2(M 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Septembeb, 



M'lion in tliis equation H = 0, tlie upper edfre in of tlie orifice is 

 ill Uie surfitce of the water, and we find liy reduction 



Q =frV(*i'ft) -16 {/-'(/-'«)} • 



^^'llen in equation (b) m = /, the trapezium becomes a rectangle, 

 and the quantity of discharge is 



d. Q=/cV(*i')-l'{(H+6)5-H!}. 



If liere II = 0, the upper edge of the orifice is in the surface of 

 tlie water, and 



I'ut the height of tlie orifice for the breadth, and the breadtb for 

 the height; and we have 



/. Q = /.-V(V)-3"'- 



Now, for the two equations (eand/), it follows that f(u-e(iual 

 rectangles, when the upper side is in the surface of tlie water, the 

 quantity of discharge varies as the square root of the height of 

 tlie orifice. 



If in the last equations i = /, the orifice is a square, and we have 



g. q = ic^Ha).ii{(u>r/)'^-n'^}. 



Divide this equation by /,-' x the area of the orifice, that is by lcl\ 

 and we have for the velocity the same result as (E § 8). 



fTo be conlinwd.J 



BRITANNIA TUBULAR BRIDGE. 



The preparations at the Menai Straits for performing the im- 

 jiortant and perilous operation of hoisting this enormous fabric to 

 its permanent position are on a scale of immense magnitude. This 

 will be the more readily understood when it is stated that the total 

 (lead weight to be lifted 100 feet above high- water mark is upwards 

 of 9,000 tons, or equivalent to the elevation to that height of up- 

 wards of 30,000 men. The stroke of the hydraulic presses em- 

 [iloyed for the purpose is six feet— that is to say, they are only 

 capable of raising six feet in one lift. The tube of 2,300 tons has 

 consequently to be sustained wiiile the presses are lowered and a 

 fresli hold obtained. This sustentation, owing to the immense 

 magnitude of the labour, will be effected by building up successive 

 layers of masonry, at every six-feet lift, under the tube to support 

 it securely in its ascent— during which, arrangements will be made 

 for another six-feet hoist, until the whole 100 feet are finislied. 

 ^Vere it not for this process of building up, the oper.ation would 

 only occupy about a day; but as it is, it will take a fortnight. The 

 pre.'aution has been adopted by Mr. Stephenson and Mr. Clarke to 

 guard against the probability of casualty, seeing that should any 

 accident occur, the labour of years and the outlay of balf-a-million 

 would be inevitably sunk. To insure security, however, some con- 

 ti-i\ances are adopted by which the sup])ortiiig chains as they rise, 

 are continually to be followed up by wedges of wood, so that in 

 tlie event of any accident arising to the" lifting machinery, no 

 iiijiuy, it is expected, would happen to the tube. 



'I'he mechanical contrivances for the purpose are the largest in 

 the world, and the most powerful ever constructed. Favoured by 

 Mr. Clarke, one of the able engineers of the works, we are enabled, 

 froin a close personal inspection and the advantage of that gentle- 

 niaii's explanations, to give a description of the vast apparatus for 

 hoisting t!ie huge burthen. The machine used to effect tliis is an 

 enormous hydraulic press; its construction is of the most simple 

 character, and consists only of an exceedingly thick and heavy 

 iniii cylinder, like a mortar. A strong piston o'r ]ilungcr, also o'f 

 iron, called the ram, works up and down within this cylinder, and 

 IS fitted with a leather collar at the shoulder, so as to render it 

 water-tight. A\'ater is forced into the cylinder by a force-pump, 

 tlirough a small orifice which may be compared to the touch-hole 

 of a gun; and this water gradually forces up the piston. The 

 whole secret of the immense power of these machines consists 

 simply in the prodigious force with which the water is driven into 

 tlieiu, and which, in the present instance, is so great that it would 

 throw the water to the heiglit of nearly 20,000 feet, which is nuu-e 

 than five times the heiglit of the neighbouring noble pinnacle of 

 f^uowdon, and 5.000 feet higher than the monarch mountains of 

 Alount IJlanc ! It, in fact, resembles the piston of a steam-engine, 

 but. instead of using steam at 30 lb. or 40 lb. pressure to the inch, 

 water is used at a pressure of bOO lb. or SOO lb. The cylinder, of 



course, is of almost adamantine strength, to enable it to sustain 

 and withstand this pressure. The sides of the largest of these 

 presses used in raising the bridge are 1 1 inches thick. The weight 

 of the cylinder, which is of cast-iron in one piece, is 16 tons alone; 

 but the whole machine complete is 40 tons. The ram or piston 

 working within it is 20 inches in diameter, and if worked to its 

 utmost power, this press would alone be quite capable of raising 

 one of the tubes. The most marvellous thing above all is this, 

 that in spite of its proportions, its stupendous action is guided and 

 controlled with the most perfect ease and precision by one man. 

