Two resistances $\mathrm{R}_1=\mathrm{X} \Omega$ and $\mathrm{R}_2=1 \Omega$ are connected to a wire AB of uniform resistivity, as shown in the figure. The radius of the wire varies linearly along its axis from 0.2 mm at $A$ to 1 mm at $B$. A galvanometer (G) connected to the center of the wire, 50 cm from each end along its axis, shows zero deflection when A and B are connected to a battery. The value of $X$ is $\_\_\_\_$ .