The TMH-2 is a hollow cathode glow modulator. The hollow cathode concentrates the discharge into a small circle. It is a small light source that can be modulated at up to 100 kHz.
The use of glow modulators was in fax machines and similar.
The 1B59 has an opaque coating on the glass but here the inner structure is visible. The cathode tube is sheathed in glass that is fixed to the pinch and thus providing external insulation. The anode is a disc with a small hole in the centre.
The IO base with just three pins fitted.
Through the dome and the top mica can be seen the anode and deeper down is the hollow cathode.
The wide glass tube envelope is 30 mm in diameter and, excluding the IO base pins, is 62 mm tall.