the apparently paradoxical behavior of the Leyden jar as a device for storing large amounts of electrical charge, by coming up with the single fluid, two states theory of electricity. In 1791, Italian Luigi Galvani published his discovery of bioelectricity, demonstrating that electricity was the medium by which nerve cells passed signals to the muscles. Alessandro Volta's battery, or voltaic pile, of 1800, made from alternating layers of zinc and copper, provided scientists with a more reliable source of electrical energy than the electrostatic machines previously used. 19th-century developments Electrical engineering became a profession in the late 19th century. Practitioners had created a global electric telegraph network and the first electrical engineering institutions to support the new discipline were founded in the UK and US. Although it is impossible to precisely pinpoint a first electrical engineer, Francis Ronalds stands ahead of the field, who created a working electric telegraph system in 1816 and documented his vision of how the world could be transformed by electricity. Over 50 years later, he joined the new Society of Telegraph Engineers (soon to be renamed the Institution of Electrical Engineers) where he was regarded by other members as the first of their cohort. The donation of his extensive electrical library was a considerable boon for the fledgling Society. Development of the scientific basis for electrical engineering, with the tools of modern research techniques, intensified during the 19th century. Notable developments early in this century include the work of Georg Ohm, who in 1827 quantified the relationship between the electric current and potential difference in a conductor, Michael Faraday, the discoverer of electromagnetic induction in 1831. In the 1830s, Georg Ohm also constructed an early electrostatic machine. The homopolar generator was developed first by Michael Faraday during his memorable experiments in 1831. It was the beginning of modern dynamos – that is, electrical generators which operate using a magnetic field. The invention of the industrial generator in 1866 by Werner von Siemens – which did not need external magnetic power – made a large series of other inventions in the wake possible. In 1873, James Clerk Maxwell published a unified treatment of electricity and magnetism in A Treatise on Electricity and Magnetism which stimulated several theorists to think in terms of fields described by Maxwell's equations. In 1878, the British inventor James Wimshurst developed an apparatus that had two glass disks mounted on two shafts.