napoleon was confined as a state prisoner at Ham, he spent much of his exile in investigating its practicability, and in making arrangements for carrying out, under the name of the "Napoleon Interoceanic Canal," a passage between the two seas from Port San Juan to Port Realejo. But we have not space to record the various early attempts to realize this project, and must therefore confine our remarks, to giving an idea of the present state of negotiations regarding it.
The recent enormous growth of Californian trade has led to the revived consideration of the scheme by the United States of America, who would be the greatest gainers by the work, and therefore are its most natural promoters; and what we propose is to give a sketch of the present state of the question, as afforded by reports and documents recently issued by the Government of the United States, from which alone authentic information can be derived.
It appears from these documents that two routes have recently been investigated :First, that of the Isthmus of Darien, shown in fig. 12, under the direction of Commander Selfridge, U.S.N.; and second, that of Nicaragua, also shown in fig. 12, under the direction of Commander Lull, U.S.N. To both of these expeditions were attached a large staff, including naval officers, civil engineers, surveyors, mineralogists, &c, and their surveys appear to have extended over the years 1871, 1872, and 1873.
The results of these surveys are thus summarized in the report of the Secretary to the Navy, submitted to the Government of the United States in 1873, from which we take the following information. Of the Darien route, it is said that it includes 100 miles of navigation of the River Atrato, which has been carefully sounded, and found to be fully capable of being navigated by the largest class of ocean-steamers. Between Atrato and the Pacific a canal or artificial cut must be formed of 28 miles in length. The canal for 22 miles of this distance passes through a plain having a gradual rise of 90 feet. There will then remain 6 miles to the Pacific, three of which will be in moderate open cutting, and 3 miles will be tunneling. It is estimated that the work will cost between £10,400,000 and £12,600,000, and that it can be completed in ten years. The tunnel, being for the passage of ships of the largest size, is proposed to be 112 feet high and 60 feet wide, and is to have 87 feet of clear headway above the surface of the water. The canal is to be 25 feet in depth, with a bottom width of 50 feet, and a. surface width of 70 feet. The locks, twenty in number, are to be 427 feet long, 54 feet wide, with a lift of 10 feet. The water supply is to be derived from the Napipi river, and the gaugings and observations made on evaporation lead to the conclusion that there is a great excess of water above the supply required for the canal. Commander Selfridge gives two alternative schemes, by which the tunneling is increased in length and the number of the locks diminished, at an estimated cost of from £17,000,000 to £18,000,000 respectively.
The exploration of the Nicaraguan route, under Com- pr0p0sea mander Lull, the position of which is also shown in fig 12, Nicaragua.) is said to have proved the existence of a practicable route, Canal, having Lake Nicaragua as its summit-level, being 107 feet above mean tide. It is proposed by this route to connect the lake with the Pacific by a canal 16'3 miles -in length, beginning at the mouth of the Rio del Medio and terminating at Brito. The first 7 '5 miles will require an excavation averaging 54 feet in depth, and will be the most expensive part of the whole work. Ten locks and one tide-lock will be required between the lake and the sea. There will be 56 miles of lake navigation.
Slack-water navigation in the San Juan from its head to the mouth of San Carlos is considered perfectly feasible, and it is proposed to improve the river by four dams, at Castillo Rapids, Balas Rapids, Machuca Rapids, and at the mouth of the San Carlos River, at all of which places there are excellent sites for dams. A short section of canal with one lock will be required to get around each, of the upper three dams. From the fourth dam to Grey town in the Caribbean Sea an independent canal will be required 41'9 miles in length with seven locks, which apparently presents no difficulty. The total length of the proposed canal is 6P7 miles, and no tunnel is required. The harbour of Grey-town has been partially destroyed by a silt which comes from the San Carlos, and others of the lower tributaries of the San Juan, and the branch of the river leading to Grey-town has become so much filled up that it is now, at the lowest stage of the water, only 324 feet wide and 6 inches deep at the fork. It is proposed to shut off this branch entirely and send all the silt-bearing water through the Colorado mouth, which empties into the sea 18 miles from Greytown, and to admit to the harbour only the water of the canal, which, being drawn from the main river above the mouth of the San Carlos, will be perfectly clean. The harbour then cleared out, will leave nothing to deteriorate it again.
Short breakwaters will be required to protect the entrances from the surf, both of which are included in the estimate for the work.
