elementary principles, which are deduced from the most accurate experiments and observations, and established either immediately from those observations, or by the most rigorous mathematical investigation; and serve to explain the facts themselves, or the appearances observed. Such, for example, is Newton's theory of gravitation.* Practice is nothing but the application of some one or another of these discoveries to some useful purpose, the skilful application and management of which, then, becomes an art. Various opinions or hypotheses may pass for theory; such as the vortices of Descartes, or the supposition of Symmes, relative to the imaginary opening near the North-pole of our earth. Such conjectures or rhapsodies may, however, be always distinguished from theory, or true science, from their not being deduced from facts or accurate experiments. They can have, therefore, no more foundation in nature than the fanciful creation of the poet, when indulging his most wild, or sublime flights and excursions; for it is not every one who bestrides his nag to Parnassus, who is a poet, nor is it every one who hails under the flag of Newton, who is a philosopher.

We now and then find, however, that practical men, who appear entirely ignorant of the theory of their art-from the nature of their avocations, which must, necessarily, afford them many opportunities for observation-occasionally make some discoveries which, to them, seem new. It happens, that even facts resulting from some of their experiments, are considered by them as entirely contrary to theory. This seems to us to be, in a great degree, one of the prominent features of this otherwise important work of Mr. Fairbairn, and it is this circumstance alone, so strongly characteristic of the works of mere practical men, however useful in other respects, that has induced us to extend our general observations much further than we at first intended, or, perhaps, the subject required.

In works where to eminent practical skill, a considerable portion of theory is united, the contrast is strikingly obvious. We could instance in illustration of this remark, among others, the works of Mr. Thomas Tredgold, and among them, his "Practical Treatise on Rail-roads and Carriages;" unques

*We might instance a variety of theories; such as the theory of the telescope or microscope, of the phenomenon of the rainbow, of music, of locomotive or stationary engines; the atomic theory, the theory of the operation of emetics or cathartics in medicine, or that of the malaria, &c. The former of these enumerated theories are founded on rigorous mathematical investigations, the latter depend, for the most part, on observation alone, or opinion. In short, there is no etfect in nature, without a cause; now it is theory that must assign that cause, and consists in assigning it by means which are convincing and satisfactory.

tionably the best hitherto published on the subject. Most of the late publications, which have come under our notice, are generally mere reports, with scarcely a ray of science to pervade the gloom that so generally envelopes these subjects.

The celebrated Prony, no less skillful as a practical engineer, than profound in every department of science, has, however, done much to dispel this obscurity, particularly in his "Nouvelle Architecture hydraulique," a work, which-though of a far superior grade in point of science, and especially mathematical, to Tredgold's-it may be doubted, whether it would benefit the practical man as much as that of Tredgold's. For works of this nature, unless adapted to the present state of knowledge among practical men, can profit them but very little. We have known some whose reputation stood high as engineers, architects, &c. and who have been engaged in controversy in extensive newspapers, and other publications, on the most difficult subjects connected with these departments, who were obliged to have resourse to those who could translate for them, the simple formulas of Tredgold from the algebraical into their vernacular language. Now of what use could Prony's works be to such engineers, when no sooner does he get hold of an elementary or physical principle, than he immediately wraps it up into so many folds and labyrinths of the modern calculus, that scarcely a trace of it remains. We should have the same objection to the able "Memoires" of M. P. S. Girard, lately published among the "Memoires" of the French Institute, on Canal Navigation; for the simple principles there developed do not require a formal display of analysis, and will be sure to deter the practical man from availing himself of them. M. Girard is, however, comparatively moderate in this regard. In such works as the "Mecanique celeste," or the "Mecanique analytique," where the great leading principles of mechanical science, are not only systematically established in detail, but also generalized and extended, the application of all the powers of the analytic art becomes necessary, and it is to such works that the man of science must have recourse; but we apprehend that, in practical works, this unnecessary display of science should be as much as possible dispensed with, particularly when the simple elementary principles themselves are, in general, more efficient, and much more satisfactory.

In the few observations we have yet to offer, we shall not occupy the time of the reader in discussing the history of either railways, canals, or locomotives, as there is scarcely an essay on these subjects, but professes to give their history, although much might be exhibited as yet on the subject, and much fairly

contested. The extent of the real claim of most inventors, is not so easily ascertained as most writers suppose. Not wishing to enter into this discussion on the present occasion, we shall now confine our observations principally to Mr. Fairbairn's work. He thus introduces his remarks::

"Since the first formation of canals in this country, there has been very few attempts made, to improve the construction of vessels, adapted to an inland navigation. The passage boats of the present day are nearly the same as they were fifty years ago; and little, or rather no improvement has taken place in the heavier description of vessels for the conveyance of goods. Probably this might have gone on in the same state of supposed perfection, had not the introduction of Railways, which are now in progress, occasioned such a sensation in the country.

"From the first commencement of canal navigation up to the present time, the average speed of conveyance has never exceeded four miles and a half per hour on passage boats, and two miles and a half on heavy flats. This seems to have been the maximum velocity, and it was taken as an established rule, that boats could not be conveyed along canals at a greater rate, without incurring loss, and a considerable increase in the cost of transit.

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My particular attention was, in the month of January last, drawn to the very obvious defects in canal navigation, by Mr. Thomas Graham of Glasgow, who had, for some years before, been giving a great deal of attention to the improvements on canal navigation, by the introduction of steam as a moving power.

