《论衡·卷十一·说日篇》
因为西北方高，东南方低，水的本性流向低处，就像火的本性趋向高处一样。
西北方高，东南方下，水性归下，犹火性趋高也。
Because the northwest is high, the southeast is low, the water inherently flows towards the low places, it is the same as the fire inherently goes to high places.