52 THE PKINCIPAL USES OF WOOD. 



curvature may be uniform throughout, or most accentuated at 

 about one-third the distance from the thicker end. The neces- 

 sary curvature is sometimes given by steaming or boiling and 

 then bending, or by hewing the piece to the proper shape ; both 

 these procedures, however, weaken the timber very considerably. 

 The framework of well-made river and canal boats is formed of 

 knees, which are pieces consisting of the stem and a strong branch 

 making an angle of from 90° to 100° with the former. The 

 branch portion, which is about half the length of the lower por- 

 tion, supports the deck. Knees are often used in sea-going boats 

 also for the same purpose. Indian river and canal boats, not 

 being decked, require no knees. The framework of a ship has to 

 bear all the enormous strains caused by the pitching and rolling of 

 the vessel, and must hence consist only of the soundest, strongest, 

 most elastic and most durable woods, weight being of course no 

 disqualification. The sides of the boat and ship are formed of 

 planks fixed transversely across the ribs by means of trenails, 

 which are large rivets of some straight-grained, strong, durable 

 wood. For curved surfaces the planks are steamed or boiled before 

 they are used, in order to render them pliant. The deck requires 

 a light wood with even grain, and one that does not shrink and 

 contract too much with varying quantities of imbibed moisture. 

 Teak is perhaps the best wood existing for decks. 



Mast pieces should be of some light but very strong and flexible 

 wood, and should be perfectly straight. Slow-grown pine contain- 

 ing only a small proportion of the soft autumn wood, and having 

 the resin distributed in a uniform manner, is the best. Such 

 pines come from, high latitudes, and, the supply being limited, are 

 extremely costlj^ The usual dimensions of mast pieces are — 

 length from 60 to 80 feet, diameter at thin end from 17 to 22 

 inches. The main-mast requires pieces nearly 100 feet long and 

 18-19 inches thick at the top. 



In iron-cased ships the plates have to be backed with teak, 

 which is the only wood that does not corrode the metal. 



AbTICLE 6. TiMBBE USED FOE JoiNEEY AND OaBIHET-MAKING. 



For furniture and house-decoration in any shape wood that 

 works easily, does not warp or split, and holds well at the joints is 

 required "Where beauty is demanded, the colour and grain of tbe 

 wood: should be suitable, and the wood should be capable of taking 

 a high polish. The mottled wood obtained from burrs and tree 

 trunks rendered knotty by numerous dormant buds and small epi- 

 corms, is always in great demand ; pieces exhibiting such marking 



