CYLINDERS for STEAM ENGINES, boring of, is an operation usually carried on at the foundery where they are cast. Though the moulder pursues the most correct method his art is capable of, yet it is impossible to be certain that when the mould has received the metal from the furnace it shall come out quite straight; and if it should come out crooked it must remain so; for the old method of boring will never make it otherwise in that respect. It is not like boring a piece of metal which is quite solid, as in boring guns, &c. All the old boring can do to a cylinder is to make it round and smooth, for there is nothing to conduct the boring bit in its progress through the piece but the form given it by the moulder; and a piece bored after this manner may look very well, yet if it is not straight it is not a cylinder and an engine executed with such a vessel as that will be good or ill in that respect, as it approaches to or is further off the degree of exactness constituting it a cylinder.

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The new method of boring (which, as is observed, article STEAM ENGINE, was first practised at Burham, a foundery belonging to Mr. Wilkinson, iron-master) insures all the perfection the subject is capable of; and when the process is conducted by an intelligent workman, if the cylinder should be cast ever so crooked, or ever so thick on one side more than another, he can take out the redundancy on that side, and but scarcely touch the other. This will be easily admitted when it is understood that, whereas in the old method of boring the instrument which performs the part of cutting the metal is guided in its progress by the already incorrect form of the piece itself; but in the new method the cutting apparatus is conducted along a thing which in itself is a master-piece of workmanship, a perfect cylinder, and is what the workmen call the boring bar, and is cast of the best pigs that can be procured, and turned with the utmost care and precision: consequently, whatever is conducted along this bar will proceed in a right line; and as it is intended that this shall be the conductor of the cutter-block, being furnished with proper cutters, it must cut the interior surface of the piece quite straight, though it may have been ever so crooked before.

Then this bar being turned very true, it is to have a groove or two cut opposite to each other, in a line parallel to its axis; then there is a socket of cast iron of such dimensions as to suit for cylinders of various diameters, and this socket is to be nicely bored and ground on the bar; and then it must have a fillet or two (according to the groove or grooves in the bar) let in on the inside, so as to slide along the bar, but not to turn round upon it: the external part must be made conical, with four or six studs upon the base of it to receive the cutter-block. The next thing

is to give a progressive motion to this socket and cutter-block while the bar is turning on its own axis; and that is done by some with a collar of metal fitted on the socket, and to that collar are connected two racks, long enough to reach through the cylinder and communicate with a pair of pinions, by which the socket is drawn or pushed along the boring bar by the means of two levers, carrying a weight at each sufficiently heavy to overcome all resistance in the operation.

Another method of giving a progressive motion to the block is to drill a hole through the whole length of the bar, to admit a single rod, to be communicated to the socket by sinking the groove (for in this case there can be but one) entirely through one side of the bar, so as to come into the hole that has just been drilled through the bar. Then a branch from the internal part of the socket must be fitted into the groove with an eye to receive the end of the rod, which is then to be furnished with a key, or a nut and washer, to keep it in its place while the bar and socket is turning round, and a weight with a rope over a pulley is applied to give motion to the socket, along the bar. This is the best way of applying this method to boring of small cylinders, because there is no incumbrance upon the socket; and if the bar is sufficiently strong it will move with great steadi

ness.

ELLIPSOGRAPH is the name given by the anonymous author of a German publication, entitled "Beschreibung eines Ellipsograph, womit man wahre Ellipsen ohne Berechnung der Brennpunkte sehr leicht beschreiben kann, &c. published at Gotha in 1794, to a simple and universal instrument for drawing ellipses. The instrument has been long known to our mathematicians, and has been described, though not in such general terms as it admits of, in Emerson's Conics, Hutton's Mathematical Dictionary, and other works; but as it has not yet been adopted for practical purposes, though it is far preferable, in our opinion, to any instrument for drawing ellipses now in use, we take this opportunity of recommending it to general

notice.

The ellipsograph consists of three flat and moderately thin rulers of wood or brass, two of which must be of equal lengths; and it may be as well if the length of these two together be equal to that of the third ruler. Let the two shorter of these rulers be pierced with a number of holes at equal distances, the holes being capable of receiving either a pin on which the rulers may turn as upon a joint, or a pencil by which the curve may be described: then by connecting these rulers either as in fig. 5. or fig. 6. pl. XIV. an ellipse may be readily described. Thus, in fig. 5. hang one end of the ruler AB upon a pin in the

middle of the ruler KL, and take the point B such that AB=BD, and AB+BD semiconjugate + semitransverse of the ellipse, the ruler BD turning upon a pin in в as a joint: take the point E so that DE semiconjugate, and put a pencil into the hole of that point: then, if the end D of the ruler BD be slidden along the edge KL of the ruler which passes through the centre A, the pencil at E will describe a true ellipse having the proposed diameters. Again, taking the method represented in fig. 6. upon the ruler AC, hang the ruler BG at B, so that AB+BE= semitransverse, while AB BD= half the difference of the semitransverse and semiconjugate axes: then, while a pin at D slides along the edge of the ruler KL the pencil at E will describe the ellipse required. The truth of this method of construction is demonstrated in Emerson's Conics, prop. 75. ellipse.

This instrument may, it is obvious, be easily made either so as to construct small ellipses, now commonly described by means of the elliptical compasses; or upon a larger scale, for the purpose of describing elliptical centring for arches of bridges, &c. In the latter case the ellipsograph may be made sufficiently strong without being any way cumbersome in practice. In the actual construction of the instrument the ruler KL should be the thickest, and the other two legs made to run upon friction rollers, as in the construction of the pentagraph.

