AMERICAN QUARTERLY REVIEW.

No. III.

SEPTEMBER, 1827.

ART. I.-Theorie du Navire par le MARQUIS DE POTERAT, Chevalier de l'ordre Royal et Militaire de St. Louis, Capitaine de Vaisseau, &c. &c. Paris, 1826, chez Didot, 2 vols. 4to. pp. 384 and 456.

Of all the objects of art, none appears, upon the first view, to give so high an idea of the extent of human power, as the Ship. It is, indeed, the most difficult achievement of the genius of man. The very act of launching a raft upon a peaceful lake, must, in the first instance, have required an effort of courage.

But how great is the interval between this rude attempt, and that state of art which constructs the Indiaman, or the first rate ship of the line! the one capable of bearing a vast cargo, of supporting the violent efforts of the winds and waves, and guided by scientific methods of pursuing its undeviating way, although for months out of sight of the land; the other, in addition, loaded with the artillery of a fortress, teeming with a legion of valiant spirits the most formidable of all offensive means furnished by the improved arts of modern warfare.

One branch of nautical science may indeed be considered as having in our own days attained a state, which leaves so little apparent room for improvement, that it may almost be called perfection. We mean that part which teaches to determine the

place of the ship, for the purpose of choosing the proper course to its destined port, or enabling it to shun the dangers it is exposed to on approaching the shore.

Such is the progress made in the construction of astronomical tables, in the manufacture of instruments, and in the methods of observation, that no uncertainty ought to remain in relation to the vessel's place, except when the sky is obscured; and the loss of a vessel, from ignorance of its true position, has become in truth a crime, and as such deserves punishment. For this happy state of things, the mariner is indebted to persons of other professions than his own. The researches necessary to attain it, may fortunately be performed independently of nautical skill; and thus it is to the patient observer of astronomic phenomena, the laborious calculator of the motions of the heavenly bodies, and the ingenious framer of delicate instruments, that they are to be ascribed. The arts of naval architecture, and mere seamanship, if at first sight more simple, than those which rest on astronomy, are, when closely examined, far more difficult. A much greater variety of knowledge is requisite to advance them beyond their present state, than need be devoted to the other department; and it rarely or never happens, that this knowledge can be united in a single individual. The strength and mode of combination of the materials, the forms of greatest stability and least resistance, the proper position and magnitude of the masts and yards, the trim of the sails, the manner of guidance, by which, on particular courses, vessels may oustrip the wind itself, are indeed, strictly speaking, investigations within the reach of science. But this science is not purely mathematical; it must rest for its basis on physical experiments, and those which the philosopher can perform in his closet, are neither sufficiently varied, nor upon such a scale as to afford a suitable foundation. The sea itself must be navigated, its action on vessels practically known, as well as that of the winds; and the mathematician should possess as preliminary knowledge, the practical acquirements of the veteran navigator. Few men, however, who devote themselves to mathematical study, have either the power or the inclination to attain this practical skill; while on the other hand, few nautical men have that preparation, growing out of mathematical knowledge, which will qualify them, to observe and apply to useful purposes, the phenomena they may witness on the ocean. In addition, the ship builder rarely possesses any great extent of science, and still more seldom a practical acquaintance with the manner in which his structures perform their allotted task; he, generally speaking, copies servilely the models and framing of his predecessors, or changes them without an enlightened purpose, at his own pleasure, or according to the suggestion of the nautical man, equally deficient with himself in the scientific part of his trade.

It is to these causes that we must attribute the different impressions produced upon us, at the first view of the finished vessel, equipped and manned, and spreading its canvass to the wind, and upon a more close examination of its parts. We then discover inherent causes of weakness, that bring about the destruction of the ship, long before that could be effected by the natural decay of its perishable materials; framings combined in an unartistlike manner; the strength of the materials ill distributed in the same vessel, and rarely proportioned to the varying sizes of different vessels; in short, multiplied errors, easy of detection, but of which the remedy is not as readily discovered. Some of these, however, are already within the reach of scientific inquiry, and many others will be brought to light by the more careful cultivation of the theory.

The qualities to be combined in a good ship are numerous, and in many respects so opposite, that it is generally considered necessary to sacrifice some of them to obtain the others. For whatever purpose a vessel is intended, it must always bear a great burthen, composed of its cargo, whether mercantile, or military, and the weight of its own materials; it must be strong and solidly built, in order to resist the effort of the several forces that are constantly acting upon it; it must be impermeable to the fluid in which it floats, lest by entering in too great quantities, the articles embarked should be injured, or the vessel actually sunk by its weight; it should have a shape and distribution of parts, that will allow it to obtain the greatest possible velocity, and to manœuvre with the greatest readiness, so that, if a merchant vessel, it may perform its voyages with proper speed, and if a ship of war, may seek, or avoid an engagement at pleasure, and choose a favourable position in respect to its enemy; its hull must be sufficiently capacious to contain all the articles it is intended to transport, and to provide for the comfortable lodgment of its crew it must possess stability, or have the property of restoring itself to an upright position, when made to deviate therefrom by the action of the wind or other extrinsic forces; its two opposite sides must be exactly similar, not only in bulk, but in weight; and in the case of a ship of war, it must carry its artillery in such a way, that the guns may be easily served, and that the water may not enter through the ports, when the vessel heels under the effort of the wind; it must not be liable to violent rolling, or pitching, by which, in an agitated state of the water, the masts might be carried away, or seas shipped, that, entering at the hatches, would destroy the comfort of the crew, damage the cargo, or even sink the vessel.

