Let us suppose that by some accident the link [fig. 216.] should have its two extremities pulled towards Y and Z, whilst an obstacle X, placed right opposite to its middle, resisted the effort. The side of the link which touches X, would be bent inwards; but if as in [fig. 218.], there is a stay A G B, the two sides would be bent at the same time; the link would notwithstanding assume a faulty shape.
In thus rejecting all the vicious forms, we are naturally directed to that which deserves the preference. It is shown in [fig. 219.] This link has a cast-iron stay with large ends, it presents in all directions a great resistance to every change of form; for let it be pulled in the direction a b, against an obstacle c, it is evident that the portions d e and d f, which are supported by the parts g e and g f, cannot get deformed or be broken without the whole link giving way. As the matter composing g e and g f cannot be shortened, or that which composes d e and d f be lengthened, these four sides will remain necessarily in their relative positions, by virtue of the large-ended stay h, whose profile is shown in [fig. 220.]
We have examined the strength of a link in every direction, except that perpendicular to its plane. [Fig. 221.] represents the assemblage of three links in the above predicament; but we ought to observe, that the obstacle C, placed between the links A B, must be necessarily very small, and could not therefore resist the pressure or impact of the two lateral links.
Process of manufacturing iron cables.—The implements and operations are arranged in the following order:—
1. A reverberatory furnace (see [Iron]), in which a number of rods or round bars of the best possible wrought-iron, and of proper dimensions, are heated to bright ignition.
2. The cutting by a machine of these bars, in equal lengths, but with opposite bevels, to allow of the requisite crossing and splicing of the ends in the act of welding.