By 1850 most of the basic electrical phenomena had been
investigated. However, James Clerk Maxwell (1831-1879), Professor of
Experimental Physics at Cambridge then came up with something entirely
new. By some elegant mathematics he had shown the probable existence
of electromagnetic waves of radiation. But it was twenty four years
later (eight years after Maxwell's death) that Heinrich Hertz
(1857-1894) in Germany gave a practical demonstration of the accuracy
of this theory. He generated and detected electromagnetic waves
across the length of his laboratory on a wavelength of approximately
one metre. His own photograph of the equipment he had set up can be
seen in the Deutsches Museum in Munich.
To detect the electromagnetic waves Hertz employed a simple form
of oscillator, which he termed a resonator. But it was not sensitive
enough to detect waves at any great distance. Before wireless
telegraphy could become practicable, a more delicate detector was
necessary.
Credit is due to Edouard Branly (1844-1940) of France for
producing the first practical instrument for detecting Hertzian waves,
the coherer. It consisted of two metal cylinders with leads attached,
fitted tightly into the interior of a glass tube containing iron or
steel filings. The instant an electric discharge of any sort occurred
the coherer became conductive, and if it was tapped lightly its
conducting property was immediately destroyed. In practice the
tapping was done automatically by a tapper which came into action the
moment the coherer became conductive.
In Russia the physicist Aleksandr Popov (1859-1905) had used a
coherer while engaged in the investigation of the effects of lightning
discharges. He suggested that such discharges could possibly be used
for signaling over long distances. Old timers may remember that
about 50 years ago Russian amateurs used to send out a QSL card with a
drawing of Popov and a caption which claimed that he was 'the inventor
of radio'.
In Italy, a young 22-year-old electrician became interested in
electromagnetic radiation after reading papers by Professor Augusto
Righi (1850-1921). It was Guglielmo Marconi (1874-1937), the son of a
well-to-do landowner who lived in Bologna, and who was married to
Annie Jameson of the well known Irish Whiskey family. Guglielmo, their
second son, had his early education at a private school in Bedford,
England, and later at Livorno and Florence in Italy. When he read
about the experiments of Heinrich Hertz and about Popov's suggestion,
he saw the possibility of using these waves as a means of signaling.
His first transmitter, shown in the accompanying photograph, did not
radiate very far. When he folded the metal plate into a cylinder and
placed it on a pole 30 feet above the induction coil and connected to
it by a vertical wire, he was able to detect the radiation nearly two
kilometres away. Marconi realised that his signaling system would be
most useful to shipping, and in those days England possessed the
world's greatest navy and the world's biggest merchant fleet.
The Italian government was not interested in young Marconi's work,
so after a family conference he was brought to London by his mother,
who had influential relatives there. Not only did they finance his
early experiments but they also put him in touch with the right sort
of people. One of these was Alan A. Campbell Swinton who became the
first President of the Radio Society of London (now the R.S.G.B.) many
years later, in 1913. Campbell Swinton introduced the young Italian
to William Preece, then Engineer-in-Chief of the British Post Office.
Preece had already been investigating various methods of 'induction'
telegraphy.
In a book entitled Wireless Telegraphy published in 1908, William
J. White of the Engineer-in-Chief's department at the G.P.O. wrote,
"The work of Sir (then Mr) William Preece, important
though it was, did not attract the attention of the
public to the extent that might have been expected.
This was due to the fact that no sooner had he
demonstrated a method of wireless telegraphy which was
a commercial possibility than his system was superseded
by another, and a better one, brought to England by Mr
Guglielmo Marconi in 1896. The possibilities of Mr
Marconi's system were at once recognised by Mr William
Preece. The experience of the elder and the genius of
the younger man, who must be given the credit of having
devised the first practical system for wireless
telegraphy, combined to turn apparently disastrous
failures into success, and now (in 1908), wireless
telegraphy has become, in less than a decade, part and
parcel of commercial and national life."
