ON THE DEVELOniENTS OF MECHANICAL ENGINEERING. 507 



become a thing of tlie past. Mr. Harrison, the engineer of the North 

 Eastern Railway, told me that about eighteen months ago that railway 

 applied for tenders for rails in any quantities between 2,000 and 10,000 

 tons, and issued alternative specifications for iron and for steel. _ They 

 received about ten tenders ; certain of those who sent them in did not 

 care to tender for iron at all, and in some cases where the alternative 

 price was quoted, that for the iron exceeded that for the steel. I have no 

 doubt whatever that in a short time it will be practically impossible to 

 procure iron, made by the puddling process, of dimensions fit for many 

 of the purposes for which a few years ago it alone was used. With 

 respect to steel, in 1831 the process in use was that of cementation, 

 producing blistered steel, which was either piled and welded to make 

 shear steel, or was broken into small pieces, and melted in pots, and run 

 into ingots weighing only some 50 lbs. or 60 lbs. each. At that time steel 

 was dealt in by the pound ; nobody thought of steel in tons. In 1881 we 

 are all aware that by Sir Henry Bessemer's well-known discovery, carried 

 out by him with such persistent vigour, cast-iron is by the blowing 

 process converted into steel ; and that by Dr. Siemens' equally well- 

 known process, now that, owing to his invention of the regenerative 

 furnace, it is possible to obtain the necessary high temperature, steel is 

 made upon the open hearth ; and we are moreover aware that by both of 

 these processes it is produced in quantities of many tons at a single 

 operation, with the result that, as instanced in the case of the North 

 Eastern rails, steel is a cheaper material than the wrought-iron made 

 by the puddling process. One cannot pass away from the steel manu- 

 facture without alluding to Sir Joseph Whitworth's process of putting 

 a pressure on the steel while in a fluid state. By this means the cavities 

 which are frequently to be found in ingots of a large size, are, -while the 

 material is still fluid, considerably diminished, and the steel is thereby 

 rendered much more sound. In conclusion of my observations on the 

 subject of iron and steel manufacture, I wish to call attention to the 

 invention of Messrs. Thomas & Gilchrist, by which ores of iron containing 

 impurities that unfitted them to be used in the manufacture of steel, are 

 now freed from these impurities, and are thus brought into use for steel- 

 making purposes. 



With respect to Bridges : in the year 1831 bridges of cast-iron existed, 

 but no attempt had been made to emj)loy wrought-iron in girder bridges, 

 although Telford and others had employed it in suspension bridges ; 

 but in 1881 the introduction of railways and the improvements in iron 

 manufacture have demanded and have rendered possible the execution 

 of such bridges as the tubular one sti-etching across the Menai Straits in 

 spans of 400 feet, and the Saltash over the Tamar, with spans of 435 feet ; 

 while the recent great improvements in the manufacture of steel have 

 rendered possible the construction of the contemplated Forth Bridge, 

 where there are to be spans of 1,700 feet, or one-third of a mile in 

 length. Mr. Barlow (one of the engineers of this bridge) has told me 

 that there will be used upwards of 2,000 more tons in the Forth Bridge 

 to resist the wind-pressure, than would have been needed if no wind 

 had had to be taken into account, and if the question of the simple 

 weight to bo" carried had alone to be considered. With respect to the 

 foundation of bridges, that ingenious man, Lord Cochrane, patented a 

 mode of sinking foundations even before the first meeting of the British 

 Association — viz., as far back, I believe, as 1825 or 1826 ; and the 



