|This electromagnetic balance was made by Yeates & Son of Dublin
in the late 19th century, and is in the Callan Museum at St. Patrick's
College, Maynooth, County Kildare, Ireland.
At the left is a solenoid with a soft iron core that is pulled downward when current passes through the solenoid. The resulting counterclockwise torque on the pivot arm is compensated by weights hanging from the arm projecting to the right. The magnitude of the magnetic force can then be related to the solenoid current.
In the background the lower half of a quadrant electrometer can be seen.