STRAIN ON Rigging. SIR.-In Mr. Tinmouth's valuable work on Rigging he regrets that no certain rule exists, by which we may determine the strain upon rigging when set up, so as to enable an officer to proportion the tension to the capabilities of the rope. I fear the following method may not be so practicable as it appears on paper, but it is at least worth investigation. Many of your readers may have observed that on shaking any stretched rope (one without ratlines) a wave is formed which moves rapidly to the other extremity, and then returns continuing this alternate motion until it is absorbed by the stiffness of the rope. This may easily be tried on the signal halliards, and if they are belayed tauter, it will be found that this velocity is increased in a certain proportion to the strain. If a rope be under a certain tension 1, and if I be such a length of the rope that its weight is equal to the tension, then v being the velocity of the wave v=vgl where g is 32.2. พ n If n be the No. of yarns in a rope, w its weight, and l its length, l = a where a is a constant for the same description of rope, But expresses the tension on each yarn, and if t is the most advantageous n strain it should be a constant, therefore the velocity of the wave should also be a constant for the same description of rope whatever its size may be. For cable laid rope a = 150 For hawser laid a = 220 Example.-On shaking a backstay, 53 inch hawser laid 120 feet long, the vibration descended 3 times in 10 seconds:-Required the tension of the rope. 3 X 2 X 120 velocity= 72 feet per second. 10 249 X 722 =182.2 lbs. 7084 nv2 7084 Required the velocity of the wave when the tension is 1 lb. per yarn. v = √ga = √ 483069.5 for cable laid. =√7084 84.2 "hawser. The value of a would however alter when the rope is much stretched, and cause considerable error. The following will be an approximation for hawser laid rope. If c be the actual circumference of the rope t = {} 2 There are probably many sources of error arising from the stiffness of the rope, and other causes: indeed, no dependance can be placed on these results, but if associated with a series of careful experiments, rules might be obtained which would be of considerable value on many occasions. Your obedient servant, To the Editor N.M. K. PETERMANN'S MAPS.-Those of our readers who approve of conveying useful information in a condensed form will be pleased with Mr. Petermann's maps of Great Britain. We have inspected two. The density of the population in different districts is expressed by shading, and that of the different towns, &c. by a little circle of colour, varying this according to the magnitude: Again the other expresses the five principal rivers-basin of Great Britain and the average proportion of rain at different parts. All this is shewn readily and without confusion at a glance, and forms a highly interesting and useful reference, giving comparative results without wading through masses of figures, &c., for them. THE BRITANNIA BRIDGE OVER THE MENAI STRAIT.-We have to record a feat of engineering success, unsurpassed, and probably unequalled in the annals of any country, that of floating the gigantic tube to its place between the piers, whence it is to be raised across the Strait. To give an idea of the ensemble of the undertaking, we annex the dimensions of the several parts of the works. The abutments on either side of the Strait are huge piles of masonry. That on the Anglesea side is 143 feet high and 173 feet long. The wing walls of both terminate in splendid pedestals, and on each are two colossal lions, couchant, of Egyptian design, 25 feet long, 12 feet high though crouched, 9 feet abaft the body, and each paw 2 feet 4 inches, each weighs 30 tons. They contain 8,000 cubic feet of stone. There is some intention of surmounting the central towers with a colossal figure of Britannia, in stone, 60 feet high. The Great Britannia tower in the centre of the Strait is 62 feet by 52 feet at its base upon the rock; its total height from the bottom 230 feet; it contains 148,625 cubic feet of limestone, and 144,625 of sandstone; it weighs 20,000 tons, and there are 387 tons of cast iron, built into it in the shape of beams and girders. It will sustain the four ends of the four long iron tubes which will span the Strait from shore to shore. The total quantity of stone contained in the bridge is 1,500,000 cubic feet. The side towers stand at a clear distance of 460 feet from the great central tower, and again the abutments stand at a distance from the side towers of 230 feet, giving the entire bridge a total length of 1840 feet. The side or land towers are each 62 feet by 52 feet at the base, and 190 feet high. They contain 210 tons of cast iron. The length of the great tube transported is exactly 470 feet, being the greatest span as yet attempted. Its greatest height is in the centre 30 feet, and diminishing towards the end to 22 feet. The rivets, of which each tube contains 327,000, are more than an inch in diameter. The total weight of wrought iron in the tube floated in one day is 1600 tons. The trains will pass through them, over the Straits, at 100 feet above high water. DREADFUL SHIPWRECK.