Which of the following is Cauchy’s formula?

• A. μ=A+Bλ2+Cλ4
• B. μ=A+\(\frac {B}{\lambda^2} + \frac {C}{\lambda^4}\)
• C. μ=A+B+CBλ
• D. μ=A+\(\frac {B}{\lambda}+\frac {C}{\lambda^2}\)