We offer an economical, sturdy version of this classic electrical measurement instrument. This closed case form electroscope uses a flexible aluminum leaf to indicate the charge. Touch the top of the knob with a charged object, and the flexible leaf will deflect away from the post. Bigger charges causes more deflection. Includes 6-1/3" x 4" x 2-3/4" electroscope, plated rod with knob and attached aluminum foil leaf.