Second Foundation
He discovered that the mental manipulations by the Second Foundation left a detectable pattern in brain wave activity, and called it a “Tamper Plateau.” Using this, he could determine who had been directly affected by the Second Foundation. With Semic, he developed a mind static device capable of protecting against this, and further refined it into a weapon against Second Foundationers. With the use of this, he and the First Foundation seemingly destroy the Second Foundation; the small group that is revealed is a decoy, though, and the Second Foundation survives on Trantor.