You put your money on the counter. The shop assistant makes out a bill; and you wonder what he will do with it next. These large stores know nothing of an open till. Yet there are no cashiers' desks visible; nor any overhead wires to whisk a carrier off to some corner where a young lady, enthroned in a box, controls all the pecuniary affairs of that department.

While you are wondering the assistant has wrapped the coin in the bill and put the two into a dumb-bell-shaped carrier, which he drops into a hole. A few seconds later, flop! and the carrier has returned into a basket under another opening. There is something so mysterious about the operation that you ask questions, and it is explained to you that there are pneumatic tubes running from every counter in the building to a central pay-desk on the first or second floor; and that an engine somewhere in the basement is hard at work all day compressing air to shoot the carriers through their tubes.

Certainly a great improvement on those croquet-ball receptacles which progressed with a deliberation maddening to anyone in a hurry along a wooden suspended railway! Now, imagine tubes of this sort, only of much larger diameter, in some cases, passing for miles under the streets and houses, and you will have an idea of what the Pneumatic Mail Despatch means: the cash and bill being replaced by letters, telegrams, and possibly small parcels.

"Swift as the wind" is a phrase often in our mouths, when we wish to emphasise the celerity of an individual, an animal, or a machine in getting from one spot of the earth's surface to another. Mercury, the messenger of uncertain-tempered Jove, was pictured with wings on his feet to convey, symbolically, the same notion of speed. The modern human messenger is so poor a counterpart of the god, and his feet are so far from being winged, that for certain purposes we have fallen back on elemental air-currents, not unrestrained like the breezes, but confined to the narrow and certain paths of the metal tube.

The pneumatic despatch, which at the present day is by no means universal, has been tried in various forms for several decades. Its first public installation dates from 1853, when a tube three inches in diameter and 220 yards long was laid in London to connect the International Telegraph Company with the Stock Exchange. A vacuum was created artificially in front of the carrier, which the ordinary pressure of the atmosphere forced through the tube. Soon after this the post-office authorities took the matter up, as the pneumatic system promised to be useful for the transmission of letters; but refused to face the initial expense of laying the tube lines.

When, in 1858, Mr. C. F. Varley introduced the high pressure method, pneumatic despatch received an impetus comparable to that given to the steam-engine by the employment of high-pressure steam. It was now possible to use a double line of tubes economically, the air compressed for sending the carriers through the one line being pumped out of a chamber which sucked them back through the other. Tubes for postal work were soon installed in many large towns in Great Britain, Europe, and the United States; including the thirty-inch pneumatic railway between the North-Western District post office in Eversholt Street and Euston Station, which for some months of 1863 transported the mails between these two points. The air was exhausted in front of the carriage by a large fan. Encouraged by its success, the company built a much larger tube, nearly 4 1 / 2 feet in diameter, to connect Euston Station with the General Post Office. This carried fourteen tons of post-office matter from one end to the other in a quarter of an hour. There was an intermediate station in Holborn, where the engines for exhausting had been installed. But owing to the difficulty of preventing air leakage round the carriages the undertaking proved a commercial failure, and for years the very route of this pneumatic railway could not be found; so quickly are "failures" forgotten!

The more useful small tube grew most vigorously in America and France. In, or about, the year 1875 the Western Union Telegraph Company laid tubes in New York to despatch telegrams from one part of the city to the other, because they found it quicker to send them this way than over the wires. Eighteen years later fifteen miles of tubes were installed in Chicago to connect the main offices of the same company with the newspaper offices in the town, and with various important public buildings. Messages which formerly took an hour or more in delivery are now flipped from end to end in a few seconds.

The Philadelphia people meanwhile had been busy with a double line of six-inch tubes, 3,000 feet long, laid by Mr. B. C. Batcheller between the Bourse and the General Post Office, for the carriage of mails. The first thing to pass through was a Bible wrapped in the "Stars and Stripes." A 30 horse-power engine is kept busy exhausting and compressing the air needed for the service, which amounts to about 800 cubic feet per minute. Philadelphia can also boast an eight-inch service, connecting the General Post Office with the Union Railway Station, a mile away. One and a half minutes suffice for the transit of the large carriers packed tightly with letters and circulars, nearly half a million of which are handled by these tubes daily.

