Chapter III.OBSERVATION OF FIRE.
The observation of fire is essentially the following operation, repeated for each shot or salvo: Locating on the ground the position of one point, which is thepoint of burst, and announcing its situation in reference to another point, which is the target.
But it has been demonstrated that it is impossible, without using the map, to determine the error in range of one point relatively to another point not on the same alignment.
The operation must consist in:
1. Spotting on the map the point of burst.
2. Reading its position in reference to the target.
The observation of the burst—that is, the spotting of the point of impact—is the same whether the observation is direct or lateral.
Draw on the map, and copy if possible on a vertical photograph, the line balloon target (alignment of the center of the objective) and draw through this point a perpendicular to the alignment. In case the observation is lateral, draw also the line battery target and its perpendicular.
To draw the line balloon target, it is not necessary to know the horizontal projection of the balloon. It is enough to find on the ground a point situated directly on the alignment of the center of the objective.
When the shell bursts, take quickly an alignment and reference points in range of the point of burst; spot this point on the map or on the photograph; give its error in reference to the line battery-target, measuring it by the scale on themap or on the photograph.(It is well to put the graphic scale on the photos.)
The delicate part of the operation consists in seeing the shot at the moment of burst. One must try to spot the apex of the inverted cone formed by the burst, without paying any attention to the more or less considerable cloud of smoke which follows and which will cause mistakes if the burst was not seen immediately. The method of situating the point is the same as that described above.
For the direction, one reference point is enough, because one can consider the alignment of the point as practically parallel to the balloon-target. For the range, a rapid study of the terrain before the fire is sufficient to allow the observer to know the reference points by which he can guide himself. His eyes must never leave the point of burst until he has fixed well in his mind its situation in reference to appropriate reference points. Not to do this would lead to errors and to loss of time while he has to find the point again with his glasses to study it some more.
When the observation is direct, the direction of the burst is, of course, known as soon as it is seen. When the observation is lateral, it is well to remember that the line battery-target can not be materialized on the ground because it is in reality anoblique alignment, leading to the same errors which we have discussed. It follows all irregularities of the ground and, on account of this, can not be followed exactly in oblique vision.
Particularly around batteries, the ground is often very irregular. There may even be little spaces of dead ground, caused by hollows which the map does not always show. The above method, applied with the help of photographs, allows you to avoid errors resulting from the existence of these hidden parts.
1.Work sitting down, with the map on your knees and leaning against the edge of the basket.
This position is preferable to all others, because it allows theobserver—
(a) To correct with his head and shoulders the movements of the basket.
(b) To have the map always before him. He can consult it at any moment, mark the necessary alignments without loss of time, use it as a desk for drawing or taking notes, or as a wind shield when looking at photographs.
The observer who works standing up must either pick up his map from the bottom of the basket every time he needs it, which is out of the question, or fasten it outside the basket; the latter solution is inadvisable, it necessitates working in the wind when the map is referred to, and every time the observer turns to look at his map he disturbs the equilibrium of the basket.
It is advisable to work standing up only on days when there is practically no wind, and the balloon is continually turning and never becomes oriented.
2.Have always within reach a flat rule, a pencil, and a duodecimeter rule.
To be able to trace an alignment on the map with precision, the rule must rest on a firm surface. This happens when the map is mounted on a drawing board; when it is mounted on a frame with rollers, the frame should have, between the two thicknesses of the map, a board level with the edges of the frame on which the rule can slide with its whole length on the map.
With a hard pencil, well sharpened, precise and neat alignments can be drawn.
The duodecimeter rule is for measuring distances on photographs and on the map; chiefly in observations of fire.
3.Hold the field glasses with both hands.
This advice, sometimes ignored by observers without expedience, has a great influence on the accuracy of information. When an observer holds the glasses in one hand, it is much more difficult for him to correct the movements caused by the balloon and to concentrate on a point. It is very important, therefore, to hold the glasses firmly with both hands, especially when you are making a delicate observation or whenyou wish to study an “objective” in detail.