The opposing force was ready to meet the attack with equal or superior numbers. The eye of the army, the aeroplane, detected the movements in every instance. THE AEROPLANE DETECTING THE MOVEMENTS OF ARMIES.--In the early stages of the war, when the Germans drove the left of the French army towards Paris, the world expected an investment of that city. Suddenly, and for no apparent reason, the German right was forced back and commenced to retreat. It was not known until weeks afterwards that the French had assembled a large army to the west and northwest of Paris, ready to take the Germans in flank the moment an attempt should be made to encircle the Paris forts. The German aviators, flying over Paris, discovered the hidden army, and it is well they did so, for it is certain if they had surrounded the outlying forts, it would have been an easy matter for the concealed forces to destroy their communications, and probably have forced the surrender of a large part of the besiegers. The aeroplane in warfare, therefore, has constantly noted every disposition of troops, located the positions and judged the destination of convoys; the battery emplacements; and the direction in which large forces have been moved from one part of the line to the other, thus keeping the commanders so well informed that few surprises were possible. THE EFFECTIVE HEIGHT FOR SCOUTING.--It has been shown that aeroplane scouting is not effective at high altitudes. It is not difficult for aviators to reach and maintain altitudes of five thousand feet and over, but at that elevation it is impossible to distinguish anything but the movement of large forces. SIZES OF OBJECTS AT GREAT DISTANCES.--At a distance of one mile an automobile, twenty feet in length, is about as large as a piece of pencil one inch long, viewed at a distance of thirty-five feet. A company of one hundred men, which in marching order, say four abreast, occupies a space of eight by one hundred feet, looks to the aviator about as large as an object one inch in length, four and a half feet from the eye. The march of such a body of men, viewed at that distance, is so small as almost to be imperceptible to the eye of an observer at rest. How much more difficult it is to distinguish a movement if the observer is in a rapidly-moving machine. For these reasons observations must be made at altitudes of less than a mile, and the hazard of these enterprises is, therefore, very great, since the successful scout must bring himself within range of specially designed guns, which are effective at a range of 3000 yards or more, knowing that his only hope of safety lies in the chance that the rapidly-moving machine will avoid the rain of bullets that try to seek him out.