The glass does not fall forever, silly. It pumps up and pumps down depending on barometric pressure. Mariners use this indication of pressure to anticipate wind and weather, which as you may know is closely tied to changes in pressure of air masses due to their differing temperatures. These differences are attributable to planetary motion, differing thermal index values of various surfaces such as sea, land, pavement and so on, and air movements caused by geophysical configurations. In turn, these temperature differences cause air to move up, down and sideways in large and complex patterns.

Louis MacNeice, however, did not know all this, one suspects. Otherwise he never would have said the glass will fall forever.

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