The property or capacity of a substance to transmit heat or radiant energy through itself.
From Greek 'dia-' (through) + 'thermē' (heat) + '-ance' (noun suffix indicating quality or state), a technical term from 19th-century physics.
Diathermance is why ovens have glass doors—the glass transmits enough visible light to see your food while still retaining heat; pure transparency alone wouldn't help much if the glass didn't also have the right thermal properties.
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