*' HYLURGT. 437 



important kinds of wood, are the oak and pine. The oak, of the 

 genus of plants called quercus, is hard, heavy, strong, and durable; 

 particularly the white oak, and live oak ; which are the species most 

 used in ship building. The pine, or genus pinus, is softer, and 

 more easily wrought ; and, from its straightness, is generally used for 

 the masts of vessels. The spruce, and cedar, resemble pine, in their 

 properties and uses : the ash, is elastic and fissile ; the elm, and 

 hickory, are tough and strong, but less durable when exposed ; and 

 the maple, and black walnut, are used for furniture, as substitutes for 

 mahogany. Chesnut, and hemlock or Canada spruce, are used for 

 fences and coarse purposes ; and the bark of the hemlock and oak is 

 used for tanning leather. Trees, after felling, or cutting, require to 

 be seasoned, or freed from the sap, by drying, before they are used 

 for building. Water seasoning, consists in laying the wood for 

 some time under water; in order that the fermenting juices may be 

 dissolved out, before drying : and timber is also rendered more dura- 

 ble, by saturation with corrosive sublimate, or blue vitriol ; as proved 

 by Mr. Kyan, and others. 



Carpentry, is the art of working in timber and boards, in framing 

 and covering buildings ; though the covering, and especially the 

 internal finishing, is distinctly called joinery. Timber, after being 

 hewed, or sawed, into a proper shape, is framed, when the pieces 

 form an angle with each other, by cutting mortices, or cavities, and 

 tenons or projections, fitting closely together. When the timbers 

 are at right angles, braces are required, extending obliquely across, 

 from one to the other, to prevent the joints from springing. The 

 great principle in framing, is, to arrange the timbers in triangles ; so 

 that each side becomes a brace to the other two. A piece of timber 

 which acts by pushing, or resisting compression, is called a strut; 

 and one which acts by drawing, or tension, is called a tie. Timber 

 may be lengthened, by uniting two or more pieces endwise ; either 

 by splicing, or, as when they are notched into each other, by scarf- 

 ing. Thick boards are called planks ; and small timber is called 

 scantling. 



4. The Strength of Materials, is ascertained, primarily, by ex- 

 periments on each different kind : but when, by trials on specimens 

 of various dimensions, the law of variation is found, the strength of 

 other pieces, of the same kind, may be approximately determined 

 by calculation. When any material is drawn asunder lengthwise, 

 the strain which it undergoes, is called tensive : when it is crushed 

 lengthwise, as may happen to a column, the strain is compressive : 

 when broken crosswise, the strain is transverse; and when fractured 

 by twisting, the strain is called torsive. Hence, to resist these dif- 

 ferent kinds of strain, there are required four corresponding kinds of 

 strength ; which may take the same names as the kinds of strain or 

 force which they resist. It is remarkable that oak is stronger than 

 iron, for equal weights of the two materials. 



The tensive strength, is directly proportional to the cross section ; 

 without regard to the length. A bar of wrought iron, one inch 

 square, will sustain about 65,000 Ibs. of tension ; and a like sized 

 bar of oak, will require about 14,000 Ibs., to draw it asunder. The 



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