- Isaac Newton's early life and achievements
The following article is part of an in-depth biography of Sir
Isaac Newton, the English mathematicianand scientist, author of the "Principia".
Sir Isaac Newton was born on
December 25, 1642 [OS: 25 December 1642 ]in Woolsthorpe-by-Colsterworth, a hamlet in the parish of Colsterworth, Lincolnshire, about eight miles from Grantham. His father (also named Isaac Newton), who farmed a small freehold property, died before his son's birth, a few months after his marriage to Hannah Ayscough, a daughter of James Ayscough of Market Overton. When Newton was only two years old his mother married Barnabas Smith, rector of North Withamto where Hannah moved; Isaac was left in the care of his maternal grandmother, Margery Ayscough. The marriage produced three children, Benjamin, Mary and Hannah Smith, to whom Sir Isaac Newton subsequently left most of his property. His family in other words were yeomenfarmers.
After a rudimentary education at two small schools at
Stoke Rochfordand Skillington, close to Woolsthorpe, Newton was sent at the age of twelve to the local grammar school, The King's School, Grantham. While attending school in Grantham, Newton lived in the house of Mr. Clark, an apothecary. According to his own confession he was far from industrious, and did poorly in his class. When Newton was in a school fight which he won, his success seems to have led him to greater exertions, and he rose to be head boy of the school. He displayed very early a taste and an aptitude for mechanical contrivances. He made windmills, water clocks, kites and dials, and he is said to have invented a four-wheeled carriage which was to be moved by the rider.
In 1656, his stepfather passed away, and Newton's mother, Hannah Smith, came back with her three children to Woolsthorpe. She took Isaac, who was fifteen years of age at the time, out of school, intending for him to become a farmer. He was frequently sent on market days to Grantham with an old and trusty servant, who made all the purchases, while Newton spent his time among the books in a neighbor's house. It soon became apparent to Newton's relatives that it was a mistake to attempt to turn him into a farmer, and he was sent back to school at Grantham.
Newton's uncle, William Ayscough, the rector of
Burton Coggles, a parish six miles away, was a graduate of Trinity College, Cambridge, and when he found that Newton's mind was devoted to mechanical and mathematical problems he urged Hannah to send her son to Trinity. Newton was admitted to Trinity College on June 5, 1661, as a subsizar, and matriculated on July 8. While at Woolsthorpe, Newton had read Robert Sanderson's " Compendium of Logic", and his tutor at Trinity found that he knew the material well enough to be excused from lectures on the subject. Nothing else is known about Newton's time at Trinity College.
Newton had stated that when he had purchased a book on
astrologyat Stourbridge fair, near Cambridge, he was unable, on account of his ignorance of trigonometry, to understand a figure of the heavens which was drawn in the book. He therefore bought an English edition of Euclid's "Elements" which included an index of propositions, and, having turned to two or three which he thought might be helpful, found them so obvious that he dismissed it "as a trifling book," and applied himself to the study of René Descartes' "Geometry". It is reported that in his examination for a scholarship at Trinity, to which he was elected on April 28, 1664, he was examined in Euclid by Dr. Isaac Barrow, who was disappointed in Newton's lack of knowledge on the subject. Newton was convinced to read the "Elements" again with care, and formed a more favourable estimate of Euclid's merit.
The study of Descartes's "Geometry" seems to have inspired Newton with a love of the subject, and introduced him to higher mathematics. In a small commonplace book, dated January 1664, there are several articles on
angular sections, and the squaring of curvesand "crooked lines that may be squared," several calculations about musical notes, geometrical propositions from François Vièteand Frans van Schooten, annotations out of John Wallis's "Arithmetic of Infinities", together with observations on refraction, on the grinding of "spherical optic glasses," on the errors of lenses and the method of rectifying them, and on the extraction of all kinds of roots, particularly those "in affected powers." In this same book the following entry made by Newton himself, many years afterwards, gives a further account of the nature of his work during the period when he was an undergraduate:
:"July 4, 1699. By consulting an account of my expenses at Cambridge, in the years 1663 and 1664, I find that, in the year 1664 a little before Christmas, I, being then Senior Sophister, bought Schooten's "Miscellanies" and Cartes' "Geometry" (having read this "Geometry" and Oughtred's "Clavis" clean over half a year before), and borrowed Wallis' works, and by consequence made these annotations out of Schooten and Wallis, in winter between the years 1664 and 1665. At such time I found the method of Infinite Series; and in summer 1665, being forced from Cambridge by the plague, I computed the area of the
Hyperbolaat Boothby, in Lincolnshire, to two and fifty figures by the same method."
