CHAPTER VIII.

GENERAL QUALITIES OF TIMBER, AND SOME OF THE MORE REMARKABLE APPLICATIONS OF IT.—FORESTS, AND PLANTING.

As the qualities of the different species of timber compared with each other have been mentioned in the individual notices, little else will be necessary here than a mere catalogue of some of the leading properties.

Oak is best on soils where it is the longest in coming to maturity; and when two specimens are equally seasoned, their value may be ascertained by trying which, bulk for bulk, is the heavier; or by soaking them in water till they can contain no more, (and one very effectual way of doing this is by fixing a disc of oak cut across the grain, in a cylindrical jar containing a quantity of water from the top, and exhausting the lower part of the jar by an air-pump); and the one which is the heaviest in the dry way, or has its weight the least increased by the water, is the best. If an oak be dead at the main top, the centre of the tree is sure to be in a state either of actual or of incipient decay; and it is not safe to use any part of it for purposes where durability or strength is required. The same holds true of all deciduous treesevergreens are not so liable to be hollow, though many of them become so in the course of a very long time. An oak, or indeed almost any other tree that grows singly, or on the outside of the forest, is always more firm and durable than one which grows within the forest, and is partially sheltered; and the more variable the climate is, not so much with regard to seasons as to shorter periods, the timber is the more

firm and durable. An oak which stands alone on a hill side, exposed to the variable weather of Britain, will, as timber, outlast two from the thick forests of Germany, or three from North America, where the summer is intensely hot, and without a cloud for many weeks together.

On

Trees which are to be used as timber should be felled in the early part of the winter when the sap is at rest; because, when the sap is in motion, the trees are apt to bleed, by which the durability of the timber is diminished. This applies to pines as well as to deciduous trees; for though they and other evergreens retain their leaves during the winter months, they do not vegetate at that season. account of the value of the bark, however, which cannot well be removed from winter-felled trees, there is a great temptation to fell oaks in the early part of the summer. In coppices, or hags, where the bark is the principal object, and the wood is to be used for charcoal or for common purposes, there is of course no harm in cutting down during the season of vegetation; but a summer-felled oak ought never to be introduced into a ship, or into the timbers of a valuable permanent building.

Oak grown on damp situations decays much sooner than that which grows on dry, and the decay is from the outside gradually to the centre. This, however, is to be understood of timber which has been felled before beginning to decay; for if decay be begun, the timber rots first at the centre.

Oak is best seasoned in water, or rather in water and in air alternately, taking care not to expose it so to the sun during the dryings as that it shall champ and split. A large beam of oak ought to soak for at least twelve months, but half that time will do for planks. It is often the practice to season planks by boiling and steaming; and when they have to be

curved or twisted, as in the bends of a ship, steaming is unavoidable; but the heat and moisture together always weaken that constituent principle of the timber upon which its strength and durability in a great measure depend.

Ash is a bad timber for any purpose in building, whether for dry or aquatic purposes, because it neither stands moisture nor the weather. Beech also is a bad timber for building, though when wholly under water it is durable. Elm is quite unfit for building, because of its tendency to warp and shrink with drought, and expand with moisture; but when wholly under water, it answers well; and bolts and nails drive better into it than into any other timber. Beech and elm answer remarkably well for the external or lower keels of ships, and also for the planks nearest the keel, as these are seldom exposed to the air: the same qualities fit them for being used as piles in the construction of bridges and harbours; though they should never be used above the low water mark.

The different species of poplar, the sycamore, the lime, and the birch are, generally speaking, unfit for building, being neither strong nor durable; birch is indeed very tough, but it is more subject to worm than almost any other timber, and moisture soon rots it. Lime, however, is much the best timber for carving, and poplar answers very well for the boardings of stairs.

The properties of chesnut have already been pretty extensively mentioned. It is probably the best of the building timbers, though it has been unaccountably neglected in this country. Our ancestors did more justice to it; and some of the finest specimens of ancient carpentry, both in scientific construction, and in tasteful execution, are made of it. When old, it is not very easily distinguished from

oak, but its colour is finer, and it does not stain by the contact of iron, which is always the case with oak when moisture gets access to it.

Mahogany is too costly and too ponderous for its strength, to be used as a building timber. But, when well seasoned, it warps and shrinks less by the heat of the sun than any other wood; and therefore it is the best timber for sign-boards. It is also excellent for doors and window-frames, but too expensive for ordinary occasions. The mahogany from the main land of America is called Bay wood; and that from the islands-chiefly Jamaica, Cuba, and HaytiSpanish wood. Before they are oiled or varnished, they are easily distinguished: the pores of bay wood are dark coloured; those of Spanish seem filled with a chalky matter.

Fir, when of the best quality, has some advantages over oak for the purposes of common building: it is lighter, far more elastic, more easily worked, straighter, and of much greater length. The best that comes in the form of deals is from Christiania and Frederickstadt, chiefly on account of the vast superiority of the saw-mills there. The fir of Norway has also been long celebrated for masts; and though more weighty, it is far more durable than that obtained from America.

APPLICATIONS OF TIMBER.

The structures in which timber has been employed, which have been, or are, the most remarkable for their magnitude and utility, are roofs of buildings, bridges and piers, light-houses, and ships. For all of these, timber appears to have been principally used before the introduction of any other material, in every place where it could be obtained: and, notwithstanding the use of stone pretty generally for piers, and since the invention of the arch,

often for bridges, and occasionally for roofs, and the more recent introduction of iron for some of those purposes, wooden structures are met with in all countries, of vast dimensions, and often of great strength and beauty.

ROOFS, &c.

In modern roofing, the timbers of the roof are generally hid by a ceiling, so that strength only is attended to; while in more ancient times, the timber itself was made at once both ornamental and useful: and in very large apartments, such as the banqueting halls of the kings and barons of the middle ages, it had the advantage in point both of grandeur and apparent stability. An extended flat ceiling appears to hang in the air; while in an ancient roof, like that of Westminster-hall, the support of every piece of timber is apparent, and the only strain which appears directly across the timber, is on the boards and rafters between the great trusses.

Westminster-hall is the largest roof of the ancient construction any where to be met with; and it is difficult to imagine a work of human art which possesses, in so equal a degree, the three requisites of beauty, strength, and durability. This hall was built by William II. (Rufus), in the year 1097; it was originally intended as a banqueting hall; and the monarch is said to have held a magnificent feast in it on the Whitsuntide after its erection. Stowe adds, that ample as are the dimensions of the hall, it did not satisfy the ambition of the king, who observed, "This halle is not bigge enough by one half, and is but a bed-chamber in comparison of that I minde to make." And Stowe adds, "a diligent searcher might yet find out the foundation of the hall, which he hadde proposed to build, stretching from the river Thames even to the common highway." All traces