menced printer on a large scale, in partnership, as has been | the charm of these novels consists. There is a power and proved by subsequent disclosures, with Scott. To this part depth in the characters themselves; they had been originally of Scott's history we shall have occasion to return here- conceived with the intense love of a strong mind; they had after. remained stored up in its memory for years, mellowing in Scott commenced his career as the most popular poet tone and growing more distinct in form, and were at last, of his day, in 1805, with the publication of "The Lay of the accidentally we may almost say, poured out with a felicity Last Minstrel.' This poem was followed in 1808 by Mar- and strength of expression of which the author was himself mion; in 1809, by The Lady of the Lake;' in 1811, by scarcely aware that he was capable. This new vein of popuDon Roderick;' in 1813, by Rokeby' in 1814, by The lar applause was worked as sedulously as the former, and, Lord of the Isles. To these may be added 'The Bridal of like it, worked out. The novels which from 1818 to 1826 folTriermain' and 'Harold the Dauntless,' published anony- lowed those we have enumerated in rapid succession, are not, mously, the former in 1814, the latter in 1816. These like them, the outpouring of long-treasured thoughts; they poems took the literary world by surprise; they were unlike bear marks of reading for the purpose of finding materials anything that had preceded them. There was an easy to fill up a previously sketched outline. They are of dif flow in their frequently slovenly versification, a condensed ferent degrees of merit, but all are inferior in depth of tone energy of thought, which even the total neglect of the and weight of metal to the works of the first four years. lima labor could not entirely conceal or obliterate, a Individual characters and incidents in some of them may pithy shrewdness in the occasional remarks upon life and be equal, but not one of them can bear comparison when manners; enough of the wild recondite spirit which the considered as a whole. author had caught from Coleridge to lend a zest to his composition; enough of the leaven of common-place to render it intelligible to the mass of readers; and an entirely new class of heroes and adventures. Much of the popularity which attached to Scott's poems was owing to the novelty of their subjects, and much to his compliance with the taste of the times; but his strong native sense, the stores of out-of-the-way knowledge upon which he could draw, and the easy flow of his versification and imagery, rendered them also works of real intrinsic merit. As the first gloss of novelty wore off, the voice of criticism was more distinctly heard. Lord Byron's more exaggerated tone of sentiment and greater power of condensed rythmical declamation made a deeper impression upon the public mind, and caused Scott's works to appear comparatively feeble by the force of contrast. The imitators too, who had caught the outward form of Scott's versification, and found plenty of heroes in old fabliaux and romances, had for a time surfeited the public with his peculiar style of poetical composition. With a prudent caution, said to be characteristic of his nation, he prepared to exchange a field of literary exertion in which he found himself in danger of losing his popularity, and after the failure of two anonymous trials (The Bridal of Triermain,' and 'Harold the Dauntless'), never attempted

to re-enter it.

Some time previous to his abdication of the laurel, the success of Miss Edgeworth's Pictures of Irish Life,' and his consciousness of an extensive acquaintance with the manners and customs of Scotland, more especially of the olden time, had stimulated him to attempt a portraiture of them in a prose imaginative narrative. The task was prosecuted for some time, but in consequence of the unfavourable opinion of a friend, laid aside. In 1814 however he resolved to make the attempt, and Waverley' was published anonymously. This book, published without any parade of announcement, and without the attraction of an author's name, made its way noiselessly and rapidly to a high place in public estimation. In the course of four years it was followed in rapid succession by Guy Mannering. The Antiquary,' 'The Black Dwarf, Old Mortality,' Rob Roy,' and The Heart of Mid Lothian,' all bearing the indisputable impress of the same parent mind. The circumstance of Scott's having published a poem in the same year in which 'Waverley' appeared, and his engagement in other literary undertakings being known, combined, with the common prejudice that a poet cannot excel as a prose writer, to avert from him for a time the suspicion of the authorship of the Waverley' novels. The taciturnity of the few entrusted with the secret defeated all attempts to obtain direct evidence as to who was the author. From the first however suspicion pointed strongly towards Scott, and so many circumstances tended to strengthen it, that the disclosures from Constable's and Ballantyne's books, and his own confession, scarcely increased the moral conviction which had long prevailed, that he was the 'great Unknown.' The light half-playfully worn veil of mystery served however, no doubt, to excite the public curiosity and to add a factitious interest to the Waverley' novels at the time of their publication. But their own merits were doubtless the main cause of their success. As narratives they have little merit: the plot is uniformly inartificial and unskilfully wrought up; the ostensible heroes and heroines, insipid or unnatural. It is in the admirable Scotch characters, in the ease and truth of their actions and conversation, that P. C., No. 1308.

