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 Isaac
Newton was born December 25th, 1642, at Woolsthorpe, near Grantham
in Lincolnshire, where his family had held a small landed property
for generations. As a boy, at the Grantham Grammar School, he
was slow in book-learning, and much absorbed in mechanical contrivances.
At 17 he entered Trinity College, Cambridge. Here he devoted
himself eagerly to mathematical study, meditating principally
on the Geometry of Descartes, published in 1637, and on
the Arithmetica Infinitorum of Wallis, published
1655. In 1667 he was elected Fellow of his college, and two years
afterward he succeeded Barrow as Professor of Mathematics. From
this chair his lectures on Optics were given. In 1672 he was
elected a Fellow of the Royal Society. In 1686 his great treatise
on Natural Philosophy, the Principia, was completed, and
the next year published. In 1687 he was one of the delegates
chosen to defend his University against the encroachments of
James II; and in 1689 he represented it in Parliament. In 1695
he was made Warden, and in 1699 Master, of the Mint. In 1703
he became President of the Royal Society, and was re-elected
every year till his death, which took place on the 28th of February
1727. He was buried in Westminster Abbey.
The splendour of Newton's discoveries has led many writers
to isolate his work from what had been done before him, and was
being done in his own time by others. But the History of Science
is a fundamental part of the History of Humanity, and the life
of no man, however great, should be treated thus. And further,
to Newton, as to others, the canon must be applied that publication
is the proper test of priority.
Kepler's three laws, that the planets moving round the sun
described equal areas in equal times, that their orbits were
elliptical, the sun being in one of the foci, and that the squares
of their times of revolution were as the cubes of their mean
distances, were discovered a generation before Newton's birth.
But they remained unreduced to any law of force. Kepler had indeed
shown that the force must proceed from the sun, and had put forward
the mistaken conjecture that it varied inversely as the distance.
Kepler was strongly convinced of the identity between terrestrial
weight and planetary attraction, and made an estimate, on this
erroneous basis, of the mutual fall of the earth and moon, supposing
no other force intervened. Ismael Boulliaud, in his Astronomia
Philolaica, published 1645, suggested that gravitation acted
not inversely as the distance, but inversely as the square of
the distance. But these views rested on vague analogies between
gravitation and the radiation of light fromm a focus; and till
they could be mathematically tested they received, and deserved,
but slight attention.
The law of falling bodies had been accurately given by Galileo. But no attempt had been
made to connect it with the laws of planetary motion. In 1665,
Newton, being then at Woolsthorpe, thought of investigating the
space through whichh the moon in a given time was deflected from
the tangent to her path--in other words, fell towards the earth.
He found that in one minute the moon fell thirteen feet. Taking
the best estimate available to him of the earth's magnitude,
from which the moon's parallax, and thence her distance, were
to be estimated, he found that, on the supposition that gravitation
acted inversely as the square of the distance, the fall of the
moon in one minute should not be thirteen, but fifteen feet.
He thereforee quietly put the hypothesis aside; a striking example
of scientific forbearance. Seven years afterwards, Picard's more
exact measurement of the earth's magnitude reached him from Paris.
Newton at once resumed his calculations, causing them, for greater
certainty, to be completed by a disinterested observer. The correcter
statement of facts was found to tally with his hypothesis of
gravitation.
It is often supposed that the problem of explaining the planetary
motions was now solved. In reality, the difficult part of the
work--that which tests Newton's intellectual greatness--had still
to be done. The problem before him was to show how Kepler's Third
Law, that the squares of the periods of the planets varied as
the cubes of their mean distances from the sun, followed mathematically
from the supposition of an attractive force, acting inversely
as the square of the distance, situate in the focus of an ellipse.
Further, this force had to be regarded not as acting upon a particle,
but on a planet; i.e. a system of particles. No vague
hypothesis could be useful here: no application of such mathematics
as were then known could suffice.
In 1673 appeared the great work of Huyghens on the Pendulum
and on Centrifugal Force. This contributed in two ways to the
solution. Huyghens' laws of centrifugal force gave the measure
of the force which retained the planets in their orbits, supposing
the orbits circular. And further, in his discussion of the Pendulum,
Huyghens had attacked the problem of a system of particles rigidly
connected, and each animated with its own tendencies to motion.
Newton acknowledged his debt to Huyghens; but in passing from
circular to elliptic motion, and above all for his demonstration
that the attractive force exercised by the molecules of a sphere
might be regarded as condensed in its center, ordinary geometry,
even after its algebraic expansion by Descartes and his mathematical
successors, was insufficient.
Foremost among these successors stood Newton. And it was at
this time--that is to say about 1666--that he constructed the
Transcendental Calculus, by the aid of which his great treatise
was written; though, for reasons which seem to us now quite inadequate,
he presented his demonstrations in the language of ordinary geometry.
On the claims for priority to the invention of this calculus
a bitter controversy arose between the friends of Leibniz and
of Newton. It is admitted now that Newton made his discovery
prior to and independently of Leibniz. But no description of
Newton's Fluxions was published until 1693. The letters of Leibniz
show that he had invented his Differential and Integral Calculus
in 1675; and a full account of it was published in the Acta
Eruditorum at Leipsic, 1684. It must be further admitted
that the differentials and integrals of Leibniz proved more fertile
in the subsequent development of mathematics than the fluxions
and fluents of Newton.
But it fell to the lot of Newton to combine the discovery
of the calculus with what was by far the most important of his
applications. And hence it is that the Principia, notwithstanding
the archaic form into which he thought fit to transpose his discoveries,
will by many be looked upon as the greatest, by all as one of
the two or three great masterpieces, of scientific intellect.
In unity of purpose, though not in native power, it surpasses
the work of Archimedes; in the importance of its application,
though not in philosophic breadth, the Mécanique
of Lagrange.
Newton's mathematical and experimental researches on light
and colour, which began with his installation as Professor of
Mathematics, were first communicated to the Royal Society in
1672, and were finally published in a complete form in 1704.
The experimental part of his work, to which the analysis of white
light into component colours of different refrangibility--a subject
opened by Descartes--is but the prelude, remains of indestructible
value.
And finally, it must not be forgotten that to Newton we owe
the establishment of the Third Law of Motion, the equality of
action and reaction: a law stated by him in that large and comprehensive
way which enables us to include among the reactions the conversion
of sensible into insensible motion; so that it illumines and
corrects much modern speculation upon work and energy.
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| This biography is
reprinted from The New Calendar of Great Men. Ed. Frederic
Harrison. London: Macmillan and Co., 1920. |
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