It may not be altogether useless just to remark, that in both methods of using the instrument the point в will describe a circular arc; and if the ruler DB had a part above B, equal to DB, the upper extremity of that part would, during the motion of the point D along KL, describe a right line. This follows evidently from what was shewn in art. 8. of the introductory part of this volume.

ENGINE to let down heavy weights. The simple method we are now about to describe was invented by father Ressin, in 1714. Suppose it were required to lower large stones from the top of a wall which is intended to be taken down: erect a frame, or set up a gin close by the side of the wall, and let the pulley P (fig. 4. pl. IV.) be firmly attached to this frame. Over this pulley must pass a cord, one end of which c has a hook to which the stone, &c. can readily be fastened; the other end D carries a vessel, which may be filled with water from the reservoir M, on the ground at the bottom of the wall. Then, while one man is fixing the stone to the hook at the top of the wall, let another put water into the vessel D at the bottom till it nearly equals the weight of the stone: after which, leaving both to the free operation of gravity, or checking the motion a little if necessary, the stone will gradually descend to the ground, while the vessel D will be carried up to a funnel A, into which the water may be

VOL. II.

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poured, and thence conveyed by a wooden or a leather pipe to the reservoir M. Then the vessel D may be suffered to descend, and the hook c will be raised to be fixed to another stone: and thus the operation may be repeated as often as is necessary.

The same method may likewise be adopted in lowering sacks from a high granary, or packages from an upper warehouse. The velocity of the descending weight may be so regulated as to have any proportion to that which gravity imparts to bodies falling freely: thus, if w denote the weight to be lowered, v that

W-V

of the vessel of water, we shall have, for the fraction

W+V

expressing the ratio of the velocity to that freely imparted by gravity when denoted by unity. Thus, if v=w, the weight will fall through of 16, or about 5 feet in the first second: if v=w, the weight will fall through of 16, or about 3 feet in the first second: the friction of the pulley being in both instances disregarded.

EPROUVETTE, powder-prover, is an instrument contrived for the purpose of comparing the strength of different kinds of gunpowder. One of the best for the proof of powder in artillery, is that contrived by Dr. Hutton. It consists of a small brass gun, about 2 feet long, suspended by a metallic stem or rod, turning by an axis on a firm and strong frame, by means of which the piece oscillates in a circular arch. A little below the axis, the stem divides into two branches, reaching down to the gun, to which the lower ends of the branches are fixed, the one near the muzzle, the other near the breech of the piece. The upper end of the stem is firmly attached to the axis, which turns very freely by its extremities in the sockets of the supporting frame; by which means the gun and stem vibrate together in a vertical plane, with a very small degree of friction. The piece is charged with a small quantity of powder (usually about two ounces) without any ball, and then fired; by the force of the explosion, the piece is made to recoil or vibrate, describing an arch or angle, which will be greater or less, according to the quantity or strength of the powder.

To measure the quantity of recoil, and consequently the strength of the powder, a circular brazen or silvered arch of a convenient extent, and of a radius equal to its distance below the axis, is fixed against the descending two branches of the stem, and graduated into divisions, according to the purpose required to be answered by the machine: viz. 1. Into equal parts, or degrees, for the purpose of determining the angle actually described in the vibration. 2. Into unequal parts, according to the chords, being in fact 100 times the double sines of the half angles, and running up to 100, as equivalent to

90 degrees; these serve to compare the velocities given by the powder. 3. Into unequal parts according to the versed sines; they are, in truth, 100 times the versed sines of our common tables, 141 corresponding with 90 degrees; these serve to

compare the forces.

The divisions in these scales are pointed out by an index which is carried on the arch during the oscillation, and then, stopping there, shews the actual extent of the vibration. Two ounces of powder give, on an average, as I have found by several trials, about 36 on the chords or about 21° on the arch. For a more minute description with diagrams, see Hutton's Tracts, vol. iii. p. 153.

The late Mr. Ramsden constructed an eprouvette, which differs from the preceding simply by the gun's recoiling in a direction parallel to itself instead of its vibrating as a pendulum. In order to this, the gun is suspended upon two hanging frames, one at each end, like ladders. They are equal in length, and serve like the joints of a parallel ruler, to make the gun rise and fall, during its recoil and return, so as always to retain a direction parallel to itself; that is, the horizontal direction. The degrees are measured upon a fixed arch, by means of a moveable index, nearly as in Dr. Hutton's eprouvette.

For other eprouvettes by Regnier, &c. the reader may consult the article POWDER PROVERS in the Pantologia. Those of D'Antoni may be seen in Capt. Thomson's Translation of his Gunnery.

FILES, machines for cutting of. There have been various contrivances for this purpose; but one of the best we are acquainted with is described in the Transactions of the American Philosophical Society, and is as follows: AAAA fig. 6. pl. X. is a bench made of well-seasoned oak, the face of which is planed very smooth. BBBBB the feet of the bench, which should be substantial. cccc the carriage on which the files are laid, which moves along the face of the bench AAAA parallel to its sides, and carries the files gradually under the edge of the cutter or chisel HH, while the teeth are cut: this carriage is made to move by a contrivance somewhat similar to that which carries the log against the saw of a saw-mill, as will be more particularly described. DDD are three iron rods, inserted into the ends of the carriage cccc, and passing through holes in the studs EEE, which are screwed firmly against the ends of the bench AAAA, for directing the course of the carriage cccc, parallel to the sides of the said bench. FF two upright pillars, mortised firmly into the bench AAAA nearly equidistant from each end of it, near the edge, and directly opposite to each other. G the lever or arm which carries the cutter HH (fixed by