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nearly simultaneous date, we deduce the modern improvements in navigation. By means of these improvements, the most distant parts of the world are brought comparatively near to each other, and the ocean, that might at first sight appear to be a barrier to the intercourse of nations, becomes their common highway, and the link that unites them in one great family. A ship of 500 tons burthen does not require more than fifteen men to navigate it, and performs the voyage between the ports of Liverpool and New-York, in an average time, that, of late years, does not exceed a month; six passages, or three complete trips, are readily performed in the course of a year, making ample allowance for detention in port, and the performance of necessary repairs. Were animal power, to be substituted for the action of the wind in this trade, such a vessel would require to propel it with the same average speed, the power of eighty horses, or of five hundred and sixty oarsmen.

Such are the advantages to be derived from the navigation of an ocean, over which blow winds, varying in intensity and direction indeed, but nearly constant in duration. Advantages of less amount, but still of important value, are derived from the navigation of great rivers and lakes, and of arms of the sea; with these, the portion of the American continent possessed by the inhabitants of the United States, is intersected in a manner that affords the most ready communication between many of its most important and interesting parts.

As rivers decrease in magnitude and importance. or as their currents become more rapid, the application of wind as a moving power, becomes of less and less value, until it is finally inferior, in every valuable result, to animal strength; for the more convenient application of this natural agent, towing paths should be formed upon the banks, and the rivers are converted into canals having but one level.

There are many rivers deep enough to permit the passage even of large vessels, and that have no obstruction, of moment, in their beds; but which, in consequence of the rapidity of their current, will not admit of a descending trade. If dams or weirs be erected across such streams, at proper distances from each other, the velocity of the intermediate water will be much lessened, its volume and depth will be proportionably increased, and, from a combination of these two circumstances, it will be fitted almost equally well for vessels ascending or descending its channel. But over the weirs the water will pour itself, when the intermediate space is full, with great velocity, forming, in most cases, a waterfall

. In order to permit the passage of vessels, spaces are left in the walls; to these are

at first adapted sluices, that, when improved, became locks. Locks may also be applied upon lateral cuts, where the river is interrupted by falls or rapids.

River navigations, unless the channel be deep and capacious, and the volume of water great, are attended with risk and uncertainty ; in summer there will be a deficiency of water; in times of heavy rain, and during the melting of the snow, in such climates as ours, the current will be so violent as to render the passage of boats downwards extremely dangerous, and upwards impossible; hence experience has shown, that it is in all cases better to construct an entire lateral cut or canal, than to trust to the natural channel of the river. Nor does the

application of canals stop here; wherever water can be found in abundance, or carried by artificial means to the summit of a dividing ridge, a canal may be constructed, and its benefits extended. On a canal, a horse that, upon a railway, does not, as we have already stated, draw more than ten tons at the rate of two and a half miles per hour, becomes capable of drawing thirty tons with equal velocity; and thus the mechanical value of the former, is to that of the latter, in the proportion of three to one, while the latter possesses a tenfold advantage over the best roads. Other circumstances, however, may arise, to place the railway more nearly on a par with the canal; it is less costly in its construction, may be used in any situation whatsoever, being applicable to the most mountainous countries ; and is independent of supplies of water, that, in some particular cases and climates, are not to be procured. In England, it is found, that a railway costs no more than a third of the price of a canal; but in this country, it is probable they would approach more nearly to an equality in this respect. It is, upon the whole, to be inferred, that if animal power be the agent employed, and local circumstances will permit, the canal is, whenever practicable, to be preferred to the railway; for the advantages of a canal may be obtained even in mountainous countries, should any substitute for locks suited to such localities be successfully introduced into practice. Of such substitutes, the inclined plane is that which presents the greatest chance of successful application; and in the printed reports of the commissioners of the Morris canal, a contrivance of this kind is described, in which we perceive no one of the difficulties to exist that have hitherto prevented the general introduction of this principle. It is to be regretted, that a delay has occurred in making a full improvement upon it; a delay that has not only impeded the progress of the scientific part of this subject, but has been most Vol. II.

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injurious to those who have embarked their funds in this once promising speculation.

The cultivated genius of our countryman, Fulton, has introduced into navigation a new power, which bids fair, upon great rivers or lakes, and upon the ocean, to supersede in a great measure both animal power, and that cheaper, although less certain agent, the wind. To him we are indebted for applying with success, the improvements made by Watt in the steam engine, to the propulsion of vessels. They have already, upon the great rivers and sounds of our Atlantic coast, superseded all other modes of conveyance in cases where the time of passage, or the certainty of arrival, are matters of importance, and thus travellers seldom are found choosing any other conveyance than the steam-boat, and even light and valuable freights are frequently shipped in them from choice. Upon the Mississippi and its branches, where the current is rapid, they monopolize the freight as well as the passengers. The safety of steam-boats upon the most tempestuous seas, has been fully tested, and the time is at hand when they are to be applied to the longest voyages. No difficulty, indeed, remains, except the great bulk of the fuel, and the improvements that are daily taking place in the steam engine, promise to obviate this in a very great degree. Nature, however, opposes a limit to the velocity that a steam-boat can acquire, even in the deepest and widest waters; the resistance of fluids increases with the

square of the velocity, and thus, to increase the power of the engine, will give no practical advantage beyond a certain limit, that is within the reach of a calculation, that, although its principles are obvious, does not appear hitherto to have been made. But in practice it will probably never be necessary to approach this limit.

