\( \left(P+\frac{a}{\nu^{2}}\right)(V-b)=RT \) represents the equation of state of some gases. Where \( P \) is the pressure, \( V \) is the volume. \( T \) is the temperature and \( a \), \( b \), \( R \) are the constants. The physical quantity, which has dimensional formula as that of \( \frac{b^{2}}{a} \), will be:
