I was prompted to post this partly in response to the posting yesterday by Thecuriousastronomer about Galileo.
William Gilbert of Colchester deserves pride of place in any account of the scientific revolution of the seventeenth century, because he was the first person to set out clearly in print the essence of the scientific method – the testing of hypotheses by rigorous experiments – and to put that method into action. He did so to such effect that his discoveries in the field of magnetism were unsurpassed for two centuries; and by a happy calendrical coincidence, his great book on magnetism was published at the dawn of the new century, in 1600.
To put Gilbert’s life and work in an historical perspective, in 1600 Elizabeth I was nearing the end of her long reign. The Spanish Armada had been defeated just twelve years earlier, and although the first attempt to plant an English colony in North America (at Roanoke Island, in what is now North Carolina) had failed in the mid-1580s, the successful attempt at establishing a permanent settlement in Jamestown, Virginia, would take place in 1606. In 1600, William Shakespeare was at the height of his creative powers, and in the 1599-1600 season the plays performed at his Globe Theatre in London were Julius Caesar, Twelfth Night, and As You Like It, while Hamlet and the Merry Wives of Windsor followed the next year. London itself was a city of some 75,000 inhabitants, with twice that number in the rapidly growing suburbs sprawling outside the city walls. It was filthy, smelly and unhygienic; bubonic plague spread by the fleas that lived on rats often broke out in summer, when those that could afford to retreated to the countryside. The poor had no such option.
Unfortunately, we know only the outlines of Gilbert’s own life, because of two disasters that occurred later in the seventeenth century. Many of his papers and experimental equipment were left to the Royal College of Physicians when he died, and both their building and Gilbert’s own former house in London were destroyed in the Great Fire of 1666. Any other material that might have been of interest to historians would have been at his house in Colchester, but that was in a part of the town destroyed during the English Civil War, at what became known as the Second Siege of Colchester, in 1648. There is a manuscript in the Bodleian Library in Oxford which gives an actual birth date, 24 May 1544. We also know that Gilbert went up to Cambridge in 1558, and 14 would be about the right age for a scholar to enter the university in those days.
Once Gilbert arrived in Cambridge, he began to leave traces which have survived to the present day. He stayed in residence at the university for eleven years, gaining both his BA (1560) and MA (1564), qualifying as a doctor (1569) and becoming a Senior Fellow (all at St John’s College). There is no record of his activities between 1569 and 1573, and this has led to fanciful accounts that he may have traveled widely in Europe, perhaps even meeting Galileo. Since Galileo was only born in 1564, however, it seems unlikely that any such meeting occurred! But the most likely explanation of Gilbert’s activities during these years after leaving Cambridge and before setting up as a physician in London in 1573 is that it was just at this time that he became seriously interested in magnetism and carried out his early experiments; but the work certainly wasn’t completed then.
Our first clue to Gilbert’s approach comes from the book itself. The preface to the book also mentions that it describes work that had been essentially complete some 18 years before it was published.
It is an intriguing coincidence (if it is only a coincidence) that Gilbert first took an important office in the Royal College of Physicians, as Censor, in 1581; and it is hard to see how the successful and busy physician that Gilbert became after that time could have found time for much scientific work, If Gilbert began his key magnetic experiments (perhaps in Colchester) in the four years ending in 1573, then spent a decade using his spare time to refine his results, that places the key experiments, the first true application of what became the scientific method, in the early 1570s, in England, before Galileo was even ten years old, and dates the completed work to the early 1580s, when Galileo was a medical student in Pisa.
The evidence that Gilbert started his medical practice in 1573 comes from references after his death (in 1603) that he had been a London physician for thirty years; but the first direct documentary evidence of his life in London dates from 1581, with that appointment as Censor, when he was already a member of the Royal College of Physicians. Throughout the rest of the century, Gilbert was a prominent member of the College, holding several offices including that of Treasurer from 1587 to 1594 and from 1597 to 1599, and being elected President in 1600.
His career as a physician was crowned by the appointment as one of the Queen’s doctors in 1601, and this too has been the subject of exaggerated interpretation down the years. Gilbert was just one of the royal panel of physicians, not singled out in any way, and he received the usual stipend of one hundred pounds a year (referred to as a “pension”) for his services. This has grown in the telling so that he is sometimes referred to as the Queen’s Chief Physician (or her Personal Physician), and the pension becomes a mythical personal bequest in the Queen’s Will. None of this is true. But it is true that although Gilbert was confirmed in his post of Royal Physician when James I (in whose honour the first American colony was named) succeeded Elizabeth in 1603, he died later that year, almost certainly of plague. His lasting memorial is the book, De Magnete, published in 1600.
