This exhibit is a mystery. First thoughts were that it was a voltage stabiliser but even at 400 Volts between pins one and two no glow was detected. It is probable that this is a radiation detector.
The construction is of a thin outer cylinder with a central metal rod within.
The top of the envelope. The central rod is fixed into a glass support suggesting a high operating voltage.
The wide glass tube envelope is 27 mm in diameter, and excluding the B4 base pins is 185 mm tall.
Updated August 05, 2015.