84 



NATURE 



[May 26, 1887 



Company's Works in Glasgow, and at Landore in South 

 Wales. Although one and a half times stronger than 

 wrought iron, it is not in any sense of the word brittle, 

 as steel is often popularly supposed to be, but it is tough 

 and ductile as copper. You can fold half-inch plates like 

 newspapers, and tie rivet-bars like twine into knots. The 

 steel shavings planed off form such long, true, and flexible 

 spirals, that they are largely used for ladies' bracelets 

 when fitted with clasps and electro-plated. 



Erection. — Facility of erection is one of the most im- 

 portant desiderata in the case of the Forth Bridge. 

 Uwing to the 200 feet depth of water, scaffolding is 

 impossible, and the bridge has to constitute its own 

 scaffolding. The principle of erection adopted was, 

 therefore, to build first the portion of the superstructure 

 over the main piers, the great steel towers, as they may 

 be called, although really parts of the cantilever, and to 

 add successive bays of the cantilever right and left of 

 these towers, and therefore balancing each other, until 

 the whole is complete. This being the general principle, 

 a great deal yet remained to be done in settling the 

 details. What was finally settled, and is now in progress, 

 is as follows : — 



After the skewbacks, horizontal tubes, and a certain 

 length of the verticals as high as steam-cranes could 

 conveniently reach were built, a lifting-stage was erected. 

 This consisted of two platforms, one on either side of the 

 bridge, and four hydraulic lifting-rams, one in each 

 12-feet tube. To carry these rams cross-girders were 

 fitted in the tubes capable of being raised so as to support 

 the rams and platform as erection proceeded, and steel 

 pins were slipped in to hold the cross-girders. Travelling 

 cranes are placed on the platforms, and these cranes, with 

 the men working aloft, are of course raised with the 

 platforms when hydraulic pressure is let into the rams. 

 The mode of procedure is to raise the platform i foot, 

 and slip in the steel pins to carry the load whilst the rams 

 are getting ready to make another stroke of i foot. When 

 a 16-feet lift has been so made, which is a matter of a 

 few hours, a pause of some two or three days occurs to 

 allow the riveting to be completed. The advance at 

 times has been at the rate of three lifts, or 48 feet in 

 height, in a week. 



The riveting appliances designed by Mr. Arrol are of 

 a very special and even formidable character, each 

 machine weighing about 16 tons. It consists essentially 

 of an inside and outside hydraulic ram mounted on longi- 

 tudinal and annular girders in such a manner as to com- 

 mand every rivet in the tubes, and to close the same by 

 hydraulic pressure. Pipes from the hydraulic pumps are 

 carried up inside the tubes to the riveters, and oil fur- 

 naces for heating the rivets are placed in convenient 

 spots, also inside the tubes. By practice, and the stimulus 

 of premiums, the men have succeeded in putting in 800 

 rivets per day with one of the machines, at a height of 

 300 feet above the sea, which, in fact, is more than they 

 accomplished when working at ground level. Indeed, 

 by the system of erection adopted, the element of height 

 is practically annihilated, and with ordinary caution the 

 -men are safer aloft than below, as in the former case they 

 are not liable to have things dropped on their heads. 



The cantilever will be erected and riveted in precisely 

 the same manner as the great towers, but owing to the 

 overhang temporary ties will occasionally be required. 

 The centre girder itself will be similarly erected, one half 

 being temporarily added on to the extremity of each 

 cantilever, and when the two ends meet at the centre of 

 a 1700-feet span they will be connected, and the temporary 

 joints, with the cantilevers, released. Roller joints are 

 provided at the cantilever ends for expansion, and at the 

 main piers the whole superstructure rests on lubricated 

 sliding bed-plates. 



The system of erection by overhanging offers great 

 advantages as regards safety, as each successive part of 



the superstructure is riveted up and completed before a 

 further portion is added. In the case of an ordinary 

 bridge the whole superstructure must first be temporarily 

 bolted up on scaffolding, and in that condition is liable to 

 be swept away by flood or hurricane at any moment. 



There is nothing new under the sun, and therefore you 

 will not be surprised to hear that in 1810, a certain Mr. 

 Pope proposed to construct a cantilever bridge, of 1800 

 feet span, across the East River, in New York, and, indeed, 

 exhibited a 50-feet model of the same. 



I have described the process of erecting the Forth 

 Bridge in sober prose ; if I had thought of doing it in 

 verse I should have appropriated bodily Mr. Pope's lyrical 

 version of his intended operations at the East River, of 

 which the following is a sample : — 



" Each semi-arc is built from off the top, 

 Without the aid of scaffold, pier, or prop ; 

 By skids and cranes each part is lowered down, 

 And on the timber's end grain rests so sound. 

 Sure all the bridges that were ever built, 

 Reposed their weight on centre, pier, or stilt ; 

 Not so the bridge the author has to boast. 

 His plan is sure to save such needless cost ; 

 A ladder on each side is lowered down, 

 And shifted from the fulcrum to the crown." 



To carry out the work at the Forth Bridge there is an 

 army of 3500 workmen, officered by a proportionate 

 number of engineers. Everything, except the rolling of 

 the steel plates, is done on the spot, and consequently 

 there are literally hundreds of steam and hydraulic engines 

 and other machines and appliances too numerous to 

 mention, many of them being of an entirely original 

 character. 



It is, of course, impossible to carry out a gigantic work 

 of the kind I have had the honour of bringing before the 

 Institution without paying for it, not merely in money, 

 but in men's lives. I shall have failed in my task if you 

 do not, to some extent, realize the risks to which zealous 

 and plucky workmen will be sure to expose themselves in 

 pushing on with the work of erecting the Forth Bridge. 

 Speaking on behalf of the engineers, I may say that we 

 never ask a workman to do a thing which we are not pre- 

 pared to do ourselves, but of course men will, on their 

 own initiative, occasionally do rash things. Thus, not 

 long ago a man trusted himself at a great height to the 

 simple grasp of a rope, and his hand getting numbed with 

 cold he unconsciously relaxed his hold and fell backwards, 

 a descent of 120 feet, happily into the water, from 

 which he was fished out little the worse after sink- 

 ing twice. Another man going up in a hoist the other 

 day, having that familiarity with danger which breeds 

 contempt, did not trouble to close the rail, and, stumbling 

 backward, fell a distance of 180 feet, carrying away a 

 dozen rungs of a ladder with which he came in contact, 

 as if they had been straws. These are instances of rash- 

 ness, but the best men run risks from their fellow-work- 

 men. Thus a splendid fellow, active as a cat, who would 

 run hand over hand along a rope at any height, was 

 knocked over by a man dropping a wedge on him from 

 above, and killed by a fall of between one and two hundred 

 feet. There are about 500 men at work at each main 

 pier, and something is always dropping from aloft. I saw 

 a hole I inch in diameter made through the 4-inch timber 

 of the staging by a spanner which fell about 300 feet, and 

 took off a man' s cap in its course. On another occasion 

 a dropped spanner entered a man's waistcoat and came 

 out at his ankle, tearing open the whole of his clothes, 

 but not injuring the man himself in any way. 



Happily, there is no lack of pluck amongst British 

 workmen ; if one man falls another steps into his place. 

 Difficulties and accidents necessarily occur, but like a 

 disciplined regiment in action we close up the ranks, 

 push on, and siep by step we intend to carry on the work 

 to a victorious conclusion. 