"At that period Mr. Graham had so far succeeded in drawing the attention of the managers of the Forth and Clyde Canal, and of the Union canal, to the superior advantage of steam power, that the committee of each of these companies had contracted for the construction of a steam boat to ply on their respective canals, in that branch of business which appeared most favourable for the introduction of steam power in each. The boat contracted for by the Forth and Clyde Canal, was on the American plan, with the paddle behind, Mr. Graham having procured a plan from New-Orleans of a boat of that description plying on the river Mississippi." pp. 5-7.

After mentioning various discussions which he had with Mr. Graham and others, Mr. Fairbairn at length forms a decided opinion that not only a regular, but a very speedy communication might be obtained by means of steam-power, provided the vessels could be built sufficiently light and spoonshaped, like those boats which Mr. Graham informed him were used on the passage between New-York and Albany, and, it was asserted, could maintain a speed of nearly fifteen miles an hour.

"Mr. Graham requested me, (continues Mr. Fairbairn) to give the subject my best consideration, in order to see how far such a light des

cription of boat, having a small draft of water, would be applicable to quick speed, and whether steam could not be used as a propelling power on canals.

"The fulfilment of Mr. Graham's instructions was surrounded with difficulties of no ordinary character; such as the resistance of fluids to moving bodies, the agitation of the surface and the consequent danger to the banks of the canal, arising from the surge or wane occasioned by vessels propelled at a quick rate. These and many other obstacles presented themselves. Not the least, however, was the power requisite to raise and maintain an accelerated velocity in bodies, opposed by such a powerful resistance.

"The source to which I looked for improvement was steam; a judicious employment of which might remove the difficulties, and furnish power sufficient to overcome all obstructions. Steam engines of the usual construction from their great weight, seemed but indifferently calculated for propelling boats on canals, as the draft of water would be increased, and greater risk of injury to the banks would be the consequence. Engines on the locomotive principle, from their portability and lightness appeared best fitted for the purpose.

"This being a settled point, the next consideration was, how to employ the engines to advantage, how to give perfect security, and at the same time, how to produce at least a double velocity, without incurring the injurious tendencies already detailed. This was certainly a desideratum more to be wished for than expected. We all know that force must be applied to a body to move it through a fluid; that such surface meets with opposition from the resisting fluid; and that resistance is stated to increase with the squares of the velocity. These points being taken for granted, it will be seen that there was much to contend with in surmounting such formidable obstacles. Taking as a datum what has been already stated, that the resistance of fluids to passing bodies is as the squares of the velocities, I had then to calculate what power would be requisite, to give the increased speed to boats of different tonnage, and to produce a force equal to the resistance, as laid down by scientific men, who have treated on this subject." pp. 9-11.

In the mean time Mr. William Houston, of Johnstone, and before Mr. Fairbairn had commenced his operations, made a very interesting experiment on the Ardrossan Canal,* the results of which he cominunicated to Mr. Fairbairn.

"The experiment made by Mr. Houston consisted in the introduction into the canal of a common gig-boat, in which ten or twelve passengers were seated; after which the boat was drawn through the canal by a single track horse, at the rate of twelve miles an hour, without either wave or surge.

It is remarked at p. 23 of this work that "it may be proper to mention that the Ardrossan Canal is throughout very narrow; at the bridges, and many other places it is only nine feet broad. It has a great number of turns and many of them very sudden."

"In pursuance of this experiment, Mr. Graham on his return to Glasgow, proposed to have it renewed on the Forth and Clyde Canal; but on examining the gig-boat, with which the experiment was made, he found it was so light and unsteady, as to give an idea of want of safety to passengers; and he was afraid that if a larger and stronger boat were built it might have the same faults, and at all events it would be so crank as to be unfitted for the application of steam power. To avoid these difficulties, and to obtain steadiness and security on the water, the idea of a twin-boat, of the description of the single boat suggested itself to Mr. Graham, and to prove the suggestion, an experiment was made of which the following account appeared in the various newspapers of the day." p. 12.

Thus far we have been particular in retaining the precise words of Mr. Fairbairn, who, surrounded as he was with difficulties of no ordinary character-for he had to contend against theory, the squares of the velocities, &c.—appears to have originated nothing of any consequence; and, as if his mind had been entirely preoccupied with that portion of theory, where the squares of the velocities are introduced, he appears to have overlooked every other, that might have had a bearing on his inquiries; as, for example, the depth at which the vessels were immersed at the different velocities; the height of the surge above the level of the canal; the inclinations of the planes, or the portions of his vessels exposed to the action of the water, the sines of which, or their squares or cubes, according to circumstances, are important functions in these inquiries. We shall presently see that it was on the developement of these principles as established by theory, that the success of the experiments principally depended, and had the operation of these laws been understood or adverted to, it would have been soon discovered how easily they could reconcile the experiments with all the apparent contradictions of, or deviations from theory. It will, in fact, be found that theory in general is far in advance-in many instances, a century or more-of experiment, and if consulted, or understood, many an expensive lesson in the school of experience, however useful when guided by science, might be dispensed with.

The following experiments were made at the suggestion of one of the committee of management of the Ardrossan Canal, and as they shew the very high rate of speed that may be obtained at a trifling expense, and without injury to the banks by any agitation of the water, we deem them too interesting to be omitted here.

"A gig, such as is used in rowing-matches was hired, and being launched on that canal, it was found that she could be drawn along