The nature of ball lightning (BL) is pure electric and can be described by simple equations following to elementary considerations of equality of translational acceleration and velocity of the ions and electrons, a spherical-like dipole BL as a whole and balance of the energy influx of atmospheric electricity and radiation losses. From these equations follows a linear relationship between the size of BL and the tension of the atmospheric field E. A typical size of the fireball (FB) r ~ 5 cm corresponds to the calculated electron temperature T(e) ~ 8000K at a pressure p = 1 at with a horizontal component of the electric field E a few kV/cm. I estimate the energy of BL and characterize the conditions of its possible experimental generation. The estimation is given of the surface tension of BL. The possibility of the hot and the most realistic thermodynamic non-equilibrium cold BL is discussed. Here we presented preliminary evaluations preceding the more detailed work in Arxiv.org [11].