Re: Nernst Lamps
Ordinary glass becomes electrically conductive at red heat: my school physics master demonstrated this by connecting a mains bulb in series with two metal bars held in two retort stands, balanced a glass rod on the bars, and heated the glass with a bunsen burner. As it approached red heat the bulb started to glow and got progressively brighter as the temperature increased. Red hot pyrex might provide a short circuit path across the glower.
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