Like many other galvanometers, a ballistic galvanometer has a coil which rotates between magnets. The ballistic galvanometer has the special feature that its rotating coil has a large moment of inertia. It is used to measure quantity of charge rather than currents, for the large moment of inertia permits the passage of a quantity of charge before the coil moves significantly. The passage of the charge produces an impulse, a momentary torque, which causes the coil then to swing slowly to some maximum position. Such a galvanometer was often used to standardize capacitors.
This galvanometer was purchased from Queen and Company for $75. probably near 1900.