Page:Popular Science Monthly Volume 2.djvu/608

588, and is usually considered by millwrights as next to hornbeam, both in strength, toughness, and general suitability for that purpose. It requires, however, to be kept very dry, for in damp situations it quickly wears out, but, when beech is immersed in water constantly, its endurance is considerable. The strength of beech is nearly the same as that of oak; it is also tougher, but its stiffness is inferior to that of oak, even to the extent of 25 per cent.

Elm, although a cross-grained, rough wood, and mostly used for rough purposes, is yet held in great estimation for its toughness and non-liability to split by the driving of bolts. It is much used in the construction of blocks for pulley-tackle, for heavy naval gun-carriages, and for the naves of carriage-wheels. It is a wood which is little affected by constant immersion in water, but decays rapidly when alternately wet and dry, and consequently is not very durable for purposes involving exposure to a wet climate. Its chief defect in ordinary use is its great liability to warp, and twist, and get out of form; and, as regards strength, toughness, and rigidity, it is inferior to oak, as well as in almost every other respect.

The fir and pine woods are members of a large family, and are of great variety, and differ much in most of their properties. These classes of timber, in addition to being employed for building purposes, are likewise the chief materials that are used in great works, where the question of strength combined with cost becomes the most prominent consideration. The most durable varieties are the larch, the pitch-pine, and the firs, from Memel and Norway, and are valued mostly on account of the large quantity of resin, pitch, and turpentine, which they contain. The Canadian pine, variously termed white or yellow, is not a strong wood, but is much used by engineers for making patterns or models, on account of its smoothness of surface, its non-liability to warp, its comparative freedom from knots, and the facility with which it can be cut. The white or yellow pine is not nearly so strong or so stiff as oak, yet sometimes it is almost equal to it in its tenacity and toughness. In such a large family as that of the resinous firs and pines, there is almost an equal variation in their strength, toughness, and rigidity.

Hornbeam is a wood which is comparatively little used, except by engineers, for the teeth or cogs of wheels, and for mallets, for which purposes it is perhaps superior to all other woods, and this is mostly due to its great toughness and remarkably stringy coherence of fibre. Its cohesive strength and other properties depend much upon its age, as a plank, and still more on the age of the tree from which the plank was taken. When in the most favorable condition, it is fully equal to the average of oak (even when considered merely as a wood), but when cut from older trees, and when over-seasoned, it is frequently found worthless, and has soon to be renewed. When of proper age and quality, it has no equal for its own special purposes.