Art. 70. - Construction Essential. - Construction is that part of the Science of Building which treats of the Laws of Pressure and the strength of materials. To the architect and builder a knowledge of it is absolutely essential. It deserves a larger place in a volume of this kind than is generally allotted to it. Something, indeed, has been said upon the styles and principles, by which the best arrangements may be ascertained; yet, besides this, there is much to be learned. For however precise or workmanlike the several parts may be made, what will it avail, should the system of framing, from deficient material, or an erroneous position of its timbers, fail to sustain even its own weight? Hence the necessity for a knowledge of the laws of pressure and the strength of materials. These being once understood, we can with confidence determine the best position and dimensions for the several pieces which compose a floor or a roof, a partition or a bridge. As systems of framing are more or less exposed to heavy weights and strains, and, in case of failure, cause not only a loss of labor and material, but frequently that of life itself, it is very important that the materials employed be of the proper quantity and quality to serve their destination. And, on the other hand, any superfluous material is not only useless, but a positive injury, as it is an unnecessary load upon the points of support. It is necessary, therefore, to know the least quantity of material that will suffice for strength. Not the least common fault in framing is that of using an excess of material. Economy, at least, would seem to require that this evil be abated.

Before proceeding to consider the principles upon which a system of framing should be constructed, let us attend to a few of the elementary laws in Mechanics, which will be found to be of great value in determining those principles.

Interior Of The Cathedral, Sienna

Interior Of The Cathedral, Sienna.

Direct And Oblique Supports