“The location of the sentinel post at night requires the most careful consideration. It depends considerably upon the degree of darkness, and consequently the value of eyesight as compared with hearing. On a very dark night, when the sentinel can see only a few yards in front of him, it is evident that his ears will be more useful than his eyes. Furthermore, the difficulties of the enemy will be increased by the darkness, and he is likely to make more noise by stumbling over unseen obstructions. On a still night a sentinel posted on high ground can hear better than when on low ground, because there is likely to be less obstruction in the way of trees and other objects to interfere with the sound waves passing through the atmosphere. It therefore appears that on a very dark night, when the ears are more efficient than the eyes, the sentinel should be posted on high ground, with low ground to his front. “When the darkness is not so great and the powers of sight more nearly approach in value the powers of hearing, it is better to place the sentinel on low ground, with the sky line to his front. This is because approaching persons will be silhouetted on the sky line and that it is difficult to see when looking down from a height into a dark valley. “The night post should always be provided with an obstacle placed from 10 to 30 yards to the front of the sentinel. It must be low, so that it will not be seen by an approaching enemy. Its value is increased if a wire or rope is attached to some object that will fall down with a loud noise when anyone trips over the obstacle.” Procedure The class is now conducted to the place where the sentinel post is to be established. _The Director_: “Lieutenant Barry, where would you locate your sentinel post?” _Lieutenant Barry_: “I would locate it at ——” (Note.—The location of the sentinel post should be determined upon after careful consideration of all the factors that enter into the problem.) The Director now distributes the sheets containing Situation No. 5. The Problem =Situation No. 5=: It has been decided to locate double sentinel post No. 1 of outguard No. 2 at this point. You, Corporal V, have arrived here with the members of the first relief. _Required_: The orders and instructions you give your sentinels. Explanation _The Director_: “The sentinels must have imparted to them all information of the enemy and our own troops. With respect to the latter, they must be fully informed of the covering patrols that have been sent out and the location of the adjoining sentinel posts. The location of the main body of the outguard should be pointed out, and, if practicable, the position of adjoining outguards. “They will be given the number of their own post and the number of the outguard from which they are posted.