Shown here is a GE Tungar Rectifier bulb, Cat. No. 189048. The filament has flexed down, indicating many hours of use. The second picture shows what a new Tungar filament looks like.
Tungar bulbs come in many different shapes and sizes. They were used in early battery chargers. Westinghouse manufactured an identical bulb under the trademark 'Rectigon'.
In the words of Wikipedia: "The General Electric Tungar rectifier was a mercury vapor or argon gas-filled electron tube device with a tungsten filament cathode and a carbon button anode."