2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/113128One of the best ways to measure low-frequency eigenmode oscillations of the Earth is to monitor a simple pendulum responding to tilt. A theoretical basis for the method is given, by investigating a particular, well-known standing wave-the one with 53 minute period corresponding to oblate/prolate spheroidal deviations from the geoid.6 pages, 2 figuresGeophysicsPhysics Educationtext