It's clearly a radioactive spark gap.
The connector is obviously for high voltages and the labeling "Do no open"(sic) clearly indicates that it contains a radioactive isotope.
A radioactive source can be applied to the anode of a spark gap to provide ready electrons.
So, have you tried a set of Firestone poloniums?
http://www.orau.org/ptp/collection/consumer products/sparkplugs.htm
The misspelling ("Do no open" vs. "Do not open") suggests that this was not mass produced.
It would be interesting to know:
1) What is the word that begins "CH" on the white insulator? (I'm sure it's not "Champion".)
2) Is there an electrical connection between the metal capsule and the ground connection? There probably is, but you can't tell for certain in the photos. If there isn't, this may be a triggerable spark gap.
3) How big is it? Perhaps 8 or 9 cm?
If polonium was used, it long dead.
I doubt that it had any use as a lightning arrestor - you don't need anything that fancy for shorting lightning.
In any case, it is probably a museum piece.