20 FARM MACHINERY 



up in the measuring, but transmitted to the implement 

 or machine where the work is being done. 



The operation of the traction dynamometer is the same 

 as that of a heavy spring balance. The spring may be a 

 coil, flat or elliptical, or an oil or water piston may be 

 used in place of the spring and the pull determined by 

 the pressure produced. 



34. Direct-reading dynamometers. The more simple 

 types of dynamometers have a convenient scale and a 

 needle which indicates the pull in pounds. A second 

 needle is usually provided which shows the maximum 

 pull which has been reached during the test. A dyna- 

 mometer of this kind is illustrated in Fig. 9. This has 



FIG. 9 DIRECT-READING DYNAMOMETER 



elliptical springs and a dial upon which the draft is regis- 

 tered. It is difficult to obtain accurate readings from a 

 dynamometer of this sort on account of vibration caused 

 by the change of draft due to rough ground or the un- 

 steady motion of the horse. 



35. Self-recording dynamometers. A recording dyna- 

 mometer records by a pen or pencil line the draft. A 

 strip of paper is passed under the needle carrying the 

 pen point, whose position is determined by the pull. The 

 height of the pen line above a base line of no load is pro- 

 portional to the pull in pounds. A diagram obtained in 



