Such was probably the whole process of ropemak ing for many ages, till the progress of the maritime art required the use of ropes of a much larger size; for this could not be advantageously effected by in creasing the number of yarns in a strand. Were we to attempt to compose a strand of a great number of yarns, the plies would not have a sufficient number of turns round their common axis to prevent them from slipping when the yarn is stretched; many of the fibres would be broken on being twisted together into one spiral, "because," as Mr. Chapman remarks, " the outward coat of threads or yarns is exposed to more stress than the internal ones, as will be very evident when it is considered that when two or three hundred yarns are all stretched at length to form one cylindric mass, they will lie at different distances from the centre of the cylinder, and that, when twisted to gether, the outside yarns form a spiral of some given number of turns round the mass of the included yarns, forming a considerable diameter, and are therefore much shortened; whilst the inner yarns take only the same number of turns round a reduced axis, and from that cause should be less shortened. Therefore it fol lows, that the outside yarns only can be in full tension, whilst those within must be more or less puckered up, according to their proximity to the centre." From these causes, cables, or large ropes which are said to be cable laid, are formed by the combination of lesser ropes twisted around their common axis, in the same manner as a shroud laid rope is formed by the combination of strands twisted round their common axis. Cables of water ropes are formed on this prin ciple, even when their size is not very great, as they are thus made more hard and compact, which makes them resist the easy admission of water.
Such is a brief and general account of the state of the rope manufacture till the end of the last century, when various successful attempts were made not only to improve the quality of ropes, but to facilitate the process of making them.
We shall now endeavour to give an account of these important improvements, taking for our guide Mr. Chapman's Treatise on the Progressive endeavours to improve the Manufacture and Duration of Cordage.
So early as 1783, Mr. Sylvester proposed to super sede the necessity of a rope ground, by employing a machine, of which he deposited a model with the So ciety of Arts, which we have had occasion to examine. In order that the manufacture might be carried on in a house, he spun the thread on a bobbin and spindle, and the yarns which composed the strands were wound on three separate reels fixed on frames, which turned individually round their axis, and also round a com mon centre, in consequence of which motions they were twisted into a rope, which was to be wound up as it was made. Mr. Chapman mentions, that the defect of the machine was, that the process of making the strands, and twisting them into a rope, was per formed by two successive operations as in a rope ground, portions of the threads being first made, and these portions afterwards combined into a rope. Our
recollection of the machine, however, is, that both operations were performed at the same time.
Be this as it may, however, the invention was given gratuitously to the public, and as the inventor took out no patent, it was never carried into effect,—the general result of most inventions, where no induce ment is held out to bring them into actual practice.
In 1784, Mr. Benjamin Seymour took out a patent for a new method of making ropes; but this seems to have been nothing more than the substitution of horses in place of men, for driving the machinery then in use.
The Rev. E. Cartwright took a patent in 1792, for his Cordelier, a machine for making ropes. This in vention appears to have been the same as Mr. Sylves ter's; but differed from it, according to Mr. Chapman, in the circumstance of the motions for twisting the strands, and making the rope, going on at the same time.
The advantages of making ropes by machinery seems to have been considered so great, that the at tention of many ingenious individuals was about this time directed to the subject.
In the year 1793, no fewer than three patents were taken out for improved methods of making ropes. Mr. R. Fothergill, of Sunderland, secured by patent, in 1793, his invention of a method of heckling and pre paring the hemp, and of spinning it into rope yarn, and of a machine for making the rope. This ma chine, which we have represented in Plate CCCCLX XXII. Fig. 1. is on the same principle Cart wright's. The object of it was, to make ropes with out the necessity of a rope ground, and to diminish the labour of the manufacturer. In the perspective view of this machine given in the figure, A represents the platform, by the revolutions of which the three strands are twisted into a rope at their place of junc tion B, from which it is drawn forward at C as it is made by the revolution of the wheel D. The three separate reels that contain the strands are shown at E, E, E, and contain the proper number and length of yarns necessary for a strand. These reels revolve round their individual axes, at the same time that they are all carried round by the frame A, which supports them. For a drawing of Mr. Fothergill's machinery for slivering and drawing out the hemp, and of his yarn spindle and bobbin, we must refer the reader to Mr. Chapman's work, already quoted. This machinery was erected on a very large scale at South wick, on the river Wear.
In the same year, Mr. J. D. Balfour, of Elsineur, took out a patent for "a new invented machine for manufacturing ropes and cordage." The principal object of Mr. Balfour's invention was, to remedy the defect in the usual method of making the strand; in consequence of which, a given number of spirals round a large cylinder, must require a greater length of yarn than the same number of spirals formed round a small cylinder, having its axis of the same length as the large one.