From Duhamel's experiments;* reduced to English weights and measures.

The writer of an article on timber, in the ' Encyclopedie Methodique,' states that the weight of a cubic foot of green oak varies from 62.5 to 66 lbs.; of a cubic foot of seasoned oak, from 53.5 to 58 lbs.; and a cubic foot of very dry oak, from 44.6 to 47.3 lbs.† The timber of very old trees is often much lighter than this. The author has tried specimens from old trees that did not exceed 38.5 lbs. per cubic foot when dry. When the specific gravity is very low it may be safely concluded that it is the wood of an old tree, and that it will be brittle and deficient both in strength and toughness.

Some experiments ‡ have been made on the loss of weight

* ' Transport des Bois,' p. 66, et seq.

† 'Art. Bois, Dict. Architecture, ' Encyclopedie Methodique.

‡ Mr. Couch's Table is published in Barlow's ' Essay on the Strength of Timber,' and contains much valuable information. Mr. Knowles, in his ' Inquiry, etc.,' has added the following ones on two cubes of oak: -

in seasoning, by Mr. Couch, at the Royal Dockyard at Plymouth, from which the following are taken: -

To these experiments the following are added, which include some varieties of wood not before tried.

Wo are also indebted to Mr. Wiebeking for some experiments on seasoning timber; and as both the kinds of timber and the times of observation are different from those already noticed, his Table is a considerable addition to our knowledge of this important subject. It is in common with all the other Tables in this work, reduced to English weights and measures.*

* ' Traite' contenant une Parlie essentielle de la Science de construire les Ponts,' p. 114.

Wood, when cut into small pieces, very soon acquires its utmost degree of dryness. Dr. Watson, Bishop of Llandaff, in the month of March cut a piece from the middle of a large ash-tree that had been felled about six weeks, and weighed it; its weight was 317 grains; in seven days it lost 62 grains, or nearly one-fifth of its weight. It was tried again in August of the same year, but had not lost any more of its weight; hence it had become perfectly dry in the short space of seven days. He also found that the sap-wood of oak lost more weight in drying than the heart-wood, in the proportion of 10 to 7.*

Mr. Pontey ascertained that the sap-wood of larch lost two-fifths of its weight in drying.f

Durability of Timber.

457. It must also be remembered, that to give durability to his materials is one branch of the carpenter's art; and that to be defective in this particular is as much to his discredit, as to be unacquainted with the geometrical or mechanical principles of carpentry.

Of the durability of timber in a wet state, the piles of the bridge built by the Emperor Trajan across the Danube is an example. One of these piles was taken up, and found to be petrified to the depth of three-fourths of an inch; but the rest of the wood was little different from its ordinary state, though it had been driven more than sixteen centuries.*

* ' Chemical Essays,' vol. iii., p. 21.

† ' Forest Pruner,' p. 88. Mr. Pontey is completely wrong when he supposes his experiments to furnish any rule for the time it would require to season larger pieces.

The piles under the piers of old London Bridge had been driven about 600 years, and from Mr. Dance's observations, in 1746, it did not appear that they were materially decayed;† indeed they were found to the last to be sufficiently sound to support the massy superstructure. They were chiefly of elm.

458. We have also some remarkable instances of the durability of timber when buried in the ground. Several ancient canoes have been found in cutting drains through the fens in Lincolnshire, which must have lain there for many ages. In the ' Journal of Science, etc.,' published at the Royal Institution, one of these canoes is described, which was found at the depth of eight feet below the surface of the ground. It was 30 feet 8 inches long, and 3 feet wide in the widest part, and appears to have been hollowed out of an oak-tree of remarkably fine free-grained timber. ‡

Also, in digging away the foundation of old Savoy Palace, London, which was built nearly 700 years ago, the whole of the piles, consisting of oak, elm, beech, and chestnut, were found in a state of perfect soundness; as also was the planking which covered the pile-heads. Some of the beech, however, after being exposed to the air for a few weeks, though under cover, acquired a coating of fungus over its surface.§

459. On opening one of the tombs at Thebes, M. Belzoni discovered two statues of wood, a little larger than life, and in good preservation; the only decayed parts being the sockets to receive the eyes. The wood of these statues is probably the oldest in existence that bears the traces of human labour.*

* Buffon, ' Preuves de la Theorie de la Terre.' † Hutton's ' Tracts,' vol. i., p. 119. ‡' Journal of Science, etc.,' vol. i., p. 244. § ' Ency. Brit.,' art. Dry Rot.

A continued range or curb of timber was discovered in pulling down a part of the Keep of Tunbridge Castle, in Kent, which was built about 750 years ago. This curb had been built into the middle of the thickness of the wall,† and was no doubt intended to prevent the settlements likely to happen in such heavy piles of building; and therefore is an interesting fact in the history of constructive architecture, as well as an instance of the durability of timber.

In digging for the foundations of the present house at Ditton Park, near Windsor, the timbers of a drawbridge were discovered about 10 feet below the surface of the ground; these timbers were sound but had become black. Hakewell says, that Sir John de Molines obtained liberty to fortify the Manor-house of Ditton, in 1396; ‡ and it is most probable the drawbridge was erected soon after that time; and accordingly the timber had been there about 400 years.