2i6 THE POPULAR SCIENCE MONTHLY. 



the practical metallurgist, viz., Nasmyth's steam-hammer. Steel can 

 be produced as cheaply as irou 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 produc- 

 tion 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 work- 

 shops. 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 * - 

 of an inch. 



In its more immediate relation to tbe objects of this Association, 

 the increased importance of iron and steel has led to numerous sci- 

 entific investigations into their mechanical properties and into the laws 

 which govern their strength ; into the proper distribution of the ma- 

 terial in construction ; and into the conditions which govern the fric- 

 tion and adhesion of surfaces. The names of Eaton Hodgkinson, Fair- 

 bairn, 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 rail- 

 way-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 ha's 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 





