Some experimental and theoretical comparisons have been made of the effectiveness of four techniques which have been commonly used for monochromatizing X‐radiation for use in diffraction studies of liquids: monochromator crystals, curved or flat; β‐filter and pulse‐height analyzer; balanced dual filters. The β‐filter/pulse‐height analyzer system alone results in unacceptable error, at both low and highs(s= 4πλ−1sinθ). Dual filters can be made quite effective, actually approaching the resolution possible with monoch