Isaac
Newton's life
can be divided into three quite distinct periods. The first is his
boyhood days from 1643 up to his graduation in 1669. The second
period from 1669 to 1687 was the highly productive period in which
he was Lucasian professor at Cambridge. The third period (nearly
as long as the other two combined) saw Newton as a highly paid government
official in London with little further interest in mathematics.
Isaac
Newton was born in the manor house of Woolsthorpe,
near Grantham in Lincolnshire. Although he was born on Christmas
Day 1642, the date given on this card is the Gregorian calendar
date. (The Gregorian calendar was not adopted in England until 1752.)
Newton came from a family of farmers but never knew his father who
died before he was born. His mother remarried, moved to a nearby
village, and left him in the care of his grandmother. Upon the death
of his stepfather in 1656, Newton's mother removed him from grammar
school in Grantham where he had shown little promise in academic
work. His school reports described him as 'idle' and 'inattentive'.
An uncle decided that he should be prepared for the university,
and he entered his uncle's old College, Trinity College, Cambridge,
in June 1661.
Newton's
aim at Cambridge was a law degree. Instruction at Cambridge was
dominated by the philosophy of Aristotle but some freedom of study
was allowed in the third year of the course. Newton studied the
philosophy of Descartes, Gassendi, and Boyle. The new algebra and
analytical geometry of Viète, Descartes, and Wallis; and
the mechanics of the Copernican astronomy of Galileo attracted him.
Newton's talent began to emerge on the arrival of Barrow to the
Lucasian chair at Cambridge.
His
scientific genius emerged suddenly when the plague closed the University
in the summer of 1665 and he had to return to Lincolnshire. There,
in a period of less than two years, while Newton was still under
25 years old, he began revolutionary advances in mathematics, optics,
physics, and astronomy.
While
Newton remained at home he laid the foundation for differential
and integral calculus, several years before
its independent discovery by Leibniz. The 'method of fluxions',
as he termed it, was based on his crucial insight that the integration
of a function is merely the inverse procedure to differentiating
it. Taking differentiation as the basic operation, Newton produced
simple analytical methods that unified many separate techniques
previously developed to solve apparently unrelated problems such
as finding areas, tangents, the lengths of curves and the maxima
and minima of functions. Newton's De Methodis Serierum et Fluxionum
was written in 1671 but Newton failed to get it published and it
did not appear in print until John Colson produced an English translation
in 1736. Barrow
resigned the Lucasian chair in 1669 recommending that Newton (still
only 27 years old) be appointed in his place.
Newton's
first work as Lucasian Professor was on optics. He had reached the
conclusion during the two plague years that white light is not a
simple entity. Every scientist since Aristotle had believed that
white light was a basic single entity, but the chromatic aberration
in a telescope lens convinced Newton otherwise. When he passed a
thin beam of sunlight through a glass prism Newton noted the spectrum
of colours that was formed.
Newton
argued that white light is really a mixture of many different types
of rays which are refracted at slightly different angles, and that
each different type of ray produces a different spectral colour.
Newton was led by this reasoning to the erroneous conclusion that
telescopes using refracting lenses would always suffer chromatic
aberration. He therefore proposed and constructed a reflecting telescope.
Newton
was elected a fellow of the Royal Society in 1672 after donating
a reflecting telescope. Also in 1672 Newton published his first
scientific paper on light and colour in the Philosophical Transactions
of the Royal Society. Newton's paper was well received but Hooke
and Huygens objected to Newton's attempt to prove, by experiment
alone, that light consists of the motion of small particles rather
than waves. Perhaps because of Newton's already high reputation
his corpuscular theory reigned until the wave theory was revived
in the 19th C.
Newton's
relations with Hooke deteriorated and he turned in on himself and
away from the Royal Society. He delayed the publication of a full
account of his optical researches until after the death of Hooke
in 1703. Newton's Opticks appeared in 1704. It dealt with
the theory of light and colour and with (i) investigations of the
colours of thin sheets (ii) 'Newton's rings' and (iii) diffraction
of light. To
explain some of his observations he had to use a wave theory of
light in conjunction to his corpuscular theory.
Newton's greatest
achievement was his work in physics and celestial mechanics, which
culminated in the theory of universal gravitation. By 1666 Newton
had early versions of his three laws of motion. He had also discovered
the law giving the centrifugal force on a body moving uniformly
in a circular path. However he did not have a correct understanding
of the mechanics of circular motion.
Newton's
novel idea of 1666 was to imagine that the Earth's gravity influenced
the Moon, counter- balancing its centrifugal force. From his law
of centrifugal force and Kepler's third law of planetary motion,
Newton deduced the inverse- square law.
In 1679 Newton
corresponded with Hooke who had written to Newton claiming:-
that
the Attraction always is in a duplicate proportion to the Distance
from the Center Reciprocall...
M Nauenberg writes
an account of the next events:-
After
his 1679 correspondence with Hooke, Newton, by his
own account, found a proof that Kepler's areal law was a
consequence of centripetal forces, and he also showed that if the
orbital curve is an ellipse under the action of central forces then
the radial dependence of the force is inverse square with the distance
from the centre.
This discovery
showed the physical significance of Kepler's second law.
In 1684 Halley,
tired of Hooke's boasting:-
asked
Newton what orbit a body followed under an inverse square force,
and Newton replied immediately that it would be an ellipse. However
in De Motu.. he only gave a proof of the converse theorem that if
the orbit is an ellipse the force is inverse square. The proof that
inverse square forces imply conic section orbits is sketched in
Cor. 1 to Prop. 13 in Book 1 of the second
and third editons of the Principia, but not in the first edition.
[M Nauenberg]
Halley
persuaded Newton to write a full treatment of his new physics and
its application to astronomy. Over a year later (1687) Newton published
the Philosophiae naturalis principia mathematica or Principia
as it is always known.
The
Principia is recognised as the greatest scientific book ever
written. Newton analysed the motion of bodies in resisting and non
resisting media under the action of centripetal forces. The results
were applied to orbiting bodies, projectiles, pendulums, and free-fall
near the Earth. He further demonstrated that the planets were attracted
toward the Sun by a force varying as the inverse square of the distance
and generalised that all heavenly bodies mutually attract one another.
Further generalisation
led Newton to the law of universal gravitation:
all
matter attracts all other matter with a force proportional to the
product of their masses and inversely proportional to the square
of the distance between them.
Newton
explained a wide range of previously unrelated phenomena:- the eccentric
orbits of comets; the tides and their variations; the precession of
the Earth's axis; and motion of the Moon as perturbed by the gravity
of the Sun. After
suffering a nervous breakdown in 1693, Newton retired from research
to take up a government position in London becoming Warden of the
Royal Mint (1696) and Master(1699).
In
1703 he was elected president of the Royal Society and was re-elected
each year until his death. He was knighted in 1708 by Queen Anne,
the first scientist to be so honoured for his work.
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