This mercury (Hg) rectifier is still in use at Auckland's MOTAT museum where it serves the museum tram line.
I took the video through the glass door and unfortunately there is a little bit of reflection and it is a bit dark.
The voices heard are from a TV nearby, talking about new diesel engine techniques.
These rectifiers are impressive to look at, and to observe the green spot on top of the mercury pool underneath the UV blue glow of the octopus like bulb capsule.
If you are visiting Auckland. The MOTAT museum is a great place to visit and absorb the technology from the bygone days.
MOTAT ( Museum Of Transport And Technology )
Link how it works:http://en.wikipedia.org/wiki/Mercury_arc_valve
TRAMWAY POWER SUPPLY
Mercury Arc Rectifier, Distribution Panel & Circuit Breakers. The power supply for the tramway is via a Hackbridge step-down transformer, Hewittic mercury-arc rectifier, distribution and fault-protection panel. Input is at 6600volts AC and output is at 550volts DC. The supply has a capacity of 675kW (approx 900hp) and can be seen in operation next to the Pumphouse. It was formerly installed (in 1951) at the Dominion Road sub-station of the Auckland Electric Power Board to supply trolleybuses in the Mt Roskill area.