Naturally occurring magnetic rocks, or lodestones, had been known since ancient times, both in China and in the Eastern Mediterranean. Our name “magnet” comes from the old term lithos magnetis, or “magnesian stone,” which may have referred to lodestones found near the town of Magnesia, in Greece, although this is no more than a supposition. But although lodestones were known in ancient times, their properties were not investigated scientifically, and they were surrounded by superstition (as in the belief that they could cure illnesses) and exaggeration, as when Pliny tells us that:
Near the river Indus there are two mountains, one of which attracts iron and one repels it. A man with iron nails in his shoes cannot raise his feet from the one or put them down on the other.
There was also considerable confusion in ancient times about the relationship between what we now call electricity and magnetism. The Ancient Greeks valued amber, which they called elektron, and is actually the fossilised remains of resin from a variety of trees. They knew that when it was rubbed, it gained the power of attracting straws, small pieces of sticks, and even thinly beaten pieces of copper or iron. But they thought that the effect was a result of the amber being heated by friction when it was rubbed, This was not a completely mad idea. The Greeks had noticed that small pieces of straw and so on are “attracted” to a fire (we now know, because of convection currents set up in the air) and thought that something similar might be happening with the amber, and although they noticed that amber could attract all kinds of small objects, while lodestone could only attract iron, it still seemed to them that the attractive power of amber was essentially the same as the attractive power of the lodestone.
Nothing new was discovered about magnetism until the eleventh century AD, when suddenly we find references to the use of magnetic compasses in navigation. The origins of the discovery of this pointing property of magnets are lost, and it is clear that whoever first made the discovery realised its enormous commercial and military value, and kept it secret as long as possible. The discovery seems to have been made first in China, and a little later in Europe, assuming that the knowledge did not spread from China westward. One reason to think that the discoveries may have been independent of one another is that from the earliest references Chinese compasses are designed to point south, while European compasses are designed to point north.
In the centuries that followed, a great deal of information, misinformation and superstition grew up as a result of interest in the compass. As it became appreciated that the lodestone had two special points, just as the heavenly sphere has two special poles, even before it was widely understood that the Earth is round it was common to make lodestones round, to mimic the shape of the heavenly sphere. Such a sphere has two magnetic poles, one of which points north and the other south.
It was known that with two such lodestones opposite poles attract and similar poles repel one another, and that if a lodestone is cut in half between the two poles, two new poles appear at the cut, each the opposite of the original pole in that half of the lodestone. It was even understood that you could find the poles of a spherical lodestone by laying bits of iron wire on the surface of the sphere and seeing how they align to point to the magnetic poles. But there was confusion about why a compass needle should point north – was it because it was attracted by the Pole Star, or was it because there was a magnetic island far to the north of Europe? Or was it just because it was in the nature of magnetic needles to point north? And although a magnetised needle would point to the north, it did not try to move to the north, even though it would both point to and move towards a lodestone placed near it. Magnetism was also still seen as having medicinal properties, and a supposed cure for gout, for example, was to bandage a piece of magnetic material tightly up against the affected limb. This at least had the merit, unlike some Medieval medical treatments, of doing no harm to the patient.
Yet another key property of the compass needle, the way it dips to point slightly below the horizontal, was only discovered in the sixteenth century, just about in Gilbert’s lifetime. Although the dip was mentioned in a letter written by the German Georg Hartmann in 1544, this was not published at the time, and the first report of the discovery to reach a wide audience came from the London-based instrument maker Robert Norman, in 1581. This discovery essentially completed the package of information about magnetism (and electricity) that Gilbert set out to explain and understand through his experiments, and to describe in his great book.
I don’t intend to take you through all of Gilbert’s work, because the important point I wish to emphasise is not what he discovered, but how he discovered it.
The full title of his masterwork is usually translated as On the Loadstone and Magnetic Bodies and on the Great Magnet the Earth. Gilbert sets out his stall as the practitioner of a new kind of investigation of the world in the preface of his book, pulling no punches as he kicks off with the assertion that:
In the discovery of hidden things and in the investigation of hidden causes, stronger reasons are obtained from sure experiments and demonstrated arguments than from probable conjectures and the opinions of philosophical speculators of the common sort
at once distancing himself from the school of natural philosophy, dating back to the Ancient Greeks, which attempted to unravel the mysteries of the Universe solely by thinking about them, without actually carrying out experiments. It’s worth quoting extensively from that preface, to make it clear that not only was Gilbert doing something new, he was well aware of the revolutionary nature of his new style of investigation:
Every day, in our experiments, novel, unheard-of properties came to light . . .
