"It is done by signals, devised after a system of the Indian's own
invention, and communicated in various ways.
"Wonderful as the statement may appear, the signaling on a bright
day, when the sun is in the proper direction, is done with a piece of
looking-glass held in the hollow of the hand. The reflection of the
sun's rays thrown on the ranks communicates in some mysterious way the
wishes of the chief. Once standing on a little knoll overlooking the
valley of the South Platte, I witnessed almost at my feet a drill of
about one hundred warriors by a Sioux chief, who sat on his horse on a
knoll opposite me, and about two hundred yards from his command in the
plain below. For more than half an hour he commanded a drill, which
for variety and promptness of action could not be equaled by any
civilized cavalry of the world. All I could see was an occasional
movement of the right arm. He himself afterwards told me that he used
a looking-glass." (Dodge's _Plains of the Great West_, _loc. cit._,
pp. 307, 308.)