Two thousand years ago, a number of Greek and Roman philosophers (notably Thales of Miletus and Pliny who was killed while trying to study the eruption of Vesuvius of the year 79 when Pompeii and Herculaneum were buried beneath the ashes) had noticed the strange antics of bits of straw and of feather which were held near a piece of amber which was being rubbed with a bit of wool. The schoolmen of the Middle Ages had not been interested in this mysterious "electric" power. But immediately after the Renaissance, William Gilbert, the private physician of Queen Elizabeth, wrote his famous treatise on the character and behaviour of Magnets. During the Thirty Years War Otto von Guericke, the burgomaster of Magdeburg and the inventor of the air-pump, constructed the first electrical machine. During the next century a large number of scientists devoted themselves to the study of electricity. Not less than three professors invented the famous Leyden Jar in the year 1795. At the same time, Benjamin Franklin, the most universal genius of America next to Benjamin Thomson (who after his flight from New Hampshire on account of his pro-British sympathies became known as Count Rumford) was devoting his attention to this subject. He discovered that lightning and the electric spark were manifestations of the same electric power and continued his electric studies until the end of his busy and useful life. Then came Volta with his famous "electric pile" and Galvani and Day and the Danish professor Hans Christian Oersted and Ampere and Arago and Faraday, all of them diligent searchers after the true nature of the electric forces.