little twist, as if it was a new discovery. We can, however, trace it as far back as the time of Duhamel, who had sufficient influence with his government to have an experiment tried on a frigate, to decide this point; in which the shrouds of one side were all of cordage of the usual hard twist, while those at the other side were of less twist, by about one half, (as nearly as we can recollect) and the cordage with lit. the twist was found to have the most decisive advantage over the other. The author mentions Duhamel once in treating on the subject, but by no means as particularly as he ap pears to us to deserve. We are also surprised to find that Mr. March's patent method of making looped cordage, (which requires no twist whatsoever, except in the yarns, not even in the primary strands,) should not have been noticed among the discoveries which he recites; besides the other merits of the invention, it had that of originality to recommend it, of which few of the others could boast. Se veral of Mr. March's inventions are mentioned in Anderson's History of Commerce, and we believe this is among the number. Having now given a fair and impartial account of the various particulars of Mr. Chapman's treatise, we think it just to recommend it as containing, in a small compass, a considerable degree of information, (on a subject extremely important to one of the most essential interests of the nation), which was before scattered in a variety of publications. Works of this description are of the greatest utility to every art and science to which they are applied, and frequently, in th's respect, excel the more honoured performances of original composition. The treatise would have been more satisfactory, had it contained the descriptive parts of the specifications of the patents it notices, at full length, with plates of reference; and would have enabled us better to judge of the accuracy of the author's observations on them. Perhaps this hint, as well as others before given, may be attended to in a second edition; but the expediency of the measure must be determined by the probability of the sale of the work; and no blame can attach to the author for not being willing to run over great risks in this way. We should have mentioned before, that three plates accompany the work, intended to illustrate the process of rope-making, which the author recommends. To shew that the use of chains herein recommended, is of great antiquity, instead of being the novelty some suppose, we shall beg leave to refer to Cæsar's description of the Gallic ships, in the third book of his Commentaries, where these words will be found: "Anchore, pro funibus, ferreis catenis revincta," which fully prove our assertion. By ART. XIV. Practical and Descriptive Essays on the Art of Weaving. construction of lcoms,or of the other The subdivision of labour into numerous branches, while it increases practical dexterity in each particular instance, tends, at the same time, to impede the progress Bbb of general knowledge of a profession. This proceeds so far in the weaving business, that the mounting of a loom being often the business of one man, and the working of it that of another, there are many weavers who work for years on a loom, of which they hardly know how to arrange a single cord or lever. That this system of division, the beneficial effects of which have been so much felt in practice, will continue to be still further extended, cannot be doubted; and that at the same time, however it may be regretted, it will, along with the practical benefits it produces, tend to preclude many useful and valuable men, from the acquisition of knowledge, which may be of essential service to them in their respective situations, and afford likewise a most rational amusement. Mr. Duncan's design is to supply the deficiencies in the former works on the subject; and in general to render his treatise on weaving as compleat as possible; in which we think he has succeeded, so as to do himself great credit, and to render the various matters he treats of, clear and perspicuous, in the highest degree. By this work the weayer may improve himself in the knowledge of his profession to his profit; and the admirer of ingenious mechanism will find much in it to interest and amuse him. It will also tend to the farther improvement of manufactures, for many thoughts will be suggested to ingenious minds, by its perusal, which will be turned to practical utility in the different lines in which they are most interested. In the work the fullest explanation is given of plain weaving, and of all the machinery connected with it; of the weaving of twilled cloth, including that of diaper, and of table cloths; of weaving double cloth, and the manufacture of carpets; of cross-weaving, comprehending the node of weaving gauze, catgut, patent net, whip net, balloon net, and of various other kinds of nets; and of spot weaving, with that of brocade spots, pressed spots, double frame lappets, and of many other sorts. The machinery, necessary for weaving those different fabrics, is clearly described, and, in most instances, is illustrated by wellexecuted plates, fourteen of which accompany the work: the different fabrics are also, in many cases, explained by figures of parts of them, magnified, as if viewed through a microscope, which exhibits them in the most satisfactory manner. Besides an account of the common machinery connected with weaving, Mr. Duncan has given descriptions of winding machines for warp; of dressing machines; of cylindrical brush machines for dressing; and of power looms, wiper looms, crank looms, and vertical looms. following tables are inserted, in the course of the work:-a warper's table, beaming table, setting-table, table of warps, and a comparative table of reeds; and various historical details of the different manufactures, particularly an account of