·

Scott's novels and poems however occupied by no means the whole of his time during the thirty years of his busy life, of which they were the luxuriant produce. He contributed to the Edinburgh Review at its commencement, and when differences of political opinion induced him to break off from that publication, he took a warm interest in the establishment of the Quarterly.' His trade connections with the Ballantynes, and through them with Con stable and other publishers, led him to project many publications, and to take an active part in them as editor or contributor. To these we owe the Life of Dryden' (1808), of Swift (1814), the biographical and critical prefaces to Ballantyne's collection of the English novelists, and his annotations to such books as Sadler's Correspondence.' His biographical and critical writings are characterised by masculine good sense, vigour, and a happy play of humour, rather than by subtle analysis or a just and delicate taste. From 1796 till 1826 Scott's life was busy and happy, and seemingly prosperous. By the patronage of friends he was rendered independent; by his own exertions he was raised to affluence. His notoriety as an author gave him an extensive circle of acquaintance. His manly and sensible character commanded respect, his bonhommie and talent for increasing the hilarity of the social hour conciliated the love of all who knew him. The continuance of apparent success increased his confidence in his own resources to a degree bordering on presumption. The ambition of his life was to enact the part of one of those feudal lords who were the favourite objects upon which his imagination dwelt. To this was owing the purchase and building of Abbotsford, the strewing of it with auld nick-nackets, and the extensive scale on which he exercised his hospitality. He endeavoured to revive old times in his mansion on the Tweed. The last few years of his prosperity were spent in a gorgeous dream. The open-air day-light masquerade of the reception of George IV. in Edinburgh, in which Sir Walter Scott was a prominent actor, was the most gorgeous scene of what we can scarcely look upon in any other light than that of an opium dream. But the worm was gnawing at the root of his magnificence. Constable, Ballantyne, and Scott were all men of sense and talent, but the spirit of enterprise was stronger in them than that of accurate mercantile calculation. From the beginning their undertakings had been on a larger scale than their capital warranted; and as difficulties thickened around them their confident spirits looked for relief to bolder and more extensive speculations. This could not go on for ever: the commercial crisis of 1825-26 precipitated, but did not cause the catastrophe.

When what is called in Scotland' a state of the affairs' of Constable and Co. and Ballantyne and Co. was made up subsequently to the bankruptcy of the two companies, it appeared that Sir Walter Scott was indebted to Constable's creditors, as a partner of Ballantyne and Co., for nearly 72,000.; and that the total amount of the debts of Ballantyne and Co. was about 110,000l., for the whole of which Sir Walter was liable as a partner. About half of the 72,000l. due to Constable and Co. being included in the debts of Ballantyne and Co., Scott's actual liabilities were somewhere about 147,000l. The presumptuous rashness with which, in order to indulge himself in the theatrical pleasure of enacting the part of one of the favourite heroes of his imagination, he incurred this immense load of debt, cannot be palliated. From 1823, if not from an earlier period, VOL. XXI.-P

novels were contracted for and paid in bills, before even the subjects or names of the future publications were fixed. This was not a mere speculation upon popularity: it was a wanton setting of health, mental and corporeal, and of life itself, upon the hazard. But to the honour of Scott, he did not flinch from the terrible responsibility he had so presumptuously incurred. Gentlemen,' he said to the creditors, Time and I against any two. Let me take this good ally into my company, and I believe I shall be able to pay you every farthing.' He surrendered the whole of his property; executed a trust-deed in favour of certain gentlemen, who were to receive the funds realised by his labours, and pay off his debts with interest by instalments; sold his house and furniture, and retired to lodgings, and resumed his literary labours with dogged resolution.It is very hard,' he said, in his deep thoughtful voice, to a friend who expressed his sympathy, thus to lose all the labours of a lifetime, and be made a poor man at last, when I ought to have been otherwise. But if God grant me life and strength for a few years longer, I have no doubt that I shall redeem it all.'

children were, the present Sir Walter, Mrs. Lockhart and Miss Anne Scott (both of whom survived their father, but are since dead), and Mr. Charles Scott.

