Oliver Heaviside’s life, spanning the years 1850 to 1925, began and ended in squalid surroundings. He was never entirely free of the dark melancholy that characterized his private as well as public persona. Beyond a little primary schooling, he was self-educated. His reading of James Clerk Maxwell’s Treatise On Electricity And Magnetism was a revelation. He mastered the mathematics and went on from there. His insights into the behavior of electricity, inside and outside of circuits, were incisive and he knew how to communicate these insights to an eager audience of electrical engineers and theoreticians.
Heaviside gave us coaxial cable and the small coils placed in series with every telephone line, counter-intuitively improving clarity by providing inductive loading. But his great gifts to twentieth-century electrical engineering consisted of concepts. Some were alterations to existing theory. He described what is now known as the Heaviside layer and explained the behavior of characteristic impedance, that puzzlement to generations of apprentice technologists. He proposed a number of terms, some a little fanciful, that we use to describe electrical parameters:
Admittance, the inverse of impedance.
Electret, a dielectric material that has and retains an electrostatic charge. It is analogous to the permanent magnet.
Impedance, the opposition in a load or conductor to the flow of current. It is made up of resistance and, added vectorially, inductive or capacitive reactance. Like resistance, it is measured in ohms.
Inductance, the property whereby change in current in a conductor induces a counter voltage in itself or in a nearby conductor. (There is self-inductance and mutual inductance.) The unit of inductance is the henry.
Permeability, the amount a material can be magnetized in the presence of an electric field. All materials including a pure vacuum are permeable to some extent. Soft iron, often used in a magnetic core, is highly permeable.
Permittance or susceptance, as it was later known, the reciprocal of magnetic reluctance. It is analogous to conductance in an electrical circuit.
Reluctance, in magnetic circuits, parallels resistance in electrical circuits. Reluctance opposes magnetic flux just as resistance limits electrical current. But the big difference is that resistance causes electrical energy to be lost forever, dissipated in the form of heat, while reluctance causes magnetic energy to be stored in a magnetic field so that when the field collapses, the magnetic energy returns to the magnetic circuit.
For mathematicians, Heaviside’s greatest contribution was in discovering how to simplify 12 of James Clerk Maxwell’s 20 field equations with complex calculus expressions, into a much simpler algebraic formulation involving a mere four equations:
ε E = ρ
∇ × E = − μ ∂ H/ ∂t
∇ · μ H = 0
∇ × H = k E + ε ∂ E/ ∂t
where E represents the electric field, H represents the magnetic field, ε is the permittivity, μ is the permeability, ρ is the charge density, and k is the conductivity.