The Ascent of Man (22 page)

That is a fundamentally new idea in scientific explanation, quite
inaccessible to his contemporaries. Robert Hooke argued with him, every kind of physicist argued with him; until Newton got so bored with all the arguments that he wrote to Leibniz,

I was so persecuted with discussions arising from the publication of my theory of light that I blamed my own imprudence for parting with so substantial a blessing as my quiet to run after a shadow.

From that time
on he really refused to have anything to do with debate at all and certainly with the debaters like Hooke. He would not publish his book on optics until 1704, a year after Hooke died, having warned the president of the Royal Society:

I intend to be no farther solicitous about matters of Philosophy and therefore I hope you will not take it ill if you find me never doing anything more in that kind.

But let us begin at the beginning, in Newton’s own words. In the year 1666

I procured me a Triangular glass-Prisme, to try therewith the celebrated
Phaenomena of Colours
. And in order thereto having darkened my chamber, and made a small hole in my windowshuts, to let in a convenient quantity of the Suns light, I placed my Prisme at his entrance, that it might be thereby refracted to the opposite
wall. It was at first a very pleasing divertisement, to view the vivid and intense colours produced thereby; but after a while applying my self to consider them more circumspectly, I became surprised to see them in an
oblong
form; which, according to the received laws of Refraction, I expected should have been
circular
.

And I saw … that the light, tending to [one] end of the Image, did suffer
a Refraction considerably greater then the light tending to the other. And so the true cause of the length of that Image was detected to be no other, then that
Light
consists of
Rays differently refrangible
, which, without any respect to a difference in their incidence, were, according to their degrees of refrangibility, transmitted towards divers parts of the wall.

The elongation of the spectrum
was now explained; it was caused by the separation and fanning out of the colours. Blue is bent or refracted more than red, and that is an absolute property of the colours.

Then I placed another Prisme … so that the light … might pass through that also, and be again refracted before it arrived at the wall. This done, I took the first Prisme in my hand and turned it to and fro slowly about its
Axis, so much as to make the several parts of the Image … successively pass through … that I might observe to what places on the wall the second Prisme would refract them.

When any one sort of Rays hath been well parted from those of other kinds, it hath afterwards obstinately retained its colour, notwithstanding my utmost endeavours to change it.

With that, the traditional view was routed;
for if light were modified by glass, the second prism should produce new colours, and turn red to green or blue. Newton called this the critical experiment. It proved that once the colours are separated by refraction, they cannot be changed any further.

I have refracted it with Prismes, and reflected with it Bodies which in Day-light were of other colours; I have intercepted it with the coloured
film of Air interceding two compressed plates of glass; transmitted it through coloured Mediums, and through Mediums irradiated with other sorts of Rays, and diversly terminated it; and yet could never produce any new colour out of it.

But the most surprising, and wonderful composition was that of
Whiteness
. There is no one sort of Rays which alone can exhibit this. ’Tis ever compounded, and
to its composition are requisite all the aforesaid primary Colours, mixed in a due proportion. I have often with Admiration beheld, that all the Colours of the Prisme being made to converge, and thereby to be again mixed, reproduced light, intirely and perfectly white.

Hence therefore it comes to pass, that
Whiteness
is the usual colour of
Light
; for, Light is a confused aggregate of Rays indued
with all sorts of Colors, as they are promiscuously darted from the various parts of luminous bodies.

That letter was written to the Royal Society shortly after Newton was elected a Fellow in 1672. He had shown himself to be a new kind of experimenter, who understood how to form a theory and how to test it decisively against alternatives. He was rather proud of his achievement.

A naturalist
would scarce expect to see ye science of those colours become mathematicall, and yet I dare affirm that there is as much certainty in it as in any other part of Opticks.

Newton had begun to have a reputation in London as well as in the University; and a sense of colour seems to spread into that metropolitan world, as if the spectrum scattered its light across the silks and spices the merchants
brought to the capital.

The palette of painters became more varied, there was a taste for richly coloured objects from the East, and it became natural to use many colour words. This is very clear in the poetry of the time. Alexander Pope, who was
sixteen when Newton published the
Opticks
, was surely a less sensuous poet than Shakespeare, yet he uses three or four times as many colour words as
Shakespeare, and uses them about ten times as often. For instance, Pope’s description of fish in the Thames,

The bright-ey’d Perch with Fins of
Tyrian
Dye,

The silver Eel, in shining Volumes roll’d,

The yellow Carp, in Scales bedrop’d with Gold,

Swift Trouts, diversify’d with Crimson Stains,

would be inexplicable if we did not recognise it as an exercise in colours.

A metropolitan reputation
meant, inevitably, new controversies. Results that Newton outlined in letters to London scientists were bandied about. That was how there began, after 1676, a long and bitter dispute with Gonfried Wilhelm Leibniz about priority in the calculus. Newton would never believe that Leibniz, a powerful mathematician himself, had conceived it independently.

