To select a signal station, choose a point perfectly in view of the communicating station; fix the exact position in which the flag-man is to stand: so arrange, if possible, that he will have behind him, when viewed from the communicating station, a background of the same color for every position in which the signals may be shown. The color of the background of a station is that of the earth or sky, against which the signals made seem to be displayed when viewed from the communicating station. For this purpose take the direction of the communicating station, and by going in front of your station, examine the position from that direction; ascertain whether the communicating station is higher, lower, or on a level with your own. If it is higher, the back ground for your signals, viewed thence, will be the color of the fields, woods, etc., behind and lower than your flag-man. If it is lower, your backgrounds will be the color of grounds, etc., behind and behind the flag-man. Do not presume the back ground is of the color of the fields near you. It may be that of the woods a long distance, sometimes miles, behind your station. If your station is on a house or an eminence, it is still very possible, that there are higher grounds somewhere behind it. The color of back grounds is generally dark. Sky-exposure back grounds are rare. They are not often found at long ranges on land. They cannot be had except on the exact crest of ridges or lands which bound the horizon of view from the other station, or on the precise apex of mountains, etc. At short ranges, they may, of course, be had by working on the tops of very high buildings, steeples, etc. Unless certain of the color of the back ground, it is safe to presume it is not the sky, and that it is not light. It is a rule always to use the white or red flag until the color of the back ground is determined. The best back grounds are darkly colored, as green fields or woods.
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