(Lockhart's Life of Scott; Notes and Prefaces by Sir Walter to the edition of his Collected Works; Publications by the Trustees of the Messrs. Ballantyne; MS. Communications.) SCOTUS. [DUNS SCOTUS.]

SCREEN, in Architecture, a term probably connected with the Latin Scrinium and the German Schrein, signifies a partition dividing off some portion of an interior or room from the rest of its plan, without similarly contracting or shutting up the space over head, a screen being a partition carried up only to a certain height, so as to admit a view beyond it. Screens are exceedingly beautiful internal features in the Gothic or pointed style, in which they were employed for a variety of purposes, not in churches alone, but in halls and other buildings. Great diversity was also displayed in them as regards both design and material; for we meet with them sometimes solid or nearly so, at others almost entirely of open-work; of stone or of timber, and occasionally composed of both; but agreeing in one respect, namely, in being more or less elaborately decorated.

Scott's works, published during the six years which elapsed between his bankruptcy and his death, which occurred on the 21st of September, 1832, possess a painful In our English cathedrals the choir is separated from the interest. They want the energy and buoyancy of his earlier nave by the organ screen, which differs from others in bewritings; they bear the impress of the lassitude of a spiriting a double screen, so as to form the gallery for the organ engaged in a hopeless task. Some of them, like the His- above, and to admit of stairs leading up to it, in the space tory of Napoleon,' are works which lay out of his line; between two partitions. Though some prefer the continensome of them, like the 'Letters on Demonology and Witch-tal mode, we are of opinion that the apparent extent of the craft,' are of a class to which humbler pens alone ought to vista is rather increased than not, by its being partially be tasked; some of them, like the gossiping notes to his interrupted below, while the prospective is continued, and collected works, are concessions to the impertinent curiosity perhaps a view of a noble east window is caught in the of the public, to which it is painful to see a great man remote distance. stooping. Neither Walter Scott nor any other really great author ought to be his own Boswell. Making allowance for every drawback however, the old fire glows in his ashes. Nor was his self-immolation altogether in vain. There can be little doubt that the disease which proved fatal to him was superinduced by excess of mental toil, but the purpose for which he sacrificed himself was attained. His debts, materially diminished before his death have since been entirely liquidated by the profits of the edition of his collected works. The certainty of this event, the consciousness that he had not shrunk from the responsibilities he had incurred, the feeling that he had deserved and retained the love and respect which waited upon him in more prosperous days, was his consolation in the dark hours of his closing life. The political party to which he was devoted was overthrown, and the institutions he venerated were in his opinion about to be swept away; his wealth had melted from his grasp, toil was the lot and prospect of his old age, the friends of his youth were dying out one by one; but the consciousness of honourable and manly endurance, and the devoted love of his children, smoothed his passage to the grave. He sought, but too late, health in a foreign climate. The worn-out frame craved to be at home and at rest. He murmured, now he knew he was at Abbotsford,' when his friend Mr. Laidlow welcomed him on his return, and for a few days enjoyed the mansion he had reared with so much love and pride. His strong frame struggled hard with the disease, but exhausted nature gave way at last, and he expired after fourteen days of total insensibility

We observed at the commencement of this sketch that it is yet too early to attempt a dispassionate estimate of Scott and his writings. Making allowance for increased facilities of communication, and more generally diffused education, the fervour of popular enthusiasm with which his works were received was not greater than was experienced by the publications of Richardson. Time alone can decide how much of his writings will survive, and what place they will permanently occupy in the estimation of the literary world. Of this however there can be no doubt, that in Scott a strong and healthy intellect was engrafted on a powerful will, that he had a natural and easy play of humour, with no inconsiderable portion of poetical imagination, and a large share of that power of apprehending and portraying character which is the great charm of Fielding. Great part of his life he indulged in a dream world of his own; but when rudely awakened by adversity, he submitted to the consequences with heroic submission. He was a great and a good man

Walter Scott was the fourth of ten children, of whom only Thomas, a younger brother, left any descendants. His own

