540
�KINEMATICS OF MACHINERY.
�cylinder itself here becoming a screw ( 15). Higher screws
S, are not unfrequently paired with T, the fusee of a clock or watch^
for example, Fig. 372, or the conic rope-drum which has lately
been much used in winding engines, or the fusee in Eobert's mule,
Fig. 373. The conoid with a rope enveloping it (Fig. 374) belongs
also to this class. The order to which these pairs belong is
therefore (/S, t ), under which the class (, t ) is a lower form. At
���FIG. 373.
�FIG. 374.
�the limit S = E we obtain the group (E }i ) of which Fig. 375
shows two examples.
The next order is furnished us by the pairing of T with H } the pair being therefore (H, t ). As a representative of the class ((7, t )
���FIG. 375.
we have the pair formed by a rope-drum and a flat belt laid spirally round it.
With H s we can pair the chain T v It gives us the order of which there are many applications.
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