Everyone knows how much iron is used in those great engineering structures that mark the present age, and of which a few examples will be described in succeeding articles. One other feature of the nineteenth century is the use of iron in architecture. Some have, indeed, protested against the use of iron for this purpose, and would even deny the name of architecture to any structure obviously or chiefly formed of that material. Stone and wood, they say, are the only proper materials, because each part must be wrought by hand, and cannot be cast or moulded; and further, iron being liable to rust, suggests decay and want of permanence, and these are characters incompatible with noble building. All this can rest only on a relative degree of truth—as, for instance, machinery is used to dress and shape both wood and stone, and the permanence of even the latter is as much dependent on conditions as that of iron. Iron used in architecture is hideous when applied in shapes appropriate only to stone; but when it is disposed in the way suggested by its own properties, and receives ornament suitable to its own nature, the result is harmonious and graceful, and the structure may display beauties that could be attained by no other materials. Be that as it may, the great and lofty covered spaces that are required for our railway stations and for other purposes could have been obtained only by the free use of iron, and everyone can recall to mind instances of such structure not devoid of elegance, in spite of the absence—the proper absence—of the Classic “orders” or Gothic “styles.” The first notable instance of the application of iron on a large scale was the erection of the “Crystal Palace,” in Hyde Park, for the great Exhibition of 1851. It was taken down and re-erected at Sydenham, and there it has become so well known to everyone that any description of it is quite unnecessary in this place. As another conspicuous example of what may be done with iron, the Eiffel Tower at Paris may be briefly described.