Conversations With Isaac Newton Read online

  So, you’re saying that there’s really only one force at work in Nature?

  No, that’s not what I’m saying at all. I believe that there are several different types of force, but that they are interrelated and all operate through a common medium.

  Did you reach any conclusions about the nature of this medium?

  Yes, I did. Gravity, I realized, is a universal force. There is some underlying way in which forces can act over empty space. I believe these forces act through the spirit of Jesus Christ. God is one, not three. He is not outside the universe, but a part of it, a unifier. However, by what means does he keep the planets in motion and particles moving? He uses gravity and these other mysterious forces. But how? I questioned this for a long time. I implored God to tell me. And then, in a flash, in a moment of divine inspiration, it came to me. God uses the body, the essence, the spirit of Christ as the medium for these forces. God’s son became incarnate once before, but he is immortal, pure spirit, and he can take on any form. He can guide the atoms of the universe. He may steer the planets in their paths and make suns burn with furious flame. I could never publish this hypothesis, of course, but it is the best explanation I have.

  It’s a very radical notion and impossible to prove, I assume?

  I imagine many people would consider it radical. And no, of course, it cannot be proven. But then no physicist can prove their own hypotheses on this matter, can they? If one day a better explanation is arrived at I will, of course, give it my due attention. Until then my hypothesis satisfies me.

  ON THE NATURE OF LIGHT

  In some of his earliest studies Newton investi­gated the properties of light. To help with his experiments and observations he created practical tools, such as his excellent reflecting telescope. He applied the same mathematical rigour he used to explain the forces governing motion and gravity to describe the true nature and behaviour of light. From this work he was able to discover a set of universal laws which he described in great detail in his second masterwork, Opticks, which was published in 1704.

  When did you first become interested in the study of light?

  My interest was first piqued while reading Descartes’s theories on the nature of light in the books owned by Mr Clark, the apothecary. Descartes believed that light was a “pressure” transmitted through a transparent medium he called “the ether”. Sight, he believed, was due to this pressure impinging on the optic nerve. He also thought that colour was produced by packets of light in the form of rotating spheres. Of course, when I first read these things I had no idea whether or not such hypotheses were true. Descartes was a great thinker but he performed few experiments, and I know his theories on the nature of light and the way it is transmitted could not have been derived from these experiments. So for me, they were far from empirical enough.

  So, what was the prevailing theory of light in the 1660s and 1670s? Was Descartes’s view the accepted wisdom?

  There were at least two different models. Some experimenters believed light was wavelike, like a vibrating string of a violin or a taut rope that has been flicked. Others held the view that light was made up of parcels or packets that were somehow transmitted through space. I was more inclined to the former description, but I was never able to prove this correct.

  Well, that isn’t really surprising, because even in my day, in the early 21st century, scientists are still uncertain about the answer to this question. So when did you start to experiment with light yourself?

  Experiments with light were the very first researches I conducted – soon after I had settled in Cambridge. In 1664 I acquired a prism at a country fair held in Stourbridge near Cambridge. I bought it for a few pennies from a stall selling quack elixirs and novelties. I began experimenting with it straightaway. The Ancients knew that a prism could produce a spectrum of colours ranging from red light to blue. I realized quickly that “normal” light is best described as white light and is split by the prism into its constituent parts. Furthermore, this happens because the prism refracts the light and bends blue light more than red, so that it produces a spectrum of colours.

  And you were able to prove this?

  Yes. I split the light with a prism, then I blocked off most of the emergent light with a sheet of paper, allowing just one colour through. I found that red was the least refracted observable colour and violet the most. This has become known as the experimentum cruces.

  But you didn’t stop there?

  No, I created another experiment in which I split light with a prism, then passed this light through a lens which focused the emergent beam onto a wall. When this happened, a white spot was produced at the target. Finally, I repeated this experiment but with a cogged wheel placed after the lens. With this wheel I was able to block out one colour coming from the lens before it was focused to a point on the wall. I found that if I blocked a colour, a coloured rather than a white spot was produced. The colour of the spot depended upon which colour I removed from the spectrum emerging from the lens.

  And am I right in saying that you put yourself at some risk with a few of the experiments you conducted in those early days?

  I think now that I may have been a little foolhardy. I nearly blinded myself and could not see properly for days after I stared at the Sun for too long trying to discern coloured rings caused by the glare. But perhaps the most dangerous thing I did was an experiment to see how the curvature of the eye affected the appearance of an object. I placed the tip of a fine dagger between the back of my eyeball and the bone of my eye socket and moved it around. This altered the shape of my eye, and as a result, I observed several strange coloured circles.

  But you decided not to publish your discoveries at this time?

  No, of course I didn’t publish them. I was a young student, barely a BA. I kept my observations to myself recorded in notebooks and I expanded on these over the years. They acted as the basic framework for my book Opticks. The Dutch scientist, Christiaan Huygens, elaborated on some of my early ideas which had appeared in brief papers through the Royal Society long before Opticks was published. His own book, Traité de la lumière, bore many of the hallmarks of my work from a decade earlier.

