The Type 4 is a bolometer, a device for measuring small levels of power. We also have the Type 7 and lack details for both.
The active component is the tiny bead at the head.
The side bars. We have no details of their function.
A closer view of the active bead. The horizontal wire is probably a support, but it could be that the horizontal rods form a dipole and the incident radiation causes a change of resistance in the bead. The bead would then be connected in a bridge arrangement.
The balloon envelope is 64 mm in diameter, and excluding the IO base pins is 140 mm tall.
Updated July 14, 2014.