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of a tool, to which the proper motion was given; after which it was painted several times, rubbed very smooth and varnished.
On the second trial of the Great Britain, on the 20th January, in the Bristol Channel, in smooth water and during a calm, the engines attained the speed of 182 strokes per minute, when the speed of the vessel through the water, measured by an experienced seaman, with the common log, was 12 knots.
18.66 x 2.945 x 25= 1375.242 feet, velocity of the screw
127.446 slip, thus the speed of the vessel was •907 to 1. of the screw.
The area of the midship section of the ship, at the time of this experiment, was 480 feet. The annexed diagram is intended to illustrate this effect thus :
The angle subtended by A, B, C, is an entire revolution of a screw 15 feet 6 inches diameter and 25 seei pitch, of which B, D is the forward effort communicated to the vessel, and C, D is the slip, or yielding of the
water. Consequently, although the apparent angle of the screw is represented by A, B, C, the real angle is only A, C, D, since A, B, D represents the velocity of the vessel.
To be Continued.
The case of the Yarmouth Suspension Bridge over the river Yare.
An accident to this bridge, involving an extensive loss of life, occurred on the 2nd May last, arising from the excessive load upon one side of the bridge, of a great concourse of human beings assembled to witness the exploits of five geese, consisting of a clown and four geese proper. The government having appointed Mr. Walker, C. E., 10 examine into the causes of the catastrophe, he drew up an elaborate report on the subject, of which we give the following abstract:
6. The bridge belonged to the late Mr. Cory, father of the present owners, and was constructed from a design of Mr. Scoles', an architect in London. At first it was only a substitute for a ferry over the river Yare to the marshes. Mr. Scholes states, that he made designs for a bridge of sufficient width for a carriage and two footways. It appears that the work was offered for competition, and that Mr. Goddard (who is since dead) was the contractor for the bridge work, according io specifications prepared by Mr. Green, a surveyor at Yarmouth. These specifications describe that the iron shall be of the best charcoal iron ; but make no mention as to the quality of the iron being tested. From a drawing which is now in Mr. Scoles' possession, there appears no reason to doubt that the main or suspending chains, and other parts of the bridge, are of the size which were intended.
There were altogether four suspending bars, two on each side to forın a chain. These bars were connected together by bolts passing through opening or eyes at each end of them. These bars were 24 inches wide by seven-eighths thick; from them rods of 1 inch square were suspended to carry the roadway, which was 14 feet 9 inches in width, and divided, by an iron kerb or carriage-way, from a footpath on each side, 4 feet in width. The length between the centre of the towers is 92 feet; the deflection of the chains was 7 feet 4 inches. An Act of Parliament, constituting the bridge a turnpike road was passed in May, 1830, and the road was opened in 1832. In 1842, the Yarmouth and Norwick Railway Act was passed, which contains a clause by which this bridge was constituted the only communication between the Railway station and the terminus, Mr. Cory agreeing to receive the tolls, stipulating to widen it, and afterwards to suspend it. It appears that on this occasion Mr. Scoles was again consulted, respecting the widening of the carriage-way to a widih sufficient for two carriages to pass abreast-the footway being formed on each side by planks, separated by iron straps attached to the framing of the bridge. This footway was therefore outside the suspending chains. That was in 1844.
The foundations appear to have been piled well, and to have stood well. Mr. Scoles showed Mr. Walker a drawing of the piling, and, if the work had been executed according to that, Mr. W. had very little doubt of the soundness of the foundation. It is stated that the crowd collected on the 2d of May, was confined to the south side; that the crowd was composed chiefly of children in the front rank, with adults behind, to see some exhibition which was to be seen on the water. They were supposed to be four or five feet deep, and it appears that they had collected on the bridge to the number of from 300 to 500. One of the witnesses before the inquest stated that he heard a crack overhead, which induced him to look up, when he saw that one of the bars or rods of the suspending.chain was broken-that two points where the fracture had taken place were entirely separated, and that in about five minutes aftewards came the fatal catastrophe. This cracking was no doubt occasioned by the snapping in pieces of the bar which first gave way. There was now only one bar left to support the whole weight, and this bar consequently gave way in five minutes after the one on the other side; the platform, being then entirely unsupported, fell into the river. In forming these bars, the two ends had been forged separately, and then welded to a third piece, a straight bar, by scarphed or diagonal joints. It was at the weldings that the bars gave way. On examining the fracture of the bar which first broke, the weldings were found to be imperfect, insomuch as evidently not more than one-third of the surfaces were united. It was found on comparison that the second bar had stretched one inch longer than the other: this must have happened during the five minutes when it had singly to bear the strain. The qualities of the pieces of iron being tested, the middle or straight parts were found greatly superior to the ends. A piece of one of the ends was very open and coarse grained, and broke off like a piece of cast-iron when a hammer was
applied to the middle of the bar, another point altogether. Had the bar been perfectly tested, the defect could not have escaped detection Another bar was tested as to fibre; it broke in pieces like a carrot. As to the strength of the bridge compared with the load, taking the load at the time of the accident to be all on the south chain, it is found by calculation that the two rods of 21" by " are capable of sustaining a temporary load of 56 tons, without injury. Taking 400 indi. viduals at 7 stones weight each, with the weight of the bridge, at 400 tons, the strength of the bars would exceed the load. The excess, however, was not sufficient, as at all times large allowances ought to be made for imperfections. The bridge appears to have been by no means too strong before the additions were made; and after this was done, the effect was most injurious, as the weight was placed outside the suspending chain. "In reference to the sufficiency of the bridge,” he says, “ to carry the greatest load which could be placed upon it, I find that its strength is somewhere a little above the weight which it would carry, but so small as not to be practically sufficient, even with. out any allowance for imperfections. Even before the additions were made, it appears not to have been sufficiently strong to insure perfect security, supposing a mass of people to have been packed upon it in the way in which I have described. It appears that on other occasions a very great number of persons had been upon the bridge, and that it had borne them without falling. When a bridge has been frequently loaded, to the utmost which it will bear, it becomes weaker and weaker each time, and the bridge may ultimately give way, al. though at first it was sufficiently strong to resist the weight put upon it.” On the whole, therefore, witness had come to the following general conclusions:
“ 1. That the immediate cause of the accident was a defect in the joining or welding of the bar which first gave way.
