within the enemy's lines.
(c) Place Sketch--when sketch must be made from one point, as when
the proximity of the enemy would prevent any movement; as from
trench observation stations, etc.; also an elaboration of the
_landscape_ or _horizon_ sketch which is used everywhere in the
trenches today. From one point an actual outline of the
opposite trench and background is made in perspective,
reference points on the horizon being marked on the edge of a
pad at arm's length. These marks are then prolonged on the
paper and the horizon is sketched. In like manner the middle
distance and the foreground come under observation and are put
on in one below the other.

Time must be allowed the men to make their stride scales and to paste
or transfer them to their alidades.

[Illustration: Plate #9]

LESSON 3. (FIELD WORK--FIVE HOURS.)

The problem is to make a Position Sketch about one mile square closing
the traverse. First considering the sketch board, compass, pencils,
etc.; next the orienting, sighting and pacing; finally the uses of
intersection and resection and in making allowance for error.

The sketch board should be about 12 to 18 inches square, being used
with or without a tripod. A cheap camera tripod is excellent. The
board should have a compass attached so that it will remain in the
same relative position on the board. If iron thumb tacks are used
avoid getting them too near the compass. A hard pencil must be used to
obtain good results. The paper must be smooth and where possible
covered with another sheet fastened on but one side which will
readily fold back when one desires to work on the sketch.

By always placing the board so that the compass reads North it will be
oriented correctly. Care must be used when near electric wires or
masses of metal as automobiles, railroad tracks, etc., which will
attract the needle from its true azimuth (N. and S. direction) and
thus throw off the whole map. In such cases it is far better to back
sight and use the compass only at intervals to verify the sights.

This brings up the matter of sighting. It is important to make long
shots thus reducing the amount of individual error. In taking a
sighting point make sure it can be recognized when reached and make
sure to look at the reverse side in order to recognize it in case of
back sighting if necessary. Always carry several large-headed pins
using one