Oliver Heaviside FRS (1850–1925) was a scientific maverick and a gifted self-taught electrical engineer, physicist and mathematician. He patented the co-axial cable, pioneered the use of complex numbers for circuit analysis, and reworked Maxwell's field equations into the more concise format we use today. In 1891 the Royal Society made him a Fellow for his mathematical descriptions of electromagnetic phenomena. Along with Arthur Kennelly, he also predicted the existence of the ionosphere. Often dismissed by his contemporaries, his work achieved wider recognition when he received the inaugural Faraday Medal in 1922. Published in 1912, this is the last of three volumes summarising Heaviside's enormous contribution to electromagnetic theory. It includes a review of his work on waves from moving sources, and an appendix on vector analysis that compares its merits to quaternions.