AMONG the most important accessories to a ship are the Cable, by which she can be anchored to the bed of the sea, and the ropes called “warps,” by which she can be fastened to the land.
Perhaps my readers may not know the old riddle—“How many ropes are there on board a man-of-war?” The non-nautical individual cannot answer, but the initiated replies that there are only three, namely, the man-rope, the tiller-rope, and the rope’s-end, all the others being “tacks,” “sheets,” “haulyards,” “stays,” “braces,” &c.
Formerly cables were always made of hemp, enormously thick, and most carefully twisted by hand. Now, even in small vessels, the hempen cable has been superseded by the iron chain, and this for several reasons.
In the first place, it is much smaller in bulk, and therefore does not occupy so much room. In the next place, it is even lighter than the hempen cable of corresponding strength; and, in the third, its specific gravity—i.e. its weight when compared with an equal bulk of water—is so great, that when submerged, it falls into a sort of arch-like form, and so attains an elasticity which takes off much of the strain on the anchor, and protects it from dragging.
We will now look to Nature for Cables.
The natural cable which will first suggest itself is evidently that of the Pinna Shell (Pinna pectinata), which fixes its shell to some rock or stone with a number of silk-like threads, spun by itself, and protruding from the base, just as a vessel on a lee shore throws out a number of cables. The threads which compose the “byssus,” as it is called, are only a few inches in length, and apparently slight. They are, however, really strong, and by acting in unison enable the shell, though sometimes two feet in length, to be held firmly to the rock. I may here mention that they have been occasionally woven into gloves, and other articles of apparel, to which their natural soft grey-brown hue gives a very pleasing appearance.
A still more familiar instance of a natural marine cable is given by the common Mussel, which can be found in thousands on almost every solid substance which affords it a hold. Even copper-bottomed ships are often covered with Mussels, all clinging by their natural cables, and it is thought that the cases which sometimes occur of being poisoned by eating Mussels, or “musselled,” as the malady is called by the seafaring population, are due to the fact that the Mussels have anchored themselves to copper, and have in consequence imbibed the verdigris.
Passing from salt to fresh water, we come to a natural cable which is very common, and yet, on account of its practical invisibility, is almost unknown, except by naturalists. I refer to the curious cable which is constructed by the common Water-snail (Limnæa stagnalis), which has already been mentioned in its capacity of a boat.
This creature has a way of attaching itself to some fixed object, such as a water-lily leaf, by means of a gelatinous thread, which it can elongate at pleasure, and by means of which it can retain its position in a stream, or in still water can sink itself to the bottom, and ascend to the same spot. This cable seems to be made of the same glairy secretion as that which surrounds the egg-masses which are found so plentifully on leaves and stones in our fresh waters, and, like that substance, is all but invisible in the water, so that an inexperienced eye would not be able to see it, even if it were pointed out.