The paper discusses the properties of the different effects which have been found to occur in the thermosphere and some conclusions which can be drawn with regard to the physics of the thermosphere. In the discussion of the diurnal variation the emphasis is on the behaviour of the diurnal amplitude in density during the solar cycle. At the height range between 200 and 300 km the amplitude has remarkably increased with decreasing solar activity. The relation between atmospheric density and temperature and the solar e.u.v. flux and the solar 10.7 cm flux-the latter serving as a convenient parameter-is discussed. The observational results for a phaseshift between the variations in the e.u.v. flux (or 10.7 cm flux) and the correlated variations in atmospheric temperature (or density) lie in the range between 0.5 and 2.3 days. During the solar minimum the atmospheric variations which parallel the 10.7 cm flux are far less pronounced than the variations correlated with geomagnetic activity. The phase shift derived from 45 geomagnetic storms and correlated density changes has been found to be 6 $\pm$ 3 (m.e.) h.