Newton thought of retiring altogether from
science into his cloister at Trinity. The Great Court was a spacious setting for a scholar in comfortable circumstances; he had his own small laboratory and his own garden. In Neville’s Court Wren’s great library was being built. Newton subscribed £40 to the fund. It seemed that he might look forward to a donnish life devoted to private study. But, in the end, if he refused to bustle among the scientists
in London, they would come to Cambridge to put their arguments to him.

Newton had conceived the idea of a universal gravitation in the Plague year of 1666 and had used it, very successfully, to describe the motion of the moon round the earth. It seems extraordinary that in nearly twenty years that followed he should have made almost no attempt to publish anything about the bigger problem of the
motion of the earth round the sun. The stumbling block is uncertain, but the facts are plain. Only in 1684 did there arise in London an argument between Sir Christopher Wren, Robert Hooke and the young astronomer Edmond Halley, as a result of which Halley came to Cambridge to see Newton.

After they had been some time together, the doctor [Halley] asked him what he thought the curve would be that
would be described by the planets, supposing the force of attraction towards the sun to be reciprocal to the square of their distance from it. Sir Isaac replied immediately that it would be an ellipsis. The doctor, struck with joy and amazement, asked him how he knew it. ‘Why,’ saith he, ‘I have calculated it.’ Whereupon Dr Halley asked him for his calculation without any further delay. Sir Isaac
looked among his papers but could not find it, but he promised him to renew it, and then to send it him.

It took three years, from 1684 to 1687, before Newton wrote out the proof, and it came out as long as – well, in full, as long as the
Principia
. Halley nursed, wheedled, and even financed the
Principia
, and Samuel Pepys accepted it as president of the Royal Society in 1687.

As a system of
the world, of course, it was sensational from the moment it was published. It is a marvellous description of the world subsumed under a single set of laws. But much more, it is also a landmark in scientific method. We think of the presentation of science as a series of propositions, one after another, as deriving from
the mathematics of Euclid. And so it does. But it is not until Newton turned
this into a physical system, by changing mathematics from a static to a dynamic account, that modern scientific method really begins to be rigorous.

And we can see in the book actually where the stumbling blocks were that kept him from pushing on after the orbit of the moon had come out so well. For instance, I am convinced that it is because he could not solve the problem at Section 12 on ‘How
does a sphere attract a particle?’ At Woolsthorpe he had calculated roughly, treating the earth and the moon as particles. But they (and the sun and the planets) are large spheres; can the gravitational attraction between them be accurately replaced by an attraction between their centres? Yes, but only (it turned out, ironically) for attractions that fall off as the square of the distance. And
in that we see the immense mathematical difficulties that he had to overcome before he could publish.

When Newton was challenged on such questions as ‘You have not explained why gravity acts’, ‘You have not explained how action at a distance could take place’, or indeed ‘You have not explained why rays of light behave the way they do’, he always answered in the same terms: ‘I do not make hypotheses’. By which he meant,
‘I do not deal in metaphysical speculation. I lay down a law, and derive the phenomena from it’. That was exactly what he had said in his work on optics, and exactly what had not been understood by his contemporaries as a new outlook in optics.

Now if Newton had been a very plain, very dull, very matter-of-fact man, all that would be easily explicable. But I must make you see that he was not.
He was really a most extraordinary, wild character. He practised alchemy. In secret, he wrote immense tomes about the Book of Revelation. He was convinced that the law of inverse squares was really already to be found in Pythagoras. And for such a man, who in private was full of these wild metaphysical and mystical speculations, to hold this public face and say, ‘I make no hypotheses’ – that is an
extraordinary expression of his secret character. William Wordsworth in
The Prelude
has a vivid phrase,

Newton, with his prism and silent face,

which sees and says it exactly.

Well, the public face was very successful of course, Newton could not get promotion in the University, because he was a Unitarian – he did not accept the doctrine of the Trinity, with which scientists in his time were
temperamentally ill at ease. Therefore he could not become a parson, therefore he could not possibly become the Master of a College. So, in 1696, Newton went to London to the Mint. In time he became Master of the Mint. After Hooke’s death he accepted the Presidency of the Royal Society in 1703. He was knighted by Queen Anne in 1705. And to his death in 1727 he dominated the intellectual landscape
of London. The village boy had made good.

The sad thing is that I think he had made good not by his own standards, but only by the standards of the
eighteenth century. The sad thing is that it was that society whose criterion he accepted, when he was willing to be a dictator in the councils of the Establishment and count that success.

An intellectual dictator is not a sympathetic figure, even
when he has risen from humble beginnings. Yet in his private writings, Newton was not so arrogant as he seems in his public face, so often and so variously represented.

To explain all nature is too difficult a task for any one man or even for any one age. ‘Tis much better to do a little with certainty, and leave the rest for others that come after you, than to explain all things.

And in a more
famous sentence he says the same thing less precisely but with a hint of pathos.

I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, while the great ocean of truth lay all undiscovered before me.

By the time Newton was in his
seventies, little real scientific work was done in the Royal Society. England under the Georges was preoccupied with money (these are the years of the South Sea Bubble), with politics, and with scandal. In the coffee houses, nimble businessmen floated companies to exploit fictitious inventions. Writers poked fun at scientists, in part from spite, and in part from political motives, because Newton
was a bigwig in the government establishment.