An entirely new technique for handling telegrams has been devised and perfected in recent years to ensure the highest possible speed and accuracy at every stage in their dispatch and delivery
GENERAL VIEW OF THE CENTRE GALLERY of the Central Telegraph Office, London, showing how the instrument tables are arranged. The machines in the foreground are teleprinters; in the background may be seen part of the great network of pneumatic tube conveyers which carry messages to and from many Post Offices in the London district.
THE amazing developments which have taken place in radiotelephony during the past few years have rather tended to distract the public’s attention from another important means of communication — the telegram. Outstanding feats of radio communication are often sufficiently romantic to be given considerable publicity in the Press, and every important development is destined to become famous as soon as it reaches the practical stage.
The telegram, however, has not been superseded by radio. On the contrary, an entirely new technique for the handling of telegrams has been devised quite recently. New machines and new systems have been perfected, old equipment and old methods discarded, and a new standard of speed and accuracy in the dispatch and delivery of telegrams has been attained.
In 1860 the-office was moved to Little Bell Alley, off Moorgate. The name of the street was changed to Telegraph Street, and in 1870 the building became the Central Telegraph Office of the General Post Office, the State having acquired the telegraph service in that year. The initials “T.S.” are still used as the telegraphic call-sign of the Central Telegraph Office.
The present building, at the corner of Newgate Street and St. Martin’s-le-Grand, was erected soon after 1870, and messages to and from all parts of the world have flowed unceasingly through its galleries for more than sixty years.
To-day the Central Telegraph Office is an outstanding example of the work of the electrical engineer. It is completely mechanized and handles an enormous volume of traffic in the course of a day. It houses a working staff of more than 3,000, and the Inland Telegraph Gallery alone handles more than 175,000 messages a day during busy periods.
Each of these systems demanded a high degree of specialized skill on the part of the operator, and a long period of technical and operational training was necessary. All these systems have been entirely superseded, for inland work, by the teleprinter, a machine which is faster and simpler in operation than the others, and one which has several other advantages.
When using a teleprinter, the operator merely spells out the message on a keyboard similar to that of a typewriter, and the machine “translates” the individual letters into a code suitable for transmission over a telegraph line. At the remote end of the line the message is received on an instrument which retranslates the code and prints the message, either on a paper strip which may be gummed to a telegraph form, or directly on the form.
The transmitting and receiving instruments are combined in the modern teleprinter, so that two-way communication may be carried out over a line which has a teleprinter at either end.
At a recent Radio Exhibition, a teleprinter line formed a part of the G.P.O. exhibit. A visitor to the exhibition could “converse”, on the typewriter keyboard, with the distant operator, a procedure which showed in a most uncanny way the speed and reliability of the system. For instance, if someone having a slight acquaintance with the typewriter keyboard spelt out “How are you?” the reply “Quite well, thanks” appeared on the paper tape almost before he had finished. The teleprinter mechanism is driven by a small electric motor, and current from a main power system is supplied for the transmission of messages. The keys are linked with a series of five levers, which are moved in various combinations according to the key which is depressed. Thus every letter typed on the keyboard is resolved into a combination of five pulses of current.
66 Words a Minute
At the receiving point these current pulses are used to operate an electromagnet, which sets a combination of five small levers in.such a way that they correspond exactly to The levers at the transmitter. The receiving levers operate a type wheel, which carries on its face all the characters in use, and this wheel is stopped in such a position that the appropriate letter is printed on the paper or tape.
Teleprinters are capable of transmitting messages at the speed of sixty-six words a minute. Nearly 400 teleprinters are used in the Inland Telegraph Gallery of the Central Telegraph Office, from which more than 350 telegraph channels link London with important towns in every part of the British Isles, and with seasonal telegraph offices at racecourses and the sites of
important sporting events. The Central Telegraph Office, as its name implies, serves as a vast clearing house for incoming and outgoing telegrams. In this way it resembles a telephone exchange. A shopkeeper at Barking (Essex) can send a telegram to a dealer in Birmingham, but the operation may not be performed directly, in the true sense of the word. The telegram must be sent from Barking to the Central Telegraph Office, which can then send it to Birmingham.
From Post Offices in the City and in the West End of London, telegrams handed in over the counters are conveyed to the Central Telegraph Office through compressed-air tubes. These street tubes, which have been enormously improved since they were first put into use, now run for some seventy-five miles underneath the streets of London, and the carriers in which the telegrams are enclosed move along the tubes at twenty miles an hour.
A BAUDOT TELEGRAPH TRANSMITTER in use on a line to Berlin. Although the more modern teleprinter is standard equipment for inland circuits, the Baudot and other types of older apparatus are still used on Continental circuits because of other countries’ preference for such systems. Quite high speeds are maintained with this old apparatus by skilled operators.
The use of pneumatic tubes facilitates the quick handling of messages from a busy office. Instead of having to “queue up” for transmission over a wire circuit, the messages may be sent off in batches every few seconds. A further advantage is that the written message is forwarded directly to the telegraphist at the head office, and one possible source of inaccuracy is eliminated.
Street tubes are extensively used, not only for connecting branch offices with the Central Telegraph Office, but also for connecting the offices of newspapers, cable companies and large business houses with the head office. “House tubes” are used for the transmission of telegram forms from one part of a building to another. They differ from street tubes only in their length, and consequently in the amount of pressure required to operate them and in the speed at which the carriers travel.
The essential factors of both types of tube are that they shall be airtight and smooth. Only in these circumstances can the friction of the moving column of air and of the carrier against the wall of the tube be kept at a minimum.
Compressed air is supplied to a tube at one end, the other being left open to the atmosphere; or, alternatively, one end may be left open and the other attached to a suction pump which exhausts the air from the tube. In street tubes, which may be as much as three miles in length, pressures up to 12 lb. per square inch are necessary. The tubes are of lead, but are laid in iron pipes for
protection. Some of them have been in use for over fifty years.
The most frequent source of trouble is damage during road repairs. The standard size of tube has an internal diameter of 2½ in., and the carriers used in such a tube will take twenty or thirty messages. As these carriers may be dispatched at intervals of a few seconds, the message-handling capacity of one of these tubes is large.
Conveyers of Special Design
Huge electrically-driven air compressors are used to operate the London street tuber, and an automatic switch room at the Central Telegraph Office contains apparatus which transfers incoming messages from the street tubes, operating at relatively high pressures, to the shorter house tubes, which work at low pressures.
An incoming message, travelling along a street tube at some twenty miles an hour in its carrier, is stopped by a grid. Thus stopped, it forms an obstruction to the flow of air, and this causes a difference in pressure to be set up across a special switch which operates a device known as a differential indicator.
When the arrival of a carrier alters the pressures across the switch, a diaphragm moves and makes an electrical contact which causes a magnetic clutch to grip and rotate the switch to a new position. The carrier is thus transferred to the low-pressure house tube, along which it travels at a slower speed until, finally, it is ejected through a trap door. From this it falls on to a band conveyer which carries it to an unloading position, where the messages are sorted and distributed to the telegraph operators for dispatch.
The importance of the Central Telegraph Office as a clearing house necessitates a large amount of physical conveyance of messages from one part of the building to another, according to the destinations of the messages. Conveyer belts of special design have been installed, and in the grip of these belts the telegram forms travel in a most uncanny manner, round corners, up vertical rises, across ceilings, and along shelves in front of the staff at their tables.
AUTOMATIC STREET TUBES link the Central Telegraph Office with Post Offices in many parts of London. These tubes are pneumatically operated, and messages placed in special carriers travel through the tubes below the streets at a speed of twenty miles an hour. Huge electrically-driven air compressors are used to operate the pneumatic tube system in London.
Suddenly, for no apparent reason, a telegram travelling smoothly along a belt will flutter down through an aperture on to a table; but this is all part of the plan, for one of the most ingenious features of the belt system is the provision of numerous “drop points’’ which ensure that a message shall reach the exact destination in the office for which it is intended.
Give of these belts, or bands, pass in front of the sorters’ tables, in which position they run vertically above one another. Telegrams are placed on the appropriate band, according to the section of the office for which they are destined. The five bands are driven by a common drum, and are separated before passing the sorting fitting. At the point where they leave this fitting an auxiliary band is added, and this is placed in contact with the uppermost of the five bands. All six are then brought together, telegrams which have been sorted being gripped between the bands.
The bands then pass to an overhead troughing, and at each delivery position the undermost band is returned to the driving drum by a convenient route. When this operation takes place, all telegram forms gripped between this band and the next one above it are dropped through a “chain chute”, which consists of a formation of wire mesh serving as a guide for the forms. Should a form become caught up, its presence may readily be seen through the meshing. These chain chutes were adopted after much experimental work with other systems. In the Central Telegraph Office the total length of band on the conveyer is 1,763 feet. It weighs 275 lb., travels at 200 feet a minute, and 1½ horse-power is required to drive it.
Making Use of Electrical Charges
Considerable trouble was experienced with electrostatic charges produced by friction between the bands and the rollers. In certain circumstances telegram forms would adhere to the bands, refusing to drop at the appropriate points. Provision is now made at the delivery positions for forcibly breaking the forms away from their bands, and some of the effects produced by the electrical charges are deliberately used for improving the efficiency of the system.
A comparatively recent development which has necessitated the installation of much new equipment at the Central Telegraph Office is the possibility of sending telegrams by telephone.
London telephone subscribers have been encouraged to dial TEL and to dictate telegrams from their homes, and the apparatus in the “Phonogram Gallery” of the Central Telegraph Office is the most modern and the largest of its kind in the world.
Eighteen complete suites of telephone apparatus are mounted on double tables with conveyer belts between them. The operators receive telegrams from subscribers, type them on message forms and place them on the conveyers, which immediately carry them to an appropriate point.
OPERATING A HUGHES INSTRUMENT, the keyboard of which resembles that of a piano. This is the oldest type of telegraph apparatus in use at the Central Telegraph Office and, with other types, will ultimately be superseded by the teleprinter. The Hughes transmitter shown in the illustration is working on a line between London and Prague.
The arrival of a TEL call is announced by the simultaneous lighting of six lamps at six different operating positions. As each position is manned by two operators, an incoming telegram is thus immediately brought to the notice of twelve people, one of whom is almost certain to be free to deal with it. Telegrams which bear a telephone number instead of an address — another practice which the public has been encouraged to use — are circulated to the forwarding positions, from which they are immediately delivered to their destinations by telephone. The telegram itself arrives later in confirmation.
The telegraph service also makes considerable use of the telephone in linking up small telegraph centres in and round London. This work is carried out in the telephone-telegram section of the Central Telegraph Office, which is connected with 673 telegraph centres. The equipment of this section is' similar to that of the phonogram section, and ingenious devices are in use for the even distribution of work over the various operating positions.
A series of buttons and lamps makes it possible to determine whether a particular office is already connected to one of the working positions, and the circulating clerks can distribute the work with a saving of time and effort. A staff of 300, employed in this gallery, can deal with 50,000 telegrams a day.
In the foreign section, overseas telegrams are handled by submarine cables and by radio. Communication with the continent of Europe is maintained chiefly by some twenty cables laid between the south and east coasts of Great Britain on the one hand, and France, Belgium, Holland, Germany and Norway on the other. These cables provide more than 100 channels of communication, and, with radiating land lines at the other ends, afford direct channels between Great Britain and some thirty centres on the Continent.
Since many European countries still have a preference for some of the older types of telegraph apparatus, the systems of Baudot, Hughes and Siemens are maintained for Continental work, each system necessitating the services of several skilled operators.
Certain distant European towns maintain a radio service with London. Incoming radio messages are received at the St. Albans (Herts) wireless station, where they are automatically amplified and passed by land line to the receiving apparatus at the Central Telegraph Office. These signals are recorded in the form of a continuous undulating line on a tape.
The tape is passed through slots at the front of a typewriter, where it is transcribed visually by an operator, who types the message out by hand. Morse code is used for transmission, but direct hand sending is not used. The Morse characters are perforated on a continuous tape by means of a typewriter keyboard of special design, and this tape is fed into an automatic transmitter which may be adjusted to transmit it at any speed desired.
Outgoing radio messages from the Central Telegraph Office are sent out from the great transmitters at Leafield (near Oxford) and Rugby. The work of Rugby Radio Station is described in the chapter “Giant of the Ether”.
Press messages, weather forecasts and messages to ships are all transmitted from an operating position in the Central Telegraph Office, which is always in direct control of the transmitter at Rugby. Apparatus in front of the operator at the Central Telegraph Office shows him which transmitters are in action and affords a constant check.
There are also direct telegraph circuits to various coastal stations, the most important of which is Portishead, Somerset, from which messages are radiated to ships which have long-range sending and receiving apparatus. Messages to and from Lloyd’s are handled over this busy circuit, which deals with hundreds of messages to and from ships in all parts of the world every day.
A DROP POINT on a belt conveyer. Telegraph forms are sent from one part of the office to another on belt conveyers, five of which pass along the shelves seen in this illustration. Another conveyer running overhead delivers forms to the table in the foreground through the specially-designed “chain chute” which has been adopted as the best method of dropping forms at their proper destinations.