CHAPTER I.

A BRIEF HISTORICAL SKETCH.

=Early Records.=—The earliest reference to pneumatic transmission of which we find any record is a paper presented to the Royal Society of London, by Denis Papin, in the year 1667, entitled “Double Pneumatic Pump.” His plan was to exhaust the air from a long metal tube by two large cylinders. The tube was to contain a piston, to which a carriage was attached by means of a cord. The “American Cyclopædia” goes on to say, “More than a century elapsed before any further effort in this direction was made. Paucbrouke’s ‘Dictionnaire Encyclopédique des Amusements des Sciences’ (1792) gives a description of a machine by M. Van Estin, by means of which a hollow ball holding a small package was propelled by a blast of air through a tube several hundred feet in length, and having many curves. This plan seems, however, to have been more an amusement than an attempt to introduce an industrial scheme. With more regard to practical results, Medhurst, an engineer of London, published a pamphlet on the subject in 1810. He proposed to move small carriages on rails in air-tight tubes or tunnels, by compressed air behind, or by creating a partial vacuum in front. In 1812 he published another pamphlet; but the plan was not put into successful operation, principally from insufficient means of exhaustion. About 1832 he proposed to connect the carriage inside such a tube with a passenger carriage running on the top of the tube; and, although the latter project has never been commercially successful, it was the first to be practically attempted. More than a score of patents were taken out on the Continent and in England and America, none of which met with any practical success. Returning to the original idea of Denis Papin, inventors attempted to accomplish pneumatic transmission by moving the load inside the tube, and in course of time achieved success. In France MM. Jarroux and Taisseau presented a project for atmospheric telegraphy before the Academy of Sciences, and they were succeeded in the same direction by MM. Brochet and Ardor.”

=Practical Beginning of the Art. The London Pneumatic Telegraph.=—London has the honor of being the first city to have a practical system of pneumatic telegraphy. The first tubes were installed by the Electric and International Telegraph Company, the work being planned and carried out by their engineer, Mr. Josiah Latimer Clark, in 1853 and 1854. The first tube to be laid was one and one-half inches in diameter, and extended from the central station, Founder’s Court, Lothbury, to the Stock Exchange, Throgmorton Street, a distance of two hundred and twenty yards. The tube was operated intermittently by connecting it to a vacuum chamber at the central station. Carriers were sent only in one direction. A steam-pump was used to maintain the vacuum. Much experience was gained from the use of this first tube. In 1858 some improvements were made by Mr. C. F. Varley, and I can best describe them by quoting from the discussion of Mr. Carl Siemens’s paper on “Pneumatic Despatch Tubes: The Circuit System” before the Institution of Civil Engineers, as recorded in the minutes of that society. “Later, about the year 1858, when a pipe two and one-fourth inches internal diameter was extended from Telegraph Street to Mincing Lane, thirteen hundred and forty yards in length, the traffic was so considerable that it was found desirable to have the power of sending messages in both directions. To effect that a smaller pipe, one and one-half inches in internal diameter, was laid between Telegraph Street and Mincing Lane, with a view to carrying the vacuum to the latter station, so as to take messages in the opposite direction. This smaller pipe was found to so wiredraw the current that the pipe would not work, the leakage past the carrier being too considerable; and accordingly a large chamber was built in the basement floor or kitchen at the corner of Mincing Lane and Leadenhall Street to collect power or vacuum for bringing the messages from Telegraph Street to Mincing Lane. This chamber was constructed of timber, fourteen feet by twelve feet broad and ten feet high, and was covered with lead. It was not strong enough to withstand the pressure; for one day, a carrier having stuck half-way, and when there was a higher vacuum than usual,—viz., twenty-three inches of mercury,—it collapsed with a loud report. At the time the landlord of the house happened to be dining in the next room, and he suddenly found himself, his table, dinner, and the door, which was wrenched off its hinges, precipitated into the room amongst the _débris_ of the chamber. The windows were forced inwards, and those on the opposite side of Mincing Lane and Leadenhall Street were drawn outwards. The damage was considerable. This accident put an end, for a time, to the attempt to send telegraph messages by means of a vacuum conveyed through this smaller pipe. About that time he (Mr. Varley) became the engineer-in-chief of the Electric Telegraph Company, and got permission from the directors to introduce a new system,—viz., compressed air,—though many persons contended that it would be impossible to blow messages through a pipe, because all attempts to blow air through long pipes had utterly failed; while others said that, if messages were sent, they would go much slower than with the vacuum.... In his (Mr. Varley’s) apparatus, for he was the first to introduce compressed air, the reverse was found to be the case, and for this reason: the tube did not consume power until a message was about to be forwarded; and in a tube thirteen hundred yards in length, and two and one-fourth inches in diameter, fifteen seconds elapsed before the vacuum was felt at the distant end after communication had been established with the exhausted chamber at the engine end of the tube, consequently the carrier did not start until after fifteen seconds had elapsed. When a message was sent by compressed air, it was sent from the end at which the power was applied, and the carrier started at once, thus gaining a start of fifteen seconds; now, inasmuch as the air in the tube had to be compressed, it started at a very high velocity, and when it reached the other end the compressed air in expanding gave it a higher velocity. The result was, in thirteen hundred and forty yards, from Telegraph Street to Mincing Lane, the carriers were drawn by vacuum, on an average, in from sixty to seventy seconds, and were propelled by compressed air in about fifty or fifty-five seconds, the difference of pressure in each case being nearly equal.”

