the art of forming hard bodies, as wood, ivory, iron, into a round or oval shape, by means of a machine called a lathe.

This art was well known to the ancients, and seems to have been carried by them to a very great degree of perfection; at least, if we believe the testimony of Pliny and several other authors, who tell us, that those precious vases enriched with figures in half-relief, which still adorn our cabinets, were turned on the lathe.

The art of turning is of considerable importance, as it contributes essentially to the perfection of many other arts. The architect uses it for many ornaments, both within and without highly finished houses. The mathematician, the astronomer, and the natural philosopher, have recourse to it, not only to embellish their instruments, but also to give them the necessary dimension and precision. In short, it is an art absolutely necessary to the goldsmith, the watchmaker, the joiner, the smith.

Turning is performed by the lathe, of which there are various kinds, and several instruments, as gouges, chisels, drills, formers, screw tales, used for cutting what is to be turned into its proper form as the lathe turns round. The following is a simple kind of lathe (fig. 1.), in which a is the footstool, b the cord, c the frame of the lathe, d d' the puppets, e e the points, f the spanging-tree.

The lathe should be fixed in a place very well lighted; it should be immovable, and neither too high nor too low. The puppets should neither be so low as to oblige the workman to stoop in order to see his work properly, nor so high that the little chips, which he is continually driving off, should come into his eyes.

The piece to be turned should be rounded (if it be wood) before it be put on the lathe, either with a small hatchet made for the purpose, or with a plane, or with a file, fixing it in a vice, and having it down till it is everywhere almost of an equal thickness, and leaving it a little bigger than it is intended to be when finished off. Before putting it on the lathe, it is also necessary to find the centres of its two end surfaces, and that they should be exactly opposite to each other, that when the points of the puppets are applied to them, and the piece is turned round, no side may belly out more than another. To find these two centres, lay the piece of wood to be turned upon a plank; open a pair of compasses to almost half the thickness of the piece; fix one of the legs in the plank, and let the point of the other touch one of the ends of the piece, brought into the same plane with the plank on which the compasses is fixed and very near the fixed leg. Describe four arches on that end at equal distances from each other at the circumference of the end, but intersecting one another within; the point of intersection is the centre of the end. In the same manner must the centre in the other end be found. After finding the two centres, make a small hole at each of them, into which insert the points of the puppets, and fix the piece so firmly as not to be shaken out, and yet loose enough to turn round without difficulty.

The piece being thus fixed, it is necessary in the next place to adjust the cord, by making it pass twice round the piece, and in such a manner that the two ends of the cord, both that which is fixed to the spang and to the foot-board, come off on the side on which the turner stands, that the piece may move against the edge of the cutting-tool and be turned. If the lathe be moved by a wheel, the manner of adjusting the cord needs no directions.

If the workman does not choose to be at the trouble to find the two centres of the piece in the manner described above, let him lay, as nearly as he can, the centre of one end upon the point of the left hand puppet, and then let him push forward the right hand puppet, striking it with a mallet till its point is as near as he can in the centre of the other end of the piece; and then fixing the right hand puppet by a gentle blow of the mallet on the key, let him turn round the piece to see by the eye if the centres have been properly found. If any part of it bellies out, let him strike that part gently with the mallet till it goes properly; then let him strike one of the puppets pretty smartly to drive the points into the piece, and afterwards fix the puppet by striking the key. If the workman cannot judge by the eye whether the piece be turning properly round its centres or not, he should apply gently the point of an instrument called a triangular graver, leaning it on the reft, and it will mark by a line the place where the piece is out of its centre; and by striking upon this line with a mallet, the piece can easily be placed properly. The reft, of which we have just spoken, ought to be placed upon the two arms of the lathe, and fixed with screws as near the piece as the workman pleases.

The piece being fixed between the two points of the puppets (or, as they are called in Scotland, the heads), the cord adjusted, and the reft fixed as near the work as possible without touching it; the workman is now to take a gouge (Fig. 2. in which a is the mouth and b the handle) of a proper size in his left hand, and hold it by the handle a little inclined, keeping the back of the hand lowermost. With his right hand, the back of which is to be turned upwards, he is to grasp it as near the end as possible on this side of the reft; then leaning the gouge on the reft, he is to present the edge of it a little higher than the horizontal diameter of the piece, so as to form a kind of tangent to its circumference; then putting the right foot on the foot-board, and turning round the wheel, and holding the gouge firmly on the reft, the piece will be cut neatly. In the same manner are the chisels, formers, and other instruments to be used, taking care that the wood be cut equally, and that the instrument be not pushed improperly, sometimes stronger than at others; and taking care also that the instrument used do not follow the work, but that it be kept firmly in the hand without yielding.

