Act 2 Scene 1: Polonius is convinced that Hamlet is crazy.
After hearing Ophelia's story about the dirty crazed out Hamlet, Polonius knows that Hamlet has gone crazy.
Come, go with me. I will go seek the king. This is very the ecstasy of love.
After receiving the letter from Ophelia written by Hamlet, Polonius rushes to the king to prove to him that Hamlet is crazy and his love for Ophelia is why. He tells the king how he told Ophelia to distance herself from Hamlet, and that is why he went into a crazed state. The letter is additional proof.
Act 2 Scene 2: Polonius convinces Gertrude and Claudius that Hamlet has gone mad.
That we find out the cause of this effect, or rather say, the cause of this defect, for this effect defective comes by cause. Thus it remains, and the remainder thus. Perpend. I have a daughter, have while she is mine, who in her duty and obedience, mark, hath given me this. Now gather and surmise.