Equation Icon  μ 1 μ σ ρ Δu = -u u u Δg σρ, (138 ) 2 Δ ενλτσ = 1ενλτσgμρΔg μρ, (139 ) 2 Δn = − n-(gσρ + uσu ρ)Δg . (140 ) 2 σρ