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The purpose of this Letter is to present some results of a recent experiment that strongly suggest that quasi‐periodic X‐ray and optical pulsations of several‐seconds duration are coherent. Until now, a thorough investigation of this point has been hindered by a lack of coordinated simultaneous observations from which direct comparisons could be made. Nevertheless, striking similarities in the temporal and spatial features of these pulsations have led to speculation that the two are physically related [Hilliard and Shepherd, 1966]. Clearly, it is of considerable importance to determine if such speculation has any basis in fact since energy and flux considerations indicate that optical and X‐ray effects reflect the precipitation of electrons of different energies (approximately 1–15 kev for the luminosity and greater than 30–40 kev for X rays reaching normal balloon altitudes). In addition to the lack of simultaneous observations, the situation regarding pulsating auroras (that is, visual and X‐ray) is further complicated by the apparent complexity of the phenomena. Optically, at least, several distinct types of pulsating forms are known and have been classified recently by Cresswell and Davis [1966]. No comparable classification exists at present for X‐ray pulsations, but a study by Barcus et al. [1966] has revealed some of their more obvious properties.

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