"When the melody rose, her voice broke up sweetly, following it, in a way contralto voices have, and each change tipped out a little of her warm human magic upon the air."

Today's Gatsby sentence, describing singing, has us picturing the woman as a vessel containing warm human magic. Because she's a contralto, her voice needs to break as it reaches for the high notes, and in these breaks, there's a tipping that spills out a little of her contents — warm human magic. The magic spills upon the air. There's rising and falling: The melody rises and the voice along with it, and the magic falls out, upon the air. It's very light, this human magic, to be on top of air. It is the sweet, warm liquid of the woman tipping out.