The attractions of the sun and moon occasion tides in the atmosphere similar to those of the ocean. The effects are, however, so inconsiderable in comparison with the disturbances produced in the equilibrium of the atmosphere by other causes, that hitherto observation has not succeeded in affording any clear or decisive evidence of them. The phenomenon however has a very considerable philosophical interest as a farther exemplification of the universality of the principle of gravitation. As the ebb and flow of the atmospheric tide must be greatest in the vicinity of the equator, and as moreover the ordinary equilibrium is less disturbed by irregular causes in that region of the globe than in the temperate zones, it was reasonable to expect that the existence of a tide in the atmosphere, depending on the position of the sun or moon relatively to the meridian of the place, would be shown, if at all, by observations made within the tropics; and that the most favourable situation for such observations might be that of a small island surrounded by a considerable extent of ocean, and therefore comparatively free from the atmospheric disturbances occasioned by variations of the terrestrial surface; and where also the tides of the ocean should be small.