The altar screen serves as a back wall to the choir, separating that division of the church from the presbytery or Lady-chapel behind it. It was therefore usually solid for the whole height to which it was carried up. That erected by Bishop Fox in Winchester cathedral is a splendid stone screen decorated with several tiers of canopied niches; and strikingly similar to it in design is the one by Abbot Whetehamstede at St. Alban's. Though not so designated, the stalls, &c. form lateral screens enclosing the lower part of the choir from the side aisles. Chartres cathedral contains a no less remarkable than fine example of such screen continued round the apsis of the choir, showing itself as a wall carried up to some height above the stalls, and divided into large compartments filled with sculpture. The fronts of chantries, small chapels, &c. in churches, may also be described as screens, the greater part of which is pierced or open-work and tracery. The examples of this class are so numerous, that to particularise any of them would be almost superfluous; nevertheless we may here mention that enclosing the monumental chapel of Prince Arthur, son of Henry VIII., in Worcester cathedral. The tomb of Henry VII., in his chapel at Westminster, is a very gorgeous piece of screen-work, executed entirely in metal, and forming an insulated shrine on a very large scale. Westminster Abbey itself contains many fine studies of screens in its chapels and chantries. Of timber screens separating the chancel and altar end from the body of the building, many specimens are to be met with in country churches, and not a few of them are worthy of being studied for the beauty of their design. In some instances, the lower part, or actual screen itself, is little more than a plain wooden partition surmounted by a range of open-work panels or arches. such screens there is a peculiar kind distinguished by the term of rood-lofts or roodloft screens, the top of them forming a kind of small overhanging gallery supported on corbets and brackets, and on which were placed the Holy Rood,' or large crucifix with a figure of the Saviour, and other images.

Of

Screens of a different character, and for a different purpose from any of those above mentioned, were employed in the halls of domestic and collegiate buildings, for the purpose of cutting off a passage leading to the butteries and offices. Such screens were almost invariably of oak or other wood, and the space over them and the passage behind served as a music gallery. Open-work was very rarely if ever introduced into them, but they had generally two open arches, or sometimes square-headed doorways. Several specimens of this class of screens may be seen in Nash's Mansions of England in the Olden Times,' some of them, as that in the Hall at Audley-end, profusely adorned with

The Great Brass Screen which encloses the Altar Tomb of Henry VII. and his Queen in his Chapel at Westminster. carved panelling and other sculpture; and the one just prevent the monotony that would otherwise take place in mentioned is further remarkable for the centre compart- so extended a front. ment being carried up higher than the rest, though not quite to the ceiling. Other instances occur where the screen is carried up two stories, so as to form either a passage on the chamber floor, or a closed gallery with glazed or latticed apertures. Of this kind are those in the halls at Knowle and at Hatfield. Of still more unusual character is the one at Wroxton Abbey, Oxfordshire, for there the screen, which has a series of small windows in it, is confined to the upper part of the hall, and is supported on an open colonnade below.

SCREEN is also employed to signify a colonnade or wall architecturally decorated, enclosing a court-yard in front of a building, as that for instance of the Admiralty, London, or the one which was erected before Carlton House, and which consisted of a single range of coupled Ionic columns placed on a lofty stylobate. Screens of this kind are sometimes had recourse to in order to connect the advancing parts of a plan together, and prevent a façade being cut up into gaps. It is by this means that the buildings forming the river front of Somerset House have been connected together into one continuous façade by screens assuming the appearance of open_Corinthian loggios above spacious bridge-like arches. Eminently picturesque in themselves, those features serve greatly to relieve all the rest, and to

Of screens or low walls carried up midway between columns whose shafts are attached to them, there are frequent instances in Egyptian architecture, and they belong to the characteristic peculiarities of that style. [EGYPTIAN ARCHITECTURE, p. 314, 315.] Somewhat similar screens might occasionally be adopted with propriety and good effect, in the Grecian style also, either behind columns or between insulated square pillars. This has in fact been done behind the second range of columns in the recessed part of the portico of the Museum at Berlin, where a screen of the kind encloses the lower part of the staircase, while the ceiling, &c. are seen over it; whereby not only is the view continued, but light is obtained for the staircase, without windows. [PORTICO.] The article just referred to affords another instance of an inner screen within a portico, viz. that shown in Fig. 9; a valuable idea, susceptible of many variations and combinations, all of them more or less picturesque; for instance columns behind the screen, caryatides upon it, colossal herma forming pilasters on its surface, &c. In the interior of buildings again, let their style be what it may, architectural screens might be employed so as greatly to enhance effect, and at the same time to add very materially to convenience. SCREW. This mechanical power generally consists of

two parts, one of which is a solid cylinder of wood or metal, on whose convex surface is formed a projecting rib or fillet, frequently called a thread, which passes spirally round in such a manner as constantly to make equal angles with lines parallel to the axis of the cylinder. The other is a cylindrical perforation through a block of some material, the surface of the perforation having on it a spiral groove corresponding to the projecting rib or fillet on the solid cylinder. The first of these parts is called a convex screw, and the other a concave screw.

