Portrait of the German physicist Georg Simon Ohm (1787-1854). His ambition was to achieve a university appointment, but he spent a long time teaching in high schools while he researched the relationship between electrical current and potential difference. In 1827 he showed that the flow of current was proportional to the potential difference and inversely proportional to the resistance of the conductor. This relationship is known as Ohm's law. Initially Ohm's work met with severe criticism, but gradually he gained renown and respect (and a professorship at the University of Munich). The unit of resistance is called the ohm in his honour.