A spherical liquid drop of radius \( R \) acquires the terminal velocity \( v_1 \) when falls through a gas of viscosity \( \eta \). Now the drop is broken into \( 64 \) identical droplets and each droplet acquires terminal velocity \( v_2 \) falling through the same gas. The ratio of terminal velocities \( \dfrac{v_1}{v_2} \) is ______.