But why should I, in so vast an ocean of books whereby the minds of the studious are bemuddled and vexed – of books of the more stupid sort whereby the common herd and fellows without a spark of talent are made intoxicated, crazy, puffed up; and are led to write numerous books and to profess themselves philosophers, physicians, mathematicians, and astrologers, the while ignoring and contemning men of learning – why, I say, should I add aught further to this confused world of writings, or why should I submit this noble and (as comprising many things before unheard of) this new and inadmissible philosophy to the judgment of men who have taken oath to follow the opinions of others, to the most senseless corrupters of the arts, to lettered clowns, grammatists, sophists, spouters, and the wrong-headed rabble, to be denounced, torn to tatters and heaped with contumely.
To you alone, true philosophers, ingenuous minds, who not only in books but in things themselves look for knowledge, have I dedicated these foundations of magnetic science – a new style of philosophizing. But if any see fit not to agree with the opinions here expressed and not to accept certain of my paradoxes, still let them note the great multitude of experiments and discoveries – these it is chiefly that cause all philosophy to flourish; and we have dug them up and demonstrated them with much pains and sleepless nights and great money expense. Enjoy them you, and, if ye can, employ them for better purposes. I know how hard it is to impart the air of newness to what is old, trimness to what is gone out of fashion; to lighten what is dark; to make that grateful which excites disgust; to win belief for things doubtful; but far more difficult is it to win any standing for or to establish doctrines that are novel, unheard-of, and opposed to everybody’s opinions. We care naught, for that, as we have held that philosophy is for the few.
Gilbert’s first objective is to draw a distinction between magnetism and the amber effect (for which he introduces the term electricity) in order to clear the air before moving on to his study of magnetism itself. In order to do this, he has to carry out a thorough investigation of electricity, and to help him he invents the first electroscope (he called it a versorium), in the form of a light needle, made of metal, “three or four fingers long” and “poised on a sharp point after the manner of a magnetic pointer” (that is, a compass needle).
When a piece of rubbed amber, or other suitable material, is brought near to one end of the needle, the pointer revolves. Using this sensitive detector, Gilbert set out to investigate the properties of electricity. The Greeks had speculated that the attraction might be caused by the warmth of rubbed amber, and in all the time since them this had remained a possible explanation of the phenomenon. It was Gilbert who took what seems to us the obvious step of warming amber by other means, and finding that this does not produce an attraction (nor, as he pointed out, do other warm objects display electric attraction). It was the rubbing, not the warmth, that mattered. In the same spirit, Gilbert later tests the old wives’ tale that garlic will demagnetise iron or a lodestone by actually rubbing them with garlic and showing that there is no effect. But this didn’t stop the old wives’ tale persisting through the seventeenth century!
Gilbert suggested that the rubbing removed a “humour” from the body, and left behind an “effluvium” surrounding the rubbed object; if you replace these terms by, respectively, “charge” and “electric field,” this is essentially the modern view of what is going on.
Above all, though, Gilbert appreciated the need for careful, repeatable experiments.
We have set over against our discoveries larger and smaller asterisks according to their importance and their subtility. Let whosoever would make the same experiments handle the bodies carefully, skillfully, and deftly, not heedlessly and bunglingly; when an experiment fails, let him not in his ignorance condemn our discoveries, for there is naught in these books that has not been investigated and again and again done and repeated under our eyes. Many things in our reasonings and our hypotheses will perhaps seem hard to accept, being at variance with the general opinion; but I have no doubt that hereafter they will win authoritativeness from the demonstrations themselves . . .
This natural philosophy (physiologia) is almost a new thing, unheard of before; a very few writers have simply published some meagre accounts of certain magnetic forces. Therefore we do not quote the ancients and the Greeks as our supporters, for neither can paltry Greek argumentation demonstrate the truth more subtilly nor Greek terms more effectively, nor can both elucidate it better . . .
To those men of early times and, as it were, first parents of philosophy, to Aristotle, Theophrastus, Ptolemy, Hippocrates, Galen, be due honour rendered ever, for from them has knowledge descended to those that have come after them: but our age has discovered and brought to light very many things which they too, were they among the living, would cheerfully adopt. Wherefore we have had no hesitation in setting forth, in hypotheses that are provable, the things that we have through a long experience discovered.
