548
�KINEMATICS OF MACHINERY.
�The use of a tension-organ in this way does not give us any
useful results. It is otherwise, however, with the pressure-organs.
If, in the first place, we replace the link I in the chain ($' P' C'}
by a fluid we can form several practical mechanisms from it. The
complete formula would in this case run :
a b c
C+ ... | ...S,Q ...... Q,P ...... G-
which would be contracted, the link c being supposed fixed, into (S', q P', q C'y. If we now take a as driving-link we get the machine ($', q P', q 6")a. This formula represents the screw-pump, the Archimedian water-lifting screw, the screw-ventilator, the main-train of Schlickey sen's clay-press, &c.
If with the same mechanism the pressure organ b be made the driver, which would give us (S', q P', q C')%, we have the simple screw turbine.*
If we place the chain on b and make a the driver we obtain the mechanisms (8 f tq P f fq (T)m which is the leading train of the screw-steamer, a is the propeller, c, the vessel and b the water.
The train of Fig. 384 is also applied in a well-known machine. If we replace b once more by a pressure organ (here specially by a liquid) we obtain a chain of which the complete formula is :
a b c
�G+
�...s,
�c
��FIG. 386.
�Placing the chain on c and making the fluid
link b the driver we obtain a mechanism
() which is that of the Jonval or
Henschel turbine, Fig. 386. To improve the
working of the machine the screws 2 and 3 are
higher screws, so that strictly the formula
should contain S, x instead of $, x .
Once more we have a series of machines placed together which differ immensely in their objects and in their constructive form, but which are formed upon one and the same kinematic chain. We shall have to mention other screw chains in 154.
�Such for example as the turbines at the mill of St. Maur described by Leblau
�
