As a child, I didn't particularly like having to ride along with my mom whenever she would drive to the bank, but one thing I did like were the tubes in the drive-through service bays. She would put her deposit slip and money in a garishly blue box, insert said box into an opening, push up slightly, and whoosh! Up it went! And then, many minutes later, the teller in the building would put my mom's receipt back in the box and send it back. It seemed amazing, particularly when I was younger, watching the box shoot upwards, gravity be damned, then curve towards and disappear into the building. If we were in the bay closest to the window, I could even watch the box descend down and land in its holding container. I have somehow remained ignorant of the name for this system of document transportation up until now. A post from The Onion today featured the phrase "pneumatic tubes" in its headline, and so I have the name now. And took a dive into my encyclopedias for more info on the matter.
The use of pneumatic tubes has assuredly declined in our digital society; the 1992 World Book, for instance, does not have an entry on them. The 1919 World Book, however, includes this entry for "pneumatic tubes" on page 4716 (volume 8):
PNEUMATIC TUBES, or PNEUMATIC DISPATCH, a system or method of sending mail, dispatches and parcels through tubes, either underground or above, by means of air pressure. In 1667 this method was first suggested by Denis Papin, who read a paper before the Royal Society of London explaining a device for sending a carrier containing mail through tubes by means of suction. Improvements on his suggestion, which were not commercially adopted until 1835, have led to the development of various forms of pneumatic transportation devices in every civilized country.
The necessary apparatus consists of a series of tubes, an air compressor and air-tight cylindrical carrying cases. The first pneumatic dispatch tubes installed only allowed the carriers to be sent in one direction, and to but one destination. This was improved upon by the use of alternate suction and pressure which allowed the carriers to travel both ways. This form was further modified by circular systems in which a current of air kept continually moving and the carriers could be withdrawn from the tubes at regular intervals or stations.
The pneumatic dispatch system has since 1870 proved successful in connection with the general post office, London, especially in the telegraph department, and there is now in use in this connection in that city a series of underground tubes over forty miles in length. The postal authorities and the telegraph companies in the United States have installed pneumatic dispatch systems in all large cities. Department stores and large retail stores in the States and in Canada employ the principle in tubes for conveying money from the counters to the cashier's desk. The development of pneumatic dispatch has not been so rapid in America as in Europe, but it is generally increasing, the system having been proved economical and efficient.
In pneumatic tubes of two and a quarter inches in diameter, worked with an air pressure of ten pounds per square inch, containing containers which hold seventy-five ordinary messenger forms, a speed is obtained in transit of a mile in two and one-half minutes. Large tubes for pneumatic dispatch, eight inches in diameter, are built for conveyance of carriers seven inches in diameter and twenty-four inches long. These tubes require an air pressure equal to thirty horse power, and the carriers are propelled through the tubes at the rate of thirty miles an hour.
Consult Batcheller's The Pneumatic Dispatch Tube System.
The diagram here is from the 1939 Comptons Pictured Encyclopedia, where it accompanies the entry on "pneumatic appliances" on page 266 of volume 11. The caption reads: This picture shows how the carriers travel back and forth in the tubes of a big store. When the carrier is inserted at any point in the system, it speeds forward until it strikes a trap door, which opens outward.
The door snaps open long enough to let out the carrier, but not long enough to let in much air. A suction fan is constantly exhausting the air from the pipes.
Large department stores are the subject of "The Wonder of a Great Store," an article features in volume 10 of The Book of Knowledge (1945). Although the article itself does not deal with the tubes, it is accompanied by a wonderful full-page photograph of a series of pneumatic tubes in the Macy's store in New York City, with the following caption: From almost every sales counter in the store a pneumatic tube runs, to carry the customer's money to a central desk, and to carry back change, if there is any, with hardly ever an error (p. 3679).
The above examples were arguably from reference works marketed towards children; we'll finish with some choice extracts from the 11th Edition Encyclopaedia Britannica and its entry on "pneumatic despatch" (volume 21, pp. 865-867). Get ready to get your math on - I had a lot of fun figuring out how to program the equations in \KaTeX.
