Latest / History of the Universe Physics & Electricity Vol. 3 / 032 - Electricity - Chapter 11 - Wireless Telegraphy Part 2

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032 - Electricity - Chapter 11 - Wireless Telegraphy Part 2 · History of the Universe Physics & Electricity Vol. 3

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  Speaker 1: Section thirty two of the Science History of the Universe,
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  Speaker 1: Volume three. This is a LibriVox recording. All LibriVox recordings
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  Speaker 1: are in the public domain. For more information or to volunteer,
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  Speaker 1: please visit LibriVox dot org. Recording by Amelia Chesley, The
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  Speaker 1: Science History of the Universe, Volume three, edited by Francis
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  Speaker 1: Rolt Wheeler. Electricity, Chapter eleven, Part two. It was at
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  Speaker 1: once first seen by many experimenters, among them Sir Oliver Lodge,
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  Speaker 1: that with the old forms of apparatus there would be
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  Speaker 1: interference between wireless stations, as the receivers would respond to
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  Speaker 1: all wavelengths. To understand how it is possible to make
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  Speaker 1: as sending or a receiving circuit which will send out
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  Speaker 1: or respond to only one kind of electric wave, let
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  Speaker 1: the pendulum analogy again be used. In order to set
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  Speaker 1: a pendulum in motion, it is necessary that the impulsive
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  Speaker 1: force should be imparted to it the same number of
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  Speaker 1: times per second in which the pendulum naturally oscillates. Even
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  Speaker 1: if stray forces are applied but are not properly timed,
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  Speaker 1: the effect on the pendulum will be small, whereas a
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  Speaker 1: very minute but properly timed force acting for some time
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  Speaker 1: will produce considerable motion in a large pendulum. All these
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  Speaker 1: characteristics of the pendulum may be applied to the electric circuit,
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  Speaker 1: the natural period of vibration, the small effect of a
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  Speaker 1: lot of waves differing in length, and the large effect
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  Speaker 1: of a succession of feeble but similar waves. Sir Oliver
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  Speaker 1: Lodge in eighteen ninety seven took out a patent for
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  Speaker 1: a syntonic system of wireless telegraphy based directly on his
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  Speaker 1: own work on the discharge of latent jars and on
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  Speaker 1: Hertz's experimental results. The transmitter consisted of two large cones
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  Speaker 1: of sheet metal, placed with their axis in a vertical
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  Speaker 1: line and having a spark gap between their apecies. In
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  Speaker 1: another form of transmitter, a single stole metal sphere separated
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  Speaker 1: by small spark gaps from the terminals of an induction
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  Speaker 1: coil was used as a radiator. Both types produced direct
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  Speaker 1: Hertzian radiation, the latter giving waves of very high frequency.
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  Speaker 1: The spherical oscillator was partially enclosed by a copper cylinder
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  Speaker 1: open at one end in order that the rays might
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  Speaker 1: be condensed in one direction. The receiver for use in
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  Speaker 1: connection with the large cones consisted of two smaller cones
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  Speaker 1: connected through the primary of a small transformer, the secondary
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  Speaker 1: of which was connected to the coherer circuit. The dimensions
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  Speaker 1: of the transmitter and receiver were adjusted to give ecifrequent
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  Speaker 1: natural vibrations and therefore resonance. No earth connection was made,
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  Speaker 1: as it was desired that the transmission should be purely
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  Speaker 1: by means of free radiations. The early conical form of
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  Speaker 1: radiator has now given place to the horizontal conductors. Stations
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  Speaker 1: in which this latter arrangement has been adopted are now
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  Speaker 1: working in various parts of the world. As soon as
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  Speaker 1: Marconi had modified his system of telegraphy, he applied it
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  Speaker 1: immediately to the conquest of record distances in radio telegraphic transmission.
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  Speaker 1: To this end, he set up a station at the
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  Speaker 1: Lizard Cornwall, which was immediately put into communication with Marconi's
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  Speaker 1: experimental station at Saint Catharine's Isle of Wight, at a
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  Speaker 1: distance of three hundred kilometers about two hundred miles, in
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  Speaker 1: which he used an aerial conductor consisting of four vertical
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  Speaker 1: wires standing about five feet from one another about one
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  Speaker 1: hundred and forty four feet in height, along with a
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  Speaker 1: strip of wire netting of the same length under the
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  Speaker 1: new system, the energy required to telegraph to a given
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  Speaker 1: distance was very much diminished, so that one hundred and
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  Speaker 1: fifty watts sufficed to communicate to the three hundred kilometer distance.
