Balancing the Acorn Cup

I moved toward the dry stone rim of the park fountain. A hollow brown acorn cup sat loose on the curved masonry. I leaned my foam staff against the stone wall. I lifted the cup with my right hand and turned it upside down. It wobbled on its stem point and tipped over. I shifted its position until the round, empty hollow faced upward instead. Then I balanced a small grey pebble directly inside the bowl. The weight seated into the curved basin without shifting. The center of gravity holds steady.