( \ I! P ENTRY. 



511 



'.10. 



ry of may slide in the groove. Besides, this form gives a 

 ' hold only in one '-iy, ami is therefore unlit for nusts 

 Tabling tin- pieces together, or keeping 

 them through in tin- pi me of the juint, would IK- mi 

 propei here, so much of the exterior fibres as aie cut 

 across by the tabling are unlit for di ti us on, and 

 therefore the compound be.im will be weaken 

 gainst a strain in the direction of the joining. The 

 one piece may also slide on the other in that line, at 

 least so far as to admit of serious headings, and the 

 Jo rni would have no rt-Mstance against twisting. 



The lateral slide is prevented in mast making, by 

 dividing the joint along the middle of its breadth, and 

 placing the projecting tahlmgs alternately on either 

 bide. (Fig. 10.) Thus , A, c, are projecting parts, 

 and d, e, f, are depressions, the other piece being 

 formed in the same way, the projections of the one 

 lit into the depressions of the other, viz. a into d, b 

 into c, and c into f, which prevents the beams from 

 sliding on each other, either longitudinally or trans- 

 versely, and resists twisting completely. 



Even this form is not without its defects ; for, in- 

 dependent of the jagged appearance of the seam, 

 which is unsightly, and lodges water ; that part of 

 the exterior side of the beam which is occupied by 

 the tabling, is not capable of resisting distension; 

 and this, in the case of a round mast or yard, becomes 

 of much consequence, as it occupies precisely the 

 most favourable situation for that purpose. The 

 mast-maker, therefore, perhaps with no other view 

 than to make a fair joint, does not carry his tabling 

 to the exterior side, but leaves two or three inches, 

 of what he calls good wood, keeping the coaks at 

 that distance from the edge of the beam, Fig. 11. 

 This is certainly a good practice ; and, of itself, suf- 

 ficient to prevent the lateral sliding. The coak is 

 thereby placed in that part of the beam which is near 

 the neutral line. It is not subject to strains, for 

 which it is not calculated, yet is sufficient, by its 

 abutment, both laterally and longitudinally, to make 

 a good connection of the pieces. 



Another method, called a running coak, is in fre- 

 quent use in the dock-yards. The coak is continued 

 the whole length along the middle, but the butts 

 project on each side of the middle line alternately, so 

 as to be one-third their breadth within and without 

 each other. This method has some advantages, as 

 the coaks have a hold both by the bottom and one 

 side, Fig. 12. 



There is still another method of forming the al- 

 ternate tabling, which not only gives a smooth seam, 

 but is als>o better fitted to resist twisting than the 

 running coak. The tables have their full depth in 

 the axis of the joining, but are sloped off towards 

 the outside like so many wedges, and end there in a 

 straight edge. This form has the full strength of 

 its fibres at the exterior side against every strain, and 

 the connection formed at the axis is sufficiently firm 

 to make the parts act together, Fig. 13. 



All these forms admit of hooping well ; and by 

 making the interior part somewhat full, we may com- 

 press the soft heart of the tree so far as to render 

 the assemblage much stronger than an entire tree of 

 equal size. 



Timber is also pieced, in order to increase its 



11. 



12. 



Fig. IS. 



Hooping, 



length; and there are a variety of methods of effect Theory ot 



ing this, omc of them very ingenious. The stroi. 

 and at the anie time the sin , .od of l--ngth- 



ening a be.un, wh- liter it be a pokt, a tie, or a rafter, 

 is to compo.se it of es, which are to placed in^of 



th.it th y niiy break joint, to use the mason's phrase, beams. 

 The necessary connection among them can be given 

 in any of the ways we have jusi mentioned, Fig. 14. PLATB 

 We are thus enabled in ties, to make certain of the CXIII. 

 cohesion of all the pieces but one ; and it is obvious, *' '* 

 that the strength increases with the number of pieces. 

 Besides, the connection among them becomes the 

 more certain, in consequence of the increase of the 

 surfaces of attachment. 



Fishing a beam is something of this kind. It con- pithing, 

 sists of clapping a piece of solid wood over a joint, 

 and attaching it firmly to both parts, either by bolts pjg. 15. 

 or tabling. (Fig. 15.) A strap is frequently placed 

 over such a joint, connecting the heads of neighbour- 

 ing bolts. This Is merely A Jlsh of iron. 



An eminent writer has said, that no tie of the same Splicing, 

 thickness of timber can be so strong as two pieces 

 laid over each other for a certain length, and bolted 

 together. (Fig. 16.) Now this is certainly wrong, pj^ ^ 

 for that very assemblage may be made stronger by 

 dowelling across the joint with a thin key. Neither 

 is the form of Fig. 17. No. 1. so strong as the other pie. 17. 

 mode, where the pieces have a square abutment, and No. 1, a 

 is every way stronger than No. 2. But as a tie, the 

 case is very different. 



The bolts are the only means of connection, and , . ^ 

 as great dependence seems frequently had upon 

 that sort of fastening, it may be worth while to 

 examine it a little more closely. It is clear, that 

 whenever we pass the joint RU, we can have on- 

 ly the tenacity of one half of the beam ASTC. 

 Now, how do we take hold of the other part 

 RUDB? It is by means of a bolt, and we hold 

 this by means of the bit beyond it. This piece 

 is only kept in its place by the connecting mat- 

 ter, which attaches it to the fibres. Our only hold 

 therefore, is a thin plate of the connecting matter 

 on each side of the bolt, and paraUel to it. The 

 second bolt gives us a hold of more of the con- 

 necting matter, but that still acts by means of 

 the same fibres ; and the third bolt does also the 

 same thing, which shews by the way the impropri- 

 ety of placing all the bolts in one line along the fi- 

 bres, as is frequently done. But besides this, when 

 the part comes to be stretched, the bolts will neces- 

 sarily yield a little, and then bear only on one side of 

 the holes ; the fibres near the junction may be expect- 

 ed to yield ; their number resisting an iron bolt is 

 small, and the position of the bolt enables it to act as 

 a lever in crippling them. Accordingly, such bolt* 

 quickly work loose, and, in reciprocating strains e- 

 pecially, the assemblage is very apt to give way at 

 once. Placing a strap over the joint to connect the 

 various bolt heads, may prevent the leverage above 

 mentioned, and will be an unquestionable benefit 

 against a transverse strain. But, even with every pre- 

 caution, the firmness which appears to be produced 

 by bolting, when carefully considered, is by no means And keys 

 so great as is generally imagined. The key placed or wedges, 

 across the joint of Figs. 18, 19, bring* as many fibres FJ i 8> t <, 



pj e- 17 

 No. S. 



