MEASUREMENT OF DIFFERENCES OF TENSION. 187 



Reymond invented a ' round compensator ' (fig. 47), in 

 which the wire of the rheochord r r' is placed on the cir- 

 cumference of a circular disc of vulcanised india-rubber. 

 The beginning and the end of the wire are connected 



FIG. 48. DIAGRAM OF ELECTRIC MEASUREMENT BY MEANS OF A UOUNP 



COMPENSATOR. 



with the clamps I and II ; from the beginning a wire 

 also passes to the clamp IV. The clamp III is con- 

 nected with the small reel r, which is pressed by 