The young turner ought to endeavour to acquire the management of the gouge and the chisel, which are the instruments by far the most frequently used, and the most necessary in this art: by them, almost entirely, are the soft woods turned; but as for hard woods and other things, as box, ebony, horn, ivory, and the metals, they are hardly ever turned except by shaving off. In that case gravers are to be used with square, round, or triangular mouths (fig. 3, 4, 5.). They should be held horizontally while applied to the wood, and not obliquely as directed for the gouge and the chisel.

After the work is completely turned, it is next to be polished; and this cannot be done with the instruments hitherto mentioned. Soft woods, as pear-tree, hazel, maple, ought to be polished with shark-fkin or Dutch rushes. There are different species of sharks; some of which have a grayish, others a reddish skin. Shark-fkin is always the better to be a good deal used; at first it is too rough for polishing. The Dutch-rub (equisetum hyemale), which grows in moist places among mountains, and is a native of Scotland. The oldest plants are the best. Before using them they should be moistened a little, otherwise they break in pieces almost immediately, and render it exceedingly difficult to polish with them. They are particularly proper for smoothing the hard woods, as box, lignum vitae, ebony, &c. After having cleaned up the piece well, it should be rubbed gently either with wax or olive-oil, then wiped clean and rubbed with its own rasps or with a cloth a little worn. Ivory, horn, silver, and brads, are polished with pumice-stone finely pounded and put upon leather or a linen cloth a little moistened : with this the piece is rubbed as it turns round in the lathe; and to prevent any dirt from adhering to any part of it, every now and then it is rubbed gently with a small brush dip in water. To polish very finely, the workmen make use of tripoli, a particular kind of earth, and afterwards of putty or calx of tin. Iron and steel are polished with very fine powder of emery; this is mixed with oil, and put between two pieces of very tender wood, and then the iron is rubbed with it. Tin and silver are polished with a burnisher and that kind of red stone called in France languine dune. They may be polished also with putty, putting it dry into shamoï-fkin, or with the palm of the hand.

To succeed in turning iron, it is necessary to have a lathe exceedingly strong in all its parts, and exceedingly well fixed. The puppets should be short, and the reft well fixed very near the work: the back of the reft should be two or three lines lower than the iron to be turned.

The lathe and other instruments being prepared, it is necessary to determine the length and thickness of the iron to be turned according to the design which is to be executed, and to make a model of it in wood a little thicker than it ought to be: Then one exactly like this is to be forged of the best iron that can be procured; that is to say, it must not be new, but well prepared and well beaten with hammers; it must have no flaws, nor cracks, nor pimples. New iron, which has not been well beaten, often contains round drops of cast iron, called by the workmen grains, which blunt the edges of the gouges, chisels, and other instruments used for cutting, break them, or make them slide. The iron being forged according to the model, it should be annealed, that is, heated red hot and allowed to cool slowly on the coals till the fire go out of itself. Some people, to soften the iron, cover it over with clay and allow it to cool. The iron cylinder being thus made, it is next to be put upon the lathe, finding the centres as formerly directed, and boring a small hole in them that the iron may not escape from the points.

The points should be oiled from time to time to prevent their being excessively heated and spoiled while the iron is turning. A crochet is then to be applied to the iron to be turned, a little above its centre, pretty gently, and by this means the inequalities of the cylinder will be taken off. Other instruments are then to be applied to mould the iron according to the model; and whenever any of them grow hot, they are to be plunged into a basin of water lying beside the workman. If the iron, after being properly turned, is to be bored like a gun-barrel, one of the puppets is to be removed and another substituted in its place, having a square hole through it, into which the collar of the iron is to be fixed firmly, so as not to shake; then borers are to be applied, like those which locksmiths use to bore keys; and beginning with a small one, and afterwards taking larger ones, the hole is to be made as wide and deep as necessary; great care must be taken to hold the borers firm on the reft, otherwise there is danger of not boring the hole straight. The borer must be withdrawn from time to time to oil it and to clean the hole. Since it is difficult to make a hole quite round with borers alone, it is necessary to have also an instrument a good deal smaller than the hole, one of the sides of which is sharp, very well tempered, and a little hollow in the middle. This instrument being fixed in a pretty long handle, is to be applied with readiness to the inner surface of the hole, and it will entirely remove every inequality that may have been there before its application.

