Prism Alignment

I descended to the final stair tread. A clear plastic wrapper, stiff and folded into a triangle, lay wedged in a concrete seam beside a smooth gray pebble. I tested the pebble's heft with my left foot; mass was adequate. Using both hands, I wedged the stone against the lower fold of the plastic. The angled sheet rose upright at sixty degrees. Low morning sunlight struck the transparent edge, fracturing into a crisp spectrum band across the gray step. I stood back fifteen millimeters to observe the beam. Focus confirmed.