the only drawing represents a self - contained cooking field . it is provided with a cooking surface 1 at cooking position 2 being formed , for instance , of a ceramic glass compound . below the cooking position 2 , there is provided a radiation heat source 4 constituted by an electric radiation heater . the emission coefficient of the heat source is designated ε 1 , and the radiation heat source 4 is insulated from its surroundings by a radiator insulation 6 such that only a small amount of the heat generated by the radiation heater 4 is emitted to the surroundings as lost heat . by for the greater amount of the heat generated is radiated from the heating surface a 1 of the radiation heater 4 in the direction of the lower surface of the cooking position 2 . during a cooking operation the bottom 10 of a cooking vessel or pot 8 is placed upon the cooking position 2 . the material 12 to be cooked is placed in the pot 8 . the degree of transmission of the cooking surface in the area of the cooking position 2 is very high so that the flow q 1 / 2 of heat radiated from the radiation heat source 4 at a heating temperature t 1 to the lower surface of the cooking position 2 can penetrate the cooking surface in the area of the cooking position 2 without any substantial loss . the flow q 1 / 2 of heat radiated from the radiation heat source 4 is thus received by the bottom surface 10 of the pot 8 , i . e . the surface a 2 to be heated , facing the cooking surface . an apparatus control 14 is connected to a control knob 16 and the radiation heat source 4 such that electric power fed to the radiation heat source 4 may be set by way of the control know 16 . in addition , the apparatus control 14 is provided with a device 17 for detecting the heating temperature t 1 and a device 18 for detecting the flow q 1 / 2 of heat . during the entire cooking operation , t 1 and q 1 / 2 are being monitored or detected continuously by way of the device 17 measuring the resistance at the radiation heat source 4 and the device 18 detecting the power level set for the cooking position 2 , respectively . furthermore , the apparatus control 14 is provided with an evaluation unit 18 and a storage or memory 20 storing a plurality of value pairs q 1 / 2 - t 1 derived from the flow q 1 / 2 of heat and the heating temperature t 1 and associated with reference emission coefficients ε 2 . the method functions in the manner hereinafter set forth with reference to the sole figure and relevant physical equations . the flow q 1 / 2 of heat from the electric radiation heat source 4 is derived from : wherein q equals q 1 / 2 , p equals the electric power fed to the radiation heat source 4 , u equals the electric voltage at the radiation heat source 4 and r equals the electrical resistance of the radiation heat source 4 . the equation substantially ignores any occurring heat loss . the physical connection between the heating surface a 1 and the surface a 2 to be heated can be derived from the above equation and the enlarged stefan - boltzmann - constant , as follows : q = c ( 1 , 2 ) ⁢ a ⁡ ( ( t 1 + 273 ) 4 + ( t 2 + 273 ) 4 ) = σ 1 ɛ 1 + 1 ɛ 2 - 1 ⁢ a ⁡ ( ( t 1 + 273 ) 4 - ( t 2 + 273 ) 4 ) , in which , in addition , to the equation symbols used supra c 1 , 2 is the radiation exchange value , a = a 1 + a 2 , t 2 the temperature of the surface a 2 to be heated and σ is the stefan - boltzmann - constant of σ = 5 . 67 * 10 − 8 wm − 2 k − 4 . the equation ignores the fact that the surfaces a 1 and a 2 are not identical in size and that a 1 is not a planar surface . it is also assumed that the two surfaces are disposed parallel to each other as is the case in the embodiment described supra . since in the present example the heating temperature t 1 is much higher than the temperatures t 2 to be expected at the bottom surface 10 of the pot 8 , and given a known heating temperature t 1 , a known emission coefficient ε 1 of the radiation heat source 4 , a known flow q 1 , 2 of heat from the surface a 1 to surface a 2 and a known construction of the self - contained cooking surface , the emission coefficient ε 2 of the surface to be heated may be defined as follows : the cooking position 2 is not heated . the cooking pot 8 , with the material to be cooked therein , is placed with its bottom 10 onto the cooking position 2 . the power level of the cooking position is set by the user by means of the control knob 16 , thus feeding electric current to the radiation heat source 4 to dissipate heat . at the same time , the heating temperature t 1 is raised . the flow q 1 , 2 of heat is detected by means of the evaluation unit 19 on the basis of the set power level and the heating temperature t 1 is detected by measuring the resistance at the radiation heat source 4 . the relations required for this purpose as well as the plurality relations between value pairs q 1 , 2 - t 1 and reference emission coefficients ε 2 stored in the storage 20 were previously determined by tests with similarly constructed self - contained cooking units , and stored in the memory 20 of the apparatus control 14 . in this manner , the deviations from theoretical physical relations referred to above and unavoidable heat losses were sufficiently compensated . once the actual heating temperature t 1 and the actual flow q 1 , 2 of heat are available in the evaluation unit 19 , the pair of values q 1 , 2 - t 1 derived therefrom is compared by in the evaluation unit 19 with stored value pairs q 1 , 2 - t 1 . the emission coefficient ε 2 associated with the most closely resembling value pair q 1 , 2 - t 1 is selected for further use in the apparatus control 14 . in the present embodiment , the method in accordance with the invention is practiced during the entire duration of heating surface a 2 . as long as the value of the emission coefficient ε 2 determined in this manner continues to change significantly , the system referred to above has not established itself . only after the ε 2 value stops changing , or its changes are within a previously established tolerable range , ε 2 or a mean value of ε 2 derived from the final values by conventional mathematical processes will be used for controlling the radiation heat source 4 and , therefore , the self - contained cooking surface . in the present embodiment , the detected emission coefficient ε 2 is used for pyrometrically measuring the temperature t 2 in a manner known per se . without prior knowledge of the emission coefficient ε 2 measuring temperature in this manner would be too imprecise for controlling the radiation heat source 4 of a cooking surface . because of different materials and different geometries of the bottoms of cooking pots the emission coefficient ε 2 varies widely from one pot to another . since usually a user makes use of different cooking pots 8 which do not have bottoms 10 of uniform emission coefficients ε 2 , the use of the emission coefficient ε 2 corresponding to any given used cooking pot 8 is required for a substantially precise control of the cooking temperature and the temperature of the cooked material 12 . they method may , however , also be practiced discontinuously , i . e . during predetermined points in time or for predetermined durations while the surface a 2 is being heated . in such an arrangement the system would have to have stabilized itself . this can be accomplished in ways well known to persons skilled in the art . practicing the method of the invention described above is not limited to the described embodiment . for instance , it could be applied to other household appliances such as other cooking implements . the method in accordance with the invention can be used in all situations in which the temperature t 2 of a heated surface is to be measure pyrometrically . it is also possible to defined the flow q 1 , 2 of heat by means of a sensor . setting of the power level of a cooking position 2 can , in the case , of upscale ovens or cooking appliances may take place by the apparatus control 14 as a function of cooked material selected by way of operating elements or detected by sensors of the apparatus control 14 .