As the channel decreases in size below a dimension that has reference to the size of the vessel, the resistance of the fluid increases, until, in small canals, this increase is found not to differ much from the ratio of the cubes of the velocities; and hence it is yet problematical, whether steam can be applied to more advantage than animal power in the navigation of canals, were there no other impediment than this. . But when steam is applied to propel a boat, a large wave is thrown back by the wheels, and in increased velocities beyond three miles an hour, a wave is also raised by the prow of the boat. These act to tear down and wear away the sides of the canal, and hence steam-boats are inadmissible into artificial navigations, and even the velocity that may be given by animal power, to lightly load

ed vessels, is injurious. This last fact has been experienced upon our western canal, where the banks have needed constant repairs, in consequence of there being no regulation for limiting the speed of the vessels, and where it has been found absolutely necessary to pave the sides of the canal. We may, therefore, conclude, that steam engines can never be introduced into boats that navigate canals, with any hope of success. Another mode has been proposed, which consists in applying endless chains to the boats; these chains are stretched between two stationary steam engines, by the machinery of which they are caused to revolve, boats may be fastened to either side of the chain, and thus drawn between the drums over which it passes. The wave thrown back by the wheels is thus obviated, but that raised in front remains, and the acceleration of the boat is retarded by a resistance increasing nearly with the cube of the velocity. From all these facts, there is every reason to believe, that the practice of inland navigation is not to reap any great benefit from the improvements that are daily taking place in the steam engine. With railways the case is far different; the friction of wheels upon solid bodies is a constant quantity, and has no relation to the velocity; hence, when a body is once set in motion, a very small additional effort is necessary to increase its speed in a very great degree. When the power applied is one whose velocity is limited, whose maximum effort is performed at a low speed, and which loses in effective power, with every acceleration, no advantage is to be derived from this principle; this is the case with animal strength. But the moment that we begin to apply steam as the moving power, the difficulty vanishes; we are yet to learn by experiment, the velocity that would become unsafe and inconvenient in the application of steam to the motion of carriages, while in calculation, that at which the resistance of the air would become a sensible quantity, is extremely remote. It is, however, only very recently, that the steam engine has assumed a shape that would fit it for the draught of carriages upon rail-roads. It is, indeed, upwards of fifty years since Cugnot attempted, and, as is said by French authors, successfully, to propel a wheel carriage by steam. But his discovery, even if successful, was abandoned, as all discoveries must be that are too much in advance of the general knowledge of the age. The possibility of the same application of steam certainly occurred to Watt, who also was aware of the ease with which his own engine could be applied to the purposes of navigation; of both these facts we have evidence from those who enjoyed his conversation, and the idea is embodied by Darwin, his intimate

friend, in prophetic verse,* at least ten years before Fulton succeeded in applying Watt's discovery to the motion of vessels, by means whose very beauty and simplicity have deprived his family of advantages that a crowd of inferior inventors enjoy.

But the engine of Watt is not applicable to the rail-road; the water of condensation is in itself a load for the machine, and the necessity of frequently replacing it by fresh supplies of cold fluid, is a complete bar to locomotion. The effect might, indeed, be produced by numerous stationary engines placed along the line of the railway, with endless revolving chains set in motion by them, but such an application would be both inconvenient and expensive.

It is to Trevithick that we owe the invention of an engine fitted for locomotion. His improvements in the high pressure engine are not prior to those of our countryman Evans; but while the latter directed his attention to navigation, the former had in view the application of steam to draught. He was so far successful, as to give to wagons heavily loaded with coal, a velocity of five miles an hour; but even in the vicinity of the mines it was found more expensive than canal navigation. In this original application of the locomotive engine, which we saw near Leeds, in England, in 1815, a fifth wheel was added to the carriage conveying the engine; this was made to revolve by the piston of the engine, through the intervention of a crank, exactly as the water wheels are propelled in Fulton's steamboat; its circumference was cut into logs which applied them. selves to the teeth of a rack laid as a third rail. In theory, there might appear to be no limit to the velocity that might thus be given after the load was once set in motion, by increasing the number of strokes of the piston, or making this wheel, instead of acting directly on the rack, turn a pinion on the axis of another wheel. But the difficulties that arise in practice from the imperfection of workmanship, and the nature of the materials of which wheels and racks can alone be cheaply and solidly constructed, are such as to affect the law of the action of friction in this particular instance. Hence a variety of simultaneous attempts occurred, but were unsuccessful. In one, an apparatus similar in its mechanism to the muscles and bones of a human leg; was used, and in another it was attempted to force the carriage forward by the friction of one of its wheels, that was made to revolve by the engine upon one of the lateral

* “ Soon shall thy arm, unconquered steam, afar

Drag the slow barge, and whirl the rapid car," &c.

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