By the end of the war photographic processes and equipment had reached a high standard of excellence. There are still, however, certain difficulties in regard to the production of accurate maps, which have not been overcome, the most obvious being the necessity of an initial framework of fixed points and of contouring. The subject is considered so important that an "Air Survey Committee," consisting of representatives of the Air Ministry, the Geographical section of the War Office, the Ordnance Survey, the School of Military Engineering and the Artillery Survey School, has recently been formed. In addition, the School of Aeronautics of Cambridge University is studying the question. The Survey of India and the Survey of Egypt are also conducting experiments. _Wireless._ From the outset, part of the German scheme of tactics was to batter down resistance by means of superior weight of heavy armament, and with the beginning of warfare of fixed position the observation and direction of our artillery fire became as important as distant reconnaissance. Besides its immense value in increasing the effect of the batteries, it had the indirect advantage of more closely binding the ties of mutual understanding between the air and ground troops, a point which fortunately seems to have been misunderstood by the Germans. In September, 1914, the first attempts were made to signal enemy movements from the aeroplanes of a Headquarters Wireless Flight which had been formed for the purpose, and this practice was continued with success throughout the Battle of the Aisne. In the earliest stages artillery co-operation was also carried out by dropping coloured lights, but from the Battle of Ypres onwards, though for some time very few wireless machines were available, this was effected by wireless or signal lamps. In his dispatch on the Battle of Loos, Sir John French wrote: "The work of observation for the guns from aeroplanes has now become an important factor in artillery fire, and the personnel of the two arms work in closest co-operation." By the Battle of the Somme artillery co-operation had assumed very large dimensions. For instance, on September 15th, 1916, on the front of the 4th Army alone, seventy hostile batteries were located, twenty-nine being silenced. Counter-battery work was so effective before the offensive which opened on the Ypres front at the end of July, 1917, that the Germans withdrew their guns and the attack was delayed for three days in order that their new positions might be located.