That Newton must have begun early to make careful observations of natural phenomena is shown by the following remarks about halos, which appear in his "Optics", book ii. part iv. obs. 13:
:"The like Crowns appear sometimes about the moon; for in the beginning of the Year 1664, February 19th, at night, I saw two such Crowns about her. The Diameter of the first or innermost was about three Degrees, and that of the second about five Degrees and an half. Next about the moon was a Circle of white, and next about that the inner Crown, which was of a bluish green within next the white, and of a yellow and red without, and next about these Colours were blue and green on the inside of the Outward Crown, and red on the outside of it. At the same time there appeared a Halo about 22 Degrees 35' distant from the centre of the moon. It was elliptical, and its long Diameter was perpendicular to the Horizon, verging below farthest from the moon."
In January 1665 Newton took the degree of B.A.. The persons appointed (in conjunction with the proctors,
John Sladeof Catharine Hall, Cambridge, and Benjamin Pulleynof Trinity College, Newton's tutor) to examine the questionists were John Eachardof Catharine Hall and Thomas Gippsof Trinity University. It is a curious accident that we have no information about the respective merits of the candidates for a degree in this year, since the "ordo senioritatis" of the bachelors of arts for the year is omitted in the "Grace Book."
It is supposed that it was in 1665 that the method of fluxións (his word for "derivatives") first occurred to Newton's mind. There are several papers in Newton's handwriting bearing dates 1665 and 1666 in which the method is described, in some of which dotted or dashed letters are used to represent fluxions, and in some of which the method is explained without the use of dotted letters.
Both in 1665 and in 1666 Trinity College was dismissed on account of the
Great Plague of London. On each occasion it was agreed, as shown by entries in the "Conclusion Book" of the college, dated August 7 1665, and June 22 1666, and signed by the master of the college, Dr Pearson, that all fellows and scholars who were dismissed on account of the pestilence be allowed one month's commons. Newton must have left college before August 1665, as his name does not appear in the list of those who received extra commons on that occasion, and he tells us himself in the extract from his commonplace book already quoted that he was "forced from Cambridge by the plague" in the summer of that year. He was elected a fellow of his college on the October 1 1667. There were nine vacancies, one caused by the death of Abraham Cowleythe previous summer, and the nine successful candidates were all of the same academic standing. A few weeks after his election to a fellowship Newton went to Lincolnshire, and did not return to Cambridge till the February following. In March 1668 he took his M.A. degree.
During the years 1666 to 1669 Newton's studies were very diverse. It is known that he bought prisms and lenses on two or three occasions, and also
chemicals and a furnace, apparently for chemical experiments; but he also employed part of his time on the theory of fluxions and other branches of pure mathematics. He wrote a paper, "Analysu per Equationes Numero Terminorum Infinitas", which he put, probably in June 1669, into the hands of Isaac Barrow (then Lucasian Professor of Mathematics), at the same time giving him permission to communicate its contents to their common friend John Collins (1624—1683), [see also James Gregory, mathematician.] a mathematician of no mean order. Barrow did this on July 31, 1669, but kept the name of the author a secret, and merely told Collins that he was a friend staying at Cambridge, who had a powerful genius for such matters. In a subsequent letter on August 20, Barrow expressed his pleasure at hearing the favourable opinion which Collins had formed of the paper, and added, "the name of the author is Newton, a fellow of our college, and a young man, who is only in his second year since he took the degree of Master of Arts, and who, with an unparalleled genius ("exitnio quo est acumine"), has made very great progress in this branch of mathematics." Shortly afterwards Barrow resigned his chair, and was instrumental in securing Newton's election as his successor.
