- This is an analysis of the behavior of the dependence of eta = rho(sub 2)/rho(sub 1) as a function of M(sub 1). For the maximal compression degree eta(sub m) = max eta(M(sub 1)), a similarity law indicating that the quantity eta(sub m) represents a universal function is established. To demonstrate this, a shock propagating in a nonionized monoatomic polytropic gas is considered. From this, the behavior of numerically calculated shock adiabatics eta = eta(M(sub 1)) is obtained. By comparing the proposed theory with existing experiments for argon, it is observed that the proposed theoretical model is in good agreement with the experiment, inspite of the fact that the theory only takes into account the first ionization mechanism of the energy losses.