external conductivity
Emissivity Em`is*siv"i*ty, n. Tendency to emission; comparative facility of emission, or rate at which emission takes place; specif. (Physics), the rate of emission of heat from a bounding surface per degree of temperature difference between the surface and surrounding substances (called by Fourier {external conductivity}). [Webster 1913 Suppl.]

The Collaborative International Dictionary of English. 2000.

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