OBSERVATION OR SCOUT-PLANES. On the French Front the old types of reconnoitring machines are being replaced as quickly as possible. They were too slow and not easy to control in case of an attack. The services rendered by the reconnoitring airplanes are of the greatest importance. Their observations supply the Command with accurate information concerning everything that is taking place within the enemy’s lines; the condition of his front; the movements of troops in his rear; thus enabling the Chief to foresee his intentions and foil his plans. In addition to reports of what they observe during their flights, the pilots obtain aërial photographs. This very important adjunct of our modern armies has been considerably improved. Photos taken at an altitude of 2500 and 3000 metres (8000 to 10,000 feet) reproduce so accurately the configuration of the land with every object on it, that trained officers are able to observe in them the smallest changes that have been made. With this object in view they compare together several photos of the same place taken at different dates. We include in our volume some aërial photographs of the German lines in the Aisne sector taken at the end of December, 1916, in January, 1917, and in April and May, 1917. The first show merely the enemy’s works before the French bombardment. The pictures taken in April of the same ground give an excellent idea of the progressive effect of the French artillery, and the last photographs, taken during the attacks of the 5th and 6th of May, show the final result of the tremendous shell-fire. In order to compare the changes effected from time to time, it is necessary to use a magnifying-glass, and to note successively each observation on a large-scale map called a “directing map.” This minute, painstaking method alone will enable the Staff to form an idea of the effect of the artillery, and the progressive demolition of the works and trenches of the enemy. Later on we will see that the observations reported by the reconnoitring aviation influence in a great measure the dispositions taken for attack. The British attach, and rightly so, such importance to a strictly accurate record of the effects of their fire, that they are not satisfied with the usual charts, but construct for their principal staffs large-scale relief-maps including both their own and the German lines, works, and batteries, as revealed to them by photographs taken from airplanes and captive balloons. Officers of the General Staff are specially entrusted with the duty of recording on this relief-map all damage and destruction as fast as it is reported. When the order of attack is given, the British chiefs, knowing as far as it is possible what works they will find destroyed, and what points will offer a more or less stubborn resistance, make their dispositions accordingly.