英文科學(xué)讀本 第四冊·Lesson 21 More about Timber

Lesson 21 More about Timber

1. The Fir. —The fir and pine family are perhaps the most valuable of all our timber trees, because they are plentiful, and therefore cheap. The wood of these trees is not so strong nor so durable as many other kinds of timber, but it is easily worked.

The family comprise a great variety of trees. The most valuable among them are the larch, the pitch-pine, and the firs and pines of Norway, Sweden, Russia, Germany, and North America. These trees are all resinous, and yield resin, turpentine, and tar. The pinewoods of North America are said to be rich enough to supply the whole world with turpentine and resin.

The white and yellow pine of the Canadian forests is not one of the strong or durable woods, but it is much in demand in this country because it is so easily worked. Engineers make great use of this wood for models and patterns. Its smoothness of surface, its comparative freedom from knots and from the liability to warp as well as the ease with which it can be cut, make it specially suitable for this purpose.

The Scotch fir yields a very valuable timber, little inferior to oak. It is obtained from Scotland, Sweden, Norway, and Russia, and is frequently named red pine, red deal, and Riga fir. The spruce and silver firs are used largely for making ladders, masts of ships, scaffolding, etc.

2. Hornbeam. —This wood, from the closeness of its grain and the remarkable toughness of its fibers, is employed by engineers for the teeth of cog-wheels. It is also used for making mallet heads. For these purposes the wood is superior to all others, owing to its stringy structure and its great cohesive strength.

3. Mahogany. —This is a beautiful close-grained wood, capable of taking a high polish. It is remarkably free from liability to shrink, warp, or twist. It is superior to all other woods in its readiness to take a firm hold of glue. It is highly valued for furniture making, but will not stand exposure to the weather. The wood of the limbs or branches is preferred for ornamental purposes, because the grain is closer, richer, and more variegated than in the trunk itself. The mahogany tree is the king of all the forest trees. In comparison with this giant most other trees look insignificant.

The best wood is that known as Spanish mahogany, which comes from the West Indies.

4. Oak. —The British oak is one of the strongest and most durable of woods. It suffers less than any other from water, or the changes in climate. It stands first among the hard-wooded timber trees for its general usefulness. It is highly prized for ship-building purposes. It is also invaluable for making roofs, for which purpose its lightness, combined with its strength and durability, specially fit it. It is well—adapted also for the staves for casks, and for carriage wheels. Indeed, it is the best possible wood for all purposes where lightness and strength are required in combination.

5. Teak. —Of all the hard woods imported into this country, teak is the most valuable. It is useful for all purposes in which we employ oak. It is equally durable, and is not subject to decay through exposure to a hot climate, nor from worms or insects. It is largely used in shipbuilding, and in making gun-carriages.