124 



MECHANICS. 



An improvement, by rendering the instrument more 

 compact, is shown in Fig. 99, where S S is the spring, 

 and directly over it is the graduated scale. 



Fig. 99. 



Elliptic Dynamometer, in compact form : S S, spring ; F, cross-lever for moving 

 index. 



An inconvenience occurs in the use of the instru- 

 ments now described from the rapid vibration of the 

 index, resulting from the quick changes in the force, 

 partly from inequahties in the soil, and partly from the 

 unsteady motion of the horses. The vibration is some- 

 times so great that the index can be hardly seen, ren- 

 dering it difficult to measure the average force. This 

 inconvenience has been removed, in a great degree, by 

 attaching to one end of the index, E {Fig: 99), a pis- 

 ton working in a cylinder filled with oil, G ; this piston 

 has a small hole through it, through which the oil pass- 



