These are the tubes that went down the pipe (image source; the same site as before). The capsule would go down the pipe to an office, and someone would lift it out and put it in the pipe to the next office, and so on. In 1931, they introduced conductive bands that went around the tube, encoding the destination address electronically. That way, capsules could be routed automatically.

Keep in mind that packet switching, which is how packets of information are routed around the internet, wasn’t invented until July 1961.

(I’ve written a couple of stories about packet switching in different contexts, one prehistoric and one steampunk.)

Matt Webb, S&W, posted 2006-04-06 (talk on 2006-02-23)