THE MEASUREMENT OF CURRENT 



87 



movable coil, recourse has been had in investigation and calibra- 

 tion work, to a wattmeter method as indicated in Fig. 45. 



The current coil of the wattmeter and a known resistance R are 

 inserted in the circuit; the connections are such that the PR 



Wooden Support (or 

 Telescope and Scale 



l<'rtro<lyn:iiiioiii'tT. 



loss in the constant resistance, R, is measured, and thus the 

 current is determined. 



Agnew Tubular Electrodynamometer. l "- This instrument is 

 primarily designed for measuring very large alternating cur- 



