A new determination of h /√( em 0) by electron diffraction

The wave-length of electrons of energy 40 to 60 keV has been determined from the diffraction patterns of transmission specimens of alkali halides and metals. The accelerating potential was measured by a special potentiometer and hence the quantity h/√(em0) was derived. The results using specimens of sodium chloride, potassium chloride, caesium iodide and aluminium were mutually consistent and their mean value was h/√(em0) = (1*00156 ± 0.00010) x 10-8 (e in e. s. u.). Specimens of gold and lithium fluoride gave anomalous results.