In order to carry out an attack with fire, we must have means available;
Ts‘ao Kung thinks that 姦人 “traitors in the enemy’s camp” are referred to. He thus takes 因 as the efficient cause only. But Ch‘ên Hao is more likely to be right in saying: 須得其便不獨姦人 “We must have favourable circumstances in general, not merely traitors to help us.” Chia Lin says: 因風燥 “We must avail ourselves of wind and dry weather.”
The material for raising fire should always be kept in readiness.
煙火 is explained by Ts‘ao Kung as 燒具 “appliances for making fire.” Tu Mu suggests 艾蒿荻葦薪芻膏油之屬 “dry vegetable matter, reeds, brushwood, straw, grease, oil, etc.” Here we have the material cause. Chang Yü says: 𫎓火之器燃火之物 “vessels for hoarding fire, stuff for lighting fires.”
3. 發火有時起火有日
There is a proper season for making attacks with fire, and special days for starting a conflagration.
A fire must not be begun 妄 “recklessly” or 偶然 “at haphazard.”
4. 時者天之燥也日者宿在箕壁翼軫也凡此四宿者風起之日也
The proper season is when the weather is very dry; the special days are those when the moon is in the constellations of the Sieve, the Wall, the Wing or the Cross-bar;
These are, respectively, the 7th, 14th, 27th, and 28th of the 二十八宮 Twenty-eight Stellar Mansions, corresponding roughly to Sagittarius, Pegasus, Crater and Corvus. The original text, followed by the T‘u Shu, has 月 in place of 宿; the present reading rests on the authority of the T‘ung Tien and Yü Lan. Tu Mu says: 宿者月之所宿也. For 箕壁, both T‘ung Tien and Yü Lan give the more precise location 戊箕東壁. Mei Yao-ch‘ên tells us that by 箕 is meant the tail of the 龍 Dragon; by 壁, the eastern part of that constellation; by 翼 and 軫, the tail of the 鶉 Quail.