The world's first patent for wireless telegraphy was awarded to
Marconi on the 2nd June 1896. In it he stated that "electrical action
can be transmitted through the earth, air or water, by means of
oscillations of high frequency." In the first public demonstration of
his equipment Marconi spanned the 365 metres between the G.P.O. and
Victoria street. Later, on Salisbury Plain, in March 1897, his
signals were detected over 7 kilometres away. On the 11th & 18th May
1897 messages were first exchanged over water. On the 27th of March
1899, during naval manoeuvres, Marconi bridged the English Channel for
the first time, a distance of about 140 kilometres. His transatlantic
triumph came on the 12th December 1901 when the morse letter 'S' was
transmitted from Poldhu, in Cornwall and received by Marconi himself
at St. John's, Newfoundland, who recorded the historic event in his
pocket book simply "Sigs at 12.20, 1.10 & 2.20".
The operation of Marconi's transmitter was itself quite
spectacular. To produce the oscillations he employed the oscillator
designed by Augusto Righi. Depressing the key closed the circuit and
brought the inductor coil into action. Vivid sparks occurred between
the balls of the oscillator, to the accompaniment of a succession of
sharp cracks, like the reports of a pistol, and some energy was sent
off the square metal plate in the form of trains of electromagnetic
waves, which radiated out in all directions. But the energy occupied
a very large bandwidth and the receivers of that period could not
separate two transmissions. William J. White of the Post Office wrote
in 1908, "The chief objection which has been raised against modern
wireless telegraphy is its want of secrecy. With a transmitter
sending out waves in all directions, it is possible for unscrupulous
persons to receive the messages and make an improper use of them.
This form of 'scientific hooliganism' has, in fact, become somewhat
notorious. When two or three transmitters are each sending out their
electromagnetic waves, the result, naturally, is utter confusion."
White added that the British Postal Administration was refusing to
grant licences for more than one system in the same area, in spite of
the fact that there had been some 'alleged' solutions of the problem.
The phenomenon of resonance was known and Dr (later Sir Oliver) Lodge
had taken out various patents between 1889 and 1898 in connection with
receivers. Marconi and his assistants ultimately solved the problem
by modifying Lodge's syntonic Leyden jar tuned circuit. They added a
tapped inductance in the aerial circuit of the transmitter and used
variable capacitors instead of fixed ones. This was probably the most
significant modification made in the development of wireless
telegraphy. (In Greek the word syntonismos 'to bring to equal tone'
is used for 'tuning'.)
Apart from the patents taken out by Sir Oliver Lodge and Dr
Alexander Muirhead, in 1897, patents were taken out in Germany by
Professor Braun of Strasbourg, who was joined by Professor Slaby and
Count D'Arco in 1903 to form the Telefunken company, and in the U.S.A.
by Dr Lee De Forest of the American De Forest Wireless Telegraph
Company who was the first to use a high A.C. voltage of 20,000 volts
to obtain the necessary high-potential discharges, thus dispensing
with the induction coil. Again in the U.S.A., Professor R.O.Fessenden
was responsible for the design of new types of transmitting and
receiving apparatus.
During this period Marconi had resisted all offers by financiers to
acquire his patents. In July 1897 he entrusted his cousin Jameson
Davis to form The Wireless Telegraph & Signal Company Ltd which soon
became Marconi's Wireless Telegraph Co., and ultimately the Marconi
Company.
William Preece of the Post Office detached one of his assistants,
George S. Kemp, to help Marconi. Kemp was destined to become his
right-hand man and served Marconi faithfully throughout his life. By
today's standards, Marconi can be said to have been a highly
successful entrepreneur. He had the great knack of selecting the
right man for the job, and inspired deep loyalty in his staff. He
regarded himself as an 'amateur' and often paid tribute to the work of
radio experimenters.
(Most of the above passages are quoted from 'A History of
the Marconi Company' by W.J.Baker, published by Methuen & Co Ltd.
reprinted in 1979.)