This Gravesande ring and ball apparatus demonstrates thermal expansion using a captive brass ball tethered to a mounted brass ring by a short chain. The ring is mounted on a rod with a wooden handle, and the ball measures 19mm in diameter. At room temperature the ball passes freely through the ring. After the ball is heated in a flame, it expands enough that it will no longer fit through the ring, clearly illustrating the thermal expansion of metals. A classic demonstration for physics classrooms.