CHAIN-CLOSURE AT DEAD POINTS.
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�at right angles the guides themselves be placed 90 apart (Fig. 147),
a single crank may serve for both mechanisms. This is frequently *
used for screw-steamers, and has also been applied to land-engines.
In this case, as in the former, the driving force (steam-pressure) in
the chain is assumed to act upon the bodies c and c'.
Another mechanism which is carried over its dead points by chain-closure is sketched in Fig. 148. Two equal and parallel cranks a and c are connected by a link ~b having a length equal to that of the fixed link d. The figure 1234 is therefore a
��FIG. 147.
parallelogram having dead points in the positions 1 2' 3' 4 and 1 2" 3" 4, and this whether the driving force be applied to a or c. The dead points may be passed by the addition to the first chain of a second one a! V c' df similar to it, in such a way that a has a common axis with of, c with c', and that each pair of cranks encloses an angle of 90, and further that d is connected with d', i.e., that both are made stationary (Fig. 149). Locomotives with coupled wheels give familiar illustrations of this arrangement.
- The arrangement with cylinders equally inclined to the vertical has been very
little used for marine engines, at least for many years, in this country : I have seen it applied to oscillating cylinders. One of its most recent applications has been at the Panteg Steel Works, Pontypool, where it forms the driving mechanism of large direct-acting Eolling Mill Engines (see Engineering, vol. xix. p. 249). The same mechanism has lately been used for large compound engines in the Guyoii
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