Dr. Young observes, that the question respecting the best disposition of the timbers of a ship is by no means so easily discussed as may be supposed by those who have considered the subject but superficially; and deprecates, on the one hand, the forming a hasty determination from a few plausible experiments, as only tending to expose those who are influenced by it to very dangerous errors; and, on the other, the total rejection of the conclusions formed from such experiments without a minute examination of the objections brought against them. He enters into a detailed enumeration of all the force that can act on the fabric of a ship, and into an exact calculation o the probable magnitude of each in such circumstances as are likely to occur; and afterwards considers how far the resistances to be opposed to those forces are sufficient to withstand their action. The strains which occasion the effect of arching are, he observes, of two kinds; the one derived from the distribution of the weight of the ship, with its contents being not duly proportioned to the pressure of the water; the other, which has not hitherto been noticed, from the simple and unavoidable application of the longitudinal pressure of the water to the lower parts of the ship only, amounting to more than one third as much as the former, in the case of a seventy-four gun ship of the usual dimensions, being equivalent to the effect of a weight of about 1000 tons, acting on a lever one foot in length, while the strain arising from the unequal distribution of the weight, and the displacement, amounts, where it is greatest, to 2600, although it is somewhat less than this exactly in the middle of the vessel. The next force investigated by the author is that of the waves, which he considers as including the consequences of the effect of the wind; and this he finds capable of becoming much greater than the former, amounting, in particular cases of the effect of a series of waves, to a strain of about 10,000 tons, and their difference more than 6000 when the waves are in a contrary direction. Hence it is inferred, that although these occasional strains exceed in magnitude the per manent causes of arching, they do not by any means make it super fluous to give the greatest strength to the fabric in the direction which is best calculated for the prevention of that effect. It is also remarked, that when fastenings have once given way to an occasional force of this land, the ship must naturally assume the form which is determined by the operation of more permanent causes; and this circumstance may lead the inattentive observer to false conclusions respecting the manner in which the injury has been sustained. The tendency to breaking transversely arises from causes precisely similar to those which have been mentioned as operating longitudinally; but their precise magnitude does not appear to be easily calculable. The force tending to produce a lateral curvature has commonly been in some measure neglected, for want of a permanent strain in a similar direction, capable of exhibiting its effects; but Dr. Young estimates its magnitude, in certain cases of waves striking a ship obliquely, to be nearly or fully equal to that of the vertical strain, as already computed. The manner in which a ship gives way when she strikes the ground is next described; and the effects of partial moisture in promoting decay are mentioned as the last of the evils which it is the object of the builder to obviate, as far as it is in his power. Dr. Young proceeds to consider the arrangements that are best adapted to obviate the various strains which are likely to occur in the fabric of a ship, and observes, that the principal, if not the only, advantage of oblique timbers is in the additional stiffness which they afford; since the ultimate strength, or the resistance at the point of breaking, is little, if at all, affected by them in the cases which have been proposed for experimental examples, though, in some other cases, the strength as well as the stiffness may be surprisingly increased by the obliquity of the substances employed.