the rise and progress of the cotton manufacture, are to be found in it, well worth attention. Many other interesting particulars of the differ ent manufactures, besides those mentioned, are given in these es says. The The matter being remarkably compressed, so as to contain much in a small space, it would be im possible to reduce the substance of a work of this nature into any compass fit for the space allotted to it in a Review; the most that can be done is to give a general account of it, with some specimens of the manner in which the author treats the subjects contained in his work; from many very good, we select the same. "It may be necessary in this place, to inquire shortly into the causes which render tweeled cloths stronger than plain, and to ascertain the difference. "In so far as the strength of tweeled cloths depends solely on the mode of weaving, that strength will be rather diminished than increased, when compared with plain cloth, containing an equal quantity of similar materials. For in the texture of plain cloth, every thread is constantly interwoven; whilst in that of tweels, they are only interwoven at intervals. Now, in the latter case, the threads can derive no mutual support from each other, except at the intervals where they are interwoven ; and that part of them which is flushed, must depend entirely on the strength of the individual threads; those of the warp being flushed upon one side, and those of the weft upon the other. The following inference will naturally arise from this: Let two webs of equal length, equal breadth, and equal in the quantity, quality, and fineness of the Let the first be plain, yarn, be woven. and the second tweeled. The quantity, quality, and fineness of the materials being equal, their strength ought to be so also. But, if by strength, we understand that quality, which opposes the most effectual, and most continued resistance to the decay of cloth, from common wearing; the tweeled web (if equally used) would be in tatters, long before the plain one was materially injured. This is the idea commonly, although inaccurately, attached to the word strength, when ap 739 plied to the fabric of cloth; and, indeed, the above remark will not be found uni versally true, for the durability of cloth, exposed only to common wearing, de pends partly upon its strength, and partly upon its flexibility. "It is not, therefore, in the effect of the mechanical operation, but in the faci lity of combining a greater quantity of materials in the same dimensions, which this mode of weaving affords, that we are to look for superior strength or durability. This may be easily illustrated. When the shed of any web is opened, every thread either above or below the thread of woof which has been driven through the web, will oppose a certain resistance to the operation of the lay in driving the shot home; and the sum of all these resistances will be the whole resistance. Now, in plain weaving, every thread is interwoven, and therefore, opposes its portion of resistance; whereas, in a four leafed tweel, every fourth thread only is interwoven, and, of course, gives resistance. The ratio of resistance, therefore, will be inversely in proportion to the number of leaves in the tweel, compared with unity. "In the warp, the friction in the reed will be diminished in the same propor. tion; for each thread, instead of changing its place at every shot, changes only once in every four shots. Consequent ly, much more warp may be crowded into the same space without injury, than could be done in plain weaving, "From the above we may safely de duce, that the strength, or durability, of a tweeled web will be somewhat less than the proportion of the materials which it contains will be to that of a plain web, supposing each to be of equal strength and quality. "But, when the fabric is very close, tweeled cloth possesses another advantage over plain, in point of durability. When the warp of plain cloth is very much crowded in the reed, and the welt driven very closely home, the threads, in order to cross each other alternately, must deviate very materially from their natural form, which is in a straight line; whereas, when woven, they become serpentine. This renders the cloth very liable to be easily cut, or chafed, espe Bbb2 cially when composed of hard, and comparatively inflexible materials. This defect is chiefly observable in stout linens, and arises from the inelastic, and inflexible nature of the fibres of the flax. But, when tweeled, as the threads only cross at intervals, the deviation from the straight line is much less, and the flexibility of the cloth, of consequence, much greater." The great expense of the mounting of draw looms being chiefly caused by the time the operation occupies, which is no less than 96 working days for one man, makes it a great object, that the materials of the mounting should be as durable as possible. Fine cord is, at present, solely used for this purpose, which, besides not lasting on an average more than eight months of constant work, is liable to alterations in length, from the changes of the atmosphere, and to other defects. The following improvement on looms for twilling, double cloth and carpets, proposed by Mr. Duncan, seems likely to be extremely beneficial, and applicable to all kinds of draw looms, in which it would ultimately produce a saving proportionably great as the parts of the harness required are numerous. "I have often thought that when looms are mounted for fancy weaving, particularly where the fabric is thick, and the power required great, the substitution of wires for cords would be a material improvement. A wire remains perfectly uniform in all seasons, and, from its superio: strength, would last for many years. Cords, on the contrary, besides being contracted or relaxed by every change of the atmosphere, are very apt to rot from