The Moon’s Silent Pull

The Moon’s pull raises and lowers Earth’s oceans about 2 times a day on most coasts; this tidal cycle repeats at intervals of about 12 hours 25 minutes. We cannot see this force directly, but we notice it in the shifting of stones wetted on the shore, in the slow climb of the waterline in the harbor. In its visualized form, the sea would seem to be responding millimeter by millimeter to the call of an invisible hand.