The first one and one-half inch tubes laid under the direction of Mr. Clark were of iron with screwed joints. They gave much trouble from roughness upon the interior, which wore the carriers very rapidly, and from water that was drawn in through leaky joints. When the extensions were made in 1858 and afterwards, two and one-fourth inch lead tubes were used with plumber’s joints made over a heated mandrel, which made the joints very smooth upon the interior. The carriers were of gutta percha in the form of a cylinder closed at one end and fitted with a cap at the other. The outside was covered with felt or drugget.

When a carrier was to be despatched, a signal was sent to an attendant at the pump end of the tube, who closed that end and connected the tube to an exhausted chamber by opening a valve. As soon as the carrier arrived, he closed the valve and opened the tube, which allowed the carrier to drop out. Mr. Varley improved the method of operating the valves by making the air pressure do the work by means of cylinders and pistons when the attendant pressed a button. He also improved the carriers by doing away with the cap and using in its place an elastic band to hold the messages in place.

We have seen that Mr. Clark designed the first tube used in connection with the telegraph, and that it was a single tube, operated in one direction only by vacuum, being operated only when there were messages to send. This was extended and improved by Mr. Varley, who increased the diameter of the tubes from one and one-half inches to two and one-quarter inches, and operated them in both directions, using vacuum for sending in one direction and compressed air for sending in the other. The air current was maintained in the tubes only when messages were sent.

Great credit is due to Sir Rowland Hill, who, in 1855, had a proposed method of conveying mails in the city of London, through nine- and thirteen-inch tubes, thoroughly investigated. It was decided at this time that the saving in time over that consumed by mail carts would not warrant the expense of installing such a system.

=The Siemens Circuit System.=—The next progressive step was made by Siemens Brothers, of Berlin, who proposed a new system called the “circuit system,” in which two tubes were used, the up tube being connected to the down tube at the distant end. The air was compressed into one end of the circuit and exhausted from the other, and, furthermore, it was kept in constant circulation. Carriers were despatched by inserting them into the air-current without stopping it, in one direction in one tube or in the opposite direction in the other. Another feature of the Siemens system was the placing of three or more stations on one double line of tubes. Carriers could be stopped at an intermediate station by inserting in the tube an obstructing screen which the air would pass but which would stop a carrier. This system is described in detail in a paper read by Mr. Carl Siemens before the Institution of Civil Engineers, London, November 14, 1871, Vol. XXXIII. of the Proceedings. The Siemens apparatus for sending and receiving carriers consisted of two short sections of tube attached to a rocking frame so that either could be swung by hand into line with the main tube. One of the tube sections was open at both ends, and was used for despatching carriers. A carrier was placed in it, then it was swung into line with the main tube, when the air-current passing through swept the carrier along. The other tube section contained a perforated screen in one end and was used to receive carriers. When it was in line with the main tube and a carrier arrived, the carrier was stopped by striking the screen, then the tube section was swung to one side and the carrier pushed out with a rod. A by-pass was provided for the air around the apparatus so that its flow was not checked when the tube section was swung. When a carrier was despatched to an intermediate station, a signal was sent, and then the section of tube containing the screen was interposed in the line of the tube to stop the carrier upon its arrival. The carriers used by Mr. Siemens were made of gutta-percha, papier maché, or tin, closed at one end and fitted with a cover at the other. They were covered with felt, drugget, or leather. The front ends of the carriers were provided with thick disks of drugget or leather fitting the tube loosely, and the opposite ends were surrounded with pieces of the same material attached to them like the leather of an ordinary lifting pump.

