184 



PHYSIOLOGY OF MUSCLES AND NERVES. 



amount of weight required for this latter purpose affords 

 a measure of the force of attraction between the iron 

 and the magnet. 



In the present case a certain deflection in the multi- 

 plier results from the difference in tension at the feet 

 of the diverting arch. It is required to measure the 

 difference. If it is in. any way possible to influence the 

 deflection of the multiplier in an opposite direction, and 

 exactly to such a degree that the multiplier no longer 

 indicates any deflection, then the two influences must 



Fig. 46. Measurement by compensation of the difference of 



TENSION. 



be equal, and the one may serve as a measure for the 

 other. The experiment indicated in these instances 

 is called ineasurement by compensation. In order to 

 apply it to the case in point, the action of one dif- 

 ference of tension is cancelled by that of another which 

 may be altered at will. The rheochord, vrhich has al- 

 ready been described, affords a convenient means of 

 doing this. 



Let R R (fig. 46) be a wire extended in a straight 

 line (the line of the rheochord) through which a current is 



