frequently allows too little substance for the tenon, lest he should weaken the mortice; and sometimes he falls into the opposite error; facts which clearly prove that he is not acquainted with a means of obtaining a maximum of strength with a given quantity of material.

Figs. 29 and 30 represent a simple mortice and tenon. The dotted

Fig. 29.

Fig. 30.

Fig. 31.

lines show the parts to be cut away. To show the thickness of the tenon, and consequently the width of the mortice, we have here one tenon and two shoulders, that is, three parts; one of which is to be allowed for the tenon, and two for the shoulders; and this will in general be found the best proportion, for if the tenon be more than that, it will weaken the shoulders of the mortice. Now if we have, as is frequently the case, two tenons in one piece, as represented in fig. 31, there will be five parts, two tenons, and three shoulders; so that each tenon will be one fifth of the thickness of the stuff, for the shoulders are all equal to the tenons. This rule may be generally observed, unless the tenon is at a considerable distance from the end of the stuff, and then something more may be allowed for its thickness, as the mortice is then not so liable to split; but it should in no case, however sound the timber, or tough the material, be more than two out of four parts; that is to say, it can never be safe to make the tenon more than half the thickness of the stuff, and that only under particular circumstances, when the mortice is near the middle of the scantling, for the piece in which the mortice is cut would, in other cases, be considerably weakened. There is frequently in joiners' work a shoulder at the bottom of the tenon that fits into the piece in which the mortice is cut, as represented in fig. 32; and the tenon is divided into two parts, as there shown, which, when the stuff is wide, is a good method, as it strengthens the piece in which the mortice is cut, without weakening, in the same proportion, the mortice itself; and we would suggest, in this case, that the piece BC, cut out from between the tenons AB

-B

Fig. 32.

and DC, be nearly, if not quite, one third of the distance AD; for if much less, the piece left between the mortice will add but very little to the strength of the piece in which the mortice is made; and the tenon would be stronger in proportion to the mortice-piece than necessary. It may be here observed, that if the width of the tenon be much more than four times its thickness, additional strength will be gained by

parts, as shown in the figure, dividing the tenons into two or more particularly if we allow a small piece at the bottom of the tenon, as represented in the drawing.

Grooving and Lapping.

This method of joining wood-work is analogous to that of mor ticing and tenoning. When it is required to join two boards toge ther by means of a tongue and groove, the groove should never exceed one third of the thickness; and often, if the piece for the tongue be formed of hard wood and liable to split, one quarter of the thickness will be sufficient. When a panel is let into a groove in the style, the joiner is often guided by the thickness of the panel itself, which should never be less than one third the thickness of the style.

In making a groove across the grain, as for partitions, it will be best, in most cases, to make it about a fifth or sixth of the substance. of the stuff. But, if the groove be formed into a dovetail, one quarter the thickness will be better, and the dovetail should be! made a little tapering, but not too much. It should, in fact, be so made as to go almost home without requiring a blow from a hammer or mallet to drive it into its place until it has nearly attained it; and all joints should be easily separated with a gentle blow before they are glued. In a lap-joint, that is, in lapping two pieces together, supposing them of equal thickness, half the substance of each should be cut away; and, if of unequal thickness, the lap should be made in the thinner piece, of about two thirds or three quarters of its thickness, according to the substance of the thicker piece; thus endeavoring in this, as in all other cases, to avoid weakening one piece more than another.

Bending and Gluing-up.

In bending and gluing-up stuff for sweep-work, much judgment is necessary, and, as the methods are various, we shall mention a few which the workman may apply, as occasion may require, one method being preferable to another, according to the nature of the work in hand,

The first and most simple method is that of sawing kerfs or notches on one side of the board, thereby giving it liberty to bend in that direction; but this method, though very ready and useful for many purposes, weakens the work, and may cause it to break when strains are thrown on the piece. But a tolerably strong sweep may be made in this manner, if, after sawing the kerfs

(particular care being taken to make them regular and even, and to saw them at regular depths), some strong glue be rubbed into each kerf. When bent into the required sweep, a piece of strong canvas should be glued over the kerfs themselves, and the glue be left to harden in the position to which the stuff is bent.

Another method is to glue up the stuff in thin thicknesses, in a cawl or mould, made with two pieces of thick wood cut into the required sweep. This method, if done with care, that is, making the several pieces of equal thickness throughout, of wood free from knots, is perhaps the best that can be devised for strength and accuracy. It is also a practice sometimes to glue up a sweep in three thicknesses, making the middle piece the contrary way of the grain to the outside and inside pieces, which run lengthwise. This method, though frequently used for expedition, is much inferior to the above, as the different pieces cannot shrink together, and consequently the joint between them is apt to give way.

A solid piece, if not too thick, may be sometimes bent into the form required. If a piece of timber be well soaked upon the intended outside of the curve, it may be bent into position, and if kept in that position till cold will retain the curvature that is given to it.

The only other method of forming a curve, necessary for us to mention, is that of cutting out solid pieces to the required sweep, and gluing them upon one another till they have the thickness required, taking care that the joints are alternately in the centre of each piece below it, something in the manner of courses of bricks one above the other. In this case, it will be necessary, if the work be not painted. to veneer the whole with a thin piece, after it has been thoroughly dried and planed level, and then made somewhat rough with either a rasp or toothing-plane. But the joiner must adopt one plan or another, according to circumstances.

