Page:Proceedings of the Royal Society of London Vol 1.djvu/518

Rh which is altogether new, and contributes to the strength on a totally different principle. When a frame-work has the form of a parallelogram, its power to preserve that form depends solely on the strength of the joints; but when the space surrounded by this outline is ﬁlled with the same kind of materials, then every part will sustain a pro- portionate share of any force applied. Accordingly, in the new system, the openings between the ribs are ﬁlled in with slips of timber nearly to the height of the orlop, or lowest tier of beams; and when these pieces have been ﬁtted, and closely wedged together, they are caulked and pitched over, so as to make the whole frame, from head to stem, to within a few feet of the greatest draught of water, one compact water-tight mass of timber. Hence, even if any of the- outer planking of the bottom were to be knocked off, the ship might not only for n time be kept aﬂoat, but permanently be secured from sinking; whereas, upon the old system, the starting of a plank has been often fatal to the ship and crew.

In addition to these principal improvements of Mr. Seppings, others of less importance are also described, and some observations are added respecting the economy of the new construction, not only with regard to the quantity of timber necessary, but also the quality, and the fa-c cility of replacing any parts that may afterwards be found decayed.

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 of 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