“ 2. That the quality of the iron and the workmanship, as far as I have been able to examine then, is defective; and I believe that the accident would not have happened had the work been properly examined at the time of construction.
“3. That the widening appears to have been made without sufficient reference to the original strength of the bridge, and the weight which it had to support, and therefore that it acted as an aggravation of the evil.
“ 4. That in the original construction of the bridge, the casualty of a great load all on one side does not appear to have been contemplated; if it had been, I think that the links on that side would have consisted of more than two bars, any one of which was unequal to the load which the bridge was likely to carry.”
Mr. Walker added, that the weight of the bridge, including the suspending chains, before the additional width was added, was 17 tons, 14 cwt. 3 qrs. 25 lbs.: with the additional width, and the railing added, its weight was 20 tons 8 cwt. 9 lbs., making an addition of 2 tons 13 cwt.
Gla-gow Prac. Mecb. & Eng. Mag.
New Railway Bills. It appears, from a table published in Herapath's Railway Magazine of August 23rd, 1845, that bills were passed during the late session of Parliament, authorizing the construction of 113 new lines of railway. These new roads are found in almost all parts of England, Scotland, Ireland, and North and South Wales.
The most important line appears to be the “South Wales," of which the length is 192 miles, and the authorized capital in shares £2,500,000, and in loan £933,333.
The next in importance is the “Caledonian,” 1354 miles long, with a capital of £2,100,000 in shares, and £700,000 authorized loan.
The 113 bills embrace new railway lines, of which the aggregate length is 2,944 miles, the aggregate capital in shares, £42,818,330, and authorized loan £14,541,791-making the authorized expenditure £57,360,121.
We make the following extracts from the last reports of the two greatest British railways—the London and Birmingham and the Great Western.
London and Birmingham Railway. The capital investment of this Great work now amounts to the enormous sum of £7,256,718 Ss. 10d., or about $34,832,000. The cost of Locomotive engines to 30th June, 1845, was
£184,098 75. 7d. Carriages and Wagons,
£290,394 178. 8d. Total cost of Working Stock,
£474,493 58. 3d. The Company have charged to depreciation of Stock from the beginning
£199,031 The following is the Statement of Revenue account, &c. Dr.
d. * Maintenance of way and stations-Repairs of the
permanent way, tunnels, bridges, draius, &c., 20,-
24,142 15 5 Locomotive power-Wages of engine-drivers and fire
men, 5,9941. 15s. 3d.; coke, 18,4591. 8s. 7d.; oil, hose-pipes, and fire-tools, pumping engines and water, 2,2631. 2s.; laborers and cleaners, waste and oil, 2,4131. 16s. 9d.; repairs of engines and tenders, 8,3391. 16s. 7d.; coals and fire-wood, expenses of stationary engine at Wolverton, repairs of buildings, gas, and incidental charges, 1,8951. 11s. 10d.; Superintendent, clerks, and foremen's salaries, and office charges, 2,1961., 11s. 4d.; cost of locomotive
power for the Aylesbury Rail way, 1,5981. 11s. 7d. Police charges, viz. :-Wages and petty disburse
ments. 5,2481. 9s. 11d.; clothing, 533l. 10s. 6d.; gratuities to switchmen, 436l.; oil, lamps, flags, &c.,
4491. 2s. 5d., Coach traffic charges-salaries of booking clerks and
petty disbursements, 3,4601. 12s. 3d.; wages and gratuities to guards, ticket-collectors, and porters, 8,4161. 1s. 3d.; clothing for the same, 4521. 6s. 6d.; gas at stations, 1,1611. 11s. 11d.; oil, coach grease, cotton waste, fuel, water, and repairs, 2,5461. 8s. 2d.; stationery and tickets, 1,0591. 145. 9d.; sundries, including horse-bire, 1661. 185. 2d.; loss on
light gold, 2531. 9s. 3d., Coach repairs, 6,039 1s. 3d.; mileage of carriages em
ployed in through traffic, 441. 1s. 9d. Merchandize traffic charges, viz. :-Salaries wages
horses, gas, and sundries, 2,5851. 15s. 5d. ; wagon
Direction, 8501. Office charges, viz :-Secretary's,
3,924 12 S
463 19 7
6,133 8 3
Parish rates and taxes,
stock, carried to Capital Account (B 2,) 14,4931.
horses, carriages, and dogs, 13,9721. Os. 9d.; par