MATERIALS OF CONSTRUCTION.
To enclose, cover, and separate the spaces, and to give to the structure its appropriate external form, we make use of the masses ivhich are com posed of the building materials. All materials have special properties, and in their choice Nature is again the master's infallible guide. She has built the mountains of solid rock, but the slender tree of elastic wood, that it may bend before the fury of the blast and spring back into its original position. She has constructed of inflexible material the skeletons of animals, but has covered the joints with elastic tissue, and has made the surrounding muscles soft and tender, yet tough enough to be the instruments of the energy which moves the animal on the earth or through the air.
The architect has a less ample choice of materials than Nature, yet he will also choose the strongest and best for a fabric that is intended to outlast centuries. Those parts which bear a superincumbent weight he will construct of the hardest and most resistant materials, while those which are present only for their own sake or to present a beautiful series of forms will be of materials that can be easily worked. But the architect must not only consider the requirements arising out of the building itself, but, if his building is to endure, must also provide against the assaults of external forces. Stone crumbles through exposufe, woodwork is
destroyed by fire, rust and impact deprive iron of its strength, and, accord ing as one or another of these foes is through circumstances most to be feared, so must the materials of the structure be chosen.
is true that in a structure erected for a modest purpose we cannot always aim at solidity alone, nor should we expect too much from a building which is designed to serve only temporary requirements. We must, however, increase our demands as the undertaking becomes more ideal. If the object is to serve an external requirement only, the structure, even if designed to be permanent, can be renewed after it has been impaired by the elements; but if it is to stand as the expression of a great idea, if it is to demonstrate to the contemporary world and to future generations what were the emotions of a people and a period, or if it is to be sacred to the Most High, it must be made of the choicest and most permanent materials—must be a monumental pile enduring as the mountains, not ephemeral like the forest foliage which is borne away by the autumn winds after the fulfilment of its summer mission.