712 TECHNOLOGY AND CIVILIZATION. 



etc., in mauy different combiuations. Opposed to this mechanism is 

 another of a different motion ; of this Fig. 2 furnishes an example. 

 The wheel a turns 1, in 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 the 

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

 as soon as the compelling force subsides. 



This arrangement is known as " obstruction^'' (Gesperre.) 



In the use just described we would call it obstructing rt'orA:(Sperrwerk) ; 

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

 pletely discriminated from running worlc (Laufwerke). 



From the given groups of mechanisms, five 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 i^i 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 in a condition of tension. We will there- 

 fore name the produced mechanism tension tcorlc (Spannwerk). The 

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

 tension works in practical use in 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 aud with it the 

 fallen weight A. A sufficiently strong structure presupposed, one can 

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

 name it accordingly ca^c/i worl- (Fangwerke). The mechanisms used in 

 mines and also in elevators for the catching of the propellers in case of 

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

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

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

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

 ceives in the brake of the railroad train. The applications of catch work 

 are also very useful and numerous. 



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

 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, movethe wheel with 

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

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

 driven mechanism is called leaj) worlc (Schaltwerk). Applications of 

 the same are known aud many. A fifth manner of conversion of the 



