[GreenKeys] Telephone opportunity in the same spirit as teletype

[Jim Haynes]

The 1938 edition of the AT&T Long Lines book "Principles of Electricity
Applied to Telephone and Telegraph Work" includes a simplified schematic
of the equipment used to make a toll call between two telephones.  The
book also includes a good explanation of how a Teletype works, and some
diagrams of different kinds of transmission such as loop current, half
duplex, full duplex, one-way polar.  You can see all the elaborate
things that can be done with polar relays.  In my youth I was fortunate
to have friends in the local telephone office who let me borrow the
book for an extended period of time.  One of the first things they
taught me was about phantom circuits.  It was quite an experience for
me to see the toll testboard and to realize that behind each jack was
a wire going to the city named on the designation strip.

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 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man