damp or moisture, which is very common in weavers' shops. I am aware, that the expence of mounting a loom with wires, will form a serious objection when a variety of work is wanted, and the mounting, of course, frequently changed. But, when there is a rational prospect of a loom being employed for a length of time upon the same pattern, I am convinced that it will be found not only the best, but eventually the cheap est plan. When a mounting is extensive, and much cordage required, great pains are frequently necessary to keep the whole regular, and much time is lost in regulating and repairing the cords. If wires are used, the leaves must be raised by levers; for wire, however much softened, does not possess sufficient flexibi lity to bend over a pully. The wires should be lackered or painted, to preserve them from rusting, and their lengths may be regulated with great accuracy, by however, is given merely as an opinion, means of temper screws. The above, for I have never known the experiment tried; but I do not entertain a doubt, that it would be found a material improvement." The wires proposed by the author, to be used for the above purposes, are of course intended to be of iron, from his directing their being lackered or painted, to prevent their rusting. We imagine copper wire would be much superior to iro wire for this purpose, notwithstanding its greater first cost; no paint can effectually keep iron wire from rusting, as may be seen in old bell wires, which are frequently rusted away through several coats of paint; the rust of iron wire would also damage the cloth, by giving it stains nearly indelible; but copper wire would be entirely free from these defects, and would remain perfect for centuries. Wire mounting would be particularly serviceable in the patent draw loom, (described in p. 169.) at least, that part of the mounting which is drawn into the comb,should always be made of wire, for the friction there must be so great against the teeth of the comb, that no cord harness can long withstand it; and accordingly the harness is always found to wear out much more quickly in the patent draw looms, than in the common ones. It may be of use to note, that though wire will not draw over pullies, as Mr. Duncan remarks, yet it is very sufficiently flexible for contraction by a lateral pull, in the same way as the tails of the mounting are contracted, or drawn down, by the simples; and it certainly would be possible to mount a draw loom entirely on this principle, without using any pullies in it. In the comparison of the patent draw loom, with the common draw loom in p. 171, Mr. Duncan has made a small mistake in the computation of the mechanical power of the part of the mounting used at the tail for drawing up the harness; when he states that as "the simples which are pulled down to raise the harness are connected to the tail, between the end which is fast and the pullies, consequently the simples act in the same ratio as a weight fixed to a moving pully, suspended by a rope passing through the pully, and of which one end is made fast, It has often been demonstrated, that a weight, say 2lbs, in this situation, will be balanced by another of only 1lb. suspended from the other end of the rope, after its passing over a fixed pulley." In this instance, Mr.Duncan has forgotten the power of oblique forces, which occur when a weight acts in any part of a horizontal cord, stretched over a pully, in which case the weight required on the cord, to balance a weight of two pounds at its extremity beyond the pully, will be as the distance it depresses the cord from the horizontal line, to the distance between the perpendicular and the point of its suspension, where it cuts the horizontal line, and the centre of the pully; or, in other words, as the sine of the angle, formed by the depressed cord with the horizontal line, is to the cosine; now, these will not be equal till the cord is depressed so far as to form an angle of 45° with the horizontal line, which, we believe, is hardly ever done in drawing down the tail by the simple; therefore, in all in termediate cases the mechanic power of the apparatus will be the reverse of what Mr. Duncan supposes, and will act in favour of the drawer, instead of in favour of the weight or harness; and the pound weight suspended at the simple will, for the greatest part of the distance, which it is requisite to pull it down, balance more than two pound at the harness; a pound weight, in fact, at the simple, will raise any weight at the harness a little way, which the cord is strong enough to bear; and as it is pulled down lower, more weight or power will be required to balance that at the harness in the proportion before mentioned. The mechanical power by which the action of a force applied to the middle of a stretched cord, tends to draw together the points by which the cord is held, deserves to be more attended to by mechanics than it has been; it is applicable to a variety of purposes, and for its simplicity well merits being ranked among the mechanic powers, the principle is equally applicable to jointed bars as to cords. Dr. Franklin, who had a mind always alive to improvement, has noticed it with some commendation,, in one of his papers, published in the Transactions of the Philadelphia Society; and Mr. Watt has applied the principle very happily for raising the chief valves in his steam engine, Mr. Duncan has very properly apologised, in the introduction, for the provincial terms used for the various operations, and parts of apparatus, mentioned in his work. It appears to us that an edition of the work, in which the English terms were substituted for the Scotch, would be more acceptable to the English artist, though not abso lutely necessary, as there are very few terms used which cannot be easily understood by the context. We think also a slight alteration |