The Leyden jar is one of the earliest forms of a capacitor, invented in the 18th century, that could store electric charge. This invention marked a significant advancement in the study of electricity, allowing scientists to experiment with electrical phenomena more safely and effectively. The Leyden jar played a crucial role in the understanding and development of electrostatics, demonstrating that electric charge could be stored and released, paving the way for future advancements in electrical technology.