When there is dust rising in a high column, it is the sign of chariots
advancing; when the dust is low, but spread over a wide area, it
betokens the approach of infantry.
高而銳 “high and sharp,” or rising to a peak, is of course somewhat
exaggerated as applied to dust. The commentators explain the
phenomenon by saying that horses and chariots, being heavier than
men, raise more dust, and also follow one another in the same
wheel-track, whereas foot-soldiers would be marching in ranks,
many abreast. According to Chang Yü, “every army on the march must
have scouts (探候之人) some way in advance, who on sighting dust
raised by the enemy, will gallop back and report it to the
commander-in-chief.” Cf. Gen. Baden-Powell: “As you move along,
say, in a hostile country, your eyes should be looking afar for
the enemy or any signs of him: figures, dust rising, birds getting
up, glitter of arms, etc.”[174]
When it branches out in different directions, it shows that parties
have been sent to collect firewood.
There is some doubt about the reading 樵採. The _T‘ung Tien_ and
_Yü Lan_ have 薪採, and Li Ch‘üan proposes 薪來.
A few clouds of dust moving to and fro signify that the army is
encamping.
Chang Yü says: “In apportioning the defences for a cantonment,
light horse will be sent out to survey the position and ascertain
the weak and strong points all along its circumference. Hence the
small quantity of dust and its motion.”