Definition of "diathermal" []

• Freely permeable by radiant heat. (adjective)

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• "Thence flow those natural conjectures, which are well worthy of experimental examination: all men do not see by the same rays; decided differences may exist in this respect in the same individual during various nervous states; it is possible that the calorific rays, the dark rays of one person, may be the luminous rays of another person, and reciprocally; the calorific rays traverse some substances freely, which are therefore called diathermal, these substances, thus far, had been called opaque, because they transmit no ray commonly called luminous; now the words opaque and diathermal have no absolute meaning."
• "Physical therapy uses infrared rays, diathermal rays, heat, ultrasound, and a variety of things."
• "Thus certain stones become both opaque and diathermal, and as the heat is caused to vary, so do they show the complete gamut between the two extremes of total opacity and complete transparency to heat-rays."