In all, there are 33 discoveries denoted by asterisks in the chapter of De Magnete on electricity, indicating that Gilbert had carried out all these experiments for himself. Although some of these discoveries might have predated him, there is no surviving record of any earlier work on any of the 33 discoveries, which range from the discovery that a wide variety of other materials (such as sapphire, sulphur, and sealing-wax) attract light objects when rubbed to the fact that solar heat concentrated on to amber with a concave mirror does not result in attraction, to the fact that an electric object attracts small pieces of material towards itself in a straight line. And, of course, the electric force, as we would now call it, attracts a wide variety of materials, not just iron. In all this work, and his theoretical explanations of the things he observed, Gilbert single-handedly established electricity as a new branch of science, distinct from magnetism. Virtually nothing was added to his work in the seventeenth century, so that it provided the jumping off point for the eighteenth-century work which led to the concept of electric charge.
In his work on magnetism, Gilbert used the spherical lodestones that I have already described, which he called terrellae, meaning “little Earths.”
It was at the very heart of his magnetic philosophy that he regarded these as models of the Earth itself, and that he thought of the Earth as a giant spherical magnet. This is an important distinction. Earlier investigators made their lodestones spherical in order to mimic the shape of the heavens; Gilbert made his spherical in order to mimic the shape of the Earth. The nature of the magnetic influence of a terrella was investigated using a magnetised compass needle, which would align itself to point to the poles of the terrella just as the terrella would align itself to point to the poles of the Earth, with no need to invoke magnetic islands to the north of Europe, or some influence from the Pole Star.
In these experiments, Gilbert was the first person to appreciate that, because magnetic opposites attract, it is the south pole of a magnet that points to the north pole of the Earth; in modern language, we sometimes refer to the “north-seeking” pole of a compass needle to make the point clear. As Gilbert puts it:
All who hitherto have written about the poles of the loadstone, all instrument-makers, and navigators, are egregiously mistaken in taking for the north pole of the loadstone the part of the stone that inclines to the north, and for the south pole the part that looks to the south: this we will hereafter prove to be an error. So ill-cultivated is the whole philosophy of the magnet still, even as regards its elementary principles.
This is not just some matter of hair-splitting semantics, or a cheap gibe at his predecessors. The point is that Gilbert recognises that it is the same process that makes a magnet that is free to move orient itself relative to a fixed magnet that makes a compass needle orient itself with respect to the Earth’s magnetism. The Earth is a magnet, and therefore understanding magnetism will help us to understand the Earth. This is the first example of trying to understand global (ultimately, universal) forces by carrying out experiments on a laboratory scale. And, as Gilbert appreciates, magnetism can then be used to provide information about what is going on deep inside the Earth, in regions we can never see.
The other aspect of Gilbert’s work that I particularly want to draw attention to takes us in the other direction – not inwards to probe the structure of the Earth, but out into space. Gilbert was among the first to appreciate that there is something more to magnetism than an attractive influence, or force; and he was the first to set out clearly just what that “something” seemed to be. In doing so, he came very close to the modern idea of a field, suggesting that the magnetic effect surrounded the Earth (and, by implication, other planets) in a sphere of influence.
This work jumped off from the investigation of magnetic dip. This was first fully described in print by Robert Norman, in a little book called The New Attractive, which he published in 1581, several years after what seems to have been Gilbert’s most productive experimental period. Since Gilbert repeated some of Norman’s experiments and described their results in De Magnete, he must have found some time during his busy life in the 1580s to do at least a little scientific work; it is also possible that some of his experiments on dip pre-dated Norman’s work, although they were not published until 1600. We shall never know, and it doesn’t really matter.
Norman tells us that he began to investigate magnetic dip (he called it “declination,” but that term has a quite different meaning today) when he got angry at the problems it caused him when he was manufacturing compasses. It was well known by then that a magnetised needle suspended from its mid-point would not lie horizontally, but with the north-seeking end pointing downwards, below the horizon. (In the Northern Hemisphere, of course. In the south, it is the south-seeking end that dips below the horizon.)
In order to compensate for this, instrument makers such as Norman had to snip a little piece off the north-seeking end of the needle so that it would balance perfectly on its pivot and make the compass usable for navigation. Norman became so cross when he spoiled a particularly fine compass by cutting too much off the needle that he decided to find out just why the magnetised needles behaved in this way, and to do so he invented a new kind of compass, the dip circle.
In a dip circle, a graduated circular rim (like the tyre of a bicycle wheel) is set up vertically, and a compass needle is supported on an axle in the middle of the wheel so that it can rotate freely in the vertical plane. Norman found that needles set up in this way always pointed downward at the same angle, 67 degrees, in London, and he conjectured that the angle of dip might be related to latitude.
