(1):

(n.) 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).

(2):

(n.) Tendency to emission; comparative facility of emission, or rate at which emission takes place, as of heat from the surface of a heated body.

(3):

(n.) Tendency to emission; comparative facility of emission, or rate at which emission takes place;