In 1869 Messrs. Siemens Bros. received an order from the British government to install an experimental line of tubes between the central telegraph station and the general post-office. This was completed in 1870, and after a half-year’s test it was extended to Fleet Street, and finally to Charing Cross. The tubes were of iron, three inches in diameter, with flanged and bolted joints. It was found, after some experience, that there was no advantage in the circuit, so the up and down tubes were separated at Charing Cross Station and worked independently.

=Recent Improvements in the London System.=—In 1870 Mr. J. W. Wilmot designed a double sluice-valve by means of which carriers could be despatched continuously without stopping the flow of air in the tubes. Mr. Wilmot further increased the working capacity of pneumatic tubes when, in 1880, he invented an intermediate automatic signaller, by means of which a carrier signals the passage of a given point on its journey, showing that the section of the tube traversed is clear, thus allowing a second carrier to be despatched before the first has reached its destination.

From this beginning the English system developed into what has been termed a “radial system;” that is to say, one principal and several minor central pumping stations have been established, and from these radiate tubes to numerous sub-stations (see Fig. 2). Some of the stations are connected with double lines for sending in opposite directions. The out-going tube from the pumping station is worked by compressed air, and the incoming tube by exhaustion. Other stations are connected by single tubes, and they are operated alternately by compression and exhaustion. Intermediate stations are located on some of the lines. For the central station the Varley valves were found too expensive and troublesome to keep in order, so they were replaced by the Wilmot double sluice-valves, which are operated manually. In recent years the sluice-valves have been in turn replaced by what are termed D-boxes, a simpler form of apparatus. At the sub-stations the tube terminates in a box into which the carriers drop. As the system has been gradually extended, tubes two and three-sixteenths inches inside diameter have been used for short lines, and three-inch tubes for long lines. The tubes are of lead laid inside a cast-iron pipe which serves as a shield, protecting them from injury. They are laid in twenty-nine foot sections, the joints being made by soldering over a steel mandrel, which is afterwards drawn out by a chain. The joints in the cast-iron protecting pipe are made by caulking with yarn and lead. “Electric signals are used between the central and sub-stations, consisting of a single stroke bell and indicator, giving notice of the arrival and departure of carriers, and to answer the necessary questions required in working. Where there are intermediate stations the tubes are worked on the block system, as if it were a railway. Experience shows that, where great exactness of manipulation cannot be obtained, it is necessary to allow only one train in each section of a tube, whether worked by vacuum or pressure. But where there is no intermediate station, and where the tube can be carefully worked, carriers may be allowed to follow one another at short intervals in a tube worked by vacuum, although it is not perfectly safe to do so in one worked by pressure. In working by pressure it has been found that, notwithstanding a fair interval may be allowed, carriers are apt to overtake one another, for no two carriers travel in the same times, because of differences in fit, unless they are placed end to end. If signalling be neglected and a carrier happens to stick fast, being followed by several others, a block will ensue which it will be difficult to clear, while the single carrier could readily have been dislodged.” (_Proceedings Institute of Civil Engineers, London_, Vol. XLIII. p. 61.)

No changes have been made in the carriers from those used in the early experiments which have already been described.

The London system has grown until it now includes no less than forty-two stations and thirty-four miles of tubes. Similar systems have been established in connection with the telegraph in Liverpool, Manchester, Birmingham, Glasgow, Dublin, and New Castle. The tubes give a cheaper and more rapid means of despatching telegrams between sub-stations and central stations than transmission by telegraph, and local telegrams can be delivered in the sender’s handwriting.

=An Underground Pneumatic Railway for Transportation of Mail.=—Before describing the systems used in the cities on the Continent of Europe, we must notice a very large pneumatic tube, or more properly called a pneumatic tunnel railway, constructed in London for the transportation of mail from one of the railway stations. The first railway of this type was constructed in 1863 by the Pneumatic Despatch Company of London, and extended from Euston to the district post-office in Eversholt Street, a distance of about eighteen hundred feet. The tunnel was flat on the bottom, having a D-shaped cross-section two feet eight inches by two feet eight inches. The carriers or carriages were cradle-like boxes fitting the tunnel, and they moved at a speed of seventeen miles per hour, carrying fifteen mails daily. In 1872 two similar but larger tunnels were built from Euston Station to the general post-office, a distance of fourteen thousand two hundred and four feet, or two and three-quarters miles. One was for the up traffic, and the other for the down. The tunnels were four and a half feet wide by four feet high, the straight part being built of cast iron and the bends of brick. The line was operated by a fan twenty-two feet in diameter, which forced the air into one tunnel and exhausted it from the other, producing a vacuum of ten inches of water, or six ounces per square inch. The carriages occupied twelve minutes in traversing the tunnels, and there was one gradient of one to fourteen. The carriages were ten feet four inches long and weighed twenty-two hundredweight. “The system was able to transport over the whole line, allowing for delays, an average of a ton per minute.” The system was used to transport the mails in bulk, but it was found to be slow and unsatisfactory, and was very soon abandoned.

