Motion and thus becomes less dense. Denser air flows in from below and the result is that irregular layers of air of different densities are formed above the flame.

• 空气受火焰加热而膨胀,于是变得比较稀薄。较密的空气从底下流人,其结果是,火焰上方形成了密度不同的不规则的空气层。