ON THE RESISTANCE WHICH A SHIP IN MOTION MEETS WITH FROM THE WATER.
We come now to the consideration of a subject. embarrassed with difficulties of no ordinary kind, and which will continue to retard the advancement of na val architecture, so long as its primary laws remain imperfectly developed. The resistance of fluids has engaged the attention of some of the profoundest philosophers; and when we mention that the labours of Newton, of Huygens, of Euler, of Daniel Ber noulli, of D'Alembert, of Don Juan, of liouguer, of Condorcet, of Borda, of Bossut, of Chapman, of Clairbois, and of many others, have furnished us with little more than theories distinguished for ingenious speculation, and examples of the beauty and power of analysis, with few, if any practical maxims to guide the constructer in the choice of the primary elements of his ship, our readers will only join us in regretting, that a subject so intimately connected with the pro gress of naval architecture, should yet be so entirely in its infancy, and so far removed from any thing like practical perfection.
In the Annals of Philosophy for December 1824, Mr. Harvey has remarked, in a paper on this inter esting subject, that had the subject been one which "individual industry and sagacity could have success fully prosecuted, there can be no doubt but its com plete solution would have been long ago achieved, or at least some large and important steps made towards its completion. But, unfortunately for the sake of science, and for the naval service of the country also, this is not the case. '' The problem," says he, " is one which involves too many difficulties for any indi vidual to contend with, unless that individual pos sessed talents of the very highest order, uninterrupt ed leisure, and the necessary command of money" " three elements," says Mr. H., often united in the same person; and as the past has not afforded a fortunate example of the kind, we may almost fear the future will not be more propitious." It is perhaps true, as the author of the foregoing quotation has remarked, that the completion of the problem of resistances will scarcely be accomplished by individual talent and industry; but it is more than probable that the germ of a correct theory, whenever it appears, will be the result of individual sagacity and thought. It certainly opens a curious and inter esting field of inquiry, why so much apparently well directed labour should have produced so little that is of practical importance and value; and why. at a pe riod, when so many other departments of physical science have attained to such high comparative per fection. the science of Hydrodynamics should yet be involved in so much uncertainty and error.
A careful analysis of all the theories that have been offered on this important subject, and of the experi ments on which they are founded, the circumstances also under which these experiments were performed, together with the peculiar views of their authors, bringing all to the test of the known and established principles of Mechanics and Hydrostatics. might perhaps unfold to us some of the causes that have re tarded its advancement•. Such a review would, at all events, as Mr. Morgan has remarked in one of his papers on Naval Architecture,* be "most likely to lead to some practical results, by ascertaining what is fairly and certainly established: and by showing the merits and defects of the different theories. be the
means of determining the propriety of adopting parts of some theories, which, as wholes. may be inadmis sible." Such a review, if attended with no higher benefits, "would at least have the advantage, by an acquaintance with what has been written on the sub ject, of preventing the unnecessary labour of retrac ing the steps of others; either leading to the further investigation of a theory, from a point to which it is arrived, or suggesting researches in other direc tions." But a remarki has been lately thrown out respect ing this subject, by the Academy or Sciences of Paris, —a body which has done more to encourage theoreti cal and experimental inquiries on this question, than any other learned society in Europe,—that " almost all the attempts which have hitherto been made for discovering the laws of the resistance of fluids, are contrary to the first rule of experiments, by which we ought to endeavour to decompose the phenomena into their most simple elements. It has been most common indeed, to observe the time employed by different bodies, in describing a given space in a fluid at rest, or the weight which keeps in equilibrium a body exposed to the impulse of a fluid in motion. But this can only make us acquainted with the total result of the diffi:rent ac tions which this fluid exerts upon each of the points of the bodies, actions which are very varied, and often op posite to each other. In this state of things, compensa tions take place, which mask the primitive laws of the phenomenon, and which render the results of experi ment inapplicable to any other case but that which has furnished them. M. Dubuat. author of the Principes d' Hydraulique, appears to have been the first who per ceived this defect; and, in order to avoid it, he en deavoured to measure the local pressures on the dif ferent parts of the surfaces of bodies exposed to the impulse of a fluid in motion. His experiments, though small in number, and not much varied in so far as the form of the body is concerned, present, nevertheless, many curious results. Under these circumstances, the academy thought it would be useful to resume these experiments, with more perfect instruments, to multiply them, and to vary the circumstances still more. And in following up these important views, the academy has proposed for the subject of a prize,t the following programme: "To examine in its details the phenomena of the resistance of water, by determining with care, by exact experiments, the pressures separately sustained by a great number of points, properly chosen in the anterior, lateral, and posterior surfaces of a body, when it is exposed to the impulse of a fluid in motion, and when it moves in the same fluid at rest; to mea sure the velocity of the water in different points of the current near the body; to construct from the re sults and observations, the curves which these cur rents form;§ to determine the point where their direc tion commences before the body; and finally, to es tablish, if possible, from tile experimental results, empirical formulae, which might be afterwards com pared with the experiments formerly made on the same subject." Let us hope that these new experi ments may be attended with all the advantages desir ed to naval architecture.