Searle's bar method is an experimental procedure to measure the thermal conductivity of the given material. A bar of material is heated by steam on one side (end) and the other side (end) is cooled down by the water while the length of the bar is thermally insulated.

This is done until the temperature gradient at all the points along the bar becomes the same. That is in the steady state the difference in the temperature of a material is the same at all points. Therefore, the temperature gradient along the bar is the same at all points.