Invention

Part 6 - Electro magnetic radiation

Francesco Maria Grimaldi noticed fringes in the shadow of an object placed in a beam of light and coined the term diffraction from the Latin word, 'to break into pieces'. His work, published in 1665, was studied by Isaac Newton.

James Gregory (1638–1675) observed the diffraction patterns caused by a bird feather, effectively the first diffraction grating. Isaac Newton believed light was a stream of particles, although his studies of the interference patterns created by the reflection of light between two surfaces (a flat surface and a touching spherical surface) supported the wave theory of light. He described, 'Newton's rings' in his 1704 treatise, 'Opticks'.

Newton's rival, Robert Hooke, and Christiaan Huyghens both believed that light was a wave but it was not until 1803 that Thomas Young used a ripple tank to demonstrated the idea of interference in the context of water waves. And, with his double-slit interferometer experiment, demonstrated that the crests and troughs of light waves can add or subtract to give bright and dark regions. He also suggested that each colour was produced by a different wavelength and that three sets of detectors in our eyes see these primary colors.

In 1804, Thomas Young observed fringes of colour in the shadow of a narrow card placed in a beam of light from a window. Another card placed to prevent the light beam from striking one of the edges of the narrow card caused the fringes to disappeared, thus supporting the wave theory of light. His experiments with the interference of light from reflection off thin films of soap and oil, and from Newton's rings, reflection off close pairs of micrometre grooves, and two slit diffraction, also supported the wave theory.

Within ten years, most of Young's work was extended by French physicist and engineer Augustin-Jean Fresnel who published calculations of diffraction in 1815 and 1818 that supported the wave theory of light. Fresnel also developed a multi-part lens for use in lighthouses known as "the invention that saved a million ships." It was much thinner and lighter than a similar conventional lens, but was capable of concentrating light into a narrow beam so that it was visible over greater distances. 

The first one of these was used in 1823 in a lighthouse at the mouth of the Gironde estuary, France; its light could be seen from more than 20 miles (32 km) out at sea. 

In 1865, James Clerk Maxwell, a Scottish scientist who studied Faraday's work, proposed that light was composed of oscillating waves in the same medium that caused electric and magnetic phenomena. He proposed that electric and magnetic fields moved as waves through space at the speed of light.

In 1855, he combined all of the current knowledge into a set of 20 differential equations and by 1873, he had reduced these to four partial differential equations (now known as Maxwell's Laws).

His unification of light and electrical phenomena prompted him to predict the existence of radio waves and inspired Albert Einstein to formulate the theory of special relativity. His work also provided the basis for quantum mechanics.

Maxwell believed that the propagation of light required a medium for the waves in the same way that water is a medium for ocean waves and air is the medium for sound waves. But the Michelson–Morley experiment could find no such 'luminiferous aether.' And, if the absolute frame of reference necessary for an aether did not exist, this eliminated the need to change the equations for a moving observer. 

Einstein's theory dispensed with the need for a stationary luminiferous aether, electomagnetic radiation could travel through the vacuum of empty space without the need for a medium.