The magnitude of the change in oxidising power of the $MnO_4^ - /M{n^{2 + }}$ couple is x $\times$ 10^$-$4 V, if the H⁺ concentration is decreased from 1M to 10^$-$4 M at 25$^\circ$C. (Assume concentration of $MnO_4^ -$ and $M{n^{2 + }}$ to be same on change in H⁺ concentration). The value of x is ___________. $\left[ {Given\,:{{2.303RT} \over F} = 0.059} \right]$