Figure denotes a rod whose ends are in thermal contact with a hot reservoir at temperature T1 and a cold reservoir at temperature T2.  The ends of the rod are covered with insulating medium, so the transport of heat is along the slit, not through the sides. The particles at the hot reservoir have greater vibration energy. This energy is transmitted by attack to the atoms at the end face of the slit. These atoms in change transfer of heat through an object in which heat is transported without direct mass transport is called as conduction.