If the waves produced are to be perceptible at any considerable distance, the transmitting instrument must be capable of absorbing a large amount of energy and radiating this energy into space in the form of waves. The storing capacity of the instrument is increased by having large plates close together, but its radiating properties are impaired if the plates are too close. The chief advance made by Signor Marconi lay in his use of the earth as one of the plates. In his wireless installation, a network of insulated wires, suspended in the air above, is one plate, the earth is the other; and the two are connected by an inductance coil. This device cannot be applied to aircraft, for obviously no connexion with the earth is possible. Both of the plates, or networks of wire, have to be carried on the airship or aeroplane. No great weight could be carried on the early type of aeroplane, and no great space was available. This brief and imperfect description has been given in order to make clear some of the difficulties which attend the application of wireless telegraphy to aircraft, and especially to aeroplanes. The theory of flight was worked out by men of science in the laboratory; flight itself was first achieved by men who had had no systematic scientific training, but who endeavoured to acquaint themselves with scientific results, and to apply them, as best they might, to the difficulties with which they were familiar in practice. So it was also with the application of wireless telegraphy to aircraft. The men of the laboratory were not familiar with all the conditions which had to be observed, nor with all the unforeseen obstacles which present themselves in practice. It remained for those who knew the conditions and the obstacles to work out the practical problem for themselves. The vibration and noise, which make it difficult in an aeroplane to hear anything but the engine, the risk of fire, and the imperfect protection of the instruments from splashes of oil and the rush of the air--all these things complicated the problem. As early as 1907 Captain Llewelyn Evans, who commanded the 1st Wireless Company of the Royal Engineers at Aldershot, lent his help to Colonel Capper of the balloon school in devising wireless communication between aircraft and the ground. The apparatus had to be extemporized. The first experiments were made by Lieutenant C. J. Aston, R.E., in a captive balloon. In May 1908 a free run was made in the balloon _Pegasus_, in which a receiving set of wireless had been installed. When the balloon was over Petersfield, Lieutenant Aston received very good signals from the Aldershot wireless station twenty miles distant. During the same month the sending of messages from the balloon was also tried with promising results.