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  Speaker 1: Encouraged by the results of the experiments in communication between
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  Speaker 1: Saint Catharines and the Lizard, Marconi put his whole heart
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  Speaker 1: into the attempt to resolve the artous problem of establishing
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  Speaker 1: transatlantic radio telegraphic communication. Repeated experiments had shown that long waves,
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  Speaker 1: either by successive reflection or diffraction, could turn round the
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  Speaker 1: surface of the Earth, so that their transmission to very
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  Speaker 1: great distances resolved itself only into a question of sufficient
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  Speaker 1: power in the transmitting apparatus and sufficient sensibility in the
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  Speaker 1: receiving But these necessitated large financial means, which would, however,
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  Speaker 1: not be wanting in a man whose business acumen was
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  Speaker 1: not less surprising than his experimental ability. Being largely subsidized
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  Speaker 1: by the Marconi Wireless Telegraph Company, Marconi began early in
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  Speaker 1: nineteen oh one, unknown to everyone, his trials, by establishing
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  Speaker 1: two specially powerful stations, at Poldew near Cape Blizzard and
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  Speaker 1: Cornwall on one side of the ocean, and at Cape
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  Speaker 1: cod in Massachusetts on the other side. The results of
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  Speaker 1: these first trials are not known, and, judging by the
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  Speaker 1: sou islands maintained in this regard, they were probably negative.
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  Speaker 1: The two stations, that had cost the sum of more
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  Speaker 1: than fifteen thousand pounds were destroyed by storms. In September
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  Speaker 1: of the same year. Marconi caused the station at Pouldu
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  Speaker 1: to be rebuilt, furnishing it with powerful machines and radiators,
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  Speaker 1: and decided to attempt communication with Saint John's Newfoundland, that
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  Speaker 1: is to say, to a lesser distance than that previously
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  Speaker 1: chosen of about fifteen hundred miles at Saint John's Newfoundland,
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  Speaker 1: where Marconi had obtained from the government every facility for
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  Speaker 1: making the trials. The installation was of the simplest character,
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  Speaker 1: consisting of a receiving station only. The area line was
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  Speaker 1: maintained at a height of about four hundred feet by
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  Speaker 1: means of a kite. Marconi had already agreed with the
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  Speaker 1: station at Pauldo that every day, at six o'clock in
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  Speaker 1: the evening, a long series of letter s should be sent.
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  Speaker 1: This letter, in the Morse alphabet, consists of three dots.
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  Speaker 1: The message was received telephonically on the twelfth of December
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  Speaker 1: nineteen oh one, Marconi announced that he had received the
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  Speaker 1: different ESS's at equal and determinate intervals, and he proclaimed
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  Speaker 1: that it was practically, physically and mathematically impossible that the
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  Speaker 1: signals could have come from any other place but Cape Lizard.
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  Speaker 1: In the summer of nineteen oh two, mister Marconi made
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  Speaker 1: an interesting comparative test of his first coherer system and
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  Speaker 1: his second magnetic detector system. The ship Carlo Alberta was
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  Speaker 1: fitted out with both sets of receiving apparatus. By previous arrangement,
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  Speaker 1: a set of signals from the Poldu station was to
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  Speaker 1: be sent out at certain hours of the day. As
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  Speaker 1: the voyage towards Kronstadt proceeded, the signals diminished in strength,
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  Speaker 1: and at a distance of nine hundred kilometers, were not
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  Speaker 1: perceptible during the day. At night, however, they continued to
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  Speaker 1: be received by both systems until the port of Karnstadt
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  Speaker 1: was reached, when only the magnetic detector responded, and that
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  Speaker 1: only feebly. The disturbing action of daylight was very marked
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  Speaker 1: in these tests. Having received an invitation from the Canadian
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  Speaker 1: government to continue his experiments in Canada, Marconi erected a
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  Speaker 1: large station at Tablehead on the island of Cape Breton,
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  Speaker 1: at the mouth of Glace Bay, and thirty eight hundred
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  Speaker 1: kilometers from Poldew. On December twentieth, nineteen oh two, mister
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  Speaker 1: Marconi sent the first radiograms across the Atlantic to the
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  Speaker 1: Kings of England and Italy. Shortly afterward, another station was
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  Speaker 1: erected at Cape cod in Massachusetts, the distance to the
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  Speaker 1: Poldu station being thirty two hundred miles or six hundred
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  Speaker 1: and sixty miles further than the Glace Bay station. On
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  Speaker 1: January sixteenth, nineteen oh three, a complete radiogram was sent
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  Speaker 1: by President Roosevelt to the King of England. Professor Fessenden
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  Speaker 1: commenced in eighteen ninety seven the development of the system,
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  Speaker 1: which is now the property of the National Electric Signaling Company.
