CARPENTRY. 



cannot fail of bring well received in this age of im- 

 provement. It is hard that the nation, which boasts 

 \'ewton and Wren as the very founders, so to 

 ik, of the modern mechanics, should neglect the 

 path which originally led it to distinction among the 

 cientilic people of Europe. Our workmen are ac- 

 knowledged to be the a!)l-.--r, the mobt scientific, and 

 intelligent in the world. They well deserve to have 

 their labours assisted, and their desire for informa- 

 tion giatilied, hy the researches oF speculative nu;i. 

 Let the latter enter th,. workshop, the building yard, 

 or the manufactory, they \\.11 find themselves in the 

 midst of an assembly of men ot stionee, where, ere 

 they can pietend to communicate instruction, they 

 will perceive that they themselves have a greal deal 

 to learn. 



It is to be hoped, that the late national establish- 

 ment for the education of master shipwrights, will 



go great way towards extending our knowledge of Carpentry. 

 the carpentry. We were glad to tee, that *- T*~' 



a superior degree of information is expected in the 

 candidates for admission, than in those of our na- 

 tional establishment for engineers. This is as it 

 should be. The nation may then expect those only 

 to be admitted, who evince at least some ability for 

 llice, and some aptitude for iiibtnotion ; and 

 who will acquire under it care that superior know- 

 ledge which may qualify them for directing the la- 

 bours of artists, confessedly the first in the world, 

 instead of issuing from the seminary with no more 

 learning or experience than what might have been 

 equally well obtained at any country school. 



We propose to divide the present article into two 

 Parts ; the first containing the Theory of Carpentry, 

 and tlie second Constructive Carpentry. 



PART I. THEORY OF CARPENTRY. 



hcory of * HE science of carpentry depends on two princi- 



Carpcntry. pies : The strength of the timber employed, and the 



^T"*' strains to which it is exposed. 



Strains are, The strains to which timber is exposed are various. 

 They are simple, when the energy of the straining force 

 acts directly in overcoming the cohesion of the parti- 

 cles ; or they are compound, when it acts by the inten- 

 Tcntion of a lever, or other mechanical power. 



imple.or The simple strains are, 



1. The piece may be pulled or drawn in length, 

 as in the case of a kingpost, the upright rod of a 

 pump, or the like ; it is then usually named a tie. 



2. It may be compressed in length, as a post or 

 strut. 



3. It may be strained laterally or crosswise, as 

 when a tenon breaks off, or a rafter fails at the wall. 



The piece of timber is also exposed to similar 

 strains, acting on the softer connecting matter, in- 

 stead of the woody fibre. It may be split or torn 

 asunder ; it may be compressed or squeezed as a 

 wedge or tree-nail ; or it may be pushed out in the 

 direction of the fibre, as sometimes happens in the 

 heel of a mortice, 

 compound. The compound strains of most importance are, 



4-: The piece may be strained directly across, as a 

 joist or lintel ; or obliquely, like a rafter.. 



5. It may be twisted, as in the axles of mills, ship- 

 rudders, and screws. 



6. It may be bended or crooked,' and then sub- 

 jected to any of these strains, or to several of them 

 together. 



I. Of the Resistance to Distension in Length. 



The resist- Substances, of which the texture is uniform, such 

 ance to dis- as metal, glass, stone, or the like, resist a strain 

 tension, which tends to pull them directly asunder, by the 

 simple force of cohesion among their particles ; and 

 suppos^g the force of every particle to be the same, 

 the total amount will be as the number of particles, 

 that is, as the area of the section. But should the 

 body be of a fibrous texture, as timber or cordage, 

 the disruption may take place, not only by the snap- 

 ping of each individual fibre, but also by their sepa- 



ration, owing to one parcel being torn from among Theory of 

 the others with which it is joined. The resistance Carpentry. 

 to the fracture in that case will be produced by the ^y -< " >/ 

 friction of one fibre against another, increased in the 

 case of ropes by twisting, and in the case of timber 

 by the softer connecting matter intermingled with the 

 ligneous fibres. 



Should we suppose, with Galileo, that the fibres >' as the 

 give way all at the same instant, then it is perfectly area o{ 

 evident, that the direct or absolute force must be pro- ' racture - - 

 portional to the area of the section. But it is doubtful 

 how far we can depend upon that principle, even in 

 this simple case ; for it was long ago observed by 

 Leibnitz, Mariotte, &c. that there was no matter 

 how hard soever, were it glass itself, but would un- 

 dergo some extension before absolute rupture. There 

 is little doubt, but this property may have some ef- 

 fect, even in the case of simple distension. It cer- 

 tainly produces important modifications in every o- 

 ther case. The fibres, in extending, may compress 

 each other, at least, unless they are perfectly parallel 

 and longitudinal a rare, and indeed only a theoretical 

 case ; while, even there, each fibre, by the diminu- 

 tion of diameter, gets loose, and is deprived of the 

 benefit of lateral friction ; so that, by snapping at 

 their weakest parts and tearing out, they may afford 

 us a surface of fracture, having any given ratio to 

 the transverse section. But at present, perhaps, it 

 will be more useful to the practical carpenter, to de- 

 fer our inquiries into this department of our subject ; 

 we shall find another opportunity of resuming them. 

 This is a subject on which theory can afford us little 

 real information ; the absolute strength must be left 

 for the object of actual and judicious experiment. 



The inquiries which have been instituted for the 

 discovery of the strength of timber by means of ex- 

 periment, are by no means so numerous as could be 

 wished ; neither have they always been conducted 

 with due attention to those numerous precautions, 

 and exact historical description, which are absolutely 

 necessary to render them useful. Heuce, there are 

 in almost all of them great and anomalous differences. 

 Many experiments have, indeed, been made on the 

 transverse strength ; perhaps the most roagnificeat - 



