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THEORY AND PRACTICE OF ENGINEERING. Book II.

Fir (Pinus sylvestris ). — Of all the species this is the most valuable for its timber ; it isproduced in most parts of Europe , and its quality varies according to the soil on which itis grown: on a stiff cold earth, the wood has a red tinge, and acquires a solidity which itdoes not attain on sandy or light lands, where it becomes in colour nearly white. Sweden and Norway, as well as Prussia, Poland, and Russia , supply the English market from theirextensive forests with both timber and deals cut out of this tree ; the timber is floatedon the Gotha to Gottenburgh, being divested of its bark, and on the Glomra toChristiana : but that most esteemed from the Baltic is the Riga , which is preferred formasts by the navy; the Russian timber is said to take so long a time in reachingCornstadt, the port from whence it is exported, as to lose much of its quality.

In Scotland this species of fir, on favourable soils, attains considerable size, and formsmost excellent timber ; one tree at Dunmore contained 300 cube feet; and its durability,particularly the red, is equal to that of the oak : there are instances of its being found inthe roof of a castle, after 300 years, as full of resin and as fresh as any newly imported fromMcmel.

The appearance of fir timber differs materially: in the best, the concentric rings areseldom so much as inch in thickness, whilst they increase in the inferior kinds; thecolour is of a reddish yellow, and it has no large transverse septa : when spongy, andpresenting a woolly texture, it is improper for the purposes of construction.

lbs. lbs.

A cubic foot of this tree in a green state weighs from 54 to 74Ditto dry - - - 31 to 41

Finns Strobus. — The white or Weymouth pine is brought into the English market fromCanada or North America : its annular rings are not very distinct, nor is its durabilityremarkable, being subject to dry rot; a cubic foot when dry weigiis 29 lbs.

Pinvs, Mitis, or yellow pine, called in England the New York , is very full of turpentine,and more durable and of greater strength than the white pine above mentioned: it does notattain so large a size, but is a more valuable timber.

Pinus Abies , or Norway Spruce, is another variety of white deal, and considerablequantities are annually imported from Christiana, which are highly esteemed for theirquality : a cubic foot weighs 34 lbs. when dry.

Holly. — The veins of this wood are scarcely perceptible, but it is valuable for manypurposes, to the joiner, cabinet-maker, engineer and turner, as well as to the wood-engraver : when dyed black it is a substitute for ebony.

lbs. oz.

When perfectly dry it weighs - - - 47 7 per cube foot.

Hornbeam . — A hard, heavy, tenacious wood, very close-grained, is diminished much indrying, and consequently loses weight: the cogs of wheels are usually made of it, forwhich purpose it is well adapted.

lbs.

When green it weighs - - - 64 per cubic foot,

half dry - - - - 57

quite dry - - - - - 51

Laburnum is in use amongst turners : pulleys and blocks are made of it, being a hardand compact wood ; it is capable of endurance when exposed to the weather, and for variouspurposes is extremely valuable.

lbs. oz.

When perfectly dry a cube foot weighs - - 52 11

Larch (Laria :).—This valuable timber comes to perfection in a good soil in about 40years : the colour of its wood is a yellowish white; on some soils, particularly if on anelevated situation, it is of a reddish brown and very hard, so much so that it is difficult toseason, as it warps and twists in every direction ; this wood not being so knotty as that ofthe fir, is excellent for all sorts of carpenter’s work, being from its strength well adaptedfor girders and principal timbers. Scammozzi thinks it the most useful of all woodsfor the purposes of construction ; it is not attacked by worms; he also mentions theenormous size of some of the trees growing in the Venetian Alps, many of which heemployed in the public buildings at Venice. The Romans used this timber, and procuredit from Rhetia and Switzerland , floating it down the Po, then by the Adriatic, the Ionianand Tyrrhenian Seas, and finally by the Tiber to the Capitol: no wood endures so longunder water : in France and Switzerland it is much used for pipes to conduct water forthe irrigation of the lands, particularly in Provence; by the Swiss it is universallypreferred ; they cover their houses with shingles made of it, and from its taking a highpolish after planing it gives an agreeable finish to the interior : the closeness of its grain,and the strength of its fibres, enable it to resist twisting; it is not subject to crack,from which cause it was selected, according to Plinv, by the painters of old, as itwas by Raphael in later times. The knots are never in a state of decay, and it is much