of a plane, and, by the resolution of forces, the ratio between the pressure and the force will be as the base of the plane is to its height; that is, as AB to BD. Now an equal force q will be in equilibrio with the pressure p on every other elementary portion of the grooves in the concave screw; therefore, there being as many forces q as there are pressures = p, the whole weight W on the screw will be to the whole sustaining force, in the case of equilibrium, as AB to BD; that is, as the circumference of the convex screw is to the distance between the threads when measured in a direction parallel to the axis.

But the screw, when applied as a mechanical power, is never used in its simple state; a lever or wheel is always fixed perpendicularly to the axis, and the moving or sustaining power is applied near the outer extremity of the lever, or at the circumference of the wheel. In this last case, the ratio between the moving-power and the resistance is as the distance between the threads of the screw is to the length of that circumference; and the velocity of a point on the axis is to that of a point on the circumference in the same ratio. The friction of a screw is however very great, and is frequently equal to, at least, the weight supported, for it will prevent that weight from descending when the mov.

A just conception of the nature of the line of direction taken by the rib or groove on the surface of the cylinder, may be obtained by drawing on a rectangular paper, whose breadth AB is equal to the circumference of the cylinder, any number of lines AB, CD, EF, &c., equidistant from each other, and perpendicular to the sides of the paper. Then joining the points A and D, C and F, &c. by right lines, and bending the paper on the surface of the cylinder, the lines AD, CF, EH, &c., will, by uniting at their extremities, become the continuous helix or spiral curve-line which the thread assumes. When the two parts are in action, the convex screw, being turned round in the other by a power applied at its surface, moves at the same time rectilinearly in the direction of its axis: occasionally how-ing-power is taken away. ever the convex screw is fixed, and then the other being turned about, it acquires at the same time a like rectilinear motion. In either case, the path described by a point on any thread during the time that the screw turns once on its Fig. 1.

axis, on being developed, becomes equal to AD or CF; and in the same time a point on the axis moves through a space equal to BD or DF.

As a mechanical power, the screw possesses the properies of an inclined plane; for W representing a weight or pressure at one end of a convex screw, whose threads are thereby made to move in the grooves of the concave screw, let that weight be supposed to act in a direction parallel to the axis, and to be uniformly diffused among all the projecting threads which are at one time in the grooves; also let p be the part of the weight which presses in the direction mM on an elementary portion Mn of the side of a groove in the concave screw. Then Mn may be considered as a small inclined plane, making with mM an angle equal to ADB: and if q be a force which applied at M in the direction NM, touching a circle whose plane passes through the screw perpendicularly to the axis, would prevent the convex screw from turning round; the pressure on Mn and the counteracting force will be in the same circumstances as the weight of any body on an inclined plane and a sustaining power which acts in a direction parallel to the base

An endless screw consists of two or more spira. fillets or threads on a rod which is capable of being turned on its axis by a power applied to the handle of a winch, or to a string passing over the circumference of a pulley attached to the rod. The threads work between teeth on the circumference of a wheel, so that while the revolution of the rod continues, the wheel turns on its own axis. If the radius of the winch or of the pulley on the screw-rod be 6 inches, and the distance between the threads of the screw be inch, a power represented by unity at the circumference of the pulley will be in equilibrio, omitting the effects of friction, with a resistance expressed by 6 x 10 X 2π, that is, by 376.99 ( being the half circumference of a circle whose radius is unity) applied at the threads of the screw or at the circumference of the wheel.

If the lines AF, CH, &c. were drawn on paper, and that paper were bent on the surface of a convex or concave cylinder, one spiral thread would be formed by the union of AF, EK, &c. at their extremities, and another by the like union of CH, GM, &c.: this is called a double-threaded screw, and it is evident that its mechanical power depends upon the ratio of AB to BF, while that of the singlethreaded screw depends on the ratio of AB to BD; that is, with apparently an equal distance between the threads on both screws, the power of the latter is double that of the former.

