Many thanks to all who have replied. The variety that existed in the old U.S. network makes for some interesting history compared to the British situation where the nationalized GPO (General Post Office) ran all but a couple of tiny independent companies and practices were pretty much standard right across the country.
Now I think about it, I've seen something like that on an old postcard from the 1950s (I think it was from a rural motel). The number shown was 421R2, or something similar to that, so presumably that's "ring 2" on the end.
Why the name "circle" digit?
I guess eavesdropping was a pretty widespread pasttime. In fact back about 25 years ago my parents were on a party line and I lashed up a similar arrangement to monitor calls. My amp was a home-brew kit using, if I recall correctly, EF80 and ECL80 tubes.
Is there any particular significance to the letters? Can anyone remember which letters were which combination of tip/ring and polarity/cadence, or is that going back a little too far?
The wiring arrangements adopted by the GPO here meant that every phone intended for party-line use could be sent out into the field wired the same way. The switch had changeover contacts and was inserted into the "A" wire (GPO terminology for what would normally be the tip side of the line) so that when pressed it opened the loop and grounded the "B" wire (normally the ring side of the line) via the hybrid and remaining circuitry. The bell would then be wired from the "B" wire to ground.
The two stations were designated X and Y. The X subscriber's set was wired the normal way, A to tip, B to ring, then all that was necessary when installing at the Y subscriber's premises was to swap A and B at the junction box. Thus X had ringing on ring and grounded ring for dialtone, while Y had ringing on tip and grounded the tip to originate a call.
In SxS offices (which formed the majority of exchanges here for many years) there was a small relay set which then simply switched the line to the appropriate uniselector or linefinder on detecting the ground-start. Incoming calls were what you all describe as terminal-per-station and could come from completely separate final selectors (connectors) for each party, thus giving complete freedom on which two numbers would share the line.
Party lines certainly survived in some areas quite a way into the
1980s. There are still shortages of pairs in some places these days, except now BT makes extensive use of DACS units to multiplex lines.Regards,
Paul