the practical metallurgist, viz., Nasmyth's steam-hammer. Steel can be produced as cheaply as iron was formerly; and its substitution for iron, as railway material and in ship-building, has resulted in increased safety in railway-traveling, as well as in economy, from its vastly greater durability. Moreover, the enlarged use of iron and steel, which has resulted from these improvements in its make, has led to the adoption of mechanical means to supersede hand-labor in almost every branch of trade and agriculture, by which the power of production has been increased a hundred-fold, while at the same time much higher precision has been obtained. Sir Joseph Whitworth has done more than any one else to perfect the machinery of this country by the continued efforts he has made, during nearly half a century, to introduce accuracy into the standards of measurement in use in workshops. He tells us that, when he first established his works, no two articles could be made accurately alike or with interchangeable parts. He devised a measuring apparatus, by which his workmen in making standard gauges are accustomed to take measurements to the a 120000 of an inch.
In its more immediate relation to the objects of this Association, the increased importance of iron and steel has led to numerous scientific investigations into their mechanical properties and into the laws which govern their strength; into the proper distribution of the material in construction; and into the conditions which govern the friction and adhesion of surfaces. The names of Eaton Hodgkinson, Fairbairn, Barlow, Rennie, Scott Russell, Willis, Fleeming Jenkin, and Galton, are prominently associated with these inquiries.
The introduction of iron has, moreover, had a vast influence on the works of both the civil and military engineer. Before 1830, Telford had constructed an iron suspension turnpike-road bridge of 560 feet over the Menai Straits; but this bridge was not adapted to the heavy weights of locomotive-engines. At the present time, with steel at his command, Mr. Fowler is engaged in carrying out the design for a railway-bridge over the Forth, of two spans of 1,700 feet each that is to say, of nearly one third of a mile in length. In artillery, bronze has given place to wrought-iron and steel; the 68-pound shot, which was the heaviest projectile fifty years ago, with its range of about 1,200 yards, is being replaced by a shot of nearly a quarter-ton weight, with a range of nearly five miles; and the armor-plates of ships are daily obtaining new developments.
But it is in railroads, steamers, and the electric telegraph, that the progress of mechanical science has most strikingly contributed to the welfare of man. To the latter I have already referred. As regards railways, the Stockton and Darlington Railway was opened in 1825; but the Liverpool and Manchester Railway, perhaps the first truly passenger line, dates from 1830; while the present mileage of railways is over 200,000 miles, costing nearly £4,000,000,000 sterling. It was
