Nikola Tesla was a Serbian American inventor, electrical engineer, mechanical engineer, physicist, and futurist best known for his contributions to the design of the modern alternating current (AC) electricity supply system. Nikola Tesla is one of those rare people who have marked their age and caused great changes in it, not only in the domain of the immediately applicable inventions, but also in the domain of new ideas and technology of the future. He is one of those people who have inspired many followers and fellow scientists. Nikola Tesla has left to us, for further study and research, not only the published materials, but also a large number of personal notes. Here is one of Nikola Tesla's most important lectures. A lecture delivered before the American Institute of Electrical Engineers, Columbia College, N.Y., May 20, 1891.