-THIRTEEN PERSONS STARVED To Death. By the Emma Sherratt, which arrived yesterday from Sydney, particulars have been received relative to the loss of the British ship Sarah Crisp, John Taylor, master, and the appalling sufferings of the crew, thirteen of whom perished from starvation. The Emma Sherratt, on her outward voyage to Hong Kong, perceiving a vessel in distress, bore down to her assistance, and she proved to be the unfortunate vessel in question. She was leak-laden and waterlogged, almost a perfect wreck. Her masts were gone, as well as everything on deck. With much care 19 persons, in a most shocking state of exhaustion, were taken off the wreck by the Emma Sherratt's boats. They proved to be John Taylor, the master, the chief mate, and 17 seamen. Their sufferings had been truly awful, having been 27 nights and days on the wreck with nothing to subsist on excepting a monkey and two fishes. All the water they had was about a couple of buckets, which they caught by some old canvas. The second mate and twelve men had died from exhaustion. The ship's loss was attributed to a plank starting, as she filled in a very short time, and turned over on her side. The crew jumped on her beam as she went over, and there held on until daylight, when they succeeded in righting the wreck by cutting away the masts. The vessel and cargo were insured to the amount of £20,000. UNITED STATES COAST SURVEY. Report of the Superintendent of the Coast Survey, to the Secretary of the Treasury, relating to Hatteras Cove, Hatteras Inlet, and Bull Bay, on the coast of North and South Carolina. Coast Survey Station, Near Annapolis, Maryland, SIR.-I have received from Lieut. Commanding J. N. Maffit, U. S. N., assis... tant in the coast survey, information in regard to the results, of reconnoissances made by him, which are of considerable importance to navigators, and which I have the honor to lay before you, with a view to their republication. They relate to a cove which has been formed since 1845, by the extension of Cape Hatteras, to the inlet southward and westward of Cape Hatteras, formed in 1846, and to the use of Bull Bay on the coast of South Carolina as a harbour of refuge. Sketches of these reconnoissances will be at once published. 1.-Hatteras Cove lies to the westward of the extreme point of Cape Hatteras, is sheltered from the north-east, and affords good anchorage in four or five fathoms water with a bottom of soft blue mud. From the anchorage Hatteras light bears N.N.E.. distant about one mile and a half. Since 1845 the S. W. spit of Hatteras has made out nearly three-eighths of a mile. 2. Hatteras inlet is twelve miles to southward and westward of the Cape. Twelve feet can be carried over the bar on the ocean side, and there is secure anchorage in five fathoms water. The entrance with a pilot is easy. Lieut. Maffit's statements refer only to the use of the inlet as a harbour of refuge. 3.-Bull Bay is about twenty-three miles north of Charleston, on the coast of south Carolina. Thirteen feet can be carried across the bar, at low water spring tides, the rise and fall of which is six and three-quarters feet: To enter, bring the north-east bluff, a point of Bull island to bear N.W. b. W. (by compass,) and run for it. When within three-quarters of a mile of the point, steer N. W., until it is passed, Then follow around the shore and anchor at pleasure in soft bottom. In leaving the bay, keep away until the outer spit is cleared, which bears S.E.b.S., from the bluff part of Bull Island, distant three and a quarter miles. Very respectfully, yours, A. B. BACHE, Superintendent U. S. Coast Survey. Hon. W. M. Meredith, Secretary of the Treasury. DIFFERENCE of Longitude between Boston and LIVERPOOL. It being considered interesting and important to the commercial marine of the United States and of the United Kingdom, to ascertain with correctness the difference of longitude between the observatory at Cambridge, Boston, and that at Liverpool, it is proposed by the United States govern. ment to accomplish this object by means of marine chronometers, to be transported across the Atlantic, to and from Boston, in the British and North American Royal Mail steamers; and for this to be effected, arrangements have been made with the authorities in this country, that when the chronometers arrive at Liverpool, on their return from Boston, they may be transmitted with all possible care and despatch to the Liverpool observatory for the intended purpose. NEW BOOKS. THE PROGRESS of the DEVELOPMENT OF THE LAW OF STORMS and the variable winds, &c.