New York is equally well served. Tubes run from the General Post Office to the Produce Exchange, to Brooklyn, and to the Grand Central Station. The last is 3 1 / 2 miles distant; but seven minutes only are needed for a tube journey which formerly occupied the mail vans for nearly three-quarters of an hour.

Paris is the city of the petit bleu, so important an institution in the gay capital. Here a network of tubes connects every post office in the urban area with a central bureau, acting the part of a telephone exchange. If you want to send an express message to a friend anywhere in Paris, you buy a petit bleu, i.e. a very thin letter-card not exceeding 1 / 4 oz. in weight, at the nearest post office, and post it in a special box. It whirls away to the exchange, and is delivered from there if its destination be close at hand; otherwise it makes a second journey to the office most conveniently situated for delivery. Everybody uses the voie pneumatique of Paris, so much cheaper than, and quite as expeditious as, the telegraph; with the additional advantage that all messages are transmitted in the sender's own handwriting. The system has been instituted for a quarter of a century, and the Parisians would feel lost without it.

London is by no means tubeless, for it has over forty miles of 1 1 / 2 , 2 1 / 4 , and 3-inch lines radiating from the postal nerve-centre of the metropolis, of lengths ranging from 100 to 2,000 yards. The tubes are in all cases composed of lead, enclosed in a protecting iron piping. To make a joint great care must be exercised, so as to avoid any irregularity of bore. When a length of piping is added to the line, a chain is first passed through it, which has at the end a bright steel mandrel just a shade larger than the pipe's internal diameter. This is heated and pushed half-way into the pipe already laid; and the new length is forced on to the other half till the ends touch. A plumber's joint having been made, the mandrel is drawn by the chain through the new length, obliterating any dents or malformations in the interior.

The main lines are doubled—an "up" and a "down" track; short branches have one tube only to work the inward and the outward despatches.

The carriers are made of gutta-percha covered with felt. One end is closed by felt discs fitting the tube accurately to prevent the passage of air, the other is open for the introduction of messages. As they fly through the tube, the carriers work an automatic signalling apparatus, which tells how far they have progressed and when it will be safe to despatch the next carrier.

The London post-office system is worked by six large engines situated in the basement of the General Post Office.

So useful has the pneumatic tube proved that a Bill has been before Parliament for supplying London with a 12-inch network of tubes, totalling 100 miles of double line. In a letter published in The Times, April 19, 1905, the promoters of the scheme give a succinct account of their intentions, and of the benefits which they expect to accrue from the scheme if brought to completion. The Batcheller system, they write, with which it is proposed to equip London, is not a development of the miniature systems used for telegrams or single letters here or in Paris, Berlin, and other cities. Such systems deal with a felt carrier weighing a few ounces, which is stopped by being blown into a box. The Batcheller system deals with a loaded steel carrier weighing seventy pounds travelling with a very high momentum. The difference is fundamental. In this sense pneumatic tubes are a recent invention, and absolutely new to Europe.

The Batcheller system is the response to a pressing need. Careful observations show that more than 30 per cent. of the street traffic is occupied with parcels and mails. These form a distinct class, differentiated from passengers on the one hand and from heavy goods on the other. The Batcheller system will do for parcels and mails what the underground electric railways do for passengers. It has been in use for twelve years in America for mail purposes, and where used has come to be regarded as indispensable.

The plan for London provides for nearly one hundred miles of double tubes with about twice that number of stations for receiving and delivery. The system will cover practically the County of London, and no point within that area can be more than one-quarter of a mile from a tube station. Beyond the County of London deliveries will be made by a carefully organised suburban motor-cart service. Thirty of the receiving stations are to be established in the large stores. The diameter of the tube is to be of a size that will accommodate 80 per cent. of the parcels, as now wrapped, and 90 per cent. with slight adaptation. The remaining 10 per cent.—furniture, pianos, and other heavy goods—are to be dealt with by a supplementary motor service. If the tubes were enlarged their object would be partially defeated, for with the increased size would go increased cost, great surplus of capacity, less frequent despatch, and lower efficiency generally. The unsuccessful Euston Tunnel of forty years ago—practically an underground railway—is an extreme illustration of this point, though in that case there were grave mechanical defects as well.

From a mechanical point of view the system has been brought to such perfection that it is no more experimental than a locomotive or an electric tramcar. The unique value of tube service is due to immediate despatch, high velocity of transit, immunity from traffic interruption, and economy. The greatest obstacle to rapid intercommunication is the delay resulting from accumulations due to time schedules. The function of tube service is to abolish time schedules and all consequent delays.

