Here is used a notation different from Kirchhoff's. Here, the emitting power E (T, i) denotes a dimensioned quantity, the total radiation emitted by a body labeled by index i at temperature T. The total absorption ratio a (T, i) of that body is dimensionless, the ratio of absorbed to incident radiation in the cavity at temperature T . (In contrast with Balfour Stewart's, Kirchhoff's definition of his absorption ratio did not refer in particular to a lamp-black surface as the source of the incident radiation.) Thus the ratio E (T, i) / a (T, i) of emitting power to absorptivity is a dimensioned quantity, with the dimensions of emitting power, because a (T, i) is dimensionless. Also here the wavelength-specific emitting power of the body at temperature T is denoted by E (λ, T, i) and the wavelength-specific absorption ratio by a (λ, T, i) . Again, the ratio E (λ, T, i) / a (λ, T, i) of emitting power to absorptivity is a dimensioned quantity, with the dimensions of emitting power.