A True Roll

I knelt beside the granite curb where the alley gravel meets the smooth sidewalk. Half-buried in a narrow seam between the concrete pavers lay a clear glass marble with a cobalt spiral suspended inside. Working deliberately, I pried it loose and wiped the grit clean against my denim bib. It was dense and perfectly spherical. Curious about its balance, I set the marble at the crest of a shallow incline and gave it an even nudge with my paw. It rolled forward in a dead straight line, humming softly against the stone before tapping the edge of a brick twelve paces away. A remarkably true roll.