Dog Phone

It's common practice in England to ring a telephone by signaling extra
voltage across one side of the two wire circuit and ground (earth in
England).  When the subscriber answers the phone, it switches to the
two wire circuit for the conversation.  This method allows two parties
on the same line to be signalled without disturbing each other.

Anyway, an elderly lady with several pets called to say that her
telephone failed to ring when her friends called; and that on the few
occasions when it did ring her dog always barked first.  The telephone
repairman proceeded to the scene, curious to see this psychic dog.

He climbed a nearby telephone pole, hooked in his test set, and dialed
the subscriber's house.  The phone didn't ring.  He tried again.  The
dog barked loudly, followed by a ringing telephone.

Climbing down from the pole, the telephone repairman found:

a.  A dog was tied to the telephone system's ground post via an iron
    chain and collar.

b.  The dog was receiving 90 volts of signalling current.

c.  After several such jolts, the dog would start barking and
    urinating on the ground.

d.  The wet ground now completed the circuit and the phone would ring.
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