  I can understand why you wouldn’t have published before you’d established yourself, but by the mid-1670s you were a respected scientist. Why did you wait another 30 years before publishing Opticks?

  I had written the bulk of this book during the 1670s, but I could not bring myself to offer it to the Royal Society. I did not trust them, especially Hooke. I waited until I felt the time was right for the Royal Society to do justice to my work – this was after Hooke was in his grave. In retrospect, I regret that my prevarication delayed publication by almost three decades, but I was not to blame.

  MAKING A QUALITY TELESCOPE

  From his earliest days at Cambridge, Newton was dedicated to astronomy. But, at the same time, he was frustrated by the poor quality of telescopes he could obtain. Never being a man to accept what was handed down to him if he believed he could do better, during the late 1660s he began to produce his own lenses and to improve the refracting telescopes available to him. However, he soon found that the performance of these devices could be improved only so far, and this pushed him into making his own high-quality optical instruments and creating a practical reflecting telescope.

  When did you first become interested in astronomy?

  Again, it was thanks to the library in the Clark’s house. There was a copy of Starry Messenger, which Galileo wrote soon after he had perfected the telescope in 1609. Galileo produced exquisite drawings of the Moon in which he detailed craters and mountains, ravines and canyons. He turned his telescope toward Jupiter and became the first to observe its moons. This book more than any others I read in that library inspired me to imagine conducting my own experiments.

  But you were shocked by the inadequacy of telescopes that you had access to.

  Yes, I certainly was. Galileo had produced the finest instruments of his day with magnifyi
ng powers of 30 or 40, but the field of view was narrow and they had a lot of what astronomers call “chromatic aberration”. This is caused by imperfections in the lenses and it means that rays of different wavelength are not brought together at the same focal point and so they produce a distorted image. I decided to take an entirely different approach. Galileo’s telescopes were all based on the design of the original inventor, the Dutchman, Hans Lippershey. They were what are called “refracting telescopes”. This type of telescope uses two lenses positioned at each end of a tube to produce a magnified image. An alternative device, called a “reflecting telescope”, uses one lens and a mirror to create an image. This had been suggested in Galileo’s day, and one had actually been built by a mathematician named James Gregory, but the image it produced was almost useless.

  But you succeeded where Gregory had failed. And is it true that you made all the components yourself?

  Yes, I succeeded in making a practical reflecting telescope, and yes I did make all the parts of the telescope myself. I tried to get a perfect mirror and exquisitely ground lenses made by specialist craftsmen in London, but they could not do it. I was forced to grind my own lens and to make my own tubes and mountings. I must admit, the end result was a beautiful thing. Reflecting telescopes can be made much smaller than refracting telescopes, which require the lenses to be placed far apart along the tube. My telescope was no more than six inches long and mounted on a tiny stand. With it, I was able to obtain a clear image at a magnification of 40.

  And this led to your first introduction to the scientific community beyond Cambridge, did it not?

  Yes. Isaac Barrow was greatly taken with my telescope, and in 1671 he arranged for it to be demonstrated before a meeting of the Royal Society. The astronomer John Flamsteed was very impressed, as were Christopher Wren and the secretary of the Royal Society, Henry Oldenburg. They even arranged a demonstration of my device for the king, Charles II, who was apparently greatly excited by it. Within a few weeks I had been invited to become a Fellow of the Royal Society.

  A FRESH START

  The 1690s marked a time of great change in Newton’s life. Since arriving in Cambridge in 1661 he had led the life of a cloistered academic, rarely involving himself in the world beyond the walls of Trinity College. In 1687 his greatest work, Principia Mathematica, was published, and consequently he was considered the most important scientist in the world. But then Newton’s life changed dramatically. In 1693 he experienced what may have been a nervous breakdown, and ceased to be involved in practical scientific experiments. Then in 1696 he moved to London where he took up an administrative post as warden of the Royal Mint.

  Would it be fair to say that sometime during the 1690s you began to lose interest in science?

  No, that is by no means true. I have never lost interest in science.

  But in 1696 you left Cambridge University and moved to London. You did very little science after that.

  But Opticks was published eight years after I left Cambridge and I remained president of the Royal Society, did I not? It was not science I grew weary of – science is an endless mystery and a never-ending inspiration to me. What is true is that, from the early 1690s, I became less interested in experiment.

  Do you feel this is because you reached a point where you could go no further?

  I think that is right, yes. With both my pure science experiments and my alchemical work I took things as far as I could go. I hit a wall, if you like. The material in my Opticks was based on work completed between the 1660s and 1690s. I continued to be interested in science and to guide its progress through the Royal Society, of which I was a very active and energetic president for 23 years. But leaving Cambridge was a declaration of intent. I had exhausted the possibilities of experiment and research and wanted to do something entirely different.

  This must have been very difficult for you. Indeed, it has been said that around this time you suffered a temporary mental collapse. Do you feel you can talk about this?

