A cloud chamber is a scientific instrument used to visualize the passage of ionizing radiation. The technique involves cooling a chamber filled with a gas vapor until the gas reaches its saturation point, causing visible condensation. When energetic particles, such as alpha or beta radiation, pass through the gas, they excite or ionize the gas molecules, creating trails of charged particles. These ionization trails act as condensation nuclei, causing water vapor to condense and form visible tracks, allowing scientists to measure the energy and trajectory of the passing radiation without the aid of electricity.