On Architecture

2. On the same principle, with the ripening of the fruits in Autumn the leaves begin to wither and the trees, taking up their sap from the earth through the roots, recover themselves and are restored to their former solid texture. But the strong air of winter compresses and solidifies them during the time above mentioned. Consequently, if the timber is felled on the principle and at the time above mentioned, it will be felled at the proper season.

3. In felling a tree we should cut into the trunk of it to the very heart, and then leave it standing so that the sap may drain out drop by drop throughout the whole of it. In this way the useless liquid which is within will run out through the sapwood instead of having to die in a mass of decay, thus spoiling the quality of the timber. Then and not till then, the tree being drained dry and the sap no longer dripping, let it be felled and it will be in the highest state of usefulness.

4. That this is so may be seen in the case of fruit trees. When these are tapped at the base and pruned, each at the proper time, they pour out from the heart through the tapholes all the superfluous and corrupting fluid which they contain, and thus the draining process makes them durable. But when the juices of trees have no means of escape, they clot and rot in them, making the trees hollow and good for nothing. Therefore, if the draining process does not exhaust them while they are still alive, there is no doubt that, if the same principle is followed in felling them for timber, they will last a long time and be very useful in buildings.

5. Trees vary and are unlike one another in their qualities. Thus it is with the oak, elm, poplar, cypress, fir, and the others which are most suitable to use in buildings. The oak, for instance, has not the efficacy of the fir, nor the cypress that of the elm. Nor in the case of other trees, is it natural that they should be alike; but the individual kinds are effective in building, some in one way, some in another, owing to the different properties of their elements.

6. To begin with fir: it contains a great deal of air and fire with very little moisture and the earthy, so that, as its natural properties are of the lighter class, it is not heavy. Hence, its consistence being naturally stiff, it does not easily bend under the load, and keeps its straightness when used in the framework. But it contains so much heat that it generates and encourages decay, which spoils it; and it also kindles fire quickly because of the air in its body, which is so open that it takes in fire and so gives out a great flame.

7. The part which is nearest to the earth before the tree is cut down takes up moisture through the roots from the immediate neighbourhood and hence is without knots and is “clear.” But the upper part, on account of the great heat in it, throws up branches into the air through the knots; and this, when it is cut off about twenty feet from the ground and then hewn, is called “knotwood” because of its hardness and knottiness. The lowest part, after the tree is cut down and the sapwood of the same thrown away, is split up into four pieces and prepared for joiner's work, and so is called “clearstock.”

8. Oak, on the other hand, having enough and to spare of the earthy among its elements, and containing but little moisture, air, and fire, lasts for an unlimited period when buried in underground structures. It follows that when exposed to moisture, as its texture is not loose and porous, it cannot take in liquid on account of its compactness, but, withdrawing from the moisture, it resists it and warps, thus making cracks in the structures in which it is used.

9. The winter oak, being composed of a moderate amount of all the elements, is very useful in buildings, but when in a moist place, it takes in water to its centre through its pores, its air and fire being expelled by the influence of the moisture, and so it rots. The Turkey oak and the beech, both containing a mixture of moisture, fire, and the earthy, with a great deal of air, through this loose texture take in moisture to their centre and soon decay. White and black poplar, as well as willow, linden, and the agnus