concrete. Concrete alone is a material strong to resist compression, but weak in tension. It is a simple idea to reinforce it by embedding steel rods in it so as to compensate for this defect and enable the combined material to resist stresses of both kinds. But to actually carry the idea out it is necessary to know the character of the stresses to which the structure is subjected, so that the/ steel rods may be placed in such directions, in such places, and in the right 'quantities as to be able to supply the tensile strength required, and so that steel may not be wasted by being placed where it is not wanted. It is safe to say that no man can do this from his own experience alone. The construction of the graceful arch bridges of reinforced concrete, now so common, and of the large variety of other .structures in which the same material is used, has been made possible only by the application to the problem of methods of calculation based upon knowledge of the elasticity of materials that has been slowly gathered through many generations, and the theories developed have been checked at every stage by elaborate tests and experiments, in which engineers have applied the methods of experimental .science. The great development in the use of this structural material would have been quite impossible otherwise.
At the discussion before the Institute of Civil Engineers on a paper describing the bridge erected over the Zambesi River, just below the famous Victoria Falls, a story was told of a chief of the Barotse, one of the neighbouring tribes, who came almost daily and sat down and watched the building of the gossamy web of steel that was gradually extended over the gorge, 400 ft. above the water below. He said it was impossible that a small thing like that could carry anything, and that it would be dangerous to walk over it. When it was completed, and he found that a train could go over it, he said it was the finger of God that kept it up. And there is a sense in which the old chief was
