the better it is, as it is more calculated to resist the different temperatures to which the work may be exposed.

3. Joining by joggles. The method of securing the joints of masonry by means of joggles is chiefly adopted for securing the joints of columns or pillars; and consists in sinking a cavity in the two pieces in such a manner as to make them correspond with each other, and inserting in that cavity a piece of metal, stone, or even wood, so that any lateral thrust may not be able to separate them. This method may, with very great advantage, be applied in the construction of domes, and works of the same nature, where it is necessary to avoid the lateral thrust as much as possible.

We may here take the opportunity of mentioning a plan proposed by Dr. Hutton, in his edition of Oznamare's Mathematical Recreations, for taking away the lateral thrust of domes and cupolas. The following is the problem proposed, and the solution given:

How to construct a hemispherical arch, or what the architects call an arc en cul-de-four, which shell have no thrust on its piers.

“Let A B, fig. 8, be two contiguous voussoirs, which we will suppose to be three feet in length, and eighteen inches in breadth. Cut out on the contig

uous sides two cavities, in the form of a dovetail, four inches in depth, with an aperture of the same extent, a, b, five or six

Fig. 9.

inches in length, and as much in breadth. This cavity will serve to receive a double key of cast-iron, as shown in fig. 9, or of common forged-iron, which is still more secure, as it is not so brittle. These two voussoirs will thus be connected together in such a manner that they cannot be separated without breaking the dovetail at the re-entering angle; but, as each of its dimensions in this place will be four inches, it will be easily seen that an immense force would be required to produce that effect; for we are taught, by well-known experiments on the strength of iron, that it requires a force of four thousand five hundred pounds to break a bar of forged iron an inch square, by the arm of a lever of six inches; consequently, two hundred and eighty-eight thousand pounds would be necessary to break a bar of sixteen square inches, like that in question. Hence there is reason to conclude, that these voussoirs will be connected together by a force of two hundred and eighty-eight thousand pounds; and as they will never experience an effort to disjoin them nearly so great, as might easily be proved by calculation, it follows that they may be considered as one piece."

They might be still further strengthened in a very considerable degree, for the height of these dovetails might be made double, and

a cavity might be cut in the middle of the bed of the upper voussoir, fit to receive it entirely the dovetail could not then be broken without breaking the upper voussoir also; but it may be easily seen that,, to produce this effect, an immense force would be required.

The second method proposed by Dr. Hutton is more properly by

9.999

A

B C

Fig. m..

the aid of joggles. Let A and B, fig. 10,, be two contiguous voussoirs, and C, fig. 11, the inverted voussoir of the next. course,. which ought to cover the

joint between A and B. Each of the voussoirs. A and B being

Fig. ..

this,

divided into two parts,, as ao and ed'; then if at ab and d we sink an hemispherical cavity, in which to introduce a globe of very hard marble, and in the upper voussoir, fig, 10, we sink similar cavities, de when laid on be, fig, 1, will form a secure joint without any lateral thrust; and the two courses cannot be separated without a force adequate to either break the solid stone, or disunite the marble globe; a force almost inconceivable, or ab least one far superior to that produced by the arch; the whole dome, or cupola, is, in fact, one solid mass, and can exert no lateral thrust upon the walls on which it is raised. Marble globes are recommended, because iron is liable to rust; but, if the joggles were made of iron, and covered with pitch before they were placed in the cavities, there would be little to fear from rust;, and particu larly as the iron is inclosed in the substance of the stene,, and quite excluded from the action of atmospheric causes.

Little need be said in this place as to morticing and tenoning, or dovetailing, except that they differ slightly from the same operations in joiners" work; for, as eement is used in the joining, they need not be so accurately cut, and are made shorter and thicker than those formed by the joiner, it being sufficient that the parts of each piece to be joined enter into each other at most five or six inches, even in large masses of stone: In small pieces, an inch or an inch and a half is sufficient; for, if the tenon or dovetail be too long, it will decrease the solidity of the joint. For greater security, a small channel is frequently eut in the shoulder of the joint, and melted lead is poured into it, which, filling up the space round the tenon or dovetail, makes the joint more secure, and the work firm

and solid

In laying some sorts of stones,, it is desirable, as far as possible, to place them in the same direction as they had when in the quarry, or, as it is termed by workmen, bedways of the stone; for, if laid in other directions, they are liable to peel and split by the action of the atmosphere..

BRICKLAYING.

Foundations.

The best soils for building upon are gravel, chalk, and stone rock.

Those most to be guarded against are sands, bog earth, clays, and made earth (no matter how hard). Where these occur, avoid piling (except in water works); plank the foundations through the centre of the walls, place long tassels in the piers, lay in chain bend, let the plates be stout, and in one piece, the whole length of each wall; all that is required is to so bind the building that it may settle altogether, and not partially..

