X-ray reflectometer for liquid surfaces using a rotating anode X-ray generator at the Institute for Experimental and Applied Physics at the University of Kiel, Germany. The liquid samples require that the sample surface is kept horizontal at all times. The reflectometer employs the beam divergence of the generated X-rays to select a vertically tilted beam impinging on the sample surface by a pair of slits located on both ends of an evacuated incident flight tube (cylindrical steel tube visible on the left side of the image). A pair of slights mounted on both ends of the detector flight tube defines the detection angle (right side of the image). For a reflectivity scan where the incident and detection angle relative to the sample surface are equal, only one motor (black housing in the center below the brass reels) is required which translates the sample stage vertically. The incident and detector flight tubes follow that motion through a mechanical coupling by being posed on reels. These brass reels supporting the arms carrying the flight tubes are visible in the center of the image. The cylindrical cell in the center with the vertically emerging metal vacuum tube contains the liquid sample in a trough. The rotating anode is contained in the metal shielding box visible on the far left. The monochromator crystal and scintillator detector are located on the far right, the cylindrical detector housing being inclined downwards corresponding to the take-off angle from the monochromator. To record the diffuse scattering in the vertical scattering plane, the detector stage can be independently moved vertically. References: T.Seydel, PhD thesis, University of Kiel (2000); T. Seydel, https://hal.science/hal-03762410; and T.Seydel et al., Rev.Sci.Instrum. 74, 4033-4040 (2003) ⟨DOI: 10.1063/1.1599068⟩.