What did Lever mean by right-handed laid rope and why was this lay preferred by ropemakers? Figure 1 shows hemp fibres (A) being spun right-handed as yarns (B), and these in turn being formed left-handed into strands (C), which are laid right-handed into ropes (D). By closing three ropes, we get a cable (E). Ashley says that these technical verbs are preferred by ropemakers, but comments that they are 'often used indiscriminately'.2 As a preface to what follows, I imagine that many people would feel that the meanings of terms like 'with the sun', 'clockwise' or 'right-handed' are self-evident, and follow some sort of onomastic natural law. In fact, they only make sense if we are told from which side of the rotational plane the movement is observed. Put more simply: point of view matters. The sun rises in the East and sets in the West, but as seen in figure 2, seen from a point above the North Pole, the earth is rotating counterclockwise, while from a corresponding point above the South Pole, it is moving clockwise. At higher latitudes, as one faces the sun, it travels across the sky from left to right in the northern hemisphere, and from right to left in the southern hemisphere. 'With the sun' is an old-fashioned alternative to 'clockwise', but when used it is tacitly assumed we are north of the equator. The arrangement of the numbers on the face of one's wristwatch is not arbitrary but reflects the system used on the clock's predecessor, the horizontal sundial, as seen in figure 3a. In the northern hemisphere the shadow of the gnomon moves from left to right, as seen by an observer looking north, that is to say with his back to the sun. If the sundial is mounted vertically like that in figure 3b, the shadow moves the opposite way.3 Because the terms 'right-hand' and 'left-hand lay' occur so often in what follows, we will for convenience shorten them to RHL and LHL. A RHL rope is commonly defined as one in which the lines dividing the strands run down and to the right if horizontal, up and to the right, if vertical, as shown in figure 4, with a comparable definition for LHL rope. The terms Z-twist for RHL and S-twist for LHL rope, are often preferred nowadays, but note that these aids to memory work only if the rope is vertical. Furthermore, we have to be quite clear that a mnemonic is not an explanation.
展开▼
