prismatically

— He managed to struggle up to a sitting position in the bed, trying to make out more of his surroundings. But the room was dark now. As his eyes adjusted, he made out a small brazier there, with a cadaverous old man in a dark robe spotted with looped crosses. On his head was something like a miter, carrying a coiled brass snake in front of it. The old man's white goatee bobbed as he mouthed something silently and made passes over the flame, which shot up prismatically. Clouds of white fire belched up.