Was in another book I read. Googling is cheating. >:|

"I'm something. I'm nothing.
I am short. I am tall.
When you fall at your sport, then I stumble and fall.
I have never been seen yet beneath a new moon.
I thrive in the evening but vanish at noon.
I am lighter than air, I weigh less than a breath;
Darkness destroys me, and light is my death."