The War in the Air; Vol. 1 / The Part played in the Great War by the Royal Air Force

by Sir Walter Alexander Raleigh

Under Major Maitland's command the airship squadron—that is to say, No. 1 Squadron—grew in strength and efficiency, but it was cut off in its youth from the aeroplane squadrons. Expert opinion, which was divided on the military value of airships, was united on their naval value. Not without protest the decision was made to hand over all the airships to the navy, and at the close of the year 1913 this was done. An airship is much more costly than an aeroplane, whether to construct or to work, and when it flies at a moderate height for the purposes of military reconnaissance, it is much more vulnerable. This, no doubt, was the consideration which determined the severance of the airships from the army. Yet the airships, during their brief period of service with the Military Wing, had demonstrated in the most convincing fashion the enormous value of aerial reconnaissance, and, more important still, had put the whole Flying Corps in their debt by adapting wireless telegraphy to the uses of aircraft. The value of this work was not at once apparent. The time before the war was spent chiefly in experiment. During the retreat from Mons no ground receiving stations could be established. But when the German rush was beaten back, and the opposing armies were ranged along a fixed line, wireless telegraphy became a necessity for aeroplanes. The machines and the plant needed for this new development were not in existence; but a good deal of the preliminary work, much more troublesome and uncertain than the multiplication of a pattern, had been done. In a very short time there appeared at the front large numbers of machines fitted with wireless. The credit of this sudden apparition belongs, in part at least, to the Royal Engineers, and to their child, the balloon school, which by a steady process of growth had been transformed into the airship squadron of the Royal Flying Corps.

The power of sending messages through space, in any direction, over great distances, is so enormous an addition to the utility of aircraft that a few words must here be said about wireless telegraphy. The discovery was made by the gradual researches of men of science. These researches had their beginning in a famous paper by James Clerk Maxwell, who subsequently became the first professor of experimental physics at Cambridge. His paper, On a Dynamical Theory of the Electro-magnetic Field, read to the Royal Society in 1864, contains a theoretical demonstration that electro-magnetic action travels through space in waves with the velocity of light. Twenty-three years later, in 1887, Heinrich Rudolf Hertz, of the University of Bonn, published the results of his experiments in producing these waves by means of oscillating currents of electricity. His investigations confirmed what Clerk Maxwell had proved mathematically. Thereafter progress was rapid, and during the closing years of the nineteenth century the problem of subduing the waves to the service of man was attacked and solved. In 1889 Professor Oliver Lodge was measuring electrical radiation. At Liverpool University College he constructed a Hertz radiator to emit the waves, and received them at various points of the building. Edouard Branly's invention of the 'coherer', an instrument designed to receive Hertzian waves, was communicated to the British Association at Edinburgh in 1893. During the same year Nikola Tesla published his researches on high frequency currents; on these much of the later work on wireless telegraphy was based. In 1895-6 William Rutherford set up at the Cavendish Laboratory apparatus by which he received signals in distant parts of Cambridge up to a distance of half a mile from the oscillator. Many other men of science, among whom was Captain H. B. Jackson, of the Royal Navy, were at work on the problem, when in 1896 Signor Guglielmo Marconi arrived in England with an apparatus of his own construction which ultimately brought wireless telegraphy to the stage of practical and commercial utility. By 1899 signals had been transmitted across the English Channel.

Man has no sense organs which record the impact of electrical waves, but he has succeeded in devising instruments which register that impact, and which make it perceptible to the organs of sight or of hearing. The operation of the electrical waves may be best explained, perhaps, by the analogy of sound. When the string of a piano is struck by its hammer it vibrates, and communicates its vibrations to the surrounding air; these vibrations, travelling outwards in waves, produce corresponding vibrations in the ear-drum of a listener. The string is tuned, by its tension and its weight, to a single note; the ear can adapt itself to receive and transmit to the brain only a limited range of notes. There are many vibrations in the air which are too rapid or too slow for reception by the human ear. The sound-waves of the piano-string produce their effect on any neighbouring body which is capable of vibrating at the same rate as the incoming waves, as, for instance, another string tuned to the same note, or a volume of air enclosed in a vessel which vibrates in correspondence. These are in 'resonance' with the vibrating string; they repeat the original disturbance and reinforce its effect.

So it is with electricity. If the electricity with which any conducting body is charged be suddenly disturbed, electrical waves are generated which travel outwards in all directions with the velocity of light. The problem of wireless telegraphy is the problem of producing these waves by means of an instrument called a transmitter, and of recording their impact at a distance by means of an instrument called a receiver. In its simplest form the transmitting instrument consists of two conducting bodies, or plates, charged the one with positive the other with negative electricity, separated from each other by air or some other insulating material, and connected by a coil of wire called an inductance coil. To explain the how and why, so far as these questions can be explained, would involve a whole treatise on electricity; for the present purpose it is enough to say that when the two plates are connected through the coil, the electrical discharge is oscillatory in character, as the current runs to and fro between the one plate and the other, and that these oscillations are radiated into space in the form of waves. The frequency of the waves, the rapidity, that is, with which wave follows wave, depends on the size and proximity of the plates and on the length and form of the coil which connects them. The receiving instrument is similarly constructed, and can be so adjusted that the waves which it would generate if it were a transmitter would have the same frequency as those it is to receive. It is thus in resonance with the transmitter, and the effect of the incoming impulses is greatly enhanced.

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.