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York University
Natural Science
NATS 1870

CrossDisciplinary Examination of Colour How do we see colouroPhysicsWhite light which is composed of all wavelengths 400700nm of colour falls into the colour object eg red paper oChemistryMolecules in the dye in paper absorb all wavelengths of light expect red so only red wavelength of the light get reflected off the paper oPhysiology1 Eye Cones detect reflected red wavelengths pass this into to brain through the optic nerve 2 Brain interprets this information from eyes synthesizes a perception of colour ie red History of Colour Ancient GreeksAntiquities Ancient Greeks OpticsSome of the key ideas in their theories wereoseeing light and darkness as separate entities from each otheroexplaining light in terms of one of the four natural elements fireomixing of light with human visionoIntromission vs Extramission theories of visionoearly forms of waveversusparticle theoriesomathematical explanationsolinear 1D colour classification systemAnaximander Light and Dark ConfusionThe first scientists but viewed light and dark as two separate entities independent of each other rather than darkness simply being the absence of light Even the daylight of our sky was considered separate from the light of the SunPythagoras Colour through Mathbelieved in the natural 77 basic coloursAnaxagoras Darkness Breakthroughthe first to finally realize that darkness is simply the absence of light and he explain the source of the phases of the moon being sunlight reflected by the moon rather than emitted by itEmpedocles Explaining Visionfour basic elementsfire water earth and airthe first philosophers to attempt to explain human vision as a union of fire Democritus Intromission Theory of VisionIntromission theory of vision we see objects around us because something external enters into our eyes to give us perception of these objects ie shedding thin films atoms of matter released by physical objects entered our eyesPlato Extramission Theory of VisionExtramission theory of vision where rays of vision or light were released from the eyes to touch the external objects and bounce back to our eyes giving us a visual sensation of them through this remote touchingAristotle Propagation through a MediumIntromission theory of vision where certain transparent media like air water and many solids would allow transmission of colours from outside objects ie objects would somehow imprint their colours on the adjacent layer of this medium eg air and it would then pass from one layer to another to eventually arrive into our eyes which are also in contact with this transparent layerNote that it wasnt the passage of light through a medium that gave us vision but the passage of colours of objects imprinted on the medium which was filled with light1A Aristotle believed that all colours themselves were the results of mixing of light and dark to differing amounts so he devised a linear colour system of 7 basic colours Aristotle wrote of colours imprinted by solid objects passing from one layer to another in a transmitting medium like air until they eventually reached our eyes This passing of a property colour through a transmitting medium could be viewed as an early form of a wave theory This is in contrast to Democritus theory of vision where tiny particles atoms released by objects traveled into our eyesan early form of a particle theoryEuclid Geometrical Opticsusing rays such as the law of reflectionPtolemy Convergence of theories of Light and VisionMiddle Ages Some of the key ideas in their theories wereomore geometrical optics work on rays from objects and light AlKindiostronger scientific emphasis on exploration of light and colourofirst correct theory of vision using external light rays Alhazenofirst 2dimensional colour classification systemGrossetesteAlKindi OutwardRadiating Rays of Lightagues each point on a luminous body emitted rays of light outward in all directions independently from each otherAlhazen Revolution in Optics and Visual Perceptionrealized about the external light light bounces of every point on the surface of physical objects and then travels to our eyes in straight lines However he includes only the central ray enter our eyes because he did not know how the eye could bend other noncentral rays so they too can enter the eye Robert Grosseteste The first 2dimension of colour classification system by adding a brightness lux scale in addition to the 7 basic colours or huesAlbertus Magnus White Contains All Coloursall colours can be contained in whiteRenaissance Some of the key ideas in their theories wereounification of geometrical optics of light rays with the internal workings of the eye for a first complete theory of vision Kepleroquantifying the exact amounts of bending of light due to its passage through media Snello ideas of light propagating through an ether colours of the spectrum linked with periodic motion Descartesoartists exploration of primary colours through paints da VinciKepler First Complete Description of the anatomy and function of Human Eyeunify the intromission theories of light bouncing off objects to enter the eye and the eye then bending the light rays through refraction to focus themSnell The Law of Refraction of Lightdetermine exactly how much light will bend while travelling in different media 30 if the density of these media is knownDescartes PreCursor Ideas of EM SpectrumIncorrect ideas of disturbance propagation through a medium and periodic motion tied to colours 2
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