From How Electricity Works:
Even though they didn’t fully understand it, ancient people knew about electricity. Thales of Miletus, a Greek philosopher known as one of the legendary Seven Wise Men, may have been the first human to study electricity, circa 600 B.C. By rubbing amber — fossilized tree resin — with fur, he was able to attract dust, feathers and other lightweight objects. These were the first experiments with electrostatics, the study of stationary electric charges or static electricity. In fact, the word electricity comes from the Greek elektron, which means amber.
The experiments wouldn’t continue until the 17th century. That’s when William Gilbert, an English physician and amateur scientist, began to study magnetism and static electricity. He repeated the research of Thales of Miletus, rubbing objects together and charging them by friction. When one object attracted or repelled the other, he coined the term “electric” to describe the forces at work. He said these forces developed because the rubbing action removed a fluid, or “humour,” from one of the objects, leaving an “effluvium,” or atmosphere, around it.
This concept — that electricity existed as a fluid — persisted into the 1700s. In 1729, English scientist Stephen Gray observed that certain materials, such as silk, didn’t conduct electricity. His explanation was that the mysterious fluid described by Gilbert could travel through objects or be hampered from traveling. Scientists even built jars to hold this fluid and study its effects. The Dutch instrument makers Ewald von Kleist and Pieter van Musschenbroek created what is now known as a Leyden jar, a glass jar containing water and a nail that could store an electrical charge. The first time Musschenbroek used the jar, he received a massive shock.
