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these lines radiate from the centre, and are termed medullary! rays ; they produce that beautiful flowered appearance in theoak, to which the name of silver grain has been given.

It will not be necessary here to treat of the seasoning ofi timber, as that subject has been treated on in another place.

| See Seasoning op Timber.

! If timber be properly seasoned, and kept in a dry situation,with a free circulation of air, it will last for several centuries,but even under the most favourable circumstances it graduallydeteriorates, it loses its elastic and coherent properties, andbecomes brittle at last. If it be kept immersed in water, itwill also last a very considerable period ; but it is not unin-jured, for if it be taken out and dried, it becomes brittle,splits, and cracks in every direction. Alternate changes ofdryness and moisture is very injurious to timber, and undersuch conditions it rapidly decays, as may he observed in the1 upper part of piles driven in a tidal river, viz,, that part

| which is contained between high and low water. Moisture,

j combined with a certain degree of heat, about 45 degrees,will gradually decompose timber, especially when exposed tothe air. This rot is usually divided into two kinds, the wetand dry rot ; these, however, are both produced by the samecauses, the only difference being that the former takes placeI when there is a free evaporation, the latter when the evapora-j tion is imperfect ; the one takes place when there is a freej circulation of air, the other when the air is confined.

| The best method of preserving timber, and preventing| decay from any of the above causes, is by proper seasoning,

I but it must he thoroughly seasoned, partial seasoning being

j of little avail. A coating of paint, tar, or other preparation,

! will help to defend the wood from injury by external causes,

! i but will be of no service if any moisture remain in the! interior, for it will only prevent its escape, and thus hastendecay. Paint is also useless, unless fresh coats be repeatedlyapplied, for it is as liable to decay as the timber itself, andj therefore requires to be constantly renewed. If the paint; he sanded over, it will be found much more durable thancommon painting. A very good preparation consists oflinseed oil and tar put on boiling, the wood being firstj thoroughly heated ; this will sink into the wood, and closeup all the pores. Charring the wood will be found anexcellent method, and is in many respects better than someof the above. No composition should, however, be appliedtill the timber has been well seasoned, for to inclose thenatural juices of the wood, is to render its rapid decaycertain.

Description of Woods. —Of oak there are several kinds,two of which belong to England—the common British oak, andthe sessile-fruited oak. The first is found in the temperateparts of Europe , and is that which is commonly met with inthe south of England. The wood has often a reddish tinge,and the larger septa are very numerous, producing largeflowers ; the grain is tolerably straight and fine, and freefrom knots. It splits freely, and makes good laths for plas-terers and slaters; and is decidedly the best kind of oak forjoists, rafters, and for any other purposes where stiff andstraight-grained wood is required. The second kind isfound in the temperate parts of Europe , and in the north ofEngland ; it is of a darker colour than the preceding, andi the larger septa are fewer in number ; the grain is smooth; and glossy. It is heavier, harder, and more elastic, and isi apt to warp and split in seasoning ; it is tough, and difficult■ to split.

: The Dursault oak is a native of France and the south of

England, but it is not so strong nor of so firm a texture asthe above. The wood of the Austrian and American speciesis not very valuable; the former being comparatively soft and

the latter coarse-grained. The mounrain red oak, &Canada , is useful for many purposes, but is light and sp 0 °c^and not very durable. The white oak, also from Aw® 1 ' ^is more valuable, being tough and pliable, and more durathan the other species. ^

The colour of oak is a fine brown of various shades ;inclined to red is the most inferior kind. The tran ^ V ^ e sSsepta are usually large and distinct, but are smaller anddistinct in the stronger kinds of wood. The texture is 8nately compact and porous. , ^ ^

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and king-posts, but is liable to twist and warp

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Beech is not much used for building, and soon rots in _ \situations ; in dry situations it is more durable, but is l*

Oak is particularly adapted for situations exposed to ^weather, and makes the best wall - plates, ties, tefflp.

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to be injured by worms ; it is best adapted for piles ana j 3works where it is constantly immersed in water. tstronger and tougher than oak, but not so stiff. The c ° gr yis whitish-brown, of different shades; the texture i suniform, and the septa smaller than in oak. . fer y

Alder has much the same qualities as beech, being jdurable in water, but rotting when exposed to damp* ^jjsubject to worms in a dry state. The colour is re uf eyellow of different shades, and nearly uniform ; the te t |, 0is very uniform, with larger septa of the same colourwood. It is soft, and works easily. .

Of plane trees, that from America is very durable m rp[,ebut they are not much used for building purposes- j 0colour and structure is similar to that of the beech,this case the septa are more numerous. , oa k,

Chesnut may be used in many places as a substitute * aJ) dthe wood is hard and compact; when young it is to u oflexible, but when old it is brittle and often shaky-not shrink and swell much, and is easier to work thanoak, and contains only a small proportion of sap wood- ^ ^ j,a9

The wood of chesnut is so much like that of oak,

frequently been mistaken for it ; it has, however.

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transverse septa, and in old wood the sap-wood isthe heart-wood browner, than in oak. . toU gl*'

Ash is superior to any other British timber for t ioO*ness and elasticity ; it is tolerably durable in a dry ®'^ (Te9 ofbut soon rots when exposed to damp or alternate c* 1 ' ,^ 0 gStwet and dry. It is too flexible for the timbers of o u ] . g 0 akand in old trees is of a brittle nature. The colonybrown, the veins being darker than in oak; inhowever, the colour is lighter. The texture is il .compact and porous, the rings being strongly marke >are no large septa. , ra bl 0 '*}

Elm is not much used for building ; it is verywater, as also when perfectly dry, but will not stan 9 plb'to the weather. It is difficult to work, but not l* a p ue^K

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it twists, shrinks, and warps much in drying-

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wood is generally darker and redder than that <the sap-wood of a yellowish or brownish white; l£and cross-grained, but has no large septa. gr sU peT'' f

The common acacia is very durable ; it is equal *

to oak in stiffness and toughness, and is very v jj^t t> p ° tfencing. The colour is a greenish yellow, with a . J^oinP*of red in the pores, and is, in structure, alternat ^ _ jt i>and very porous, so that the rings are very distuno large septa. . . jpe ,, e y

There are several species of poplars, of whic ^ 4 1bardy, black, and common white, are mostly esteein^ ^ aB dare all very durable when preserved in a dry st» t j, n easpen or trembling poplar will last a considera j- 0 j- la oposed to the weather. They are not well adapt e