Scribing

Scribing is the operation by which a piece of wood-work is made to fit against an irregular surface. Thus, for instance, the plinth of a room is made to meet or correspond with the unevenness of the floor. To deter nine the portion which is to be cut off from a partition, or any wood-work where a floor or ceiling is irregular, it is only necessary to open the compasses to a width equal to the greatest distance between the plinth and the floor; and, passing one leg over the uneven surface, the other leg will leave a mark on the plinth. If the wood be cut away on that line, a surface will be obtained which will make a good joint with the floor or ceiling. But the chief use of the art of scribing is to enable the joiner so to connect the moulding of panels or cornices, that when placed together, they shall seem to form a regular mitre-joint. This method has certainly one advantage over the common method of mitring, for, if the stuff should shrink, little or no alteration will be made in the appearance, but, under the same circumstances, a mitre

would open, and the joint would be shown. The method adopted is this: To cut one piece of the moulding to the required mitre, and then, instead of cutting the other to correspond with it, cut away the parts of the first piece to the edge of the first moulding. which will then fit to the other moulding, and appear as a regular mitre.

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Finishing of Joiners' Work.

Joiners' work is generally intended to increase the beauty of a building. When a joiner works in wainscot, oak, or mahogany, his chief object must be to obtain a surface perfectly smooth and even. When the framing is glued together, the glue which oozes out, and may be spilt upon the work, must be allowed to remain a few minutes and chill, and may then be carefully scraped off with a chisel; and the parts which cannot be thus cleaned may be washed with a sponge dipped in hot water and squeezed nearly dry. This not only saves trouble in operations which follow, but prevents staining, always produced when glue is suffered to remain till quite hard, particularly on wainscot, which turns black in every joint or place where the glue is suffered to remain. After this operation, which, though it may appear tedious to some workmen, will be found a saving of time, the work should remain till perfectly dry; and, when the joints and other parts have been levelled with a smoothing plane, the whole surface may be passed under a smooth scraper, and finished with fine glass paper. It will be sometimes necessary, when the grain is particularly cross, to damp the entire surface with a sponge "to raise the grain," and then again to apply the glass-paper. The work will then be ready for polishing with wax, or varnishing, and the good appearance of the work will be in proportion to the time and trouble expended in the process.

In cleaning pine, the same precautions must be taken for the removal of glue left upon the joints, or spilt upon the work, as already described. This being done, the work may be cleaned off with a piece of glass-paper that has been rubbed with chalk, or, in some cases, with a piece of hearthstone. The work is then ready for the painter; but as there are knots and other places where the turpentine contained in the wood is apt to ooze out, either with or without the increase of heat, and thus spoil the appearance of the finishing, those parts are done over with a composition, and the process is called priming. This is properly the painter's business; but it must sometimes be done by the joiner, for the sake of saving his work. The composition used for this purpose is made with red lead, size, and turpentine, to which is sometimes added a small quantity of linseed oil. Priming has also the advantage of preventing the knots from being seen through the paint. Some workmen omit in this composition the oil and the turpentine, but the size of itself is apt to peel off, and does not thoroughly unite itself with the wood.

Another method of cleaning-off pine is sometimes adopted. When the surface has been made quite smooth with the plane, it is rubbed with a piece of chalk, and the whole is cleaned with a piece of fine pumice-stone, as in the former process it was done with glasspaper; but if the grain should be still rough, the work may be damped with a sponge, and the operation repeated when dry.

As, in finishing interior work, it is now customary to imitate the graining of different kinds of wood, it is necessary that the joiners' work should be well finished for if a good even surface be not provided, it will be impossible for the painter to produce the effect he desires. Every defect in the ground will, in fact, he more visible under a delicate graining than when the surface is covered with successive coats of color but, even in the latter case, work well prepared will not only look better, but the color will not be so apt to chip and peel off as when the surface is not properly levelled.

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TERMS USED IN BUILDING.

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Abacus.-The upper member of the capital of a column, that on which the architrave rests. It has different forms in the several orders: In the Tuscan or Doric, it is a square tablet; in the Ionic, its edges are moulded; in the Corinthian, its sides are concave, and frequently enriched with carving.

Abutment. That part of a pier from which the arch springs.

Acanthus-A plant whose leaves are carved on the Corinthian and Composite capital. They are differently disposed, according to circumstances; and the leaves of the laurel and parsley are sometimes employed in their place.

Acroterium-A pedestal on the angle or apex of a pediment, intended as a base for sculpture.

Altitude. The perpendicular height of anything in the direction of the plumb line. The length of a body is measured on the body itself, and remains constant, its altitude varies according to its inclination to or from the perpendicular.

Alto Relievo. A sculpture, the figures of which project from the surface on which they are carved.

Amphiprostylos-An order of Grecian temples, having columns in the back as well as the front.

Amphitheatre. A double theatre, employed by the ancients for public amusements. The colosseum at Rome, built by Vespasian, is one of these.

Annulet.-A small square moulding, used to separate others; the fillet which separates the flutings of a column is sometimes known by this term.