The number of trades parcels annually delivered in London is estimated at more than 200,000,000. A careful canvass has been made of 1,000 shops only, which represent a very small fraction of the total number in the county. As a result it has been ascertained that these 1,000 shops deliver no fewer than 60,000,000 parcels yearly, a fact that seems to more than justify the foregoing estimate; on the other hand, it is known from official data that the parcel post in London is represented by less than 25,000,000, or one-ninth of the total parcel traffic. With a tube system in operation, every parcel, instead of waiting for "the next delivery," would leave the shop immediately. After being despatched by the tube it would be delivered at a tube station within a quarter of a mile at least of its destination, and thence by messenger. The entire time consumed for an ordinary parcel would be not over an hour, and for a special parcel fifteen to twenty minutes. They require from three to six hours or longer at present.

The advantages of the tube system to the public would be manifold. Customers would find their purchases at home upon their return, or, if they preferred, could do their shopping by telephone, making their selections from goods sent on approval by tube. The shopman would find himself relieved from a vast amount of confusion and annoyance, less of his shop space given up to delivery, and his expenses reduced. Small shops would be able to draw upon wholesale houses for goods not in stock, while the customer waited. Such delay and confusion as are frequently occasioned by fogs would be reduced to a minimum.

While the success of the project is not dependent on Post Office support, the Post Office should be one of the greatest gainers by it. The time of delivery of local letters would be reduced from an average of three hours and six minutes to one hour. Express letters would be delivered more quickly than telegrams. This has been demonstrated conclusively again and again in New York and other American cities where the tubes have been in operation for years. The latest time of posting country letters would be deferred from one-half to one hour, and incoming letters would be advanced by a similar period. The parcels post would gain in precisely the same way, but to an even larger extent.

If the Post Office choose to avail themselves of the opportunity, every post office will become a tube station and every tube station a post office. Thus the same number of postmen covering but a tithe of the present distances could make deliveries without time schedules at intervals of a few minutes with a handful instead of a bagful of letters.

The sorting of mails would be performed at every station instead of at a few. Incoming country mails would be taken from the bags at the railway termini, and the same bags refilled with outgoing country mails, thus avoiding needless carriage to the Post Office and back. No bags at all would be used for local mails, the steel carriers themselves answering that purpose.

At every tube terminal a post-office clerk would be stationed, so that the mails would never for an instant be out of post-office control. Its absolute security would be further ensured by a system of locking, so that the carriers could only be opened by authorised persons at the station to which they were directed. These safeguards offer a striking contrast to the present method that entrusts mail bags to the sole custody of van drivers in the employ of private contractors.

If the mails were handled by tube, business men would be able to communicate with each other and receive replies several times in one day, and country and foreign letters could always be answered upon the day of receipt. The effect would be felt all over the Empire.

Would the laying of the tubes seriously impede traffic? The promoters assure us that the inconvenience would not be comparable to that caused by laying a gas, water, or telephone system. When one of those has been laid the annoyance, they urge, has only begun. The streets must be periodically reopened for the purpose of making thousands of house connections, extensions, and repairs. When a pneumatic tube is once down it is good for a generation at least. It is not subject to recurrent alterations incidental to house connections and repairs. In three American cities the tubes have been touched but three times in twelve years, and in those cases the causes were a bursting water main and faulty adjacent electric installations. The repairs were effected in a few hours.

From a general consideration of the scheme we may now turn to some mechanical details. The pipes would be of 1 foot internal diameter, made in 12-foot lengths. "Straight sections," writes an engineering correspondent of The Times, "would be of cast-iron, bored, counter-bored, and turned to a slight taper at one end, to fit a recess at the other end (of the next tube), to form the joints, which could be caulked. Joints made in this way are estimated to permit of a deflection of 2 inches from the straight, so that the laying and bedding need not be exact. Bent sections are to be of seamless brass; these are bored true before bending. The permissible curvature is determined upon the basis of a maximum bend of 1 foot radius for every 1 inch of diameter; the 1 foot diameter of the London tubes would consequently be allowed a maximum curvature of 12 foot radius. Measured at the enlarged end, the over-all diameter of each pipe is 17 inches, and as two such pipes are to be laid side by side, with 18 inches between centres, the clear width will be 35 inches. The trenches are therefore to be cut 36 inches wide, and in order to have a comparatively free run for the sections, it is proposed to cut the trenches 6 feet deep."

