The 2A is an early photocell from Western Electric. The connections are by the flying leads with attached pegs.
The glass carries the makers name, Type designation and made in USA. Also the serial number - 49298.
The paper label shows that this exhibit was last tested in 1930.
The spherical cathode has a small aperture to admit the light. The anode is the ring within.
A closer look at the anode ring. It is a tape about 2mm wide and 23 mm in diameter.
The balloon envelope is 58 mm in diameter, and excluding the pins is 110 mm tall.
Updated July 19, 2014. shape:balloon construction:pinch type:photocell age:1920.1930 base: pin: