Humans have witnessed the phenomenon of electricity in the forms of lightning, static electricity, and magnetism since the dawn of time. Electricity was not seriously studied, however, until the 17th century. Early electrical pioneers studied various electrical phenomena, and built devices both to generate and to measure electrical charges. In 1892 Hendrik Antoon Lorentz, a Dutch physicist, advanced the electron theory. This theory, which explains electricity as a reaction between positively and negatively charged electrons, formed the basis for modern electrical theory. Based on Lorentz's work, early engineers such as Thomas Edison pioneered methods allowing the widespread use of electricity as a power source.