Two charged conducting spheres \( S_1 \) and \( S_2 \) of radii \( 8 \, \text{cm} \) and \( 18 \, \text{cm} \) are connected to each other by a wire. After equilibrium is established, the ratio of electric fields on \( S_1 \) and \( S_2 \) spheres are \( E_{S1} \) and \( E_{S2} \) respectively. The value of \( \frac{E_{S1}}{E_{S2}} \) is ______.
