Although he was well known in the scientific world during his life, it was not until after his death that people realized how much he had changed the study of mathematics and physics. He used complex numbers to study electrical circuits and did a lot of work on electromagnetic wave theory which made it necessary to find new ways of working with differential equations. He did work on Maxwell's field equations and vector analysis. In fact, he was the inventor of Vector Calculus. Part of the ionosphere is co-named after him: the Kennelly-Heaviside layer. His personality was very eccentric and he is a good example of what many people think of as a mad scientist.