To cut a screw upon the cylinder, some persons use an instrument consisting principally of a female screw; but this is rather an improper instrument; for if one presses too violently, or inclines it ever so little to the right or left, he runs the greatest risk of spoiling the screw. To avoid this danger, some use it only to trace out the lines of the screw, and afterwards finish it with a file. But the following is a much better way. Take a tap for making a female screw, the threads of which have been cut very accurately, and exactly of the size of the screw which you want; and having put it in the opening which you have traced in the collar of the axis

PLATE DXL.

Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5.

VARIATION of the Compafs.

Fig. 1.

Fig. 3.

Fig. 2.

W. Prain Sculpt. axis on which the screw is to be cut, folder it with tin, sal-ammoniac, and rosin, as exactly corresponding to the axis as possible. Take then a puppet with a hole cut into a corresponding female screw, into which the male screw is to be put. The axis on which the screw is to be cut must be placed exactly horizontally between the two puppets. The reft is then to be brought as near as possible to the place where the screw is to be cut, and a small hollow should be cut in that part of it which is exactly opposite to the place where the screw is to be cut, to hold your instrument firmly and prevent it from shaking. The instrument with which the screw is to be cut should be very sharp, and its point should make an angle of 60° with the screw to be cut ; and if you with the screw to be cut very deep, it should make an angle a little larger. The lathe being now put in motion, the tap fixed at the end of the axis will move gradually through the female screw in the puppet; and your instrument in the mean time will trace a similar male screw on the axis fixed in the lathe. Many persons, after having in this manner drawn the outlines of the screw, finish it with a screw-tale of three teeth corresponding exactly to the size of the screw, or with a triangular file; but this last method is rather improper.

For turning ovals, a lathe of somewhat a different construction is used. The axis or spindle, having on it the pulley over which the band-cord passes for turning the lathe, is fixed between the two puppets so as to turn round easily : one end of it passes through one of the puppets, and to it is firmly fixed a circular plate of brads, so that it turns round along with the spindle. Upon this plate two brazen segments of circles are fastened, the circumferences of which correspond to the circumference of the plate : their chords are parallel, and equally distant from the centre of the plate, so that they leave a distance between them. They have a groove in each of them : in these grooves another plate is placed which exactly fills up the space between the two grooves, but is shorter than the diameter of the large circular plate on which it is laid. This plate is made to slide in the grooves. To its centre is fixed a short spindle, on which the piece of wood to be turned is fixed. When the lathe is set a going, the circular plate moves round, and carries the piece along with it; the plate of brads on which the piece is fixed being fixed loosely in the grooves already described, slides down a little every time that the grooves become perpendicular to the floor (and there are particular contrivances to prevent it from sliding down too far); and by these two motions combined, the circular one of the large plate, and the straight one of the small, the circumference of the piece of wood to be turned necessarily describes an oval; and gouges or other tools being applied in the usual manner supported on the reft, it is cut into an oval accordingly. The small plate may be made to slide either more or less in the grooves; and by this contrivance the transverse diameter of the oval, or rather ellipse, may be made longer or shorter at pleasure.

1. The method of moulding boxes of shell and horn.—In the first place, form a proper mould, which must consist of two pieces, viz. of a circle about half an inch thick, which should slope a little in order to draw out the moulded shell the more easily; and a ring fitted to the outside of the circle, so that both together make the shape of a box. These two pieces being adjusted, it is necessary to round the shell to be moulded of such a size that when moulded, it will be a little higher than the ring of the mould, that there may be no deficiency. The mould is then to be put into a press on a plate of iron, exactly under the screw of the press; put then the shell upon the circle of the mould, so that its centre also is exactly opposite to the screw of the press: then take a piece of wood formed into a truncated cone, and not so thick as the diameter of the circle of the mould, nor so deep as the ring: then put a plate of iron above the cone, and screw down the press gently and cautiously till the whole is well fixed: then plunge the whole into a cauldron of boiling water placed above a fire. In 8 or 10 minutes the shell or horn will begin to soften; forew the press a little firmer that the wooden cone may sink into the softened shell: repeat this from time to time till the cone is quite sunk in the mould; then take out the press and plunge it into cold water. When it is cold, take the box now formed out of the mould, and put into the inside of it a new mould of tin exactly of the form you with the inside of the box to be; do the same with the outside, put it again into the press and plunge it into boiling water; screw the press gradually till the box receive the desired form.

