Of course the great and leading event of the nineteenth century in the matter of inventions relating to ships was the introduction of steam as the motive power. Of this we have treated in the chapter on steam engineering. The giant, steam, demanded and received the obeisance of every art before devoting his inexhaustible strength to their service. Systems of wood-working and metal manufacture must be revolutionised to give him room to work, and to withstand the strokes of his mighty arm. Lord Dundas at the beginning of the century had an iron boat built for the Forth and Clyde Canal, which was propelled by steam. But the departure from the adage that “ships are but boards” did not take place, however, until about 1829-30, when the substitution of iron for wood in the construction of vessels had passed beyond the experimental stage. In those years the firm of John Laird of Birkenhead began the building of practical iron vessels, and he was followed soon by Sir William Fairbairn at Manchester, and Randolph, Elder & Co., and the Fairfield Works on the Clyde. The advantage of iron over wood in strength, and in power to withstand tremendous shocks, was early illustrated in the _Great Britain_ built about 1844, the first large, successful, seagoing vessel constructed. Not long thereafter this same vessel lay helpless upon the coast of Ireland, driven there by a great storm, and beaten by the tremendous waves of the Atlantic with a force that would have in a few hours or days broken up and pulverised a “ship of boards,” and yet the _Great Britain_ lay there several weeks, was finally brought off, and again restored to successful service. Wood and iron both have their peculiar advantages and disadvantages. Wood is not only lighter, but easily procured and worked, and cheaper, in many small and private ship-yards where an iron frame and parts would be difficult and expensive to produce. It is thought that as to the fouling of ships’ bottoms a wooden hull covered with copper fouls less, and consequently impedes the speed less; that the damage done by shocks or the penetration of shot is not so great or difficult to repair, and that the danger of variation of the compass by reason of local attraction of the metal is less. But the advantages of iron and steel far outnumber those of wood. Its strength, its adaptability for all sizes and forms and lines, its increased cheapness, its resistance to shot penetration, its durability, and now its easy procurement, constitute qualities which have established iron ship-building as a great new and modern art. In this modern revolution in iron-clad ships, their adaptation to naval warfare was due to the genius of John Ericsson, and dates practically from the celebrated battle between the iron-clads the _Merrimac_ and the _Monitor_ in Hampton Roads on the Virginia coast in the Civil war in America in April, 1862.