Sir Isaac Newton Biography
In mechanics, Newton enunciated the principles of conservation of both momentum and angular momentum. In optics, he built the first practical reflecting telescope and developed a theory of colour based on the observation that a prism decomposes white light into the many colours which form the visible spectrum. He also formulated an empirical law of cooling and studied the speed of sound.
In mathematics, Newton shares the credit with Gottfried Leibniz for the development of the differential and integral calculus. He also demonstrated the generalised binomial theorem, developed the so-called “Newton’s method” for approximating the zeroes of a function, and contributed to the study of power series.
Newton’s stature among scientists remains at the very top rank, as demonstrated by a 2005 survey of scientists in Britain’s Royal Society asking who had the greater effect on the history of science, Newton or Albert Einstein. Newton was deemed the more influential.
Newton was also highly religious, though an unorthodox Christian, writing more on Biblical hermeneutics than the natural science he is remembered for today.
The famous three laws of motion:
Newton’s First Law (also known as the Law of Inertia) states that an object at rest tends to stay at rest and that an object in uniform motion tends to stay in uniform motion unless acted upon by a net external force.
Newton’s Second Law states that an applied force, on an object equals the rate of change of its momentum, with time.
Since the second law applies to an object with constant mass (dm/dt = 0), the first term vanishes, and by substitution using the definition of acceleration.
The first and second laws represent a break with the physics of Aristotle, in which it was believed that a force was necessary in order to maintain motion. They state that a force is only needed in order to change an object’s state of motion. The SI unit of force is the newton, named in Newton’s honour.
Newton’s Third Law states that for every action there is an equal and opposite reaction. This means that any force exerted onto an object has a counterpart force that is exerted in the opposite direction back onto the first object. A common example is of two ice skaters pushing against each other and sliding apart in opposite directions. Another example is the recoil of a firearm, in which the force propelling the bullet is exerted equally back onto the gun and is felt by the shooter. Since the objects in question do not necessarily have the same mass, the resulting acceleration of the two objects can be different (as in the case of firearm recoil).
Unlike Aristotle’s, Newton’s physics is meant to be universal. For example, the second law applies both to a planet and to a falling stone.
The vector nature of the second law addresses the geometrical relationship between the direction of the force and the manner in which the object’s momentum changes. Before Newton, it had typically been assumed that a planet orbiting the sun would need a forward force to keep it moving. Newton showed instead that all that was needed was an inward attraction from the sun. Even many decades after the publication of the Principia, this counterintuitive idea was not universally accepted, and many scientists preferred Descartes’ theory of vortices.
Optics
From 1670 to 1672, Newton 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.
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, he observed that colour is the result of objects interacting with already-coloured light rather than objects generating the colour themselves. This is known as Newton’s theory of colour.
From this work he concluded that the lens of any refracting telescope would suffer from the dispersion of light into colours (chromatic aberration), and as a proof of the concept he constructed a telescope using a mirror as the objective to bypass that problem. Actually building the design, the first known functional reflecting telescope, today known as a Newtonian telescope, involved solving the problem of a suitable mirror material and shaping technique. Newton ground his own mirrors out of a custom composition of highly reflective speculum metal, using Newton’s rings to judge the quality of the optics for his telescopes. By February of 1669 he was able to produce an instrument without chromatic aberration. 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.
Newton argued that light is composed of particles or corpuscles, which were refracted by accelerating toward the denser medium, but he had to associate them with waves to explain the diffraction of light (Opticks Bk. II, Props. XII-L). Later physicists instead favoured a purely wavelike explanation of light to account for diffraction. Today’s quantum mechanics, photons and the idea of wave–particle duality bear only a minor resemblance to Newton’s understanding of light.
In his Hypothesis of Light of 1675, Newton posited the existence of the ether to transmit forces between particles. The contact with the theosophist Henry More, revived his interest in alchemy. 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 science. (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.)
In 1704 Newton published Opticks, in which he expounded his corpuscular theory of light. He considered light to be made up of extremely subtle corpuscles, that ordinary matter was made of grosser corpuscles and speculated that through a kind of alchemical transmutation “Are not gross Bodies and Light convertible into one another, …and may not Bodies receive much of their Activity from the Particles of Light which enter their Composition?” Newton also constructed a primitive form of a frictional electrostatic generator, using a glass globe (Optics, 8th Query).
Isaac Newton died on March 31, 1727 (New Style calendar), in London, and he was buried in Westminster Abbey.
References:
#Britain Express Retrieved in 02/21/2009 from: http://www.britainexpress.com/History/bio/newton.htm.
#Ball, W.W. Rouse (1908). A Short Account of the History of Mathematics. New York: Dover.
# “Sir Isaac Newton”. School of Mathematics and Statistics, University of St. Andrews, Scotland. http://www-history.mcs.st-andrews.ac.uk/Mathematicians/Newton.html. Retrieved on 2005-03-08.
# “The Newton Project”. Imperial College London. http://www.newtonproject.sussex.ac.uk/prism.php?id=1. Retrieved on 2005-03-08.
#Ball, W.W. Rouse (1908). A Short Account of the History of Mathematics. New York: Dover.
# “Sir Isaac Newton”. School of Mathematics and Statistics, University of St. Andrews, Scotland. http://www-history.mcs.st-andrews.ac.uk/Mathematicians/Newton.html. Retrieved on 2005-03-08.
# “The Newton Project”. Imperial College London. http://www.newtonproject.sussex.ac.uk/prism.php?id=1. Retrieved on 2005-03-08.