To combine and unite such properties in a perfect manner, is a task that would require the union of consummate experience, and the most profound science; but rarely have these been com

bined, in the efforts which have been made to improve naval science. The construction of ships has, for the most part, been confided to mere workmen; their navigation to nautical men, exposed from their youth to the dangers of the sea, and who, worn out by the fatigues of their laborious profession, have neither the leisure nor the tranquillity of mind necessary for the study of the extensive and complicated science in which the principles of their art are to be sought; the theory is, on the other hand, cultivated by those alone, who, from the very nature of their pursuits, instinctively shun the fatigues, inquietudes, and dangers in which the seaman passes his life. We may thus easily conceive how it happens, that the theory of naval architecture and seamanship is still far behind the practice, and that improvements in the structure and navigation of ships, have grown rather out of observations on the accidental properties of vessels of different forms and constructions, than from the cultivation of scientific principles. Still, we are not to be ungrateful for the assistance which has been drawn in these observations from the investigations of scientific persons, who have facilitated the methods of discovering and applying remedies proper for the defects of some vessels, and of ascertaining to what particular features in others their good properties were owing. To them too, we are indebted for rules and principles which will direct and limit the variations that may safely be made in the models at present in use, and guide us in the draught of new ones, suited to those changes in the force and magnitude of the several rates of vessels, which are continually making, in the strife between the various nations of the civilized world, in respect to the good qualities of their ships of war. Such, in truth, is the value of scientific inquiry in this important branch of the useful arts, that those nations who have been most ready to adopt in practice, the suggestions of science, have uniformly possessed ships the best suited for sailing and fighting, and the least liable to the dangers of the sea. Of this we have a most marked illustration in the long contest for naval supremacy between France and England; the former nation having, from the close of the war of 1756, nearly down to that of the American war, baffled the fleets of England, and reaped all the advantages that would have flowed from actual victories, by the superiority of their ships in speed, and readiness of manoeuvre; nor was this advantage lost, except by an entire change in the system of naval tactics, which diminished for the moment, the importance of these qualities, and brought into play the more practised seamanship of the English. Throughout this period, we constantly find the French, after doubtful engagements, in which the apparent honour rather inclined to the side of their enemy, striking the severest blows upon the British colonies and commerce; and it appears now to be admitted, that

had the new tactics been fully understood and anticipated, and been met with a corresponding change of disposition, the advantages they derived from the structure of their vessels, might still have been maintained. This remarkable change in naval tactics is now allowed, upon all hands, to have been the result of the abstract reasonings of a landsman, (Clerk, of Eldin). It was cautiously and almost reluctantly followed by seamen, and was first implicitly and unreservedly adopted by Nelson, who, at the Nile and Trafalgar, showed the wonderful effects of which it was capable.

The Spaniards imitated the French in the application of science to their naval affairs, and thus, in the wars of the French Revolution, their ships were remarkable for a combination of all the good qualities both of French and English naval architecture, of which the most remarkable instance is to be found in the Santissima Trinidada, a ship of four decks, uniting vast force, to speed and stability, and built at a time when the French had almost abandoned, in despair of success, the construction of ships even of three decks; and when English ships of the second rate were so deficient in the necessary qualities, as to be by no means a fair match for the larger class of French two-decked ships, under equal cireumstances of crew and officers.

The first instance we meet, of an attempt to apply the principles of theoretic mechanics to the nautical arts, is that of Pardies, in 1673, who, in a treatise on statics, inserts as a problem, the method of determining the course of a vessel, acted upon by a lateral wind. He was followed by the chevalier Renau, in 1689, who proceeded upon the same basis as the former author, but who adopted, in addition, the received doctrine, that the resistances of fluids to surfaces, was in the ratio of the squares of the velocities, and of the squares of the sines of the angles at which the fluid struck the surfaces. We shall have occasion hereafter to point out the error of this doctrine. The publication of Renau's work, led to an investigation of his theory by the celebrated Huygens, and in the discussion that ensued, James and John Bernouilli took an active part. The work of the latter of these two distinguished brothers, published by him at Basle, in 1714, is a brilliant example of mathematical skill, but has not for its basis a sufficient theory derived from experiment. It is therefore hardly susceptible of any practical application.

Passing over a variety of writers of inferior note, we proceed to the treatises of Bouguer upon the masts of vessels, published in 1727, and upon the construction and motion of vessels, printed in 1746. The first of these, although derived from more correct principles, than the works of previous authors, contained deductions which are impracticable in their application, but the second is of a much more valuable character. The extent of the