On the character of variability of SS 433 spectrum with the 6-day period (June-August, 1981)

New spectral data (∼280 spectra) for the object SS 433 obtained during 35 nights in the summer of 1981 with the 1000-channel spectrophotometer of the 6-meter telescope within the range λλ 5300-7900 A with a resolution of ∼4 A are analysed. The behaviour of hydrogen and helium relativistic line profiles with time is studied and the following parameters for them are determined: equivalent widths Wλ, central intensities Rc, halfwidths Δλ(1/2) and radial velocities z. No full similarity in the behaviour of the parameters listed, either in the ''positive'' or in the ''negative'' systems of these lines, has been found. A detailed study has been given to the radial velocity variations in the main components of relativistic hydrogen lines Hα and Hβ with a 6-day (nutation) period, a phase relation of the amplitude of these variations with precessional period has been revealed. It is the first time that significant and considerable variation of Wλ and Rc components of the relativistic line Hα- with nutation period has been detected, a possible interpretation of this variation is given, estimates are made of some physical and geometrical parameters of relativistic jets. A phase relation of W-barλ variations of relativistic hydrogen lines in the spectrum of SS 433 with the precession period has been found