Report on the Progress and State of Applied Mechanics. 219 



those which are now in progress for tl\e purpose of supporting Mr. 

 Stephenson's tubular bridge across the St. Lawrence at Montreal, — the 

 largest viaduct in the world. 



49. The most remarkable examples of originality in Cabpentey 

 occur in America, where the comparative abundance of timber makes it 

 the leading material for bridges and viaducts. The feature by which 

 the carpentry of the present day is chiefly distinguished from that of 

 former times, is the profuse use of iron in the form of bolts, straps, tie- 

 rods, and sockets. Machine tools have of late heen extensively applied 

 to the shaping of timber in various ways. 



50. Metal-work is the branch of construction, by whose advance- 

 ment the present time is chiefly distinguished. The processes by which 

 metals of all kinds, and especially iron, are formed into various shapes 

 and put together, such as casting, rolling, welding, forging, wiredrawing, 

 punching, boring, planing, turning, screw-cutting, rivetting, &c., are 

 every day being improved, and the use of machinery to perform them 

 is becoming more and more general. One of the most striking features 

 of the progress in metal-work which is now going on, is the improve- 

 ment in accurate workmanship, due to a greater or less extent to a long 

 series of mechanical engineers, past and present, and especially to Mr. 

 Whitworth, who, by means of instruments for mechanically magnifying 

 small distances, enables a degree of accuracy to be achieved by means of 

 the sense of touch, which no existing microscope would enable the sense 

 of sight to attain. Accurate workmanship in machines is the most 

 effectual means of diminishing friction, wear, and breakage, of obtaining 

 economy of time, money, and materials, and of insuring efficiency of 

 action. The success of Mr. Whitworth's well known improvements in 

 fire-arms and projectiles is in the main due to accurate workmanship. 



51. When structures are classed according to their Pukposes, they 

 may be distinguished, for the most part, into Mines, Houses, Lines of 

 Conveyance, Harbours, and Vehicles, including Ships, which last class 

 partakes of the character of machines. 



52. On the subject of Mines, we shall say little, as being a special 

 branch of engineering, which would be treated of in a more satisfactory 

 way by a mining engineer. We may only remark, that great progress 

 has been made for some time past in the art of providing for the health 

 and safety of miners, by causing an adequate supply of air to circulate 

 in the workings. 



52 (a). In the same manner, we pass over the subject of Houses of 

 all kinds, as being the province of the Architect more than of the 

 Engineer. 



53. Amongst lines of conveyance, we shall first mention RoAns. The 



