1. A method of a non-contact exhaust gas measurement in metallurgical installations in hot and dirty air ( 8 ), in particular, in a converter ( 1 ) with a FTIR-spectrometer ( 2 ) which is mounted at a distance from a metallurgical installation and a measurement beam ( 3 ) of which is directed in a suitable opening ( 4 ) of an exhaust gas channel ( 6 ) as a measurement point in an exhaust gas ( 7 ), wherein in accordance with a measurement beam length in the exhaust gas ( 7 ), an exhaust gas volumetric segment in form of a cylinder of the measurement beam length is metrologically detected, and thereby obtained measurement values are presented by the FTIR-spectrometer ( 2 ) as spectra dependent on an exhaust gas composition and which enable, with inclusion of an exhaust gas temperature and using a previously established mathematical model that was obtained based on a temperature-dependent energy balance, calculation of the exhaust gas composition without a time delay, characterized in that a) firstly, the mathematical model, on which the calculation of the exhaust gas composition is based, is adapted to a hot and dirty surrounding air ( 8 ) that is also caught by the measurement beam ( 3 ), and to specific temperatures and exhaust gas compositions of a corresponding metallurgical installation, in particular, of a converter ( 1 ), and correspondingly is reworked anew, whereby reference spectra are produced by calibration, and b) in addition to spectroscopical determination of the exhaust gas composition, flow characteristics (laminar or turbulent components) of the exhaust gas are determined and used to support calculations when the model is established, c) the measurement point ( 4 ) for the FTIR-spectrometer ( 2 ) is so selected that a linear measurement beam ( 3 ), which is emitted by the FTIR-spectrometer ( 2 ), can be guided through the first front measurement opening ( 4 ) of the exhaust gas channel ( 6 ), then in a free passage through the exhaust gas ( 7 ) and, finally, through a rearside second measurement opening ( 5 ) of the exhaust gas channel ( 6 ) to a rearside cold background ( 10 ) outside of the exhaust gas channel ( 6 ).