This paper presents a review of the observational evidence on the direction of rotation of the spiral pattern in ordinary and barred spirals. The reasons for the divergences in the interpretation of various objects according to the classical (Slipher-Hubble) viewpoint and according to the Stockholm school are analyzed. A list of critical objects is assembled which permits an unequivocal solution of the ambiguities from a variety of criteria, both classical and new, applied to structural details visible on the best Mount Wilson-Palomar photographs, supplemented by new Lick spectra. In all cases where the required data are available, these criteria indicate that the arms are trailing in the rotation.
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A 1958 study studied this question.