At such important junctures in the history of shipbuilding as the introduction of steam power for propulsion in place of sails, and the employment of iron in place of wood for the hulls, precedent and experience lost much of their value under the new conditions. The association of civil and mechanical engineers with shipbuilding at these crises was of immense advantage. Such men as Fairbairn and Brunel, who had previously gained high reputations in other branches, were enabled by their scientific skill in designing bridges and other structures in wrought-iron, to achieve much, and to take the lead in ship design and construction. “To men of this class,” says Mr W. H. White, in the article already alluded to, “careful preliminary investigation and calculation naturally formed part of the work of designing ships; ‘rule of thumb’ was not likely to find favour, even if it had been applicable, which it was not, under the circumstances. At first, much was done on imperfect methods, comparatively in the dark; failures were not rare; yet progress was made, and gradually greater precision was attained, in the attempt to design steamers capable of proceeding at certain assigned speeds when laden to a given draught. In fact, the construction of steamers rendered imperative a careful study of the laws of fluid resistance, and of the cognate investigation of the mechanical theory of propulsion—both of which subjects lay practically outside the field of the designers of sailing ships. The speed of a sailing ship is obviously dependent upon the force and direction of the wind; her designer, therefore, chooses forms and proportions which will enable a good spread of canvas to be carried, on a handy stable vessel. Questions of resistance to the progress of the ship were therefore subordinated to sail-carrying power and handiness in sailing ships; whereas in steamers designed for a certain speed the question of resistance occupies a primary place, seeing that the engine power must be proportioned to the resistance. Consequently, while keeping in view stability, handiness, and structural strength, the designer of a steamer has a more difficult task than the designer of a sailing ship, and the difficulty can only be met if faced intelligently by scientific analysis. Hence it happened, as was previously remarked, that a more general appreciation of the value of scientific methods accompanied the development of steam navigation and iron shipbuilding in the British mercantile marine.”