When the hundred miles of piping have been laid, the entire system will be tested to a pressure of 25 lbs. to the square inch, or about two and a half times the working pressure. Engines of 10,000 h.p. will be required to feed the lines with air, for the propulsion of the carriers, each 3 feet 10 inches long, and weighing 70 lbs.

In order to ensure the delivery of a carrier at its proper destination, whether a terminus or an intermediate station, Mr. Batcheller has made a most ingenious provision. On the front of a carrier is fixed a metal plate of a certain diameter. At each station two electric wires project into the tube, and as soon as a plate of sufficient diameter to short-circuit these wires arrives, the current operates delivery mechanism, and the carrier is switched off into the station box. The despatcher, knowing the exact size of disc for each station, can therefore make certain that the carrier shall not go astray.

It may occur to the reader that, should a carrier accidentally stick anywhere in the tubes, it would be a matter of great difficulty to locate it. Evidently one could not feel for it with a long rod in half a mile of tubing—the distance between every two stations—with much hope of finding it. But science has evolved a simple, and at the same time quite reliable, method of coping with the problem. M. Bontemps is the inventor. He located troubles in the Paris tubes by firing a pistol, and exactly measuring the time which elapsed between the report and its echo. As the rate of sound travel is definitely known, instruments of great delicacy enable the necessary calculations to be made with great accuracy. When a breakdown occurred on the Philadelphia tube line, Mr. Batcheller employed this method with great success, for a street excavation, made on the strength of rough measurements with the timing apparatus, came within a few feet of the actual break in the pipe, caused by a subsidence, while the carriers themselves were found almost exactly at the point where the workmen had been told to begin digging.[23]

There is no doubt that, were such a system as that proposed established, an enormous amount of time would be saved to the community. "A letter from Charing Cross to Liverpool Street," says The World's Work, "occupies by post three hours; by tube transit it would occupy twenty to forty minutes, or by an express system of tube transit ten to fifteen minutes. Express messages carried by the Post Office in London last year (1903) numbered about a million and a half, but the cost sometimes seems very heavy. To send a special message by hand from Hampstead to Fleet Street, for example, costs 1s. 3d., and takes about an hour. It is claimed that it could be sent by pneumatic tube at a cost of 3d. in from fifteen to twenty minutes, and that for local service the tube would be far quicker than the telegraph, and many times cheaper."

It has been calculated that from one-sixth to one-quarter of the wheeled traffic of London is occupied with the distribution of mails and parcels; and if the tubes relieved the streets to this extent, this fact alone would be a strong argument in their favour. It is impossible to believe that tube transmission on a gigantic scale will not come. Hitherto its development has been hindered by mechanical difficulties. But these have been mostly removed. In the United States, where the adage "time is money" is lived up to in a manner scarcely known on this side of the Atlantic, the device has been welcomed for public libraries, warehouses, railway depÔts, factories—in short, for all purposes where the employment of human messengers means delay and uncertainty. Twenty years ago Berlier proposed to connect London and Paris by tubes of a diameter equal to that of the pipes contemplated in the scheme now before Parliament. Our descendants may see the tubes laid; for when once a system of transportation has been proved efficient on a large scale its development soon assumes huge proportions. And even the present generation may witness the tubes of our big cities lengthen their octopus arms till town and town are in direct communication. After all it is merely a question of "Will it pay?" We have the means of uniting Edinburgh and London by tube as effectually as by telephone or telegraph. And since the general trend of modern commerce is to bring the article to the customer rather than to give the customer the trouble of going to select the article in situ—this applies, of course, to small portable things only—"shopping from a distance" will come into greater favour, and the pneumatic tube will be recognised as a valuable ally. We can imagine that Mrs. Robinson of, say, Reading, will be glad to be spared the fatigue of a journey to Regent Street when a short conversation over the telephone wires is sufficient to bring to her door, within an hour, a selection of silver ware from which to choose a wedding present. And her husband, whose car has perhaps broken a rod at Newbury, will be equally glad of the quick delivery of a duplicate part from the makers. These are only two possible instances, which do not claim to be typical or particularly striking. If you sit down and consider what an immense amount of time and expense could be saved to you in the course of a year by a "lightning despatch," you will soon come to the conclusion that the pneumatic tube has a great future before it.