ssance, 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