TECHNOLOGY AND CIVILIZATION. 713 



groups results, if oueuses perhaps a narrow, coruer-shaped segment of 

 a wheel and forms with it an obstruction for the passage between the 

 points 1 and 2, in the fashion, I will say, of a door. Then through clos- 

 ing the obstruction at 2, the passage can be retarded or stopped ; 

 through loosening, it will be opened. We will name the mechanism in 

 this form, closing worlc (Schliesswerk). It exists in closing doors, win- 

 dows, closets, chests, in the form of locks, and so on in known and 

 numerous changes. We see here the wide domains of the lock, which 

 offers millions, yes miilionfold variations of closing work. 



The sixth, and j^erhaps from the standpoint of the mechanic the most 

 remarkable change of the obstruction, is the checking or checlc icorlc 

 (Hemmwerk), as we will say. It exists if we set free the obstruction 

 by light touches upon the button at 5 and immediately closing it again. 

 If this occur regularly the progress of the wheel a may serve, among 

 other purposes, for measuring time. In clocks this checlc worlc is largely 

 used. The regular release of the obstruction takes place by means of 

 an even-timed body, the pendulum. Variations of check work exist 

 in many other machines. 



Thus we see there are many examples of obstruction ivorls (Gesperr- 

 werken), as we may call them collectively, i. c, works in which the ob- 

 structing ratchet plays a part. But let us look still farther. It often 

 occurs that obstruction works are combined and the action of one trans- 

 mitted to the other. A fine example is furnished by the set-trigger of 

 target rifles. This trigger is nothing else than a little tension work, 

 very easily loosened, in consequence of which the firmer held tension 

 work of the cock is loosened, one thus working upon the other. Such 

 a combination we may call a tension work of a higher order, or, in case 

 of a similar combining of obstruction works we speak of an obstruc- 

 tion work of a higher order. An illustration is furnished by the mo- 

 tive work of a clock, where the weight and spring tension work 

 (Gewichts-und Fedderspannwerk) drives the obstruction work (das 

 Hemmwerk), thus workiug in the second order. Clearly, we have here 

 a principle, for the transmission of motion can occur between obstruc- 

 tion work and wheel work, and so on. For example, there is attached 

 to the check work of the clock a cog-wheel work which moves the 

 hands. Naming motive works in general, several examples of which 

 we have noticed drive tcorlcs (Treibwerken), the wheel work of a clock 

 must be a drive work of the third order, consisting of tension work, 

 check work, and wheel-running work arranged the one over the other. 



Having taken so broad a view in this field of observation, we turn to 

 another quite different in aspect. 



If we notice our machines in practical use we find among them a 

 number in Avhich fluidity serves as force and motion transmitter, as the 

 hj'draulic press, the pump, spouting machines, water wheels, the tur- 

 bines, etc. But not only liquid but gaseous fluids we similarly convert 

 into gas motors, air machines, and especially into steam-engines. Close 



