In a recent New Yorker there was passing reference to a person making a killing and then suffering financial collapse as a participant in the pneumatic mailing tube industry. I am familiar from 1940's movies with the sending of mail in tubes within a building but apparently there were schemes to develop city wide pneumatic mailing systems. Just as railways defeated canals, however, the advent of broadly applied electronic communications would have stopped widespread development of pneumatics. Apparently Paris still uses a network which was first started in 1866 - although it is such a silly idea, descriptions of it could be an elaborate niche joke, which would make this reference even sweeter:

The standard work in France on the pneumatic post is 'Cent ans de tubes pneumatiques' J Boblique, Echo de la Timbrologie, 1966.