2. Method of preparing green wood so that it will not split in the turning.—Cut the wood into pieces of a proper size, put them into a vessel full of potash ley. Boil them about an hour; take the cauldron from the fire, allow the ley to cool; and take out the wood and dry it in the shade.

3. Method of giving an ebony-black to hard and fine woods.—After forming the wood into the defined figure, rub it with aquafortis a little diluted. Small threads of wood will rise in the drying, which you will rub off with pumice-stone. Repeat this process again, and then rub the wood with the following composition: Put into a glazed earthen vessel a pint of strong vinegar, two ounces of fine iron-filings, and half a pound of pounded galls, and allow them to infuse for three or four hours on hot cinders. At the end of this time augment the fire, and pour into the vessel four ounces of copperas, and a chopin of water having half an ounce of borax and as much indigo diffolved in it; and make the whole boil till a froth rises. Rub several layers of this upon the wood; and when it is dry, polish it with leather, on which you have put a little tripoli.

3. Method of giving to plum-tree the colour of brazil wood.—Slake lime with urine, and bedaub the wood over with it while it is hot: allow it to dry; then take off the coat of lime, and rub it with shamoy skin well oiled. Or, steep the wood in water, having a quantity of alum diffolved in it: then, having allowed brazil wood to diffolve in water five or fix hours, steep the wood in it, kept lukewarm during a night; and when it is dry, rub it, as before directed, with shamoy skin well oiled.

5. Method of giving a fine black colour to wood.—Steep the wood for two or three days in lukewarm water in which a little alum has been diffolved; then put a handful of logwood, cut small, into a pint of water, and boil it down to less than half a pint. If you then add a little indigo, the colour will be more beautiful. Spread a layer of this liquor quite hot on the wood with a pencil, which will give it a violet colour. Turning. When it is dry, spread on another layer; dry it again and give it a third; then boil verdigris at difference in its own vinegar, and spread a layer of it on the wood: when it is dry, rub it with a brush, and then with oiled shamo skin. This gives a fine black, and imitates perfectly the colour of ebony.

6. Method of cleaning and whitening bones before using them.—Having taken off with a saw the useless ends of the bones, make a strong ley of ashes and quicklime, and into a pailful of this ley put four ounces of alum, and boil the bones in it for an hour; then take the vessel containing the ley off the fire, and let it cool; then take out the bones and dry them in the shade.

7. Method of foldering shells.—Clean the two sides of the shells which you wish to join together; then, having joined them, wrap them up in linen folded double and well moistened; then heat two plates of iron pretty hot that they may keep their heat for some time; and putting the shells rolled up between them under a press, which you must screw very tight, leave them there till the whole is cold, and they will be foldered. If you do not succeed the first time, repeat the process.

8. Method of moulding shells.—Put six pints of water into a kettle; add to it an ounce of olive or other oil; make the water boil; then put in your shell, and it will grow soft. Take it out and put it into a mould under a press, and it will take the figure you want. This must be done quickly; for if the shell cool ever so little, the process will fail. It will not require much pressure.

9. Method of tinging bones and ivory red.—Boil shavings of scarlet in water. When it begins to boil, throw in a quarter of a pound of ashes made from the dregs of wine, which will extract the colour: then throw in a little rock alum to clear it, and pass the water through a linen cloth. Steep the ivory or bone in aquafortis, and put it into the water. If you wish to leave white spots, cover the places destined for them with wax.

10. To tinge ivory black.—Steep the ivory during five or fix days in water of galls with ashes made with dried dregs of wine and arsenic; then give it two or three layers of the same black with which plum-tree is blackened, in order to imitate ebony. Or, dissolve silver in aquafortis, and put it into a little rose-water. Rub the ivory with this, and allow it to dry in the sun.

11. Method of hardening wood to make pulleys.—After finishing the pulley, boil it seven or eight minutes in olive oil, and it will become as hard as copper.

12. To make Chinese varnish.—Take of gun lac in grains four ounces; put it into a strong bottle with a pound of good spirit of wine, and add about the bulk of a hazel nut of camphor. Allow them to mix in summer in the sun, or in winter on hot embers for 24 hours, shaking the bottle from time to time. Pass the whole through a fine cloth, and throw away what remains upon it. Then let it settle for 24 hours, and you will find a clear part in the upper part of the bottle, which you must separate gently, and put into another vial, and the remains will serve for the first layers.