[Tu Mu says that the previous paragraphs had reference to the fire breaking out (either accidentally, we may suppose, or by the agency of incendiaries) inside the enemy’s camp. "But," he continues, "if the enemy is settled in a waste place littered with quantities of grass, or if he has pitched his camp in a position which can be burnt out, we must carry our fire against him at any seasonable opportunity, and not await on in hopes of an outbreak occurring within, for fear our opponents should themselves burn up the surrounding vegetation, and thus render our own attempts fruitless." The famous Li Ling once baffled the leader of the Hsiung-nu in this way. The latter, taking advantage of a favourable wind, tried to set fire to the Chinese general’s camp, but found that every scrap of combustible vegetation in the neighbourhood had already been burnt down. On the other hand, Po-ts’ai, a general of the Yellow Turban rebels, was badly defeated in 184 A.D. through his neglect of this simple precaution. "At the head of a large army he was besieging Ch’ang-she, which was held by Huang-fu Sung. The garrison was very small, and a general feeling of nervousness pervaded the ranks; so Huang-fu Sung called his officers together and said: "In war, there are various indirect methods of attack, and numbers do not count for everything. [The commentator here quotes Sun Tzŭ, V. §§ 5, 6 and 10.] Now the rebels have pitched their camp in the midst of thick grass which will easily burn when the wind blows. If we set fire to it at night, they will be thrown into a panic, and we can make a sortie and attack them on all sides at once, thus emulating the achievement of T’ien Tan.’ [See p. 90.] That same evening, a strong breeze sprang up; so Huang-fu Sung instructed his soldiers to bind reeds together into torches and mount guard on the city walls, after which he sent out a band of daring men, who stealthily made their way through the lines and started the fire with loud shouts and yells. Simultaneously, a glare of light shot up from the city walls, and Huang-fu Sung, sounding his drums, led a rapid charge, which threw the rebels into confusion and put them to headlong flight." [_Hou Han Shu_, ch. 71.] ] ] ] ] ] 10. (5) When you start a fire, be to windward of it. Do not attack from the leeward. [Chang Yu, following Tu Yu, says: "When you make a fire, the enemy will retreat away from it; if you oppose his retreat and attack him then, he will fight desperately, which will not conduce to your success." A rather more obvious explanation is given by Tu Mu: "If the wind is in the east, begin burning to the east of the enemy, and follow up the attack yourself from that side. If you start the fire on the east side, and then attack from the west, you will suffer in the same way as your enemy."] 11. A wind that rises in the daytime lasts long, but a night breeze soon falls.