Page:Proceedings of the Royal Society of London Vol 1.djvu/519

Rh 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, mounting, in particular cases of the eﬁ'ect 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 oc- casional force of this kind, 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 con- clusions respecting the manner in which the injury has been sustain- ed. The tendency to breaking transversely arises from causes pre- cisely similar to those which have been mentioned as operating lon- gitudinally; but their precise magnitude does not appear to be easily calculable. The force tending to produce a lateral curvature has com- monly 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, ad- vantage 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 in- creased by the obliquity of the substances employed. In a ship, the utility of oblique timbers must depend in great measure on the chang which are observable in cases of arching, whether they con- sist most in an alteration of the angular situation of the parts, or in the want of continuity from a failure of the fastenings. From actual observations made at Chatham, he concludes that half of the effect produced depends on one of these causes, and half on the other; and infers. that so far as a change of the angular position of the timbers is found to take place, the addition of oblique braces must be of the