Answer:
Useful tool for who in darkness dwell. Within you, corrupting like a deadly spell.
What is the freedom of birds and the pen of old men?
What is up that’s also down? What’s a smile and a frown?
My first is nothing but a name; my second is more small; my whole is of so little fame it has no name at all.
Thirty white horses on a red hill, First they champ, Then they stamp, Then they stand still.
I’m grown from darkness but shine with a pale light. Very round I am and always a lady's delight.