712 TECHXOLOaV AND CIVILIZATION. 



etc., ill many dirtereiit combinations. O[)i)o.se{l to this mechanism is 

 another of a d i Here nt motion ; of this Fig. 2 furnishes an example. 

 The wheel a turns 1, iu a fixed frame and has saw or similar shaped 

 teeth in which, at 2, a ratchet catches. This ratchet hinders the wheel 

 from following the pulling of the weight A at the margin of the wheel 

 a. But if the wheel be turned as we wind a cord, 4, on which hangs tlie 

 weight, the ratchet permits the wheel to go forward but retards it again 

 as soon as the compelling force subsides. 



This arrangement is known as '• ohstn(ctio)r (Gesperre.) 



In the use just described we would call it obstructinQ ?ro/7i-(Sperrwerk); 

 its backward and forward motion varying, thus requiring it to be com- 

 pletely discriminated from runniiu/ icorJc (Laufwerke). 



From the given groups of mechanisms, live others are possible. 



If we next imagine the ratchet to be raised, through pressure upon 

 the button at 5, the obstruction being released, the weight A falls down, 

 taking or drawing with it the wheel a. The resulting motion can be 

 utilized in many ways : quickly, as through a push with a ram, slowly, 

 gradually, as by a clock ; also m the running work of the telegraph, 

 changing always according to supply. 



Through winding on spokes, the mechanical labor can always be use- 

 fully changed. Instead of lifting a weight A, one can also place an 

 elastic body, i. e., a spring iu a condition of tension. We will there- 

 fore name the produced mechanism tension worJ: (Spannwerk). The 

 crossbow was a spring tension work ; there are millions of spring 

 tension works iu practical use iu flint-locks. 



We procure a third mechanism through a slight change of the man- 

 agement, namely, by allowing the ratchet that was previously released 

 to be again caught. This then catches up the wheel a and with it the 

 fallen weight A. A sufficient!}' strong structure presupposed, one can 

 also make the mechanism serve for catching up heavy masses, and we 

 name it accordingly cafc/i icorlc (Fangsverke). The mechanisms used iu 

 mines and also iu elevators for the catching of the pro[)ellers in case of 

 rope-break, are such catch icork. If one considers that the wheel teeth 

 can be made so tine as to be invisible, whereby the circumference of the 

 wheel a will be smooth and the obstructing ratchet simply a friction 

 body, the obstruction changes into a friction obstruction, as one per- 

 ceives in the brake of the railroad train. Tlieai)i)lications of catch icitrli 

 are also very useful and numerous. 



A fourth mechanism one would secure out of the groups in (luestion, 

 if one attached, but on a moving arm, perhaps a second similar ratchet 

 to the nearer one, fastened to it, the last having a swinging motion. 

 Through this motion one can then, intermittingly, move the wheel with 

 the intention of lifting the weight, since the tirst ratchet always catches 

 the wheel when it begins to let the weight sink. The thus formed and 

 driven mechanism is called leap icork (Sch.iltwerk). Applications of 

 the same are known and many. A lifth manner of conversion of the 