=The Berlin Pneumatic Telegraph.=—In 1863 the Prussian government applied to the firm of Siemens and Halske, of Berlin, for a proposition to establish a system of pneumatic tubes in that city for the transmission of telegraph messages. A proposition was accordingly submitted, and the work was completed in 1865. This first line consisted of two parallel wrought-iron tubes, two and one-half inches in diameter, one tube being used exclusively to send in one direction, and the other in the opposite direction. They extended from the telegraph station to the Exchange, requiring a total length of five thousand six hundred and seventy feet of tube. The two tubes were looped together at the Exchange, and a continuous current of air was made to circulate in them by a double-acting steam air-pump, located at the telegraph station. Air was compressed into one end of the tube and exhausted from the other. With nine inches of mercury pressure and vacuum the passage was made in ninety-five seconds to the Exchange, and seventy-five seconds from the Exchange. It was similar to the line established in London by the same firm some years later, which we have already described, except that there was no intermediate station. After the line had been in use for a year and a half, the Prussian government had it extended, first, from the telegraph station to the Potsdam gate, with an intermediate station at the Brandenburg gate. After these preliminary experiments, further extensions were made until a net-work of tubes extended over the city of Berlin, including no less than thirty-eight stations and over twenty-eight miles of tubes; but in laying down this net-work a departure was made from the Siemens system. Air was no longer kept constantly circulating, but power was stored up in large tanks, some being exhausted and others filled with compressed air, which was used when required to send messages, usually at intervals of five or fifteen minutes. The exhausted tanks were permanently connected with the closed tubes, which were opened when required for use. The tanks containing compressed air were connected to the tubes when messages were sent. The internal diameter of the tubes was 2.559 inches. They were laid in circuits, including several stations in a circuit, and the carriers travelled only in one direction around the circuit. Some outlying stations were connected by a single tube with central pumping-stations, these single tubes being worked in both directions. Years of experience have shown the disadvantages of this circuit-system, and it has gradually been changed to the radial system, such as is used in London, until now nearly all the stations are grouped around the central pumping-stations, to which they are connected directly by radiating tubes. The Siemens apparatus has been replaced by simpler and less expensive valves and receiving-boxes, the latest form of which was designed and patented by Mr. Josef Wildemann.

=The Paris Pneumatic Telegraph.=—We will now glance at the system used in Paris, which has some novel features. In 1865 it was decided to establish a system, and the first experimental line, from Place de la Bourse to the Grand Hôtel, on the Boulevard des Capuciens, was laid in 1866. Instead of using a steam-engine to drive an air-compressor or exhaust-pump, air was compressed in tanks by displacement with water from the city mains. In 1867 this line was extended to Rue de Grennelle St. Germain, with an intermediate station at the Rue Boissy d’Anglais, and another line with stations at Rue Jean Jacques Rousseau, Hôtel du Louvre in the Rue de Rivoli, the Rue des Saints Pères, and terminating in the central station. In 1868 the system was changed to a polygonal or circuit system by removing the station in the Rue de Rivoli to the Place du Théâtre Français and connecting the latter directly with the Bourse. Other changes and extensions were made in 1870 and 1871, until three polygons or circuits were formed, with five or six stations in each circuit, and several outlying stations were connected by independent tubes. In the middle of the year 1875 seventeen stations had been connected and plans were made for twenty-one more. Instead of maintaining an air-current around each circuit by machinery located at one of the stations on the circuit, at least three of the five or six stations comprised in the circuit have means of supplying compressed air or of exhausting it, and each side of the polygon, or section of the circuit between two stations, is operated independently of the rest of the circuit (see Fig. 3). Carriers are sent on from station to station around the circuit, either by compressed air from the last station from which they were sent or by means of exhaustion at the next station towards which they are moving. The carriers are made up in trains of from six to ten, with a piston behind them that fits the tube closely and forces them ahead. Each carrier is addressed by means of a label for its destined station. Trains are despatched around the circuits at stated times, usually at fifteen-minute intervals. As they arrive at the various stations, carriers are taken out and others put in, and the trains sent on their way. The carriers consist of iron cylinders, closed at one end, with a leather case that slides over them and closes the open end. They weigh, when filled with thirty-five messages, twelve and one-half ounces, and they will travel about twelve hundred miles before the leather cover is so worn that it must be thrown away. The pistons are made of a wooden cone, covered with iron, and having a “cup-leather” upon the rear end that fits the tube closely. The sending and receiving apparatus consists of sections of tube closed at one end, having a door on the side, through which carriers are inserted or despatched. A peculiar form of fork is used for picking them out. The air is controlled by valves opened and closed by hand.

