Page:The Kinematics of Machinery.djvu/71

 these and the "active" parts, for in the various mechanisms constructed out of the same chain, the same part of the machine may sometimes be fixed and sometimes movable.

In the mechanisms which can be constructed out of a chain of the above-described arrangement, the motion of a link next the fixed link is determined by the nature of the element by means of which it is paired to that link; this one pair of elements alone influences its motion. With the link upon the further side of this one the case is different, its motion depends upon the motion of its neighbour-elements as well as upon the motions due to the elements at its points of attachment; in our illustration, for instance, it is influenced by four pairs of elements.

. 12.

Its motion relatively to the fixed link is however as determinate as if the two were connected by one pair of elements only. Hence we can again use the method by which in the first instance we obtained the chain,—we can, that is, combine an element of a new pair with it and so further extend the chain. In order to obtain at the same time the requisite closure, this extended chain must be brought back again into connection with the link at which it started. We obtain in this way a  kinematic chain, as distinct from which we may call the one described above a  chain. Fig. 12 shows such a compound chain, formed of  links of exactly the same description as those used before. Two of the links now contain three elements:—


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