ART. 1. Carpentry is the art of combining pieces of timber to support weight or to resist pressure.

The theory of carpentry is founded on two distinct branches of mechanical science: one informs us how strains are transmitted through a system of framing, and is determined by that part which treats of the equality and distribution of forces; the other, how to proportion the parts, so that they may be sufficiently strong to resist the strains to which they are exposed, or that which treats of the strength or resistance of materials. Each of these will be considered in the most simple manner the subject will admit of, with the addition of rules and practical remarks.

2. Timber is wrought into various forms according to the principles of geometry; and these forms can be preserved in their original shape only by adjusting the stress and strain according to the laws of mechanics. Hence the importance of studying both these sciences is evident, and particularly the latter; as, if the stress and strain be not accurately adjusted, the most careful attention to geometrical rules and the most skilful workmanship will be exerted in vain. For instance, if the centering of an arch were to be framed ever so truly to the curve required, what would it avail if the form changed with every course of stone laid upon it? And it must be remarked, that this is not an imaginary case, but one that has frequently happened; and not only to men ignorant of mechanics, but also to some of the most celebrated engineers that France ever produced.

The engineers of our own country have been more successful; they have gradually succeeded in improving the principle and in constructing centres which are superior to any of those designed by the French engineers. The greatest defect of the English centres is an excess of strength, which on principles of economy it would be desirable to avoid.

3. Of equal importance to the art of adapting materials to the requirements of science, is a knowledge of the nature and properties of those materials.