In the "everyone's linking to this today" category, here's some of Molly Wright Steenson's work on pneumatic tubes, part of her forthcoming dissertation. Part II here. The impetus for tubes? Encoding and decoding Morse codes, plus high urban and economic density.
Why did it make sense to send a telegram via pneumatic tube? It was a set of factors related to urban conditions in the 19th century. Cities with high population, heavy commerce and finance and urban congestion made good candidates for pneumatic tube networks. Moreover, in Europe, the pneumatic tube mostly relieved a communication boom caused by inexpensive telegraphy and saturated telegraph networks. Devised as an auxiliary to the telegraph, a medium that could only transmit 40-50 messages of 20 words per hour in 1860, the pneumatic tube network addressed the issue of rapid, reliable communication within the city (though telegraphy still made sense for messages sent over longer distances).
The accompanying images give me shorpy envy.
(via Cory, via Bruce)