"Now this passage here,"—Aziz tapped a page with his finger—"refers to the fourth element as ‘firewood.’ It’s usually translated simply as ‘wood.’ I’ve always thought that wood was a curious choice as an element, but what if the original translation was ‘burning wood’? When wood burns it produces smoke—not just particles of soot but also various gases. Ko Hung might have used ‘burning wood’ as a metaphor for ‘air.’ That would make more sense."