It describes how the narrator views the street he walks in, bathed by the moonlight, and how it somehow makes everything he sees and his memories vague and indistinct. An example of that is how a streetlamp can emit "sound" as well as light. It is also implied that somehow that time of night, being "midnight" has the power to unconsciously "shake" the narrators thoughts and memories without him knowing or being aware of it, like a madman would not be aware that he is shaking a dead flower.