The author Mary Shelley use the word chimerical in that line because she said that the powers of Cornelius Agrippa were improbable and because she wanted to say this in a fancy way.
Hope this Helps :)
BTW, Mary Shelley is the author of Frankenstein <span />
When he eats the White Witch's food, Edmund is brought under her power, and experiences a craving for both Turkish Delight and the power that she promises him.
The answer to your question is :
The cat is grey.