But his great insight, the idea that Gilbert picked up on and developed, was that the magnetic needle is not being attracted towards the North Pole; it simply points to the North Pole, indicating the direction of something (which we would now call the magnetic field) in the vicinity of, in this case, London. He said that “In my judgment [the point attractive] ought rather to be called the point respective.” He reinforced this conclusion with a particularly subtle experiment, which Gilbert repeated and described in De Magnete. He took a piece of iron or steel a couple of inches long, and thrust it through a piece of cork. He then filled a glass vessel with water, and by painstakingly carving away at the cork little by little, made the needle float horizontally in the water, a few inches below the surface, suspended by the buoyancy of the cork, “like to the beam of a pair of balances being equally poised at both ends.” Then:
Take out the same wire without moving the cork, and touch with the [lodestone], the one end with the south of the Stone, and the other end with the north, and then set it again in the water, and you shall see it presently turn upon his own centre, showing the aforesaid declining property, without descending to the bottom, as by reason it should, if there were any attraction downwards.
So the needle is lining up with what we would now call the magnetic field, but which Norman refers to as a “virtue.” He says “I am of opinion, that if this virtue could by any means be made visible to the eye of man, it would be found in a spherical form extending round the Stone.”
Gilbert was able to go further, by investigating the way dip varied around his terrellae – remember that it is a key contribution to scientific thinking that he regarded these models as miniature Earths, and that he could therefore extrapolate from their behaviour to the behaviour of the real Earth. He was able to show that the angle of dip does indeed vary with latitude, and he found another way of showing that what is being measured is a direction, not an attraction, by demonstrating that for a spherical terrella the dip was always the same at any particular latitude, whatever the strength of the lodestone. If the dip were due to an attraction, you would expect it to be more pronounced if the magnetism of the stone were stronger, but this is not the case. The needle takes up its orientation relative to the terrella (or the Earth) as a whole, not because of the strength of an attraction towards the pole. “This movement,” says Gilbert, “is produced not by any motion away from the horizon towards the earth’s centre, but by the turning of the whole magnetic body to the whole of the earth.”
This idea of the Earth extending an influence out into space around itself links with Gilbert’s speculations about the nature of the Universe itself and the place of the Earth within it. In doing so, he makes another conceptual leap. Having used terrellae as models for the Earth, he now uses the Earth as a model for other objects in the Universe. Copernicus had published his De Revolutionibus only in 1543, the year before Gilbert was born, and as the fate of Galileo highlights, in Gilbert’s lifetime it was still far from being received wisdom that the Earth is just a planet orbiting the Sun, unsuspended in the void. Indeed, it was still a matter of debate whether the Earth rotated on its axis, or the heavens revolved around the Earth – although Gilbert left his readers in no doubt about where he stood on that question.
As Gilbert pointed out, “either the earth whirls in daily motion from west to east, or the whole heavens and the rest of the universe of things necessarily speeds about from east to west.” But the stars are so distant from us that they would have to travel at enormous speeds to complete the circuit in 24 hours. He dismissed the idea of the “adamantine spheres” out of hand – “what structure . . . can be imagined so strong, so tough, that it would not be wrecked and shattered to pieces by such mad and immeasurable velocity?”
This is a question that simply would not have occurred to his predecessors. They regarded the heavens as something mystical, not subject to the same rules as solid objects here on Earth. But here is Gilbert, almost a century before Newton, implicitly assuming that the same laws of physics apply to the most distant stars as to a lump of matter on Earth. Science is encroaching on what used to be the territory of religion, with dire consequences for some scientists in some parts of Europe. It was still possible to be burned at the stake for expressing such views in Catholic countries; in England, you might get burned for being a Catholic, but not for offering a scientific opinion about the nature of the Universe. So Gilbert is free to say that “the space above the earth’s exhalations is a vacuum,” and that “the entire terrestrial globe, with all its appurtenances, revolves placidly and meets no resistance” in that vacuum.
This is an implicit recognition of something studied in more detail by both Galileo and Newton – the idea of inertia, that an object once set in motion will continue to move as long as it is not affected by external forces (such as friction). Gilbert does not explicitly say that the Earth also moves around the Sun, but he refers approvingly to the work of Copernicus (“a man most worthy of the praise of scholarship”) in the context of the motion of the other planets round the Sun.
De Magnete summarises a body of work which marks the beginning of the application of the scientific method of investigating the world, and pointed the way for Galileo, Newton, and the other seventeenth century pioneers. Most of all, though, it explained clearly for the first time the nature of the experimental scientific method.
Oh yes — and we know from his correspondence that Galileo read and admired De Magnete.
Adapted from my book Science: A History.