  Yes, I’m aware of these stories, and the fact is, no one but I knows what this episode entailed, and even I have only a distorted memory of it. I think too much has been made of it. Apparently, I wrote a couple of strange letters to colleagues and a couple of visitors to Cambridge reported that I was in an especially uncommunicative state of mind.

  All this was when?

  1693.

  This was also soon after you parted company with Nicolas Fatio du Duillier and about the time you stopped your alchemical studies. Is there any connection between these things?

  As I explained earlier, for me knowledge is all-embracing. I don’t compartmentalize learning. So, alchemy, the Hermetic tradition, ancient religions and science all meld together. I have always tried to find answers to the greatest mysteries, and these studies were my tools. By the 1690s, I had been using those tools for some three decades and I was, well, very tired. People have tried to explain my strange mood in 1693 as the result of inhaling too many noxious gases in my laboratory, or perhaps the result of mercury poisoning. Others have tried to suggest that my so-called nervous breakdown came as a result of delving too deeply into the occult. I’m afraid the real reason is altogether more prosaic. I was worn out. I had gone as far as I could with the resources available to me, and I needed a fresh start.

  And that came in the form of a position at the Royal Mint in London?

  Yes. I saw it as an exciting adventure, a challenge. I moved to the capital and I became an administrator. I have always been interested in organization. That has been one of my strengths as a scientist: I always recorded my discoveries with great clarity and method. This is also what is required of any good administrator. As well as this, I was excited by the prospect of being at the centre of such an important institution as the Royal Mint, at the very heart of the financial world.

  It was also, of course, a job made for a scientist because there were technical aspects to the position where a knowledge of chemistry was an important bonus.

  Absolutely. I was initially offered the position of Warden of the Mint, and then in 1700 I became Master of the Mint. I was most attracted to the task because I was required to use my scientific knowledge in making the minting process as efficient as possible. Indeed, I succeeded in streamlining the production of coin metal at the Mint.

  I understand you were merciless when it came to “clippers” who snipped off and sold bits of gold and silver coins?

  Clippers are common thieves. They are no better than those who rob the innocent or steal from homes. Actually, their crimes are even worse because they are crimes against the state, and their actions threaten to undermine the status quo. I view clippers as traitors. And yes, before you ask, I did indeed attend every hanging of a clipper, even though I did not need to do so. I am proud of this. I also hunted down suspects with great fervour. As far as I am aware, none escaped my net.

  There was one particular villain you pursued and did actually bring to trial for treason, wasn’t there?

  You are referring to William Chaloner. Some people have viewed the man as a romantic figure, a heroic anti-Establishment daredevil, if you will, but he was actually a traitor, and he met a traitor’s end.

  You insisted he face a charge of treason and you ignored all pleas for clemency.

  Yes, I did. His trial took place a little over a year after I started at the Mint, and I wanted to set an example. Chaloner was not some petty thief, he was a brazen forger and counterfeiter. He faced the ultimate punishment. He was dragged on a sledge to Tyburn gallows where he was hanged until almost unconscious, disembowelled, then quartered.

  Do you not feel your actions were unnecessarily ruthless, even inhumane?

  Not in the slightest. Indeed, I find this a strange question. Any of my contemporaries would have done precisely the same thing. Criminals cannot be allowed to get away with their crimes, and those who flout the law must be made examples of.

  LONDON LIFE

  Newton’s character had always b
een a strange amalgam of the hermit and the social climber. His childhood spent in Grantham, then a rather small, sleepy town, made him curious about the big city, but at the same time he guarded his privacy with unusual vigour. He was an introverted man, but he aspired to achieve recognition beyond the academic world, and so craved the attention of Establishment figures. His position at the Royal Mint set him up perfectly to fulfil this desire, and Newton seized with both hands the opportunity it offered. His beautiful niece stayed at his London house and became socially advantageous to him.

  Was it difficult adjusting to your new life in London after leaving Cambridge?

  Yes and no. Throughout my final decade in Cambridge I spent more and more time in the capital. Toward the end of the 1680s I had represented the University of Cambridge as a Member of Parliament, and this was an incredibly eventful period in British history. William of Orange took over the monarchy in a bloodless coup, the Glorious Revolution of 1688. I was involved in that process, along with my parliamentary colleagues, in what was called the Convention Parliament. I visited London frequently, from as early as the 1660s. I used to catch the stagecoach from the Rose public house in Cambridge to the Swan tavern in Gray’s Inn Lane in the heart of London. The journey was long and uncomfortable. I purchased much of my library in a district called Little Britain and it was here I found chemicals and alchemical apparatus. It was also in London that I bought the equipment I needed to produce my telescopes and other optical equipment. Sometimes I stayed for a few weeks. Even so, it took me a while to get used to the change in my lifestyle. In Cambridge I had a very comfortable set of rooms and my laboratory had served me well – it had evolved considerably over the decades I spent in experiment. However, Cambridge is a small town and the university is very self-contained. I had little to do with the other Fellows, and I shunned almost all social activities linked to my college.