-By Lieut. Colonel W. Reid, C.B., F.R.S.-Weale, London. With unwearied zeal Col. Reid has again followed up the subject of storms, to the elucidation of which he has already contributed so largely, with another volume, the title of which is the foregoing. A cursory glance, for as yet we have not had an opportunity to look closely into it, enables us to say that the Colonel has collected much interesting, and to the seaman, most useful information, from all quarters of the globe, from whence information was to be had; and this he has abundantly illustrated with little charts of the localities of which he treats. The subject of hurricanes we have long ago said is one with which the commanders of ships should be well acquainted, and the repetition of these books leaves him less chance of escaping from blame, which might attach to his ignorance of it. We shall return to this important volume in another number. NEW CHARTS. Published and Corrected in the Admiralty, and Sold by R. B. Bate, 21, Poultry, July, 1849. AZORES OR WEStern Islands, Capt. A. T. E. Vidal, R.N., 1844. Price 1 CORVO AND FLORES Ditto, Ditto, 66 1 FAYAL CHANNEL, HORTA AND PINE BAYS, with views SANTA MARIA AND THE FORMIGAS 66 NIKARIA ISLAND, Archipelago, Capt. Graves, R.N., 1845. 66 1 PORT ALBANY, (N.E. Coast of Australia) Capt. O. Stanley, R.N., 4848. “ 1 WANGARURN HARBOUR (New Zealand) Mr. J.G. Neps, Master R.N., 1845 1 6 1 86 Ditto, 1 0 690006 LAUNCH OF THE GENERAL SCREW STEAM SHIPPING COMPANY'S VESSEL, "BOSPHORUS." Exchange Buildings, July 11th, 1849. On Saturday afternoon last, another Screw Steam Iron Vessel destined to run between Liverpool and Constantinople, was launched from the extensive building and iron works of Messrs. Mare and Co., of Blackwall. There were a number of distinguished persons present, amonst whom we noticed the Turkish Ambassador and suite; Edward Zohrab, Esq., the Ottoman Consul General; Capt. Ford, of the Ottoman Steam Navy; Jas. Laming, Esq., Managing Director; Mr. Clarke, and Mr. Lang; Mr. Josh. Maudslay, the eminent Engineer; Mr. White, of Cowes; Mr. Campbell, C.E.; Colonel Wilson and Lady; the Marquis of Lisbon; Viscount and Viscountess Moncorva, with the Baron and Miss Moncorva; Lady Morgan; Lady Blake; Mr. Milner Gibson; B. Balfour, Esq. Director, and Ladies; W. H. Howes, Esq.; and John Margetson, Esq. a Director; and a large party of Ladies and Gentlemen. Miss S. Zohrab, niece of the Turkish Consul, performed the ceremony of naming the vessel, by throwing the customary bottle of wine at her bows, and naming her the "Bosphorus," as she glided slowly and sinoothly into her native element amidst the cheers of all present. She rose most buoyantly, and as she settled on the water a little by the stern, she drew forth general admiration for her beauty and symmetrical proportions, which are length between the perpendiculars 175 feet, breadth 25 feet, and depth 16 feet, making her burthen in tons of 530. Subsequently, the Company adjourned to the Mould Loft, where they were very handsomely entertained by the principal of the firm. In drinking success to the "Bosphorus" a compliment was paid to his Excellency the Turkish Ambassador, who in reply expressed his satisfaction at what he had witnessed, and said he should feel much pleasure in promoting the interest of the Company to the utmost of his power. The health of the pretty Sponsor of the Bosphorus was then drank, and in succession those of Mr. Zohrab; the Chairman of the General Screw Steam_Shipping Company; Mr. Jas Laming, the Managing Director; Capt. Ford, the Superintendant; Mr. Maudslay, the Engineer; and Mr. Waterman, the Architect. A very interesting conversation then took place, on the merits of Commercial Screw Vessels, and a meed of justice was rendered to Mr. Laming, for his invaluable labors in working out the success of the Screw Propeller, as applied to Merchant vessels in an economical point of view. It was then stated that by his extraordinary indefatigability he fully realised the most sanguine expectations of those connected with him in his enterprise. Upon these grounds it was anticipated, that under the patronage and support of the Ottoman Government, the new undertaking of the General Screw Steam Shipping Company, would prove a remunerative in vestment. The "Bosphorus," after she was launched, was immediately towed round to the East India Docks, there to receive her engines, which are of 80 horse power. She is to be fitted with all despatch, and two sister ships, the "Hellespont" which will be launched shortly, and another, are building by Messrs. Mare, and Co., for the same service, the Company being satisfied that in the "Bosphorus" they have an excellent model for Screw Steaming, as they have also a strong and well built ship for the purpose required. |