2. Height of observer.
3. Visibility.
Distance from the target is inevitable, but can be lessened by advanced positions and winch tracks. During active operation it has sometimes been possible to approach balloons within 4,500 meters (4,921 yards) of the line.
The low height of the balloon compared with an aeroplane is a drawback, as it brings a question of dead ground and exaggerated perspective.
Visibility is the determining factor of the balloon’s usefulness. In very high winds, very misty or cloudy weather, observation is impossible, and owing to its stationary nature the balloon can not, by any special effort on the part of its observers, overcome unfavorable conditions in the same way as is possible in the case of aeroplane observation.
On the other hand, a balloon flying at a height of 1,500 meters (1,640 yards) and 7,000 meters (7,651 yards) from the line, under favorable weather conditions, combines in a marked degree many of the advantages of air and ground observation.
In the first place, glasses can be used. Secondly, the balloon observer can converse direct with the battery commander by telephone. Apart, therefore, from ease and certainty in reporting observations, the telephone system enables an elastic program of work to be drawn up and admits of personal conversation between the battery commander and the observer, often permitting mistakes or misunderstandings to be cleared up during shoot instead of afterwards.
Finally, owing to the continuous nature of his observation from the same spot, the balloon observer is able to learn his country in the greatest detail and can keep a close watch on suspected roads or areas of country.
LIAISON BETWEEN BALLOONS AND ARTILLERY
The work of balloons is principally with the artillery, and close liaison between these two branches is indispensable if the best results are to be obtained. This close liaison should be promoted on the following lines: