The B-H looks to be a cold cathode gas filled device. Two electrodes have ceramic insulated leads, the third is un-insulated and appears to touch the closed dome.
A side view showing the dome and the glass and ceramic insulation.
A close-up of the underside of the dome. The central wire is not insulated from the dome but also not securely bonded to it.
The balloon envelope is 44 mm in diameter, and excluding the UX4 base pins is 89 mm tall.
Updated June 22, 2013.