From the high ratio which the resistance bears to the moving power in the screw, the use of this machine for moving or compressing bodies is very great; it is also extensively employed in the construction of philosophical instruments for measuring small angles or distances. [M1CROMETER.]

The ingenious screw-machine which was invented by Mr. Hunter, and is described in the Phil. Trans.' vol. 17, consists of one convex screw which works in the interior of another convex screw. The latter works in a concave screw which is fixed; and the former is capable of moving in a rectilinear direction only, being prevented from turning on its axis with the rotation of the exterior screw. Also the number of threads in an inch on the convex surface of this last is less by one than the number in an inch on the convex surface of the other: suppose the first number to be 10 and the other to be 11; then one revolution of the exterior screw would cause the whole machine to move forward through a space equal to inch, but in the same time the interior screw is carried backward through inch. Therefore the forward motion of this last is equal to

or

inch; and to produce an equal effect in a simple screw, the latter should have 110 threads in an inch.

Mr. Barlow of Woolwich mentions a compound machine of this kind in which the exterior screw had 100 threads in an inch, and the interior screw 101 threads; therefore one turn of the machine caused the latter to move through the very minute extent of to inch, and this space was further subdivided into hundredths by means of a micrometer head applied to the exterior screw.

The endless screw is a component part of graduating machines, counting machines, &c.; it is also employed in conjunction with a wheel and axle to raise heavy weights.

SCREW. The preceding article having explained the principle of the screw, it remains only to notice some of the contrivances used for making screws; which we shall commence by an account of the manufacture of those commonly used by carpenters for fastening pieces of wood, or of wood and metal together. These are, in this country, usually called wood-screws, and in Scotland screw-nails.

contrivance are given in the thirteenth volume of the 'Repertory of Arts.' Screw-bolts and other screws for working in metal are manufactured in a similar manner to wood-screws, when the number required is sufficient to justify the expense of adjusting the machinery. When this is not the case, they are, if small, often cut by hand, without the aid of a lathe. The die, or resembles The blanks for wood-screws were formerly forged by the instrument for cutting an external or male screw, workmen who make nails, they being in fact very nearly a common nut, but is usually divided into two parts, which the same as countersunk clout-nails, with the exception of are fitted, when in use, into an iron stock or die-frame, with their ends not being pointed. Some manufacturers make long handles. Notches are cut in the die, across the directheir blanks of round rolled iron, cut into the required tion of the threads, in order to produce cutting angles, and lengths, and pinched when red-hot between a pair of dies in to afford room for the escape of the portions of metal rethe chaps of a vice, while the heads are formed with a moved in cutting the worm. The die, which is formed of hammer, or the stamp of a fly-press. But it appears to be steel, and well tempered, is inserted in the die-stock, with the best plan, at least for screws not exceeding about a its two halves a little distance apart, but capable of being quarter of an inch in diameter, to form the blanks of iron- brought together by regulating screws fixed in the die-stock. wire, cut by a machine, and having the heads struck up in The bolt or pin to be made into a screw is formed to the rea die without the application of heat. After forming the quired size by turning or otherwise, and then made fast in a head, the next process is filing or turning the necks and vice, while its end, which should be slightly tapered for the heads in a lathe; after which the nick, or groove to receive purpose, is placed in the die. The operator then proceeds the end of the screw-driver, is cut with a circular saw. In to turn the die-stock so as to worm the die on to the bolt; the infancy of screw-making the thread was formed with a not by a continuous motion in one direction, but by a series file, but this process has long been superseded by the use of of turns backwards and forwards. When the die has prodies and cutters, which are applied in various ways. The ceeded as far on the bolt as the worm is required to extend, cutting of the worm is sometimes performed in a lathe, the it is taken off, screwed up a little closer, and again applied blank being fixed in a chuck, and projected during its in the same manner; and the process is repeated, closing revolution between a pair of stationary cutters; the the die a little after each operation, until the worm is cut longitudinal motion of the blank, and consequently the to the required depth. The continuous motion of the die is size or inclination of the thread, being determined by a impracticable, on account of the great resistance it has to regulating or pattern screw attached to the mandril, which overcome, as the worm is not formed merely by cutting must therefore be changed for every different degree of away, but partly by compressing the metal, and squeezing fineness; while the shape of the thread or worm depends on it up into the thread. In working a similar apparatus by the form and position of the cutters. Small screws are machinery, the dies are sometimes made in four pieces, the frequently wormed by a similar apparatus turned by a die-frame is stationary, and the bolt or screw-pin itself rewinch-handle attached to the mandril; and sometimes by volves. In this case the rotation is continuous, but in means of a steel tap-plate. This method of forming the other respects the operation resembles that described. In worm is that described in Hebert's 'Engineers' and Me- the 'Mechanics' Magazine,' vol. xxv., p. 376, is published a chanics' Encyclopædia;' but another plan, originally intro- description, with cuts, of a curious kind of die and die-stock duced by Mr. Nettlefold, of Holborn, is now very commonly invented by Mr. Tracey, in which the two halves of the die adopted. In this case the worm is formed by means of a may be so varied in their relative position in the stock, that pair of stationary cutting dies; between which the blank the same die will cut either a right-hand or left-hand screw, is projected by an apparatus which gives it an alternating either single or double threaded. In cutting large screws, rotatory motion. The dies themselves regulate the size especially with a square thread, a steel cutter is sometimes of the thread, without the use of a pattern screw, and they used with the die, whether turned by hand or fixed in a must therefore be changed for every variety of screw. The lathe; and some instruments for cutting male screws in peculiar motion of the blank resembles that of a bolt wood consist of a sharp steel cutter, fixed in a block, having wormed by hand, as hereafter described. a female screw; the wooden die, or rather nut, being used merely to regulate the motion of the cutter. Very small metal screws are cut by a steel tap-plate, wormed and notched in a similar manner to the dies above described, but having several holes varying slightly in size, the worm being formed progressively by using at each operation a smaller hole than at the preceding one.

