WIRELESS TELEGRAPHY--PRACTICAL APPLICATIONS
A fairly good idea of the principles and apparatus of wireless
telegraphy should have been gained in reading Chapter XX., but so
far little has been said about its practical use. If we leave their
power out of consideration, wireless stations may be divided into two
classes: fixed stations on land, and moving stations, if the expression
may be allowed, on ships. For moving stations wireless telegraphy
has the field all to itself, but for communication between fixed
stations it comes into conflict with ordinary telegraphy by wire or
cable. As regards land messages over comparatively short distances,
say throughout Great Britain, wireless telegraphy has no advantages
over the older methods; and it is extremely unlikely that it ever will
be substituted for the existing cable telegraphy. For long distances
overland wireless has the great advantage of having all its apparatus
concentrated at two points. A long land line passing through wild
country, and exposed to all kinds of weather, requires constant labour
to keep it in good repair, and when a breakdown occurs at any point,
the repairing gang may be miles away, so that delay is caused. On the
other hand, whatever may go wrong at a wireless station, no time is
lost in effecting the necessary repairs, for everything is on the spot.
At present there is no great competition between wireless and ordinary
telegraphy for overland messages of any kind, but the case is different
when we come to communication across seas and oceans. Already the
cable companies have been affected considerably, and there is little
doubt that they will feel the competition much more seriously before
long. The general public, always conservative in such matters, have
not yet grasped the fact that telegrams can be handed in at any
telegraph office in the British Isles, and at most telegraph offices
in the United States and Canada, for wireless transmission across the
Atlantic, via the Marconi stations at Clifden and Glace Bay. The cost
is remarkably small, being eightpence a word for ordinary messages.
It is impossible to state with any accuracy how many land wireless
stations there are in the world, but the list given in the _Year-Book
of Wireless Telegraphy_ for 1915 enumerates about 700 stations. This
list does not include private or experimental stations, and also many
stations used exclusively for naval or military purposes are not given.
The information available about these 700 stations is incomplete in
many cases, but about 500 are controlled by various departments of
the governments of the different states. Of the remainder, about 100
are controlled by the Marconi Company, the rest being in the hands of
various wireless, commercial, or railway companies.
Amongst the most important land stations are the Clifden and Glace
Bay transatlantic stations. They are very similar in plan, and each
has a separate aerial for sending and for receiving. Contrary to the
usual practice, continuous current is used to charge the condensers.
In Chapter IV. we saw how a current of high voltage could be obtained
by connecting a number of cells in series, and at these stations the
necessary high voltage is produced by connecting a number of powerful
dynamos in series, on the same principle. Along with the dynamos
a huge battery of accumulators, consisting of about 6000 cells, is
used as a sort of reservoir of current. These stations have a normal
range of considerably over 3000 miles. Last year a large transmitting
station was completed at Cefndu, near Carnarvon. This station, which
is probably the most powerful in existence, is intended to communicate
directly with New Jersey, United States, as an alternative to the
Clifden-Glace Bay route.
Other powerful stations are Poldhu, in Cornwall, of which we shall
speak later; the French Eiffel Tower station; the German station at
Nauen, near Berlin, which last year succeeded in exchanging messages
with Windhoek, German South-West Africa, a distance of nearly 6000
miles; and the extremely powerful station at Coltano, Italy. France has
three stations in West Africa with a night range of 1600 miles; and
Italy one in Somaliland with a normal range of about the same distance.
The recently opened Chinese stations at Canton, Foochow, and Woosung
have a range of 1300 miles by night, and 650 miles by day. With the
fall of Tsingtau, China, Germany lost a wireless station capable of
signalling over 1350 miles at night. Japan has six stations with a
night range of over 1000 miles. Massawa, on the Red Sea, has a range
of 1600 miles, and New Zealand has two stations with ranges of 1200
miles by day, and 2500 miles by night. Australia has a large number of
stations with a normal range of about 500 miles. In the United States,
which has a very large number of stations, Arlington, Virginia, covers
1000 miles, and Sayville from 600 to 2300 miles. South America has not
many high-power stations, but Cerrito, in Uruguay, has a range of about
1000 miles.
Until a thoroughly practical system of long-distance wireless telephony
is developed, wireless telegraphy will remain the only possible
means of communication between ships and shore, or between one ship
and another, except where the distance is so small that some method
of semaphore signalling can be used. In the days when wireless was
unknown, a navigator was thrown entirely upon his own resources as
soon as his vessel was out of sight of land, for no information of any
kind could reach him. Even with a wireless installation on board, the
captain of a vessel still needs the same skill and watchfulness as of
old, but in the times of uncertainty and danger to which all ships
are liable, he often is able to obtain information which may prevent
disaster. In order to determine accurately his position, a navigator
requires to know the exact Greenwich Mean Time, and he gets this time
from his chronometers. These are wonderfully reliable instruments, but
even they may err at times. To avoid the possibility of mistakes from
this cause, wireless time signals are sent out at regular intervals by
certain high-power stations, and as long as a vessel is within range of
one of these stations the slightest variation in the chronometers may
be detected immediately. Amongst these stations are the Eiffel Tower,
giving time signals at 10 a.m. and at midnight; and Norddeich, Germany,
giving signals at noon and midnight. These time signals have proved
most useful also on land, more particularly for astronomers and for
explorers engaged on surveying work.
In addition to time signals, other valuable information is conveyed
by wireless to ships at sea. A ship encountering ice, or a derelict,
reports its discovery to other ships and to the shore stations, and
in this way vessels coming along the same route are warned of the
danger in time to take the necessary precautions. Weather reports are
issued regularly from various shore stations in most parts of the
world. The completeness of the information given varies a good deal
with different stations, but in many cases it includes a report of
the existing state of the weather at a number of different places,
a forecast of the winds likely to be encountered at sea, say at a
distance of 100 miles from land, and warnings of approaching storms,
with remarks on any special atmospheric conditions at the time of
sending. In Europe weather reports are issued daily from the Admiralty
station at Cleethorpes, the Eiffel Tower, and Norddeich; and in the
United States more than a dozen powerful stations are engaged in this
work.
Another valuable use of wireless is in carrying on the work of
lighthouses and lightships during snowstorms or dense fogs, which
the light cannot penetrate. So far not much has been done in this
direction, but the French Government have decided to establish wireless
lighthouses on the islands outside the port of Brest, and also at
Havre. Automatic transmitting apparatus will be used, sending out
signals every few seconds, and working for periods of about thirty
hours without attention.
The improvement in the conditions of ocean travel wrought by wireless
telegraphy is very remarkable. The days when a vessel, on passing out
of sight of land, entered upon a period of utter isolation, is gone
for ever. Unless it strays far from all recognized trade routes, a
ship fitted with a wireless installation is never isolated; and with
the rapidly increasing number of high-power stations both on land and
sea, it soon will be almost impossible for a vessel to find a stretch
of ocean beyond the reach of wave-borne messages. The North Atlantic
Ocean is specially remarkable for perfection of wireless communication.
For the first 250 miles or so after leaving British shores, liners are
within reach of various coast stations, and beyond this Poldhu takes
up the work and maintains communication up to about mid-Atlantic.
On passing beyond the reach of Poldhu, liners come within range of
other Marconi stations at Cape Cod, Massachusetts, and Cape Race,
Newfoundland, so that absolutely uninterrupted communication is
maintained throughout the voyage. On many liners a small newspaper is
published daily, in which are given brief accounts of the most striking
events of the previous day, together with Stock Exchange quotations and
market prices. This press news is sent out during the night from Poldhu
and Cape Cod. During the whole voyage messages may be transmitted from
ship to shore, or from shore to ship, with no more difficulty, as
far as the public are concerned, than in sending an ordinary inland
telegram.
The transmitting ranges of ship installations vary greatly, the range
of the average ocean liner being about 250 miles. Small ships come as
low as 50 miles, while a few exceptional vessels have night ranges
up to 1200 or even 2500 miles. Although an outward-bound vessel is
almost always within range of some high-power shore station, it is
evident that it soon must reach a point beyond which it is unable to
communicate directly with the shore. This difficulty is overcome by a
system of relaying from ship to ship. The vessel wishing to speak with
the shore hands on its message to some other vessel nearer to land or
with a longer range, and this ship sends forward the message to a shore
station if one is within its reach, and if not to a third vessel, which
completes the transmission.
The necessity for wireless installations on all sea-going vessels has
been brought home to us in startling fashion on several occasions
during the last few years. Time after time we have read thrilling
accounts of ocean disasters in which wireless has come to the rescue in
the most wonderful way. A magnificent liner, with its precious human
freight, steams majestically out of harbour, and ploughs its way out
into the waste of waters. In mid-ocean comes disaster, swift and awful,
and the lives of all on board are in deadly peril. Agonized eyes sweep
the horizon, but no sail is in sight, and succour seems hopeless. But
on the deck of that vessel is a small, unpretentious cabin, and at a
desk in that cabin sits a young fellow with strange-looking instruments
before him. At the first tidings of disaster he presses a key, and out
across the waters speed electric waves bearing the wireless cry for
help, “S.O.S.,” incessantly repeated. Far away, on another liner, is a
similar small cabin, and its occupant is busy with messages of everyday
matters. Suddenly, in the midst of his work, comes the call from the
stricken vessel, and instantly all else is forgotten. No matter what
the message in hand, it must wait, for lives are in danger. Quickly
the call is answered, the position of the doomed ship received, and
the captain is informed. A few orders are hurriedly given, the ship’s
course is changed, and away she steams to the rescue, urged on by the
full power of her engines. In an hour or two she arrives alongside,
boats are lowered, and passengers and crew are snatched from death and
placed in safety. This scene, with variations, has been enacted many
times, and never yet has wireless failed to play its part. It is only
too true that in some instances many lives have been lost, but in these
cases it is necessary to remember that without wireless every soul on
board might have gone down. The total number of lives already saved by
wireless is estimated at about 5000, and of these some 3000 have been
saved in the Atlantic.
Ship aerials are carried from one mast to another, as high up as
possible. The transmitting and receiving apparatus is much the same as
in land stations, so that it need not be described. In addition, most
liners carry a large induction coil and a suitable battery, so that
distress signals can be transmitted even when the ordinary apparatus
is rendered useless by the failure of the current supply. Most of the
wireless systems are represented amongst ship installations, but the
great majority of vessels have either Marconi or Telefunken apparatus.
Every wireless station, whether on ship or on shore, has a separate
call-signal, consisting of three letters. For instance, Clifden is
MFT, Poldhu MPD, Norddeich KAV, s.s. _Lusitania_ MFA, and H.M.S.
_Dreadnought_ BAU. Glace Bay, GB, and the Eiffel Tower, FL, have two
letters only. In order to avoid confusion, different countries have
different combinations of letters assigned to them exclusively, and
these are allotted to the various ship and shore stations. For example,
Great Britain has all combinations beginning with B, G, and M; France
all combinations beginning with F, and also the combinations UAA to
UMZ; while the United States is entitled to use all combinations
beginning with N and W, and the combinations KIA to KZZ. There are also
special signals to indicate nationality, for use by ships, British
being indicated by - - -- -, Japanese by -- - -- -, and so on.
Wireless telegraphy apparently has a useful future in railway work.
In spite of the great perfection of present-day railway signalling,
no railway company is able to avoid occasional accidents. Some of
these accidents are due to circumstances which no precautions can
guard against entirely, such, for instance, as the sudden breakage
of some portion of the mechanism of the train itself. In many cases,
however, the accident is caused by some oversight on the part of the
signalman or the engine-driver. Probably the great majority of such
accidents are not due to real carelessness or inattention to duty,
but to unaccountable freaks of the brain, through which some little
detail, never before forgotten, is overlooked completely until too
late. We all are liable to these curious mental lapses, but happily in
most cases these do not lead to disaster of any kind. The ever-present
possibility of accidents brought about in this way is recognized fully
by railway authorities, and every effort is made to devise mechanism
which will safeguard a train in case of failure of the human element.
The great weakness of the ordinary railway system is that there is no
reliable means of communicating with the driver of a train except by
the fixed signals, so that when a train has passed one set of signals
it is generally beyond the reach of a message until it arrives at
the next set. On the enterprising Lackawanna Railroad, in the United
States, an attempt has been made to remove this defect by means of
wireless telegraphy, and the experiment has been remarkably successful.
Wireless communication between moving passenger trains and certain
stations along the route has been established, and the system is being
rapidly developed.
The wireless equipment of the stations is of the usual type, and does
not call for comment, but the apparatus on the trains is worth mention.
The aerial, which must be low on account of bridges and tunnels,
consists of rectangles of wire fixed at a height of 18 inches above
the roof of each car. These separate aerials are connected together by
a wire running to a small operating room containing a set of Marconi
apparatus, and situated at the end of one of the cars. The earth
connexion is made to the track rails, and the current is taken from
the dynamos used to supply the train with electric light. With this
equipment messages have been transmitted and received while the train
was running at the rate of 70 miles an hour, and distances up to 125
miles have been covered. During a severe storm in the early part of
last year the telegraph and telephone lines along the railroad broke
down, but uninterrupted communication was maintained by wireless,
and the operations of the relief gangs and the snow-ploughs were
directed by this means. For emergency signalling this system is likely
to prove of enormous importance. If signals are set wrongly, through
some misunderstanding, and a train which should have been held up is
passed forward into danger, it can be stopped by a wireless message in
time to prevent an accident. Again, if a train has a breakdown, or if
it sticks fast in a snow-drift, its plight and its exact position can
be signalled to the nearest station, so that help may be sent without
delay. The possibilities of the system in fact are almost unlimited,
and it seems not unlikely that wireless telegraphy will revolutionize
the long-distance railway travelling of the future.