Author`s previous results for the description of the jet exiting from a nozzle into still air is referenced and commented on. Both the plane jet and the round jet are treated, the latter one also as a heated jet. Empirical relations are given for the four parameters which exclusively describe the flow field. It is shown that these are related to the geometry, i.e. to the size and shape of the nozzle. The energy distribution in the jet is examined under the sole assumption that the jet`s velocity field is self similar. It is concluded that the energy in the turbulent fluctuations is convected and dissipated similarly to the energy in the main flow.