## 1873 – electromagnetic waves

In 1873, James Clerk Maxwell published a textbook called, “A Treatise on Electricity and Magnetism” which compiled all known electromagnetic theory at that date including some of his previous work on equations related to electricity and magnetism. Maxwell theorized that light was an electromagnetic wave and tied together light, electricity and magnetism which had been previously considered to be three different things. In 1887, Hertz confirmed this.

His previous work contained eight basic equations, but this treatise concentrated on four equations which would eventually become known as “Maxwell’s Equations”:

• Ampere’s Law – developed by Ampere, provides a mathematical description of the connection between an electric current and a magnetic field and demonstrates that electricity produces a magnetic field. Maxwell added a correction to this.
• Faraday’s Law – developed by Faraday, provides a mathematical description of how a changing magnetic field can induce an electric current in a conductor. This is effectively the inverse of Ampere’s law.
• Gauss’ Law – developed by Gauss, shows that electric charge that is static also generates an electric field. This is related to Coulomb’s law.
• The Fourth Equation – also known as Gauss’ Law for Magnetism, shows that magnetic field lines are closed loops, with no set starting or stopping point. This also seems to show that magnetic monopoles can’t exist.

These four equations were eventually reworked by Heaviside, Gibbs and Hertz into their modern form.

PRECURSOR:
1783 – Coulomb’s law
1820 – electricity and magnetism combined – Oersted
1826 – Ampere’s law
1834 – Lenz’s law
1835 – Gauss’ law derived – Gauss
1843 – quaternions – Hamilton
1861 – “On Physical Lines of Force” – Maxwell
1864 – “A dynamical theory of the electromagnetic field” – Maxwell
1867 – Gauss’ law published – Gauss

CONCURRENT:

SUBSEQUENT:
1884 – vector equations – Heaviside
1892 – Lorentz force