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strand is a term occasionally applied to a strand-laid rope itself, when three of these are made into a cable-laid rope, by being twisted round their common axes), Messrs. Chapman have, to prevent misconstruction, described as being composed of any given number of yarns twisted together round their common axes; and which cannot of itself be called a rope, although a component part of one. I conceive that no one sending an indefinite order for a rope, would consider his order complied with if the rope-maker was to send him a primary strand composed of rope-yarns twisted together, which, when stretched at length and left to itself, would immediately open out. It'would avail little for the rope-maker to say, 66

you have only to cut the strand into three parts, and twist them together the contrary way, and they will then become a rope.” He might with nearly as much propriety have sent the rope-yarns, or even the hemp, for each of them would have been constituent parts, but not the thing wanted. From these premises it clearly follows, that Messrs. Chapman's flat-bands, or strand-belts, are not made of ropes; but of a distinctly different thing which they have defined; and consequently they can have no exclusive claim to any other description of flat bands, even if they were composed of rope-yarns, which are the immediate constituent parts of a primary strand, the same as the latter is of one description of rope, every kind of which is fairly included in Mr. Curr's patent; because a rope of any description is for its purposes a complete manufacture. It is evidently not so with primary strands for the reason already given, that the twist would open out, and they would become a loose body of yarns; therefore any new process of combining such strands together, or any new form when combined, is certainly

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patentable, more particularly if useful to the public; consequently, if Messrs. Chapmans' invention also possess this qualification, it has; as to distinctive difference, all that can be wanted. It appears that a strand-laid rope composed of three strands, is one sixth part shorter than the strands it is formed of, and only twice the strength of a single strand. It therefore follows that irt point of strength, or in reduction of quantity to produce the sanie strength, the invention must be highly advantageous to the public; provided the duration of strand-belts-be, in any instances where they are applicable, nearly equal to that of flat ropes; and there is nothing in theory against their being completely so.

Prior to the inventions of either Nr. Curr or Messrs. Chapmans, flat bands have been made various ways it the different forms of girth-web made from untarred rope-yarn or hempen-yarn; but this application of yarn, or the application of this species of belt to the drawing of coats from mines, to which purpose it is not inapplicable, operates against neither of the inventionis in question, although they are all composed of the same primary manufacture, viz. of hempen yarn, which is as

distinct from a primary strand as such a strand is from a *rope. The distinction may be still continued, although the process shall have approached much nearer : viz. all

for a strand stretched at length and bound together, so as to form what sailors calla salvagee, and which Duhamel and others have supposed to be the strongest mode of combining the strength of yarns*, may

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A salvagee is much stronger than a common primary strand (the only one known when Dahamel and other authors wrote, ,,who are quoted in the Encyclopedie), but inferior to a strand made on the

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be used in any manner. The salvagee differs from a primary strand only in not being twisted, which is much hearer to a primary strand, than that strand to a rope. Yet I do not conceive that Messrs. Chapman could have a just plea to prevent any person so inclined from stitching these salvagees together side by side, and applying thein to the drawing of minerals. Neither can they or Mr. Curr have any just plea to prevent any one from stitching together, side by side, knittles *, sennet, or gaskets (all of which are composed of rope-yarns), and applying the flat band thus made of them to the drawing of minerals, to which they would be perfectly applicable. Messrs. Chapman contemplated all these combinations, and saw the relative imperfections of each, as well as those of ropes themselves laid side by side; and

new principle, by which all the yarns bear alike, or nearly so, at the point of breaking. This circumstance arises from the inequality of rope yarns, which if simply stretched in one mass, no otherwise combined than by ligatures, would, on a general tension of the whole, each of them break in its weakest purt; but when twisted into such

strand as described, they combine one with another, and each yarn bears its average strength, which, as the weak parts are gencrally a small portion of the length of each yara, is much further beyond the least strength of each yarn than what is lost by the angle they form to their common axis when twisted into a strand. Thus a primary strand made on the best principle is the strongest application of rope-yarns: therefore, any more advantageous coinbination of strands than has been used before must be a beneficial invention.

* Knittles are flat lines composed of three rope-yarns platted to. gether. Sernet consists of five, seven, nine, or any larger unerea bumber of yarns, combined together in a platted form by a process not necessary to take up the reader's time in describing, but which produces some resemblance of two cylindric bodies connected together. When this manufacture is made with an eye at one end, and tapered at the other, it is called a gasket, and is ased, when ship." sails are farled, to wrap round them, and bind them to the yards. VOL. XIII.-SECOND SERIES.

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having decided hy experiments the superior strengthen and conceived the probable utility to the public and to themselves that would result from this novel combination of primary strands; they, similarly to the practice of many others wł:o have invented useful combinations, applied for and obtained his Majesty's Letters Patent. · I have purposely used the word combination, because by much the major part of inventions are new combinations, and nothing more ; whether in machines which are necessarily formed of wheels, screws, &c. which have individually and conjointly been used various ways; or in manufactured articles, which are formed of wood, iron, hemp, flax, wool, &c. all of which have been used individually and conjointly.

I conceive that no invention is entitled to public protection but on the basis of utility. The obtaining of any end to which the public are in possession of an equivalent would defeat itself, because no one would be induced to pay for its adoption. If, on the other hand, an improvement has been granted to an inventor, I conceive that any small deviation to obtain the same end only would be a piracy; but, if it either be to obtain one more valuable, or to shorten the process, and reduce the quantum of materials, without adopting any part of tàe other than what is common, then the invention is obviously a new one; and on this ground the patent for strand belts has been found to stand conspicuously, particularly at this period, when hemp is so much wanted for the purposes of our navy both military and commercial.

Exclusively of the circumstances peculiar to the thing itself, I conceive there is both novelty and utility in performing the operation of combining strands or other pli

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able substances together by a locomotive machine, because it admits of the operation being performed when the se. parate parts are extended at length and equally stretched, which is of great importance; as, from the want of this circumstance, flat ropes have been found to break their stitches when exposed to sudden jerks, which has occasioned their disuse at some collieries in Northumberland and Durhain. Consequently, this part of the invention also is supported on the basis of utility, and not a mere evasion; which neither necessity nor inclination would have led the parties to have had recourse to. If I have placed this subject in a new light, no other merit is due to me than that which necessarily arises from a combina. tion of practice and theory.

I am, Gentlemen,

Yours, &c. Newcastle, May 4, 1808.

WM. CHAPMAN.'

Description of a cheap Apparatus for filtering and purifying

Water, invented by Mfr. J. I, HAWKINS, of No. 79, Titchfield-Street.

Communicated by him in a Letter to the Editors.

GENTLEMEN, AGREEABLY to the intention announced in the account of the Museum of Useful and Mechanical Inventions, inserted in your last number, I now send you the description of another of the articles there deposited for public exhibition.

A cheap Apparatus for filtering and purifying Water.

This apparatus consists of a vessel of wood, metal, earthen-ware, or other convenient material, having

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holes

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