500 



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 sufficient 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 unexceptionable ; 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 ; hut 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. 



Some further Observations on Atmospherical Refraction. By Stephen 

 Groombridge, Esq. F.R.S. Read March 31, 1814. [Phil. Trans. 

 1814, p. 337.] 



In the author's former communication to the Society on the sub- 

 ject of atmospheric refraction, he considered the observations of stars 

 that were more than 80 from the zenith as not to be sufficiently de- 

 pended upon for the determination of refraction in general ; and 



