Acoustic Mapping Line

Midday observation required an audible distance reference to complement the visual optic. Near the stone capstone's edge, I discovered a dry acorn shell cap and a stiff, dropped twist-tie made of black coated wire. I uncoiled the wire into a rigid horizontal antenna with both hands. Forcing one end firmly into the crumbly mortar joint, I balanced the light acorn cup across the free projecting tip. When afternoon gusts strike the pillar, the suspended shell oscillates and taps against the rough stone rim with a measured rhythm. Audible pulse calibrated. The outer airspace is now tracked.