Although the properties of timbers generally are better known than those of the other building materials that have already been discussed, it is necessary for the proper investigation of our subject to consider the leading characteristics that bear on their economic value, and in doing so I shall trace the timber through the various stages of its existence.

Structure.—As you are probably aware, the structure of ordinary timber is, to all intents and purposes, identical with that of a brick wall: it is composed of vertical and horizontal layers, breaking joints, and cemented together in much the same way. The vertical joints, consisting of the annual rings and medullary rays, are quite clear and distinct; but the horizontal ones, made from the interlacing of bundles of woody fibre of irregular lengths, are only visible to the microscopist. It is this difference in the length of the scarf, or joint, that makes splitting timber so much easier than cutting it across the grain. The concentric rings represent the growth in a year or season; they are generally very distinct in timber! grown in a cold climate, where there is a decided period of repose in the the vegetation; but in many tropical trees the rings are scarcely discernable, and some botanists allege that occasionally so many as four rings are formed in one year. The medullary rays are thin plates of woody matter that radiate from the pith to the bark, and form the weft which interlaces with the warp of the annual rings. Although believed to exist in all timbers, these rays cannot be traced in the firs and pines of the old country, but are very conspicuous in oak, beech, and other hard woods; this rule does not hold good in Otago, for there are few timbers hard or soft in which they do not appear. These medullary rays are what give the peculiar watered figure called silver grain, which is so much prized by cabinet makers and other manufacturers of fancy wood-work.

Growth.—The principal agent in the formation and development of woody fibre and tissue is the sap, which performs the same functions in plants that blood does in animals. After being extracted by the roots from the soil, it rises through the trunk to the leaves, and is there subjected to certain chemical changes that fit it for the formation of timber. In saplings, the fluid permeates and rises through the whole trunk; but in old trees with solid heart-wood, it is confined to the sap-wood and the bark. At this I stage the heart-wood contributes nothing to the other parts of the tree page 135 except in supporting them. The leaves are the lungs of the plant, but, instead of making the original fluid thinner, and purifying it by the extraction of carbonic acid and the addition of oxygen as in animals, they make the sap thicker, and add carbonic acid, which is the food of plants. The precise nature of the chemical process carried on in the leaves, and the exact constituents of its product, are imperfectly understood. After the sap has acquired the necessary ingredients, it returns through the outer layer of the wood and the inner layer of the bark, leaving in its course a deposit of ligneous matter on each, and permeating to a greater or less intent all the rings of sap-wood. The deposits made on the bark and wood harden into rings of timber and bark, the former to increase the size of the tree and the latter to replace the scales that are continually falling off the outer surface. The conversion of sap into heart-wood is attributed to the combined action of the juices and the compressive force exercised by the shrinkage of the outer rings and bark; but against this idea we have the fact of the change being generally sudden: one ring may be perfect heart, and the next sapwood of a very inferior quality. Whatever be the cause of this ripening of the timber, the process is not simultaneous with its growth, for the rings of sapwood always decrease in number as the tree approaches maturity, and there are frequently fewer rings on one side than the other.

Climate, situation, and soil, exercise a great influence on the character of timber. Among different trees the best timber is obtained from tropical countries, but in the same species the product of cold climates is found to be the strongest and most durable. Most authorities, ancient and modern, pronounce in favor of slow growth in timber trees as essential to perfection; but I observe that Mr. Laslett, Inspector of Timber to the Admiralty, entertains an opposite opinion formed from observations on oak and fir trees. I can easily understand the possibility of rapid growth being conductive to strength and durability, as it proves that the plant is well fed fed in vigorous health. Although the wood may be soft and porous in the young tree, it does not follow that the old one will inherit these qualities; the energy that puts forth strong shoots is in all probability sufficient to provide them with a proportionate supply of woody fibre and the other essentials of strength.

Timber grown in open ground is stronger and more durable than that from the dark forest, but, on the other hand, it is more subject to twists, shakes, and irregularity of composition, and the trees are often stunted and crooked. The effect of the weather is well shown on the southern side of Otago Peninsula, where the trees are blown into shapes as grotesque as could be seen in a Dutch garden.

