So I keep hearing that the maxwell equations are variant under Galilean transform. Tired of simply accepting it without seeing the maths, I decided to do the transformation on my own. To make things easy, I only tried Gauss' law, furthermore I constricted the field to the x axis only. So I have E(x,t). ∇°E(x,t)=ρ(x)/ε So now I will transform to another inertial frame x' that is moving with speed u with respect to the original frame x. x'=x-ut t'=t What originally was ∂E/∂x=ρ(x)/ε became ∂E/∂x'-(1/u)∂E/∂t=ρ'(x')/ε. Is this basically what they mean when they say it isn't invariant? I looked at this again, and noticed that if the electric field is independent of time, then the Galilean transform of this turns out to be invariant, coincidence?