Page:The Kinematics of Machinery.djvu/588

 KINEMATICS OF MACHINERY.

�4 necessarily becomes a prism-pair, and the organ T is fixed at both ends ta the prism into which c has been changed. Fig. 419 shows

��FIG. 417.

�this chain, in which it is specially noteworthy that on account i of the fixing of the organ T we have a chain of

three links only instead of four. Its complete formula runs

��c <+ R, T ...... v. Pi P-"... j_ ... c-.

In contracted form this would be (C'R^ The chain is used here and there, placed both upon c and upon d.

A common pulley-tackle is an unconstrained closed chain, or at least is constrained only by force-closure ; here therefore we need not consider it. If it be made complete by pair-closure, it becomes (as we saw also in 43, with the simplified roller arrangement) a compound chain. The oases thus obtained are very interesting

�FIG. 418.

��Fio. 419.

�in themselves, but do not come into this part of our subject (cf. p. 568). This is true also of a number of other important applications of tension-organs.

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