Isaac Newton

Sir Isaac Newton, PRS (25 December 1642 (OS) – 20 March 1727 (OS) / 4 January, 1643 (NS) – 31 March 1727 (NS) was an English physicist, mathematician, astronomer, philosopher, and alchemist. Recognised as a genius of the highest order, he is widely regarded as the most influential scientist in history. He wrote the Philosophiae Naturalis Principia Mathematica (published 5 July 16871), where he described universal gravitation and, via his laws of motion, laid the groundwork for classical mechanics. Newton also shares credit with Gottfried Wilhelm Leibniz for the development of differential calculus. While they both discovered calculus nearly contemporaneously, their work was not a collaboration.

Scientific research

Optics

From 1670 to 1672 he lectured on optics. During this period he investigated the refraction of light, demonstrating that a prism could decompose white light into a spectrum of colours, and that a lens and a second prism could recompose the multicoloured spectrum into white light.

Related Topics:
1670 - 1672 - Optics - Refraction - Light - Prism - White light - Spectrum - Lens

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He also showed that the coloured light does not change its properties, by separating out a coloured beam and shining it on various objects. Newton noted that regardless of whether it was, reflected or scattered or transmitted, it stayed the same colour. Thus the colours we observe are the result of how objects interact with the incident already-coloured light, not the result of objects generating the colour. For more details, see Newton's theory of colour.

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From this work he concluded that any refracting telescope would suffer from the dispersion of light into colours, and invented a reflecting telescope (today, known as a Newtonian telescope) to bypass that problem. By grinding his own mirrors, using Newton's rings to judge the quality of the optics for his telescopes, he was able to produce a superior instrument to the refracting telescope, due primarily to the wider diameter of the mirror. (Only later, as glasses with a variety of refractive properties became available, did achromatic lenses for refractors become feasible.) In 1671 the Royal Society asked for a demonstration of his reflecting telescope. Their interest encouraged him to publish his notes On Colour, which he later expanded into his Opticks. When Robert Hooke criticised some of Newton's ideas, Newton was so offended that he withdrew from public debate. The two men remained enemies until Hooke's death.

Related Topics:
Telescope - Dispersion - Newtonian telescope - Newton's rings - Quality - Optics - 1671 - Royal Society - Robert Hooke

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In one experiment, to prove that colour was caused by pressure on the eye, Newton slid a darning needle around the side of his eye until he could poke at its rear side, dispassionately noting "white, darke & coloured circles" so long as he kept stirring with "ye bodkin."

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He once said, in a letter to Hooke dated 5 February 1676:

Related Topics:
5 February - 1676

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:If I have seen a little further it is by standing on the shoulders of Giants.

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In changing this quotation of Didacus Stella (Lucan (vol. II, 10)) from "Pigmies placed on the shoulders of giants see more than the giants themselves", Newton was perhaps making a more personal point than the mere expression of modesty — Hooke was a man of short stature.

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Although is it widely known and accepted that there was considerable antagonism between Newton and Robert Hooke, Newton does make the occasional respectful reference to Hooke's work. For example in Opticks, Book I Part II, referring to the combining effect of colour filters, Newton refers to Hooke's experiments: " ... Mr Hooke tried casually with glass wedges filled with red and blue Liquors, and was surprised at the unexpected Event, the reason of it being then unknown; which makes me trust the more to his experiment, though I have not tried it myself." Thus Newton was not completely without respect for Hooke.

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Newton argued that light is composed of particles; thus he could not explain the diffraction of light. Later physicists instead favoured a wave explanation of light to account for diffraction. Today's quantum mechanics recognises a "wave-particle duality"; however photons bear very little semblance to Newton's corpuscles (e.g., corpuscles refracted by accelerating toward the denser medium).

Related Topics:
Diffraction - Wave - Quantum mechanics - Wave-particle duality - Photon

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Newton is believed to have been the first to explain precisely, the formation of the rainbow from water droplets dispersed in the atmosphere in a rain shower. Figure 15 of Part II of Book one of Opticks shows a perfect illustration of how this occurs.

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In his Hypothesis of Light of 1675, Newton posited the existence of the ether to transmit forces between particles. Newton was in contact with Henry More, the Cambridge Platonist who was born in Grantham, on alchemy, and now his interest in the subject revived. He replaced the ether with occult forces based on Hermetic ideas of attraction and repulsion between particles. John Maynard Keynes, who acquired many of Newton's writings on alchemy, stated that "Newton was not the first of the age of reason: he was the last of the magicians." Newton's interest in alchemy cannot be isolated from his contributions to science2. (This was at a time when there was no clear distinction between alchemy and science.) Had he not relied on the occult idea of action at a distance, across a vacuum, he might not have developed his theory of gravity. (See also Isaac Newton's occult studies.)

Related Topics:
1675 - Ether - Henry More - Cambridge Platonist - Grantham - Alchemy - John Maynard Keynes - 2 - Occult - Action at a distance - Isaac Newton's occult studies

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Gravity and motion

In 1679, Newton returned to his work on mechanics, i.e., gravitation and its effect on the orbits of planets, with reference to Kepler's laws of motion, and consulting with Hooke and Flamsteed on the subject. He published his results in De Motu Corporum (1684). This contained the beginnings of the laws of motion that would inform the Principia.

Related Topics:
1679 - Mechanics - Planet - Kepler's - Laws of motion - Flamsteed - 1684

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Philosophiae Naturalis Principia Mathematica (now known as the Principia) was published in 1687 with encouragement and financial help from Edmond Halley. In this work Newton stated the three universal laws of motion that were not to be improved upon for more than two hundred years. He used the Latin word gravitas (weight) for the force that would become known as gravity, and defined the law of universal gravitation. In the same work he presented the first analytical determination, based on Boyle's Law, of the speed of sound in air.

Related Topics:
Philosophiae Naturalis Principia Mathematica - 1687 - Edmond Halley - Boyle's Law

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With the Principia, Newton became internationally recognised. He acquired a circle of admirers, including the Swiss-born mathematician Nicolas Fatio de Duillier, with whom he formed an intense relationship that lasted until 1693. The end of this friendship led Newton to a nervous breakdown.

Related Topics:
Swiss - Nicolas Fatio de Duillier - 1693 - Nervous breakdown

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:For a detailed discussion on the writing of Principia, see the writing of Principia Mathematica.

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