hourly experiences and dangers are a wonderful solvent of that prejudice. It is not in the laboratory that the Derby is won, or the manoeuvres and tactics of the air worked out. Major Brooke-Popham's squadron on Salisbury Plain was the first to get to work. In its origin, as has been told, it was the old aeroplane company of the Air Battalion, so that it was free from some of the difficulties which attend the creation of a new unit. It had at its disposal about ten machines of various types, and, for transport, one Mercedes car belonging to Captain Eustace Loraine and another belonging to the Government. Besides instructional flights and practice in reconnaissance, which were of course a regular part of the business of the squadron, it devoted its attention at once to co-operation with other arms, and especially to the observation of artillery fire. It was fortunate in getting the whole-hearted support of Colonel the Hon. F. Bingham, who was at that time commandant of the school at Shoeburyness, and chief instructor of the artillery practice camp at Larkhill. The great difficulty was to devise a sufficient method of signalling to the guns. Wireless telegraphy, which was destined to provide the solution of this problem, was then at an early stage of its development, and the apparatus was too cumbrous and heavy to be carried on the machines. Experiments were made with flags, with written messages carried back and dropped to the gunners, and finally with coloured Very lights. Progress was slow. Only a small amount of ammunition was allowed to the gunners. On windy days flying was far from safe; on calm days there was sometimes fog, or, if the weather was hot, the air became dangerously bumpy. Nevertheless the squadron flew in strong winds, and took every opportunity of demonstrating to the troops on the plain that it was worth their while to cultivate relations with the new arm. Towards the end of May there was a big field day, and though the wind was almost a gale, four machines went up, flown by Major Brooke-Popham, Captain Fox, Captain Hamilton, and by Major Burke, who had come over from Farnborough on purpose. The important thing at this time, and for long after, was to show the infantry what aeroplanes could do for them. At a later time, during the war, it became necessary to teach the infantry what aeroplanes could not do for them--that they could not, for instance, supply them with a complete defence against enemy aircraft.