ENDNOTES  page 398

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Ent: *

Gorgias (483–375 BC) Greek pre-Socratic, wrote On Nature or the Non-Existent.  It was a refutation of the Eleatic thesis (that there can be no creation, being cannot come from non-being, a thing cannot arise from that which is different from it).  Only fragments of his work survived.  Gorgias argued that nothing exists but if something did exist nothing can be known of it and even if something can be known, this knowledge cannot be communicated and even if communicated, it cannot be understood.  He wanted to show it was as easy to demonstrate the Eleatic idea, that being is one, unchanging & timeless, as it was to prove that being has no existence at all.  He also seems intent on the notion that true objectivity is impossible since the human mind can never be separated from its possessor.  Philosophers have labelled Gorgias a nihilist, one who believes nothing exists, or that the world is incomprehensible, and that the concept of truth is fictitious.

 

 

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wave-motion of light: *

The initial wave concept surfaced in 1665 when Hooke (1635–1703) developed a "pulse theory" to explain the origin of colours, comparing the spreading of light to waves in water.  C. Huygens (1629–1695) worked out a mathematical wave theory & proposed light was emitted in all directions as waves in a medium he called the Luminiferous ether.  T. Young (in 1800) discovered sound waves interfered with each other & went on to show that light behaved as waves.  He proposed different wave lengths caused different colours & explained colour vision.  Euler supported wave theory & argued diffraction could be explained with such a theory.  AJ Fresnel developed his own wave theory (1817); in 1821 he used mathematical proofs to claim that polarization could be explained only if light wave were entirely transverse. 

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While this placed Newton’s corpuscular theory of light in doubt, wave theory required a medium & Huygens’ luminiferous aether began to lose support in the late 19th century.  Newton's theory implied that light would travel faster in a denser medium; wave theory implied the opposite.  Since the speed of light could not be measured accurately, it was impossible to decide between wave theory & Newton.  However in 1850 Foucault was able to make a sufficiently accurate measurement; his results supported the wave theory.

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In 1845 Faraday discovered the plane of polarization of linearly polarized light is rotated when the rays travel along the magnetic field direction in the presence of a transparent dielectric (Faraday rotation).  This linked light to electromagnetism.  In 1847 he proposed light was a high-frequency electromagnetic vibration, able to propagate in the absence of a medium (such as the ether).

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Inspired by Faraday Maxwell began his study electromagnetic radiation & light; he discovered self-propagating electromagnetic waves travelled through space at a constant speed (the speed of light as previously measured).  In 1862 he concluded light was a form of electromagnetic radiation & provided mathematical descriptions of the behaviour of electric & magnetic fields, (Maxwell's equations, 1873).  Maxwell's theory & later experiments by Hertz led directly to the development of radio, radar, television, electromagnetic imaging & wireless communications.

see image below