Elderly guidebooks let you visit Paris in the past. We have three. Two date from 1927 – Muirhead’s Paris and its Environs (Blue Guides), and the Express Guide to Paris and Environs (Publications Anglo-Américaines) – and one from 1950: Nagel’s Paris (Blue Guides). We bought them mainly for their maps, which are not only charming, but helpful in locating streets or buildings that have since vanished.

The guidebooks also describe services that have disappeared – the Petite Ceinture railway, river steamers (bateaux-omnibus), the central tramway network, public baths, subscription libraries for foreigners, and télégrammes pneumatiques. The guidebooks recommend the latter, also known as cartes-télégrammes, pneus, or petits bleus, for rapid communications within Paris.

Pneus were cheaper than conventional telegrams, particularly if the message was long, because the sender did not pay by the word, but by weight (60 centimes for 7 grams in 1927; about 45 old francs for the same weight in 1950). The sender could hand-write a message and deposit it in a special box at a post office; it would arrive at its destination one or two hours later.

Paris’s pneumatic telegraph system started in 1866, connecting the Bourse (stock exchange) with a telegraph office in the Grand Hotel (the one near the Opéra with Café de la Paix on the ground floor), about 800 metres away. Stock exchanges depend on quick communications and fortunes can be made by those who are first to receive crucial information.

The pneumatic message system differed from the pneumatic clock system we described in an earlier blog. The clocks needed an unobstructed stream of air emitted at regular intervals to push a lever that moved the workings of the clock. With the pneumatic mail system, a canister obstructed the stream of air in the airtight tube. The canister was sucked or pushed along by the difference in air pressure on either side of it.

How did it work? From early childhood we learn to use differences in air pressure. Consider the pea-shooter (which children are probably now forbidden to use). The pea is in a tube, the child blows into the tube. The air pressure behind the pea is greater than that in front of it and the pea hurtles out of the pea-shooter.

Or consider drinking with a straw. You put the straw in your mouth and close your lips about it to create a seal. The liquid comes up the straw. By sucking in you have lowered the air pressure in the straw – that is, created a partial vacuum – and the higher air pressure on the surface of the liquid in the glass forces the liquid up the straw. It is all about creating a difference in air pressure and then putting it to work.

The 19th century was a period  of gloriously inventive technology and many people explored how to use compressed air and pneumatic systems. An Englishman, George Medhurst, experimented with pneumatic transport, and in 1810 invented a pneumatic railway. A Scot, William Murdoch, is credited with inventing the pneumatic dispatch tube. The system used positive air pressure to push a capsule several inches in diameter along a tube.

In 1853 the technology came into practical use in London with a 1.5-inch diameter, 220-yard pneumatic tube joining the Central station and the Stock Exchange station of the  Electric and International Telegraph Company in London. Berlin followed in 1865 and Paris in 1866.

A year after its inauguration, the Paris system consisted of a one-way circular route with a single tube running from the Bourse to the telegraph offices on rue Jean-Jacques Rousseau, then to the rue de Rivoli, then across the river to the rue des Saints-Peres, from there to the Central Telegraph Office on the rue de Grenelle, then back to the rue Boissy d’Anglas on the right bank, and finally back to the Grand Hotel. After 1888, the tubes were doubled, so the system did not have to be just one-way.

The main conduit was an airtight tube with sealable hatches. Messages were carried in cylinders that could be opened at one end to insert the papers. The earliest messages were telegrams arriving at telegraph offices; later, letters or postcards could be used. The illustration below, from The Engineer, 18 December 1891, shows the London system.

Cylinders could be made of metal, wood or (in the 20th century) plastic. Slightly smaller in diameter than the tube, at either end they had protective bumpers as well as buffering material around the circumference to prevent air from blowing by.

In the Paris system, air pressure at the rear of the canister pushed it on its journey from a central station; it returned when vacuum pressure at the front pulled it back. This push-pull system meant that a single station on the network could provide the power for both sending and retrieving canisters.

When the canister arrived at its destination, a worker would open a door in the tube, remove the canister, and close the door to reseal the tube. To send another canister on its way, the worker would open another door, insert the canister, and close the door. Off the canister went, moved either by pressure or vacuum.

The Paris system grew over time and according to Douglas Self, whose website is a feast of information on retro technology, in 1874, “Trains of canisters departed every quarter of an hour from Rue de Grenelle, covering the 1500m to the next bureau (Rue Boissy-d’Anglas) in 90 seconds. The canister carrying messages for local distribution was removed, another carrying messaged handed in at that bureau was added, and the train sent off to the next destination, Grand-Hotel. From there it proceeded to La Bourse, Place Theatre-Français and Rue des Saint-Peres. It finally returned to Rue de Grenelle, having taken 12 minutes on its round trip. Each train was composed of ten canisters, together weighing about four kilograms. Under either vacuum or pressure of about 10 psi the train had an average speed of 1 kilometre in 60 seconds,” or 60 kilometers per hour.

The final part of the message system used older technology: messenger boys on foot or on bicycles to deliver the letters or telegrams to their destination. This illustration is from Mon Dimanche, 17 mai 1903.

Gradually, more and more pneumatic stations were added. As with the clock system, the tubes ran through the sewers. They were iron, with an internal diameter of 65 mm, joined with stepped flanges to prevent air leakage. As much as possible, the tubes were laid in straight lines; any curves had a radius between 5 and 20 metres. The tighter the curve, the greater the probability that a cylinder would jam.

The system covered 467 km at its height in the 1930s. In areas where noisy equipment was not permitted, water power from city mains generated both pressure and vacuum in the stations. In less sensitive areas, steam-engine-powered equipment was used.

The network, shown in this 1926 map from Gallica, had two main hubs: the Bourse on the right bank, and the central telegraph office on the left (the same building we described in the blog about the Chappe telegraph system).

The black dots are the power houses, the single circles are telegraph offices that sent and received messages, and the double circles had both message offices and power equipment.

With the exception of a line to Neuilly, the system operated within the old walls of the city (also shown on the map).

Before 1898, senders had to use the official petit bleu stationery, which was sealed and perforated on three sides: the sender sealed it up and the recipient tore along the perforations to open the message. They were rather like airmail forms, also blue, which we remember using up to about the 1980s.

Later, one could write an ordinary letter and send it through the same system. This video clip from the movie Baisers Volés (Stolen Kisses) by François Truffaut shows a regular letter going through the system.

The citywide pneumatic system continued into the early 1980s, and smaller pneumatic systems are still used in hospitals, major libraries, and other large  institutions and businesses, in Paris and elsewhere.

Paris’s city network lasted a long time, probably because until late in the 20th century, individual landline telephones were unreliable and hard to obtain in France (people waited months for installation). Now, with text messaging, petits bleus seem impossibly quaint, although rather romantic.

Text by Norman Ball and Philippa Campsie, with thanks to Mireille Duhen for finding the video and other sources of information.