7 The 100 Most Influential Inventors of All Time 7favourable at night than during the day. This circumstance
is due to the fact that the upward travel of the waves is
limited in the daytime by absorption in the lower atmo-
sphere, which becomes ionized—and so electrically
conducting—under the influence of sunlight. In 1902 also,
Marconi patented the magnetic detector in which the
magnetization in a moving band of iron wires is changed
by the arrival of a signal causing a click in the telephone
receiver connected to it. During the ensuing three years,
he also developed and patented the horizontal directional
aerial. Both of these devices improved the efficiency of
the communication system. In 1910 he received messages
at Buenos Aires from Clifden in Ireland over a distance of
approximately 6,000 miles (10,000 km), using a wave-
length of about 5 miles (8,000 metres). Two years later
Marconi introduced further innovations that so improved
transmission and reception that important long-distance
stations could be established. This increased efficiency
allowed Marconi to send the first radio message from
England to Australia in September 1918.
In spite of the rapid and widespread developments
then taking place in radio and its applications to maritime
use, Marconi’s intuition and urge to experiment were by
no means exhausted. In 1916, during World War I, he saw
the possible advantages of shorter wavelengths that
would permit the use of reflectors around the aerial, thus
minimizing the interception of transmitted signals by the
enemy and also effecting an increase in signal strength.
After tests in Italy (20 years after his original experiments
with reflectors), Marconi continued the work in Great
Britain and, on a wavelength of 50 feet (15 metres), received
signals over a range of 20–100 miles (30–160 km). In 1923
the experiments were continued on board his steam
yacht Elettra, which had been specially equipped. From a