180 STEAM ENGINES 



Attachment of Indicator Cord. The cord leading from a 

 reducing motion to the indicator drum should be in two pieces 

 with a hook on one of the free ends, preferably the end next to 

 the indicator, and a loop in the end fastened to the reducing 

 motion. This makes it possible to disconnect the indicator 

 from the reducing motion when desired, and decreases the wear 

 on the instrument. The length of the string should be care- 

 fully adjusted so as to give the drum the correct amount of 

 motion. If the string is too short, it will be broken; and if 

 too long, there will be lost motion and the card will not repre- 

 sent the true length of the engine stroke. It may also result 

 in damage to the indicator. 



A convenient arrangement is shown in Fig. 10. The hook a 

 is attached to the indicator cord, and the cord e from the 

 reducing motion is passed through a plate b, as shown. By 



FIG. 10 



slackening the cord at the point d, the plate may be slipped 

 to any position along the cord. The length is thus easily 

 adjusted. When the indicator is in operation, the hook is 

 hooked into the loop. By unhooking the two cords the indi- 

 cator may be stopped to put on a card. 



The stretching of the indicator cord may introduce serious 

 errors in the diagram. Hence it is better, if possible, to use 

 a wire instead. If a cord is used, it should be as short as 

 convenient. It should also be thoroughly stretched before 

 being used. 



Errors of Reducing Motions. The forms of reducing motions 

 shown in Figs. 3, 4. and 7 are imperfect, because the motion 

 imparted to the cord is not exactly proportional to the move- 

 ment of the crosshead. The only forms of reducing motion 

 that are absolutely accurate are those in which the distance 

 from the pivot to the point of attachment of the cord always 