In doubtful foundations, it is advisable to have a trench dug out to the depth of 2 feet to 3 feet below the footings of the brickwork, and about twice the width of the footings, which is to be filled up with concrete, composed of stone lime ground and ballast, or coarse gravel, to be anixed with water, in the proportion of one of lime to five or six of gravel; immediately that it is made up it must be shot into the trench from a stage, 6 feet above, which will cause it to fall in a solid mass; and in a few hours afterwards it will be as firm as a rock.

It is strongly recommended to have good plates; whatever may be slighted in other parts these should not be neglected-they are the soul and support of a building, and cannot, if put in too sinall, be taken out and replaced, as other timbers may; the difference in large houses will rarely amount to twenty-five dollars.

Bond the work-English bond-using all whole bricks, a course of stretchers and headers alternately.

Particular care must be taken that all the internal joints of brickwork are well flushed up with mortar; too frequently the workmen are apt to neglect doing it; the consequence is, that all the interior joints are hollow, and allow the damp to penetrate to the inside, no matter how thick the wall may be. Another serious defect in brick work is in not properly bonding the facing to the backing, particularly if the facing be "malms or bricks, which cost an extra price; generally the headers are only bats or half bricks, instead of being a stretcher or a whole brick to bond in with the brickwork at the back; there ought to be at least one stretcher in every 3 feet to each course, if there be not the wall will split or divide into two thicknesses.

In building arches of a large span, it is advisable to build them in half brick rims, with vertical or radiating bond every 3 or 4 feet in the girt; if this latter precaution be not adopted, the consequence will be, that when the centre is struck, the rims will divide and weaken the arch, and perhaps cause a total failure.

In selecting bricks, clap them together-if they ring well, and,

when broken, show that they are burnt through, they will answer the purpose. A hard clamp burnt gray stock is all that is wanted for strength; for water-works and foundations use clinker burnt mark stocks. Avoid samnel or place bricks, and chuffy stocks, and generally prefer hand tempering to pugging the clay.

In mixing of mortar, it is advisable to see that the laborer properly turns up the mortar, and that the lime is thoroughly corporated with the sand throughout; avoid using too much water, as it drowns the line and weakens it; in large works it is best to mix the lime and sand in a mill-cement must be mixed in small quantities

TABLE

Showing the Quantity of Earth to be removed, the Number of Bricks and Gallons in one foot in depth or length

In the measurement of brickwork no allowance is to be made in quantity for small or difficult works.

Flues to be measured solid.

Timbers inserted in walls not to be deducted.

Two inches to be allowed for bedding plates, where no brickwork is over them.

All cuttings to be measured superficially, excepting to bird's mouths and squint quoins, which are to be run.

The net quantity of brickwork being found, it is to be reduced to the standard thickness of a brick and a half, and brought into statute rods of 5 yards square, or 272 superficial.

Ovens, coppers, and solid walls, of irregular thickness, to be cubed and brought into the standard thickness, by multiplying by 8 (the number of 14 inches in a foot), and dividing by 9 (the number of 14 inches in a brick and a half, or 13 inches, the standard thickness).

Facings of all descriptions to be measured and charged extra, per foot superficial.

272 feet superficial is a rod of brickwork, 14 brick, or 134 inches thick, the standard thickness, to which all brickwork, of whatever thickness, is reduced.

306 cubic feet, or 11 cubic yards, equal to 1 rod of reduced brickwork.

4352 stock bricks to 1 rod reduced, 4 courses 1 foot high. 4533 ditto, if the 4 courses measure 11 inches high.

These calculations are without allowing any waste, which is more than amply compensated in dwelling-houses, by not deducting flues and bond timber; in such work, 4300 stocks, or 4500 place, are sufficient

5371 bricks laid dry to 1 rod.

4900 ditto in wells and circular cesspools.

A rod of brickwork contains 235 feet cube of bricks, and 71 feet of mortar (4 courses to a foot); which will weigh, upon an average calculation, 15 tons.

A rod of brickwork requires 14 cubic yard of chalk lime, and 3 single loads or yards of drift; or 1 cubic yard of stone lime, and 34 single loads or yards of sand; or 36 bushels of cement, and 36 of sharp sand.

16 bricks to a foot of reduced brickwork.

7 ditto to a foot super of facing.

10 ditto to a foot super of gauged arches.

30 bricks on edge, and 45 bricks flat, to 1 yard of bricknogging.

36 stocks laid flat, and 52 ditto on edge, to 1 yard of paving. 36 paving bricks laid flat, and 82 ditto on edge, ditto.

A load of mortar, 27 feet cube, requires 9 bushels of lime and 1 yard of sand. A hod contains 20 bricks.

Lime and sand loses one third of its bulk when made into mortar -likewise cement and sand.