S-BAL42 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.39571\,\lambda^2}{\lambda^2 - 0.0112219} + \frac{0.0718505\,\lambda^2}{\lambda^2 - -0.0252117} + \frac{1.27129\,\lambda^2}{\lambda^2 - 134.498}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.92 \times 10^{-6} + 2(1.21 \times 10^{-8})\,\Delta T + 3(-3.34 \times 10^{-11})\,\Delta T^2 + \frac{4.43 \times 10^{-7} + 2(5.78 \times 10^{-10})\,\Delta T}{\lambda - 0.195}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$