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  Speaker 1: For two years he was engaged by the United States
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  Speaker 1: Government for special research in the subject, and had the
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  Speaker 1: advantages of all the resources of a government department at
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  Speaker 1: his command. His inventions are very numerous and in many
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  Speaker 1: respects original, and his results show a precision and a
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  Speaker 1: practicality not attained by many other experimenters in the same field. Magnetic,
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  Speaker 1: thermal and electrolytic detectors, methods of exact tuning, and even
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  Speaker 1: wireless telephony are covered by Fessenden's patents. Among these, perhaps
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  Speaker 1: that which has contributed most to the success of the
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  Speaker 1: system is the burrider. In its original form, this was
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  Speaker 1: a thermal receiver depending for its action on the change
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  Speaker 1: of resistance in a very fine platinum wire when carrying
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  Speaker 1: the jig current. Latterly, the continuous wire has been discarded
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  Speaker 1: in favor of an electrolytic coil, one electrode of which
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  Speaker 1: is an extremely fine point. The apparatus has been described
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  Speaker 1: more fully under wave detectors. An important feature of this system,
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  Speaker 1: which greatly aids secrecy of transmission, is the arrangement of
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  Speaker 1: the sending key, which does not break the circuit, but
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  Speaker 1: merely alters the wavelength of the waves given out by
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  Speaker 1: cutting out some inductance. Thus, unless a receiving station is
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  Speaker 1: tuned with extreme accuracy to the transmitter, it will receive
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  Speaker 1: instead of signals, only a long continuous dash. Hence, only
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  Speaker 1: a very sharply tuned receiver will receive a message at all.
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  Speaker 1: In the latest forms of apparatus, the difference in frequency
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  Speaker 1: between the waves sent out during spaces and those sent
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  Speaker 1: as signals is only one quarter percent. Interception by rivals
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  Speaker 1: is therefore almost impossible. Festenden is apparently the first to
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  Speaker 1: use an aerial consisting of a steel tube standing on
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  Speaker 1: an insulating foundation and held in position in insulated stays.
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  Speaker 1: The following guarantees are made for the festened In system
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  Speaker 1: by the holding company. Guarantee for a distance one kilowat
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  Speaker 1: set two hundred fifty miles, five kilowat sets four hundred miles,
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  Speaker 1: twenty kilood sets seven hundred to seven hundred and fifty miles.
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  Speaker 1: Guarantee for the prevent used to prevent other sending stations
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  Speaker 1: from interfering with the receipt of messages. Where the distance
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  Speaker 1: of the interfering station from the receiving station is more
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  Speaker 1: than one percent of the distance between the sending and
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  Speaker 1: receiving stations, a difference in wavelength of three percent is
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  Speaker 1: sufficient to cut out the interference without the signals being
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  Speaker 1: appreciably weakened, interfering and sending stations being of equal power.
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  Speaker 1: Guarantee for the secrecy center. With our latest form of
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  Speaker 1: secrecy center, the variation in wavelength is guaranteed to be
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  Speaker 1: only one quarter percent between space and dots. We guarantee
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  Speaker 1: that no other system can read the messages. Guarantee for
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  Speaker 1: wave measurer. We guarantee this device to be capable of
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  Speaker 1: detecting difference of wavelength of one quarter percent, and to
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  Speaker 1: be capable of measuring wavelengths at a distance from the
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  Speaker 1: sending station. There are also devices whereby atmospheric discharges will
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  Speaker 1: not interfere with reception, and a device for modifying the
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  Speaker 1: intensity of emitted waves without altering their length communicate with
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  Speaker 1: nearby stations. A report giving a description of the fasten
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  Speaker 1: In system as applied to transatlantic signaling between Massachusetts and
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  Speaker 1: Scotland may be of interest here. The power is developed
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  Speaker 1: by a boiler engine alternator equipment having a maximum capacity
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  Speaker 1: of twenty five kilowatts sixty cycles current. A transformer steps
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  Speaker 1: up to the voltage to about twenty five thousand, thus
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  Speaker 1: charging the condensers, which are discharged by a means of
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  Speaker 1: a gap adjustable so as to effect the discharge at
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  Speaker 1: any desired point of the cycle. The receiver used is
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  Speaker 1: the liquid bretder in its latest form. The aerial is
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  Speaker 1: formed by a tower extending to a height of four
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  Speaker 1: hundred and fifteen feet above the ground level and supporting
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  Speaker 1: a sort of umbrella formed of wires at its top.
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  Speaker 1: The tower is essentially a steel tube three feet in diameter,
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  Speaker 1: supported every one hundred feet of its height by a
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  Speaker 1: set of four steel guys, there being thus sixteen guys
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  Speaker 1: in all. The tower is pivoted at its base on
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  Speaker 1: a ball and socket joint and is insulated from the
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  Speaker 1: ground for a voltage of one hundred and fifty thousand.
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  Speaker 1: The guys are insulated from the tower as well as
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  Speaker 1: from the ground. Besides, they are divided into fifty foot
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  Speaker 1: sections by means of strain insulators. One of the most
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  Speaker 1: serious problems to be solved was the construction of these
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  Speaker 1: strain insulators, which, while capable of safely transmitting the maximum
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  Speaker 1: stress of about twenty thousand pounds, also resist an electrical
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  Speaker 1: tension of fifteen thousand volts each. The maximum deflection of
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  Speaker 1: the top of the tower in a ninety mile hurricane
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  Speaker 1: is computed to be fifteen and a half inches. A
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  Speaker 1: wave chute, containing over one hundred miles of wire and
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  Speaker 1: extending over six acres is a very essential feature of
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  Speaker 1: the installation. On January third, nineteen o six, the first
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  Speaker 1: signals were received from the American Sex, and shortly afterward
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  Speaker 1: communication was established so that messages were freely exchanged at night.
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  Speaker 1: The intensity of the signals received by telephone was at
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  Speaker 1: times so great that the messages could easily be read
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  Speaker 1: with the diaphragm three inches from the ears of the operator.
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  Speaker 1: A station twenty miles distant from Brent Rock, using about
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  Speaker 1: thirty kilowatts and sending on a wavelength differing not much
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  Speaker 1: more than three percent from that of the Scottish station,
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  Speaker 1: was cut out while messages were received from Macrinhanish. A
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  Speaker 1: system differing in many respects from the other systems has
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  Speaker 1: been devised by Sir Oliver Lodge and doctor Meirhead. The
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  Speaker 1: rotating steel disc coherer described under wave detectors is used
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  Speaker 1: by them. Another feature is the use of two capacity
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  Speaker 1: areas at both sending and receiving stations, by the adjustment
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  Speaker 1: of which they may be brought into tune. This system
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  Speaker 1: has been installed in many places with great success, and
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  Speaker 1: although it has not yet operated over such distances as
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  Speaker 1: the US Marconi and Festendon systems, it compares favorably with
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  Speaker 1: them in syntonizing power and has the advantage of using
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  Speaker 1: the siphon recorder. The Telefunken system is based on the
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  Speaker 1: patents of Professor Slabby and Braun and of Count von Arco.
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  Speaker 1: It may be considered as striking a mean between the
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  Speaker 1: earlier systems of Marconi and lodgemere Head, though of course
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  Speaker 1: with many variations and elaborations. In detail, a system of
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  Speaker 1: wires similar to those used by Marconi forms the aerial
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  Speaker 1: and the earth connection is given by a large capacity
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  Speaker 1: as in the lodgemere heead apparatus, A coherer and receiving
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  Speaker 1: circuit in many respects similar to the Marconi arrangement is employed.
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  Speaker 1: The DeForest system has had quite an extended commercial application,
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  Speaker 1: especially in the United States. It has the advantage of
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  Speaker 1: very rapid signaling twenty five to thirty words per minute
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  Speaker 1: having been reached. Communication by this system has been established
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  Speaker 1: between Manhattan Beach, New York and Colon, Panama, a distance
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  Speaker 1: of two thousand in one hundred and seventy miles. The
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  Speaker 1: extension of wireless telegraphy and the study of the relations
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  Speaker 1: of electrical discharges in radioactive bodies bids fair to be
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  Speaker 1: the most fruitful of the fields of the immediate future.
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  Speaker 1: The age has been well called the Age of electricity,
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  Speaker 1: and much amazement, ever, is expressed that man should utilize
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  Speaker 1: so well a force concerning which he knows so little.
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  Speaker 1: The complete understanding of the phenomena of atomic force and
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  Speaker 1: of radioactivity may go far to unlock many of the
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  Speaker 1: closed doors of nature, and the electrical scientist of today
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  Speaker 1: is steadily approaching that understanding. End of section thirty two
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  Speaker 1: and end of the Science History of the Universe, Volume three,
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  Speaker 1: Physics and Electricity by Francis Rohl Wheeler