The manufacture of wood-screws has been greatly improved by the exertions of the gentleman just alluded to, whose patent screws are far superior, in every respect, to those of the ordinary make; while, by the extensive application of machinery, they are produced at a price little exceeding that of the common imperfect article. Much attention is paid to the perfection of the worm in these screws. It is Female or interior screws are commonly cut by means of cut deeper than usual, and the thread is made nearly flat a steel tap, which, in its most usual form, is simply a screw on the upper side, while the under side is considerably in- of which great part of the worm is removed by filing two, clined; so that while the screw enters the wood more three, or four flat faces along its whole length, the angles easily than those of the usual make, it offers much left by this operation forming a series of obtuse cutters. greater resistance to any force tending to tear it out. A The tap should be made somewhat conical, that it may enter very common defect in wood-screws is having the worm ter- the hole readily, and cut the worm by degrees. In some minate in a rough thin shell, which frequently becomes cases two taps are used, the first only of which is tapered. bruised, and tears away the wood in such a manner as to The head of the tap is squared, to fit into the middle of a leave very little hold for the screw. This defect is best long handle, by which it can be turned with considerable remedied by making the point of the screw smooth and purchase; and it is worked to and fro, in a similar manner conical. The best wood-screws are made to taper slightly to the die for an external screw, the nut being held stafrom the head downwards; and a further improvement, tionary. The taps for cutting screws in wood are comwhich we believe has been recently introduced by Mr. monly fluted on the sides, to make them cut the more Nettlefold, consists in making the worm shallower towards readily, and to afford more room for the escape of the cutthe head than at the point, by which the screws are rendered tings. The tap invented by Mr. Jones, and described in less liable to be twisted in two at the upper part of the the forty-eighth volume of the 'Transactions' of the Society worm, when turned into hard wood with great force, as when of Arts, answers the purpose of a tapering tap for commenca brace is used instead of the common screw-driver. ing the screw, and a cylindrical one for completing it, the lower part being tapered, while the upper is left cylindrical. Mr. Jones recommended the fluting or notching of the tap in the form represented in section at c in the annexed figure,

Several attempts have been made, and some appear to have been tolerably successful, to produce screws by casting. In the ordinary method of casting in sand, the chief obstacle in the way of casting screws consists in the difficulty of removing the pattern from the mould. Mr. Maullin, a manufacturer who obtained a patent in 1800 for a method of overcoming this difficulty, accomplished his object by an apparatus for screwing the patterns (of which a great number might be used together) out of the mould, so as to leave the impression of the thread uninjured. The details of this

a