CONSTRUCTIVE CARPENTRY shows the method of reducing wool into firms. and joining the parts, as directed by the rides id' DESCRIPTIVE CARPENTRY. or by the laws of strength. and the;eby limning, a complete It is much to be regretted that the first principles of this department of the art are frequently so little understood bv those who are called upon to put them into practice. The young carpenter too often fidlows blindly in the track of those \dm have gone before him, without inqiiiry, and with out even attempting to understand the mechanical construc tion of the work he has just put together. \VC do not mean that the practical builder must necessarily make himself* master of the higher branches of science, but that it would obviously he of advantage to him that. he should acquire that general knowledge of the elementary principles of the art, which would enable him to select the best materials, and employ them in the best manner.
Every species of construction should he. characterized by stability, and a careful regard to economy of materials. These objects can only be obtained by judicious combinations of the substances used, so that the greatest amount of strength be secured with the smallest expenditure of mate rial. • 'Unless the builder possess it considerable knowledge of the principles of mechanics, unless he be acquainted with the eff2ct of pressure, and the resisting powers of ditfert nt materials, he cannot comprehend, much less design, such combination : but becomes a nacre labourer putting together the several parts of a work, without knowing their relative dependence on each other, or the streng,h, or want of strength, of the whole. He is. indeed, from the want of such knowledge as we have described, incapable of judging what are the best flirins of construction, or which of several modes of uniting timbers it is most advisable to make use of It is the province of constructive carpentry to show this, and the carpenter who is desirous to make himself thoroughly acquainted with his business, should study to acquire not only a practical knowledge of its details, but also some insight into the principles on which it is founded.
Construdi ye carpentry, it has been observed, is the method of reducing wood into forms. and the combining of several parts into a complete, 1111A N•hole. In most works, especially those of magnitude, it will frequently be necessary to join one or more pieces of timber, in order to obtain beams, &c., of sufficient size, and in order to economize material. The processes by which these objects are effected is a subject of' the greatest importance, as OR their being, properly and sub. stantially performed depends the stability of the structure in which they are used. Under this article then we propose to describe some of the most approved methods of uniting tim ber, and to treat of the following operations, vis., the length ening of beams, either by scarfing or joining thml in pieces; the strengthening of beams by trussing: the methods of join ing two timbers at angles. in any giVeIl direction ; and lastly, the mode of connecting several timbers, in order to pertbrin certain fonetions required by the design.
To lengthen a piece of tit tsar, is to join or fasten two separate pieces, so that a portion of the cud of the one piece shall lap upon a portion of the end of the other, the sides of both ntaking but one continued surface, and fiirming a close joint, called a scarf It is evident. that in the formation of a continued straight timber, if the joint consist of a plane, or planes, at right angles to two opposite sides of the compound piece, lint not at right angles to the plane of the other two opposite sides, the plane, or several planes, forming the scarf, will make the oblique constituted by the surface of each piece on the same sidr, supplements to each other: or w hateVer oblique angle or angles the one piece makes with a side, the corresponding angle or angles formed by the joint or joints with the same continued surthee of the other, will, together, iris two right angles, and thus the solid part of the one will he equal and similar to the void of the other.