Two iron solid discs of negligible thickness have radii \( R_{1} \) and \( R_{2} \) and moment of inertia \( I_{1} \) and \( I_{2} \), respectively. For \( R_{2} = 2 R_{1} \), the ratio of \( I_{1} \) and \( I_{2} \) would be \( \frac{1}{x} \), where \( x = \) ______.