Several methods are used to compress and exhaust the air. The most novel method consists in having tanks in which a partial vacuum is produced by allowing water to flow out of them into the sewer, or in having the air compressed by allowing water from the city mains to flow into the tanks and displace the air. Water jets have also been used, operating similar to a steam-injector. At some of the stations water turbines drive the air-pumps, and at others steam-engines are used.

The tubes of the Paris system are of wrought iron, in lengths of from fifteen to twenty feet, the joints being made with flanges and bolts. The interior diameter is 2.559 inches with a maximum variation to 2.519 inches. The bends are made with a radius of from six to one hundred and fifty feet. Water frequently gives trouble by accumulating in the tubes. Traps are placed at low points to drain it off.

The speed of the trains of carriers in the Paris tubes is from fifteen to twenty-three miles per hour, and the average time that elapses from the receipt of a message until its delivery is from forty to forty-five minutes.

=The Pneumatic Telegraph of other Cities.=—A system similar to the one just described is used in Vienna. It differs some in details of apparatus, but the carriers are despatched around circuits in trains, stopping at each station, where some carriers are removed and others inserted. Brussels also is not without its system of pneumatic tubes for the transmission of telegrams.

=Pneumatic Tubes in America.=—Turning our attention now to our own country, we cannot pass without mention some experiments of Alfred E. Beach with pneumatic railways, made nearly thirty years ago. His first experiment upon a large scale was made at the American Institute Fair held in New York City in 1867. Here he had constructed a circular wooden tube, one hundred and seven feet long and six feet in diameter. A car that would seat ten people ran upon a track laid down inside the tube, and was propelled by a helix fan ten feet in diameter, making two hundred revolutions per minute. He next tried his railway upon a practical scale, constructing an eight-foot tunnel for two hundred feet under Broadway, starting at the corner of Warren Street. A car was propelled by a large rotary blower located in the basement of a building near by. The blower was kept constantly running, and the car was sent alternately in one direction and then the other by changing valves at the blower. Few people know that this experimental line still exists under Broadway as Mr. Beach left it.

The most extensive use of small pneumatic tubes in this country has been in our large retail department stores for despatching cash to and from a centrally located cashier’s desk. Seamless brass tubes are usually used, and, since the tubes are short, the air is either compressed or exhausted by means of positive rotary blowers. At the outlying stations the tubes are usually open to the atmosphere, while at the central station simple forms of valves are used for sending and receiving. An outgoing and a return tube are always used, and the air is kept in constant circulation. The carriers are of metal with felt packing rings and open on the side. These cash-carrying systems have come into use during the past twenty-five years.

The Western Union Telegraph Company uses small tubes to transmit its messages to a considerable extent in some of our large cities. In 1876 four lines were laid in New York City from the main office on Broadway: two to the branch office at No. 14 Broad Street, one to 134 Pearl Street, and one to the Cotton Exchange. Since then this company has laid a double line about two miles in length under Broadway to its up-town office. It also uses tubes to send messages from the receiving desks to the operating rooms within the buildings.

Many of our large hotels use pneumatic tubes to transmit messages to the different floors and offices of the buildings, taking the place of messenger, or bell boys, who formerly did this service.

We call especial attention to the fact that in all the systems that we have mentioned which are in use both in this country and in Europe, none of the tubes are larger than three inches internal diameter; also that in all the systems, except in Paris where the carriers are despatched in trains, the carriers are so light and move so slowly that they can be stopped by allowing them to come in contact with some solid object, such as a box into which the carriers drop. Very few of the tubes are more than two miles in length, and most of them are less than one mile. A speed of more than thirty miles per hour has seldom been attempted, and usually it is much less than this.