322 KINEMATICS OF MACHINERY.
use a shorter word well known to engineers, skew, as in Fig. 253. The chain will be written :
C+ ... || ... Ct C~ ... _L ... PP~ ...
... P+P- ... _L ... C~.
The symbol for crossed disappears, and makes room for that of oblique. If, as in former cases, we make prominent in the con- tracted formula the characteristic symbol of relation of the links, it will in this case be (O'^P^-). The links b and d are again equal and similarly placed, so that the chain gives us, like (C" 2 ' P^-), three mechanisms, namely
The turning skew (double) slider or swinging ) skew cross-block ........ . j
The turning skew cross-block ......
The swinging skew (double) slider ....
Besides these special cases, the crossed-slider chain has, lastly, two more special forms, which we can only mention here. These are the forms obtained if, instead of three only, we take all four links of infinite length.
If we make c = d = oo as before, and then make b and a also infinite but having a finite difference, we get the chain shown in .Fig. 254, of which the following is the formula :
a I c d
G Y +../i...Pi P-... -f ...<7i<7-...JL...Pi P-...I...O-
FIG. 254,
We may call this a single crossed-slide chain, and write it shortly as (CP + (7P- 1 -). All its links are dissimilarly placed, it there- fore gives us four mechanisms. If the lengths of c and d have a difference as well as those of b and a, but the two differences are unequal, we obtain the chain of Fig. 255, which we may call a double crossed slide chain C P { The links a and c are here
