One possibility would be to use a time-varying voltage rather than
a steady voltage across the plates of the two capacitors. The time
varying electric field will produce a magnetic fields that can be measured
by placing each capacitor inside a pickup coil. If the driving voltage is
identical the pickup signals should be identical....
As I recall this type of experiment was done to verify Maxwell's
prediction about "displacement currents".
Mark
Dr. Mark H. Shapiro
Physics Department
California State University, Fullerton
P.O. Box 6866
Fullerton, California 92834-6866