In the experimental set up Davisson and Germer there is a filament of tungsten coated with barium oxide, which on heating with the electric current from a battery emits large number of electrons. There is a hollow metallic cylinder with a hole along the axis. This hollow metal cylinder surrounds the filament and is kept at negative potential, so that the electrons emitted from filament may form a convergent beam of electrons. The hollow metallic cylinder acts as cathode. The other cylinder with a fine hole along its axis is kept at positive potential with respect to the cathode, acts as anode. The cathode and the anode form an electron gun, by which a fine beam of electrons can be obtained under different accelerating potentials applied between cathode and anode. There is a nickel crystal cut along the cubical diagonal and one more instrument is electron detector rotating on a circular scale and is connected to a sensitive galvanometer to record the amount of current.