Problem 2.247

One end of a rod, enclosed in a thermally insulating sheath, is kept at a temperature $T_{1}$ while the other, at $T_{2 \cdot}$. The rod is composed of two sections whose lengths are $l_{1}$ and $l_{2}$ and heat conductivity coefficients $x_{1}$ and $x_{2} .$ Find the temperature of the interface.