Careful gauging at the lowest stage shows that Lake Nicaragua, which has a surface area of 2700 square miles, and a drainage area of 8000 square miles, will supply thirty-eight times the maximum possible demand of water.
The depth of water is to be 26 feet, the width, at bottom 72 feet, and at surface 150 feet. The locks, twenty-one in number, with a lift of from 8 to 10 feet, are to be 400 feet long and 72 feet wide. The estimate is stated at £15,900,000.
M. Lesseps, in a lecture on the Suez Canal, delivered before the Société des Gens de Lettres at Paris, has given it as his opinion that unless the Atlantic and Pacific can be united by simply piercing the Isthmus from sea to sea without locks, as at the Suez Canal, the proposed scheme cannot possibly succeed as a commercial enterprise, because of the inadequacy of a canal with locks to pass the traffic that will frequent it, and also of the uncertainty of sufficient water to supply the lockage and evaporation. This latter objection, however, seems to be disproved by the researches of the American engineers who have investigated the sub-ject. A further difficulty arises in maintaining a sufficient sea-water depth to the canal even after it has been formed. On this point the writer of this article, judging from docu-ments prepared under the sanction of the Government of the United States and submitted to him by an authorized official of the Government, arrived at the conclusion that there are very formidable obstacles to the establishment and future maintenance of a deep-water entrance to the proposed Nicaraguan Canal at Greytown in the Caribbean sea. These obstacles involve the engineering problem of maintaining permanent deep water through an extensive shallow foreshore composed of soft materials and exposed to heavy-seas. The reports state " that at Greytown there are now islands where twenty years ago there was water enough to float a frigate." It remains to be seen whether the same difficulties apply to the entrance to the proposed Darien scheme ; and, to show that such fears may not be un-founded, we may remind the reader that the difficulties exist, as we have stated, at the Mediterranean entrance to the Suez Canal.
The question as to the best route for transit between the Atlantic and Pacific is, it will be seen, still far from being solved, but the necessity for free access from sea to sea remains an acknowledged fact. Its importance, especially to the United States, but in some degree to all the world, is such that, great as are the engineering difficulties, this long-cherished bold idea may yet become a stupendous reality. (D. s.)
Reference is made to the following works:Chapman, On Canal Navigation; Frisi, On Canals; Fulton, On Canal Navigation; Tatham's Economy of Inland Navigation; Valiancy's Treatise on Inland Navigation; Principles and Practice of Canal and River Engineering, by David Stevenson, 2d edition, A. andC. Black, Edinburgh ; Report of the Secretary of the United States Navy for 1873
Quarterly Review, No. cxlvi. p 281
Frisi On Canals, p. 154.
Quarterly Review, No. cxlvi. p 281
Travels of Marco Polo, by Col. Yule, C.B.
Smeaton's Reports, vol. i. p. 55, London, 1812.
Smeaton's Reports, vol. i. p. 74, London, 1812.
History of Inland Navigation, particularly those of the Duke of Bridgewater, London, 1768 ; Hughes's Memoir of Brindley ; Weale's Quarterly Papers, London, 1843.
5 Smiles's Lives of the Engineers.
1 Life of Telford, London, 1838.
2 Fulton's Canal Navigation.
Minutes of Proceedings of Institution of Civil Engineers, vol. v. p. 340.
Stevenson's Sketch of Civil Engineering in North America,
London, John Weale.
3 Minutes of Proceedings of Institution of Civil Engineers, vol. xiii j p. 205.
IV. - 99
Ibid., p. 25. 5 Ibid., p. 1.
1 Minutes of Proceedings of o Institution of Civil Engineers, vol
xxvi. p. 1.
Ibid., p. 6.
Ibid., p. 10.
Lift of Telford: Caledonian Canal.
Report on, the Caledonian Canal to the Admiralty, 1849, by James
Veitch, R.E., and David Stevenson, C.E.
Mémoires du Baron de Tott, sur les Tures et les Tartares, Amsterdam, 1785, vol. ii. p. 271.
Proceedings ofthe Royal Society, 1870, p. 132.
Report on the Maritime Canal connecting the Mediterranean at Port Said with the Red Sea at Suez, February 1870.
The History of the Suez Canal, by F. de Lesseps, translated by Bir H. D. Wolff, 1876.
1 Minutes of Proceedings of o Institution of Civil Engineers, vol
xxvi. p. 1. 2 Ibid., p. 6. * Ibid., p. 10.