Newton was elected Lucasian professor on October 29 1670. It was his duty as professor to lecture at least once a week in term time on some portion of
geometry, arithmetic, astronomy, geography, optics, statics, or some other mathematical subject, and also for two hours in the week to allow an audience to any student who might come to consult with the professor on any difficulties he had met with. The subject which Newton chose for his lectures was optics. These lectures did little to expand his reputation, as they were apparently remarkably sparsely attended; frequently leaving Newton to lecture at the walls of the classroom. An account of their content was presented to the Royal Societyin the spring of 1672.
The composition of white light
On December 21, 1671 he was proposed as a candidate for admission to the Royal Society by Dr Seth Ward,
bishop of Salisbury, and on January 11, 1672 he was elected a fellow of the Society. At the meeting at which Newton was elected, he read a description of a reflecting telescopewhich he had invented, and "it was ordered that a letter should be written by the secretary to Mr Newton to acquaint him of his election into the Society, and to thank him for the communication of his telescope, and to assure him that the Society would take care that all right should be done him with respect to this invention."
In his reply to the secretary on January 18, 1672, Newton writes: "I desire that in your next letter you would inform me for what time the society continue their weekly meetings; because, if they continue them for any time, I am purposing them to be considered of and examined an account of a philosophical discovery, which induced me to the making of the said telescope, and which I doubt not but will prove much more grateful than the communication of that instrument being in my judgment the oddest if not the most considerable detection which hath hitherto been made into the operations of nature."
This promise was fulfilled in a communication which Newton addressed to
Henry Oldenburg, the secretary of the Royal Society, on February 6, 1672, and which was read before the society two days afterwards. The whole is printed in No. 80 of the " Philosophical Transactions."
Newton's "philosophical discovery" was the realisation that white light is composed of a spectrum of colours. He realised that objects are coloured only because they absorb some of these colours more than others.
After he explained this to the Society, he proceeded: "When I understood this, I left off my aforesaid glass works; for I saw, that the perfection of telescopes was hitherto limited, not so much for want of glasses truly figured according to the prescriptions of Optics Authors (which all men have hitherto imagined), as because that light itself is a heterogeneous mixture of differently refrangible rays. So that, were a glass so exactly figured as to collect any one sort of rays into one point, it could not collect those also into the same point, which having the same incidence upon the same medium are apt to suffer a different
refraction. Nay, I wondered, that seeing the difference of refrangibility was so great, as I found it, telescopes should arrive to that perfection they are now at." This "difference in refrangibility" is now known as dispersion.
He then points out why "the object-glass of any telescope cannot collect all the rays which come from one point of an object, so as to make them convene at its focus in less room than in a circular space, whose diameter is the 50th part of the diameter of its aperture: which is an irregularity some hundreds of times greater, than a circularly figured lens, of so small a section as the object-glasses of long telescopes are, would cause by the unfitness of its figure, were light uniform." He adds: "This made me take reflections into consideration, and finding them regular, so that the Angle of Reflection of all sorts of Rays was equal to their Angle of Incidence; I understood, that by their mediation optic instruments might be brought to any degree of perfection imaginable, provided a reflecting substance could be found, which would polish as finely as glass, and reflect as much light, as glass transmits, and the art of communicating to it a parabolic figure be also attained. But these seemed very great difficulties, and I have almost thought them insuperable, when I further considered, that every irregularity in a reflecting superficies makes the rays stray 5 or 6 times more out of their due course, than the like irregularities in a refracting one; so that a much greater curiosity would be here requisite, than in figuring glasses for refraction.
"Amidst these thoughts I was forced from Cambridge by the intervening Plague, and it was more than two years before I proceeded further. But then having thought on a tender way of polishing, proper for metal, whereby, as I imagined, the figure also would be corrected to the last; I began to try, what might be effected in this kind, and by degrees so far perfected an instrument (in the essential parts of it like that I sent to
London), by which I could discern Jupiter's 4 Concomitants, and showed them diverse times to two others of my acquaintance. I could also discern the Moon-like phase of Venus, but not very distinctly, nor without some niceness in disposing the instrument.
"From that time I was interrupted till this last autumn, when I made the other. And as that was sensibly better than the first (especially for day-objects), so I doubt not, but they will be still brought to a much greater perfection by their endeavours, who, as you inform me, are taking care about it at London."
Newton's theory of colour
After a remark that
microscopes seem as capable of improvement as telescopes, he adds:
:I shall now proceed to acquaint you with another more notable deformity in its Rays, where in the intermediate degrees of refrangibility. And this analogy 'twist colours, and refrangibility is very precise and strict; the rays always either exactly agreeing in both, or proportionally disagreeing in both.
Further on, after some remarks on the subject of compound colours, he says:
:I might add more instances of this nature, but I shall conclude with this general one, that the colours of all natural bodies have no other origin than this, that they are variously qualified to reflect one sort of light in greater plenty then another. And this I have experimented in a dark room by illuminating those bodies with uncompounded light of diverse colours. For by that means any body may be made to appear of any colour. They have there no appropriate colour, but ever appear of the colour of the light cast upon them, but yet with this difference, that they are most brisk and vivid in the light of their own daylight colour. Minium appears there of any colour indifferently, with which 'tis illustrated, but yet most luminous in red, and so Bise appears indifferently of any colour with which 'tis illustrated, but yet most luminous in blue.:And there place a clear and colourless prism, to refract the entering light towards the further part of the room, which, as I said, will thereby be diffused into an oblong coloured image. Then place a lens of about three foot radius (suppose a broad object-glass of a three foot telescope), at the distance of about four or five foot from thence, through which all those colours may at once be transmitted, and made by its refraction to convene at a further distance of about ten or twelve feet. If at that distance you intercept this light with a sheet of white paper, you will see the colours converted into whiteness again by being mingled.
:But it is requisite, that the prism and lens be placed steady, and that the paper, on which the colours are cast be moved to and fro; for, by such motion, you will not only find, at what distance the whiteness is most perfect but also see, how the colours gradually convene, and vanish into whiteness, and afterwards having crossed one another in that place where they compound whiteness, are again dissipated and severed, and in an inverted order retain the same colours, which they had before they entered the composition. You may also see, that, if any of the colours at the lens be intercepted, the whiteness will be changed into the other colours. And therefore, that the composition of whiteness be perfect, care must be taken, that none of the colours fall besides the lens."
He concludes his communication with the words:
:This, I conceive, is enough for an introduction to experiments of this kind: which if any of the R. Society shall be so curious as to prosecute, I should be very glad to be informed with what success: That, if any thing seem to be defective, or to thwart this relation, I may have an opportunity of giving further direction about it, or of acknowledging my errors, if I have committed any.
The publication of these discoveries led to a series of controversies which lasted for several years, in which Newton had to contend with the eminent English physicist
Robert Hooke, Edouard Lucas(mathematical professor at the University of Liège), Franciscus Linus(a physician in Liège), and many others. Some of his opponents denied the truth of his experiments, refusing to believe in the existence of the spectrum. Others criticized the experiments, saying that the length of the spectrum was never more than three and a half times the breadth, whereas Newton found it to be five times the breadth. It appears that Newton made the mistake of supposing that all prisms would give a spectrum of exactly the same length; the objections of his opponents led him to measure carefully the lengths of spectra formed by prisms of different angles and of different refractive indices; but he was not led thereby to the discovery of the different dispersive powers of different refractive substances.
Newton carried on the discussion with the objectors with great courtesy and patience, but the amount of pain which these perpetual discussions gave to his sensitive mind may be estimated from the fact of his writing on November 18, 1676 to Oldenburg: "I promised to send you an answer to Mr Lucas this next Tuesday, but I find I shall scarce finish what I have designed, so as to get a copy taken of it by that time, and therefore I beg your patience a week longer. I see I nave made myself a slave to philosophy, but if I get free of Mr Lucas's business, I will resolutely bid adieu to it eternally, excepting what I do for my private satisfaction, or leave to come out after me; for I see a man must either resolve to put out nothing new, or to become a slave to defend it."
It was a fortunate circumstance that these disputes did not so thoroughly damp Newton's ardour as he at the time felt they would. He subsequently published many papers in the Philosophical Transactions on various parts of the science of optics, and, although some of his views have been found to be erroneous, and are now almost universally rejected, his investigations led to discoveries which are of permanent value. He succeeded in explaining the colour of thin and of thick plates, and the inflexion of light, and he wrote on double refraction,
polarizationand binocular vision. He also invented a reflecting quadrant for observing the distance between the moonand the fixed stars—the same in every essential as the historically important navigational instrument more commonly known as Hadley's quadrant. This discovery was communicated by him to Edmund Halleyin 1700, but was not published, or communicated to the Royal Society, till after Newton's death, when a description of it was found among his papers.
Conflict over oratorship elections
In March 1673 Newton took a prominent part in a dispute in the university. The public oratorship fell vacant, and a contest arose between the heads of the colleges and the members of the
senateas to the mode of electing to the office. The heads claimed the right of nominating two persons, one of whom was to be elected by the senate. The senate insisted that the proper mode was by an open election. The Dukeof Buckingham, who was the chancellor of the university, endeavoured to effect a compromise which, he says, "I hope may for the present satisfy both sides. I propose that the heads may for this time nominate and the body comply, yet interposing (if they think fit) a protestation concerning their plea that this election may not hereafter pass for a decisive precedent in prejudice of their claim," and, "whereas I understand that the whole university has chiefly consideration for Dr Henry Pamanof St John's College and Mr Craven of Trinity College, I do recommend them both to be nominated." The heads, however, nominated Dr Paman and Ralph Sandersonof St John's, and the next day one hundred and twenty-one members of the senate recorded their votes for Craven and ninety-eight for Paman. On the morning of the election a protest in which Newton's name appeared was read, and entered in the Regent House. But the vice-chancellor admitted Paman the same morning, and so ended the first contest of a non-scientific character in which Newton took part.
On March 8, 1673 Newton wrote to Oldenburg, the secretary of the Royal Society:
"Sir, I desire that you will procure that I may be put out from being any longer Fellow of the Royal Society: for though I honour that body, yet since I see I shall neither profit them, nor (by reason of this distance) can partake of the advantage of their assemblies, I desire to withdraw."
Oldenburg must have replied to this by an offer to apply to the Society to excuse Newton the weekly payments, as in a letter of Newton's to Oldenburg, dated June 23, 1673, he says, "For your proffer about my quarterly payments, I thank you, but I would not have you trouble yourself to get them excused, if you have not done it already." Nothing further seems to have been done in the matter until January 28, 1675, when Oldenburg informed the Society that "Mr Newton is now in such circumstances that he desires to be excused from the weekly payments." Upon this "it was agreed to by the council that he be dispensed with, as several others are." On February 18, 1675 Newton was formally admitted into the Society. The most probable explanation of the reason why Newton wished to be excused from these payments is to be found in the fact that, as he was not in holy orders, his fellowship at Trinity College would lapse in the autumn of 1675. It is true that the loss to his income which this would have caused was obviated by a patent from the crown in April 1675, allowing him as Lucasian professor to retain his fellowship without the obligation of taking holy orders. This must have relieved Newton's mind from a great deal of anxiety about financial matters, since in November 1676 he donated £40 towards the building of the new library of Trinity College.
Universal law of gravitation
It is supposed that it was at Woolsthorpe in the summer of 1666 that Newton's thoughts were directed to the subject of gravity. They are said to be inspired by Newton's seeing an apple fall from a tree on his mothers farm, a version for which there is reasonable historical evidence (see [http://www.sfu.ca/physics/ugrad/courses/teaching_resources/demoindex/mechanics/mech1l/apple.html] ). In one version of the story, the apple is supposed to have fallen on Newton's head; this version appears to be invented by
Isaac D'Israeli. Voltaireis the authority for the former version of the story. He had his information from Newton's favourite niece Catharine Barton, who married John Conduitt, a fellow of the Royal Society, and one of Newton's intimate friends. How much truth there is in what is a plausible and a favourite story can never be known, but it is certain that tradition marked a tree as that from which the apple fell, till 1860, when, owing to decay, the tree was cut down and its wood carefully preserved. Johannes Keplerhad proved by an elaborate series of measurements that each planetrevolves in an elliptical orbit around the sun, whose centre occupies one of the foci of the orbit, that the radius vector of each planet drawn from the sun sweeps out equal areas in equal times, and that the squares of the periodic times of the planets are in the same proportion as the cubes of their mean distances from the sun. The fact that heavy bodies have always a tendency to fall to the earth, no matter at what height they are placed above the earth's surface, seems to have led Newton to conjecture that it was possible that the same tendency to fall to the earth was the cause by which the moon was retained in its orbit round the earth.
Newton, by calculating from Kepler's laws, and supposing the orbits of the planets to be circles round the sun in the centre, had already proved that the force of the sun acting upon the different planets must vary as the inverse square of the distances of the planets from the sun. He therefore was led to inquire whether, if the earth's attraction extended to the moon, the force at that distance would be of the exact magnitude necessary to retain the moon in its orbit. He found that the moon by her motion in her orbit was deflected from the tangent in every minute of time through a space of thirteen feet. But by observing the distance through which a body would fall in one second of time at the earth's surface, and by calculating from that on the supposition of the force diminishing in the ratio of the inverse square of the distance, he found that the earth's attraction at the distance of the moon would draw a body through 15 ft. (4.57 meters) in one minute. Newton regarded the discrepancy between the results as a proof of the inaccuracy of his conjecture, and "laid aside at that time any further thoughts of this matter." (See
But in 1679 a controversy between Hooke and Newton, about the form of the path of a body falling from a height, taking the motion of the earth round its axis into consideration, led Newton again to revert to his former conjectures on the moon. The estimate Newton had used for the radius of the earth, which had been accepted by geographers and navigators, was based on the very rough estimate that the length of a degree of latitude of the earth's surface measured along a meridian was 60
nautical miles. At a meeting of the Royal Society on January 11, 1672, Oldenburg, the secretary, read a letter from Paris describing the procedure followed by Jean Picardin measuring a degree, and specifically stating the precise length that he calculated it to be. It is probable that Newton had become acquainted with this measurement of Picard's, and that he was therefore led to make use of it when his thoughts were redirected to the subject. This estimate of the earth's magnitude, giving 691 miles (1112 km) to 10°, made the two results, the discrepancy between which Newton had regarded as a disproof of his conjecture, to agree so exactly that he now regarded his conjecture as fully established.
In January 1684, Sir
Christopher Wren, Halley and Hooke were led to discuss the law of gravity, and although probably they all agreed in the truth of the law of the inverse square, yet this truth was not looked upon as established. It appears that Hooke professed to have a solution of the problem of the path of a body moving round a centre of force attracting as the inverse square of the distance, but Halley declared after a delay of some months that Hooke "had not been so good as his word" in showing his solution to Wren, and started for Cambridge, in the month of August 1684, to consult Newton on the subject. Without mentioning the speculations which had been made, he asked Newton what would be the curve described by a planet round the sun on the assumption that the sun's force diminished as the square of the distance. Newton replied promptly, "an ellipse," and on being questioned by Halley as to the reason for his answer he replied, "Why, I have calculated it." He could not, however, put his hand upon his calculation, but he promised to send it to Halley. After the latter had left Cambridge, Newton set to work to reproduce the calculation. After making a mistake and producing a different result he corrected his work and obtained his former result.
In the following November Newton redeemed his promise to Halley by sending him, by the hand of Mr Paget, one of the fellows of his own college, and at that time mathematical master of
Christ's Hospital, a copy of his demonstration; and very soon afterwards Halley paid another visit to Cambridge to confer with Newton about the problem. On his return to London on December 10, 1684, he informed the Royal Society "that he had lately seen Mr Newton at Cambridge, who had showed him a curious treatise "De Motu"," which at Halley's desire he promised to send to the Society to be entered upon their register. "Mr Halley was desired to put Mr Newton in mind of his promise for the securing this invention to himself, till such time as he could be at leisure to publish it," and Paget was desired to join with Halley in urging Newton to do so. By the middle of February Newton had sent his paper to Aston, one of the secretaries of the Society, and in a letter to Aston dated February 23, 1685, Newton thanked him for "having entered on the register his notions about motion." This treatise "De Motu" was the starting point of the "Principia", and was meant to be a short account of what that work was intended to embrace. It occupies twenty-four octavopages, and consists of four theorems and seven problems, some of which are identical with some of the most important propositions of the second and third sections of the first book of the "Principia".
the writing of Principia Mathematicafor information on the next part of Newton's life.
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