The influence of situation and soil on the growth of trees is very re- page 136 markable, as the following table, compiled from the "Forester," will show, I It gives the diameter in inches at eight feet from the ground, of various I kinds grown in favorable and unfavorable situations:—

	Favourable Situations.	Unfavourable Situations.
Oak, 80 years old	31½ inches	11½ inches
Scots Pine, 50 years old	17 inches	7¼ inches
Larch, 35 years old	17 inches	8 inches
Spruce Fir, 35 years old	15 inches	6 inches

There is a considerable difference of opinion as to the proper season for felling timber; while all authorities are agreed in considering it the time page 137 when there is least sap in the tree, the time itself is not decided. One party argues that as vegetation is suspended during winter, there must be little sap in the timber. But the other maintains that midsummer is the best season for felling, as all the juices that rise in spring are then expended informing leaves. With deciduous trees, and in a cold climate, the chances are greatly in favour of winter felling, but, with evergreens and in a warm climate, there seems little choice between summer and winter. Of course there is a very marked difference in the quality of timber felled in winter and spring, and in summer and autumn. Experiments made in Germany to settle this point gave the following results. Timber cut in December was impervious to water end-wise; in January, a few drops percolated through in 48 hours; in February, two quarts went through in that time; and the March cut timber allowed two quarts to run through in two and a half hours. It is to be regretted that these experiments were not carried over the whole year, as the result would go a long way towards deciding the relative merits of winter and summer felling. Notwithstanding the fact that spring is admitted on all sides to be the worst season of the year for felling timber, it is the one in which the "indestructable" English oak is cut; this is in consequence of the bark, which is used for tanning, being more valuable when the sap is rising. Summer is considered the best time for cutting alder and beech in England; it is also the season in which oak is felled in I Italy and pines in Germany.

The ancients believed that the moon had a ripening influence on timber, consequently it was felled during her last quarter. The same belief was embodied in the Code Napoleon, and prevails to this day in the forests of Germany and Central America. It has a commercial significance in the latter place, for mahogany that is guaranteed to have been cut during the proper phase of the moon commands a higher price than any other. This lunar influence is probably quite imaginary, but when we consider the effect of the planets' attraction on the ocean, it is not unreasonable to suppose that vegetable juices may be attracted in a similar manner, at the same time we would expect a manifestation twice a month, as in the tides, instead of once only.

Qualities of Timber.—The chief attributes of good timber are—a minimum amount of sapwood, compactness of texture, and depth of colour there colour exists. The proportion of sap-wood varies in trees of different ages and kinds—chestnut, fifteen and half inches in diameter, has three eighths of an inch of sap all round; oak, seventeen inches diameter, has one and quarter inch of sap; and Scotch fir, twenty-four inches diameter, two and half inches of sap. The ordinary defects in growing timber are the shakes, or cracks and hollows that appear in the heart of full grown and page 138 over ripe trees. A small straight crack in the centre of a log does little harm, but when it is of a star shape, and has a twist in the length of the timber, its strength as a beam is seriously impaired, and it cannot be cut into planks. Another defect, known as the cup shake, consists in want of cohesion between the annual rings; it is less common but more serious than the one just described. The heart cavity is caused entirely by over ripeness in the trees, and its extent is in direct proportion to the time they have been allowed to stand after maturity. The cup shake is rare in Otago, but the other two defects occur in several kinds—a straight heart crack filled with gum or resin is very common in rimu, and the hollow heart is always met with in aged totara and cedar.

The same sizes of timber would be equally well seasoned by steeping for tea days in running water, and afterwards drying under cover for a month. The other methods of seasoning complete the work in a few hours and upwards, but what is gained in time is frequently lost in strength and durability; the only real benefit they bestow is the saving of shrinkage.

