Abstract: that for practial emitters the measured values of the constant in Richardson's equation are always less than 120 A/cm2T is due to the nonuniformity of work function not to the reflection of electron at the surface potential barrier. For monocrystal faces, the measured and theoretical values agree. In fact, emission comes from those surface electrons already penetrated into the potential barrier before excitation. These furface electrons can neither move freely through vacuum non through conduction band of the metal, otherwise different crystal faces would not have different work functions. The adsorption of foreign atoms increases the energy and number of the surface electron and then lowers the work function.