 This hydraulic giant was constructed by Messrs. Easton and Amos, 

 engineers, of Southwark. It stands on two beams, on a lofty kind 

 of eyrie, at the top of one of the towers, whence a grand and open 

 view is obtained of tlie Straits seaward, wliile its elevation above 

 the ravine is upwards of 200 feet. The i)ress is composed of 

 wrought-iron, rivetted together at the to)) of the side towers, 

 where, with its assistant machinery, it occupies a large chamber to 

 itself, about 29 feet above the level to which the bridge has to be 

 raised. The sensations experienced on looking down from this 

 lofty elevation over the rushing stream of the Straits, and the 

 great tubes and machineries strewn round about below are of a 

 peculiarly impressive character. In addition to this large press 

 there are two smaller presses, with rams 18 inches in diameter, 

 placed side by side at a similar level in the Britannia tower, and 

 which act in conjunction with the large press. 



The chains, by which the power exerted by the presses in their 

 lofty position is communicated to the tubes at the base of the 

 tower, resembles the chains of an ordinary suspension bridge, and 

 are similar to those of the bridge at Hungerford. They are ma- 

 nufactured by the patent process of Messrs. Howard and Raven- 

 hill, of London, and consist of flat links, 7 inches long, 1 inch 

 thick, and 6 feet in length, with an eye at each end, and are bolted 

 together in sets of eight and nine links alternately. The weight 

 of these chains employed in lifting the 2,000 tons is about 100 tons, 

 far exceeding that of the well-known eque.striau statue of the Duke 

 of Wellington at Hyde-|)ark, which has hitherto been regarded as 

 one of the greatest "lifts" of the age. Tliese chains are attached 

 to the tube at two feet from the end, and in order to get sufficient 

 purchase at the part, three strongs frames of cast-iron are built 

 into each end of the tube. The innermost end only stiffens and 

 supports the sides while the tube is resting on its ends. The two 

 outer frames are the lifting frames; the chains are attached to 

 them by three sets of massive cast-iron beams, placed across the 

 inside of the tube, one above another, their ends fitting under deep 

 shoulders or notches in the lifting frames, where they are secured 

 by screw bolts. As an additional security, two very strong wrought 

 iron straps pass over the upper pair of beams, and descend into 

 the bottom cells beneath the frames, w here they are strongly keyed. 

 The weight of these lifting frames and cast-iron beams is 200 tons, 

 and it is a matter of wonder even among the engineers themselves 

 how machinery can be made strong enough to raise the ponderous 

 load. The way in which the chains are connected with the press 

 is by an exceedingly thick and heavy beam of cast-iron, strength- 

 ened bj' wrought-iron ties across the top. It rests like a yoke upon 

 the shoulder of the ram, and is called the cross-head of the press; 

 the two chains pass through square holes at either end of the cross 

 head, and are securely gripped at the top of it by an apparatus 

 called the clams, consisting of two strong cheeks of wrouglit-irun, 

 drawn together by screws like a blacksmith's vice. Tlie beams on 

 which the presses stand, the cross-heads, and all the parts that are 

 subjected to a very heavy strain, are either constructed of, or 

 strengthened by, wrought-iron, which is found to be less brittle and 

 more trustworthy than cast-iron. As the tube is 12 feet longer, 

 allowing a feet at each end, than the distance between the towers 

 in which the presses work, recesses or grooves are left in the face 

 of each of G ieet deep, in order to receive the additional length, 

 and of sufficient width to allow the end of the tube to slide up 

 easily within them. These recesses extend from the bottom of 

 the towers to nearly the height of the hydraulic macliines; it is in 

 the low end of these recesses, on a soft bed of timber, placed to 

 recei\'e it, that the great tube, since its successful floating, lias 

 been lying in state across the estuary of the Straits, until these 

 vast mechanical equipments for ballooning it to its permanent level 

 were completed. 



Mr. Ste]iheiisoirs Report, of the 9tli ult., to the Chester and 

 Holyhead Kailway Company, on the jireseiit prospects of tiie Bri- 

 tannia Bridge, is given at page 287 of our present number. 



