Page:Proceedings of the Royal Society of London Vol 1.djvu/520

Rh greatest utility; an opinion in favour of which he adduces the autho- rities of Bouguer, Gobert, and Don George Juan. He then proceeds to calculate how far Mr. Seppings’s braces are strong enough to sus- tain alone the force to which it has been proved that their situation is likely to expose them; and ﬁnds that they will support, without being crippled, such a change as may be expected when a seventy- four arches about two feet, but not more; and that they will afford a resistance fully suﬁicient to withstand a strain much greater than that which has been attributed to the pressure of the waves, and to the usual causes of arching. Dr. Young does not apprehend any evil from the omission of the internal planking between the parts, nor from the removal of the partial remedy which the immersion of the ends, produced by arching, affords to the unequal distribution of the weight and pressure. The ﬁlling-in between the timbers in the hold he considers as wholly unexceptiouable ; and remarks, that wedges may easily be driven in such a manner, while the ship is on the stocks, as to have a tendency to render the keel convex rather than concave below, and to prevent the common effect of arching when the ship is launched, without any other superiority of strength or workmanship ; and that, Without some such accidental cause, no ship when launched could be wholly free from a perceptible degree of arching. He doubts the superiority of Mr. Seppings’s iron fasten- ings of the beams when acting as ties; and observes, that the obli- quity of the planks of the decks diminishes in some degree the strength of the tie with respect to arching; but remarks, that it may per- form a very important service in rendering the ship more capable of resisting the lateral strains, which, although sometimes very violent, have been little considered by theoretical reasoners: and he suggests that it may be possible to ﬁx the carlings between the beams in such a manner as to contribute more materially to the strength in this respect. In case of the ship's grounding on a hard bottom, Dr. Young is disposed to think Mr. Seppings’s construction somewhat weaker than the common one, on account of the omission of the ceiling; although an experiment made on the Tremendous proved that a force more gradually applied could be sustained without injury. And he concludes from the whole examination, that none of the objections which have been hitherto advanced appear to be sufﬁciently valid to warrant a discontinuance of the cautious and experimental introduc- tion of Mr. Seppings’s arrangements, which has been commenced by order of the Board of Admiralty.

In the author's former communication to the Society on the subject of atmospheric refraction, he considered the obsemtions of stars that were more than 80° from the zenith as not to be sufﬁciently depended upon for the determination of refraction in general; and