We have utilized the tip of a scanning tunneling microscope to perturb a specific local structure (the C defect) of Si(100) at 80 K, and observed the dynamical symmetric⇔buckled transition of the surrounding dimers. The observed large-scale transition implies that the configuration of the dimers is determined by a detailed balance among many elastic long-range forces generated by the surrounding C defects. ©1998 American Institute of Physics.