[This message has been edited by Webmaster (edited 05-25-2005).]

This is a fused lightning arrestor for a telephone line. The cap covers a pair of carbon spark-gaps. The bottom terminal is for ground.

The two terminals labeled "L" are for the incoming telephone line, The two labeled "I" are for the telephone instrument, and the terminal labeled "G" is for ground.

Note that the terminal on the upper right is corroded, but none of the others are.
Can anybody explain why that particular terminal would be corroded, but not the opposite side?

That sort of thing is common when DC wiring gets wet. Electrolysis causes one terminal (the cathode, IIRC) to corrode very quickly, while the other electrode is hardly effected.

Remember that the telephone loop current is DC. That's the same sort of corrosion of one pole that you can see on an automotive battery terminal, or on other DC switching equipment.

Snap!

Or the French knife switch, posted in PFD.
Alan