The ultimate transverse shrinkage in the seasoning of boards twelve inches square and half an inch thick, is found to be for oak, 1/12 the breadth; Riga fir, 1/32; Virginia pine, ½7; larch, ½7; elm, ½4; kauri, 1/64

Decay and Preservation.—The causes of decay in timber are of three kinds—1st. Chemical decay—a natural decomposition by the action of the air and moisture; 2nd. Vegetable decay or dry rot, a decomposition that takes place through the growth of fungi; and 3rd. Animal decay, waste by the destruction caused by worms and insects. The first of these is to all intents and purposes a slow combustion effected by the acids of the atmosphere, and greatly accelerated by changes from wet to dry. Most timbers will last a long time if kept constantly wet or constantly dry in an equable temperature, but the best only will stand exposure to severe alternations from wet to dry; the most trying situation for timber in this respect is in posts in the ground, decay always attacks it first at the surface, between wet and dry. I am not aware of any cure for this natural decay; charring, painting or tarring will retard its progress, but the only safe course is the use of a durable timber well seasoned. In connection with this I may notice a practice that exists among our settlers of inverting posts when putting them in the ground to increase their durability; like the lunar influence already noticed this was long thought to be only an imaginary benefit, but lately the matter has become an established fact. Experiments made in England on oak posts from the same tree showed those put in the ground with the top upwards as they grew, to be rotten in twelve years, while their neighbours that were inverted showed no symptoms of decay in sixteen years. This is explained by assuming that the capillary tubes are provided with valves which open upwards, on inverting the post these valves oppose the rising of moisture.

The relative durability of the timbers in common use in England has been ascertained by inserting pieces 2 5/8 inches square into the ground; they decayed in the following order:—

Lime, American Birch, Alder, and Aspen	3 years.
Willow, Horse Chestnut, and Plane	4 years.page 140
Birch	5 years.
Elm, Ash, Hornbeam, and Lombardy Poplars	7 years.

Oak, Scotch Fir, Weymouth Pine, and Silver Fir, were only affected to a depth of half an inch in seven years, and Larch, Juniper, and Arbor Vitæ were not touched at all in that time.

Vegetable decay or dry rot, is a regular disease induced in unseasoned timber by defective ventilation. In most parts of the world this is the worst enemy that timber has; we hear of ships being destroyed, and houses being made uninhabitable in an incredibly short time through its ravages and even cargoes of timber are seriously affected on the voyage from America to England. Hitherto this disease has been little known in Otago, not because any precautions are taken against it, but simply on account of the defects in our wooden buildings which give ample ventilation. I have seen several instances of dry rot in brick and stone buildings in Dunedin, but few in wooden ones; it is however very common in the timber work of mines.

The third cause of decay in timber, that by animals, is also of minor importance in Otago: the marine animals have caused some little trouble, but the land ones are scarcely known as destroyers in material that has been used. The latter class consist of a small beetle supposed to be much the same as the English one, and the large white worm that used to be eaten by the Maoris. These beetles are very destructive, particularly in carvings, but they are easily destroyed by fumigations; the large worm is very common in old trees lying in the forest, and I have seen it in piles that had not been barked, but never in wrought timber.

The marine animals most destructive to timber are the Teredo navalisor marine worm, and Limnoria terebrans, a small boring crab of the leech family, both of which are common in New Zealand waters. Captain Hutton finds that our Teredo is somewhat different from the European one, consequently it is called the Teredo antarctica. The Teredo is a worm-like animal from three to twenty-four inches in length, and from a quarter to an inch in diameter, according to the nature of the wood in which it has taken up its abode. It is furnished with a wonderful boring apparatus, like a pair of shell augurs, by which it perforates the hardest timber with astonishing rapidity. The smaller animal, which Mr. Kirk says is allied to Limnoria lignorum, although scarcely larger than a grain of rice, is as destructive as the Teredo. Large numbers attack the timber and speedily destroy it by fairly eating it away; indeed some animals of this species art able to penetrate stone.

The effectual preservation of timber in all conditions is a problem not yet solved. Oleaginous and bituminous substances retard the progress of page 141 decomposition, but without thorough seasoning and ventilation they are of little value. On the contrary, anything that closes the pores of the timber while it contains sap promotes decay. One of the best preservatives of timber is the creosoting process, invented 40 years ago by Mr. Bethell, which consists in extracting the natural juices by pumping and refilling the pores with creosote. Timber prepared in this manner resists decay of all kinds for a long time, but on account of the inflammable nature of the preparation and its obnoxious smell, timber that has undergone the process cannot be utilized in ordinary architectural work.