PNEUMATIC DESPATCH, the name given to a system of transport of written despatches through long narrow tubes by the agency of air pressure. It was introducted in 1853 by J. Latimer Clark, between the Central and Stock Exchange stations of the Electric and International Telegraph Company in London. The stations were connected by a tube 1½ in. in diameter and 220 yds. long. Carriers containing batches of telegrams, and fitting piston-wise in the tube, were sucked through it (in one direction only) by the production of a partial vacuum at one end. In 1858 C. F. Varley improved the system by using compressed air to force the carriers in one direction, a partial vacuum being still used to draw them in the other direction. This improvement enables single radiating lines of pipe to be used both for sending and for receiving telegrams between a central station supplied with pumping machinery and outlying stations not so supplied.
[...] ...it is found more economical to transmit local message-work by tube rather than by wire, as skilled telegraphists are not required, but only tube attendants. [...]
The tubes are in all cases of lead...
Great care is exercised in making the joints in the lead pipes. Before the tube is placed in its trench a strong chain is passed through it, and a polished steel mandrel, 6 in. long and slightly less in diameter than the diameter of the tube, is heated and attached to the chain, and pushed half its length into the end of the tube already laid; the new length of tube is then forced over the projecting end of the mandrel until the tube ends (which have been previously cut flat) butt perfectly together; an ordinary plumber's joint is then made. By this means the tube is made perfectly air-tight, and the mandrel keeps the surface of the tube under the joint as smooth as at any other part of its length. After the joint is completed, the mandrel is drawn out by the chain attached to it, the next length is drawn on, and the above process repeated. The tubes are laid about 2 ft. below the surface of the ground.
The tubes radiate from the central to the branch offices, the principal offices having two tubes, one for "inward" and the other for "outward" traffic. At the smaller offices both the inward and the outward traffic is carried on through one tube. The "carriers" are made with gutta percha bodies, covered with felt, the front of the carrier being provided with a buffer or piston formed of several disks of felt which closely fit the tube; the messages are prevented from getting out of the carrier by the end being closed by an elastic band, which can be stretched sufficiently to allow the message forms to be inserted. The 3-in. carriers will hold 75 ordinary message forms, the 2¼-in. carriers 25 forms, and the 1½-in. carriers 20 forms. The carriers are propelled in one direction (from the central office) by "pressure," and drawn in the opposite direction by "vacuum," the standard pressure and vacuum being 10 ln and 6½ lb per sq. in. respectively, which values give approximately the same speed.
The time of transit of a carrier through a tube when the air pressure does not exceed 20 lb per square inch is given very approximately by the empirical formula: —
where l = length of tube in yards, d = diameter of tube in inches, P = effective air-pressure in pounds per square inch, t = transit time in seconds. For vacuum the formula is:—
where P1 = effective vacuum in pounds per square inch.
The horse-power required to propel a carrier is approximately, for pressure:—
for vacuum:—
For a given transit time the actual horse-power required is much less in teh case of vacuum than in the case of pressure working, owing to the density of the air column moved being much less: thus, for example, the transit time for 10 lb pressure is the same as for 6½ lb vacuum, but the horse-power required in the two cases is as 1.83 to 1. [...] The transit time for a 2¼-in. tube is 16% more than for a 3-in. tube of the same length, when both are worked at the same pressure, but the horse-power required is 50% less; it is not advisable, therefore, to use a tube larger than is absolutely necessary to carry the volume of traffic required.
[...]
As a rule, only one carrier is despatched at a time, and no second carrier is inserted in the tube until the arrival of the first one at the farther end is automatically signalled (by an electric apparatus) to the despatching office. On some of the long tubes a carrier, when it passes the midway point in the tube, strikes a trigger and sends back an electrical signal indicating its passage; on the receipt of this signal a second carrier may be despatched. This arrangement has been almost entirely superseded by a signally apparatus which by a clock movement actuates an indicating hand moves the latter to "tube clear" a certain definite time (30 to 40 seconds) after a carrier has been inserted in the tube. By this arrangement carriers can be despatched one after the other at comparatively short intervals of time, so that several carriers (separated by distinct intervals) may be travelling through the tube simultaneously. It is necessary that the carriers be separated by a definite interval, otherwise they tend to overtake one another and become jammed in the tube. Although the stoppage of a carrier in a tube is of exceedingly rare occurance, it does occasionally take place, through picks being driven into the tube by workmen executing repairs to gas or water pipes, but the locality of such a stoppage is easily determined by a simple inspection along the route of the tube. In no case is any special means of testing for the locality from the central office found necessary.
[...]
