Last post we covered the foundation for which spectroscopy was built, the work of Sir William Herschel, who discovered the infrared through his experiments. Continuing our journey, James Clerk Maxwell was a Scottish mathematician and scientist responsible for the classical theory of electromagnetic (EM) radiation, which was the first theory to describe electricity, magnetism, and light as different manifestations of the same phenomenon.

Maxwellâ€™s equations for EM are recognized as the â€œsecond great unification in physicsâ€ (the first was realized by Isaac Newton after his publication of â€œA Dynamical Theory of the Electromagnetic Fieldâ€ in 1865). In his publication Maxwell demonstrated that electric and magnetic fields travel through space as **waves** moving at the speed of light (note that we will revisit light traveling as a wave in a later post). Importantly, the phenomenon of the unification of light and electrical led to his prediction of the existence of radio waves.

Maxwell had studied and commented on electricity and magnetism as early as 1855 when his paper â€œOn Faradayâ€™s lines of forceâ€ was read to the Cambridge Philosophical Society. This paper presented a simplified model of Faradayâ€™s work about how electricity and magnetism are related. Importantly, Maxwell reduced all current knowledge into a linked set of differential equations with 20 equations and 20 variables.

Later Oliver Heavidside reduced the complexity of Maxwellâ€™s Theory down to four partial differential equations, known now collectively as Maxwellâ€™s Laws or Maxwellâ€™s Equations.

Maxwellâ€™s quantitative connection between light and EM is considered one of the greatest accomplishments of 19th century mathematical physicists.

Before we go, we are leaving you all with one last fun fact about Maxwellâ€¦ Maxwell was interested in the study of color vision and from 1855 to 1872 he published a series of investigations concerning the perception of color, color-blindness, and color theory.

Maxwell used recently developed linear algebra to prove Thomas Youngâ€™s theory that the reason that two complex lights (i.e., composed of more than one monochromatic light) could look alike but be physically different is because colors are perceived through three channels in the eyes (i.e., the trichromatic color theory). He did this by inventing color matching experiments and colorimetry.

These experiments further extended to Maxwellâ€™s development of color photography, whereby he proposed that if:

- Three black-and-white photographs of a scene were taken through red, green, and blue filters,
- Transparent prints of the images were projected onto a screen using three projectors equipped with similar filters and superimposed on the screenâ€¦
- The result would be perceived by the human eye as a complete reproduction of all colors in the scene.

_This series will be continued with Max Planckâ€¦ _