CARPENTRY is the art of cutting out, framing, and joining large pieces of wood to be used, in building. The only difference between Carpentry and Joinery is, that whilst the former includes the larger and rougher description of work, which is essential to the construction and stability of an edifice, the latter term comprehends the exterior finishing and ornamental wood-work. To enter into a detailed account of the numerous tools used in Carpentry, and the processes of forming, by their application, the almost illimitable variety of matters that are comprehended in constructive carpentry, would of course re5uire a volume to itself; and as the subject is foreign to the leading objects of this work, we shall under this head confine ourselves to some general obser vations of a practical nature, alike useful to the engineer as well as the car penter. With regard to the tenacity or strength of wood, it has been found by Muschenbroek and other eminent experimentalists, first, that the wood which surrounds immediately the pith or heart of the tree is the weakest, and that this weakness is greater as the tree is older. It is of importance that this fact be known, as a common notion exists of a contrary nature. Secondly, the fibres next to the bark, commonly called the white or blea, are also weaker than the rest ; and the wood gradually increases in strength as it recedes from the centre to the blea. Thirdly, the wood is stronger in the middle of the trunk than at the springing of the branches, or at the root ; and the wood forming a branch is weaker than that of the trunk. Fourthly, the wood on the northern sides of all trees that grow in Europe is the weakest, while that on the south-eastern side is the strongest; this difference is most remarkable in hedge-row trees, and such as grow singly. The heart of a tree never lies in its centre, but always towards its northern side, and the annual coats of wood are thinner on that side. In conformity with this, it is a general opinion of carpenters that timber is stronger in proportion to the thickness of its annual plates. The trachea, or air vessels, being the same in diameter and number of rows in trees of the same species, occasion the visible separation between the annual plates; for which reason, when these are thicker, they contain a greater portion of the simple ligneous fibres. Fifthly, all woods are moat tenacious whilst green, but attar
the trees are felled, that tenacity is considerably diminished by their drying. By the experiments of Muschenbroik, it appears that the absolute strengths of a square inch of the following different kinds of wood are as stated The woods mentioned were all formed into slips of uniform dimensions, and as much cut away from each, as to form a parallelopiped of one-fifth of an inch, that is, one-twenty-fifth of a square inch in section; and the weights which were required to tear these asunder, formed the data of the above calculations. Muschenbroelt gives a very minute detail of his experiments on the ash and walnut, in which be states the weights required to tear asunder slips taken from the four sides of these trees, and on each side in a regular progression from the centre to the circumference. The numbers in the foregoing, corresponding with these two woods, may be considered, therefore, as the average of more than fifty trials of each. He mentions, also, that all the other numbers were calculated with the same care. For these reasons some confidence may be placed in the results, though they carry the degree of tenacity considerably higher than those enumerated by some other writers. Pitot and Parent state, that a weight of 60 lbs: will just tear asunder a square line of sound oak, but that it will bear 50 lbs. with safety. This gives 8640 for the greatest strength of a square inch, or rather less than one-half of Muschenbroik's estimate ; but the latter is, we think, the most entitled to confidence, as the experiments were made upon greater masses of the material. It should, however, be observed, that two-thirds of the achial weight which may be sustained by a body, will greatly impair the strength after a considerable time, and that one half the absolute tenacity indicated by experiment, should be the utmost that an engineer should calculate upon in his constructions. Woods of the same denomination often differ greatly in their tenacity ; those with a very straight fibre suffer less injury from a load that is insufficient to break them immediately. Mr. Emerson mentions the following as the loads which may be safely suspended to an inch square of the several bodies hereafter enumerated ; but the term safely can hardly apply to the four first-named bodies.