This section is from the book "Applied Science For Metal Workers", by William H. Dooley. Also available from Amazon: Applied Science For Metal Workers.
The Nernst lamp has a filament of compressed oxides of certain rare metals. This filament conducts electricity only when heated to a high temperature, and as it is not combustible it need not be enclosed in an exhausted vessel. A small encircling coil of platinum wire (called a heater) through which a current of electricity passes brings the filament to incandescence.
 
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