Popular Science Monthly/Volume 59/August 1901/Gilbert of Colchester
|GILBERT OF COLCHESTER.|
PROFESSOR OF PHYSICS IN MANHATTAN COLLEGE, NEW YORK CITY.
AT a period when natural science was taught and studied in the schools of Europe from text-books, we find Gilbert of Colchester proclaiming by example and advocacy the paramount value of experiment for the advancement of learning. He was unsparing in his denunciation of the superficiality and verbosity of mere bookmen, and had no patience with writers who treated their subjects 'esoterically, reconditely and mystically.' For him, the laboratory method was the only one that could secure fruitful results and effectively push back the frontiers of knowledge.
It is true that men of unusual ability and strong character strove before his time to adjust the claims of authority in matters scientific. While respectful of the teachings of recognized leaders, they were not awed into acquiescence by the customary academical 'magister dixit.' On the contrary, they wanted to test with their eyes in order to judge with reason; believing in the supreme importance of experiment, they sought to acquire a knowledge of nature from nature herself.
Such were Albert the Great and Friar Bacon. Albert did not bow obsequiously to the authority of Aristotle or any of his Arabian commentators; he investigated for himself and became, for his age, a distinguished botanist and physiologist.
Roger Bacon, after absorbing the learning of Oxford and Paris, wrote to the reigning Pontiff, Clement IV., urging him to have the works of the Stagyrite burnt in order to stop the propagation of error in the schools. The Franciscan monk of Ilchester has left us in his Opus Majus a lasting memorial of his practical genius. In the section entitled 'Scientia Experimentalis,' he affirms that "Without experiment, nothing can be adequately known. An argument proves theoretically but does not give the certitude necessary to remove all doubt, nor will the mind repose in the clear view of truth, unless it find it by way of experiment." And in his Opus Tertium: "The strongest arguments prove nothing so long as the conclusions are not verified by experience. Experimental science is the queen of sciences and the goal of all speculation."
No one, even in our own times, ever wrote more strongly in favor of the practical method than did this follower of St. Francis in the thirteenth century. Being convinced that there can be no conflict between scientific and revealed truths, he became an irrepressible advocate for observation and experiment in the study of the phenomena and forces of nature.
The example of Albert and of Friar Bacon, not to mention others like Vincent of Beauvais, the Dominican encyclopedist, was, however, not sufficient to wean students and professors from the easy-going routine of book-learning. A few centuries had to elapse before the weaning was effectively begun; and the man who powerfully contributed to this result was Dr. William Gilbert, the philosopher of Colchester.
Gilbert was born in Colchester* in 1540 in a house which, thanks to the appreciation of the authorities of that ancient town, the writer found in an excellent state of preservation on the occasion of his visit in quest of Gilbertiana.
Having received the elements of his education in the grammar school of his native town, Gilbert entered St. John's College, Cambridge. He graduated in 1560, 'commenced' M. A. in 1564, and took his M. D. degree in 1569. On leaving the university, he traveled for some time on the Continent, where he made the acquaintance of several distinguished scholars. On his return to England he practised, we are told, 'with great success and applause.' His reputation obtained for him the presidency of the Royal College of Physicians for the year 1600, and ultimately led to his being appointed physician in ordinary to the Queen (Elizabeth).
We are not here concerned with Gilbert as a physician and still less as a courtier. His claims to enduring recognition are of a higher order, for we regard him not only as the author of a monumental work of physical research, but also as founder, by word and deed, of the Experimental School of philosophy.
In his address to the 'candid reader' at the beginning of De Magnete he pointedly says:
Further on he adds:
On one occasion, lie hears that Baptista Porta, whom he calls 'a philosopher of no ordinary note' said that a piece of iron rubbed with a diamond turns to the north. He suspects this to be heresy. So, forthwith he proceeds to test the statement by experiment. He was not dazzled by the reputation of Baptista Porta; he respected Porta, but respected truth even more. He tells us that he experimented with seventy-five diamonds in presence of many witnesses, employing a number of iron bars and pieces of wire, manipulating them with the greatest care while they floated on corks; and he concludes his long and exhaustive research by plaintively saying: "Yet never was it granted me to see the effect mentioned by Porta."
Though it led to a negative result, this probing inquiry was a masterpiece of experimental work.
Gilbert incidentally regrets that the men of his time "are deplorably ignorant with respect to natural things,"' and the only way he sees to remedy this is to make them "quit the sort of learning that comes only from books and that rests only on vain arguments and conjectures," for he shrewdly remarks that "even men of acute intelligence without actual knowledge of facts and in the absence of experiment easily fall into error."
Acting on this intimate conviction, he labored for eighteen years over the theories and experiments which he sets forth in his great work on the magnet. "There is naught in these books," he tells us, "that has not been investigated, and again and again done and repeated under our eyes." He begs any one that should feel disposed to challenge his results to repeat the experiments for himself "carefully, skilfully and deftly, but not heedlessly and bunglingly."
It has often been said that we are indebted to Sir Francis Bacon, Queen Elizabeth's Chancellor, for the inductive method of studjing the phenomena of nature. This is an error, for all investigators employed it from Archimedes the Syracusan down to Gilbert, the contemporary of Lord Verulam. Bacon's merit lies in the fact that he not only minutely analyzed the method, pointing out its uses and abuses, but also that he admitted it to be the only one by which we can attain an accurate knowledge of the physical world around us. His sententious eulogy went forth to the world of scholars invested with all the importance, authority and dignity which the high position and worldwide fame of the philosophic Chancellor could give it. But while Bacon thought and wrote in his study, Gilbert labored and toiled in his workshop. By his quill. Bacon made a profound impression on the philosophic mind of his age; by his researches, Gilbert explored two vast provinces of nature and added them to the domain of science. Bacon was a theorist, Gilbert an investigator. For eighteen years and more he shunned the glare of society and the throbbing excitement of public life; he wrenched himself away from all but the strictest exigencies of his profession, in order to devote himself undistractedly to the pursuit of science. And all this more than twenty years before the appearance of Bacon's Novum Organum, the very work which contains the philosopher's 'large thoughts and lofty phrases' on the value of experiment as a means for the advancement of learning. During that long period Gilbert haunted Colchester, where he delved into the secrets of nature and prepared the materials for his grand work, De Magnete. The publication of this Latin treatise made him known in the universities at home and especially abroad: he was appreciated by all the great physicists and mathematicians of his age; by such men as Sir Kenelm Digby; by William Barlowe, a great 'magneticall' man; by Kepler, the astronomer, who adopted and defended his views; by Galileo himself, who said: 'I extremely admire and envy the author of De Magnete.'
If any one then deserves to be called the founder of the "experimental school of philosophy, we contend that it is not Bacon the thinker and essayist, but Gilbert the methodical worker and fruitful discoverer.
The originality of Gilbert's work and the character of his discoveries, together with the reputation which he enjoyed in the greater seats of learning, ended by giving umbrage to Bacon, and the world saw the strange spectacle of a great chancellor forgetting the teachings of his own philosophy and becoming jealous. He even carried his ill feeling so far as to write belittlingly of the conclusions of his illustrious rival, saying in his De Augmentis Scientiarum that "Gilbert had attempted a general system upon the magnet, endeavoring to build a ship out of materials not sufficient to make the rowing-pins of a boat."
It will be interesting to see what these 'rowing-pins' were, for then we shall have a scale by which to judge the intensity of Bacon's jealousy and the magnitude of his belittling ability.
Gilbert's electrical work is contained in Book II of De Magnete; and we may say at once that the second chapter of that famous book is the first chapter on electricity ever written. Nothing was known before Gilbert's time save the attraction for light bodies observed in rubbed amber and jet.
Gilbert goes to work and devises an instrument to enable him to study readily the electrical behavior of rubbed substances. He called it a Versorium, we should call it an electroscope. "Make to yourself," he says, "a rotating needle of any sort of metal three or four fingers long and pretty light and poised on a sharp point." He then briskly rubs and brings near his versorium glass, sulphur, opal, diamond, sapphire, carbuncle, rock-crystal, sealing-wax, alum, resin, etc., and he finds that all these attract his suspended needle, and not only the needle, but everything else. His words are remarkable: 'Ad electrica feruntur omnia.' Here is a great advance on the amber and jet, the only two bodies previously known as having the power to attract 'straws, chaff and twigs,' the usual test-substances of the ancients. Pursuing his investigations, he finds a class of bodies which perplex him, because when nibbed they do not affect his electroscope. Among these he enumerates: bone, ivory, marble, flint, silver, copper, gold, iron, even the lodestone itself. The former class he called electrica, electrics, deriving the term from electron, the Greek name for amber; the latter class he termed anelectrica, non-electrics.
Science therefore owes to Gilbert the terms electric and electrical; the term electricity was a coinage of a later period, due probably to the illustrious Irish philosopher, Robert Boyle, who uses the term in his work On the Mechanical Production of Electricity, published in 1675. Gilbert never uses electricitas, but speaks of corpora electrica, effluvia electrica, attractio electrica, motus electricus and the like. Had Gilbert chosen the Latin name for amber, succinum, as he might have done, we should not be speaking to-day of electricity, electrostatics, electro-optics, electrics, dielectrics; but should probably be using succinic for electric, succinical for electrical, succinicity for electricity, together with a series of harsh-sounding derivatives and compounds.
As we said, Gilbert was perplexed by the anomalous behavior of his anelectrics. He toiled and labored hard to find out the cause. He undertook a long, abstract, philosophical discussion of the nature of bodies which, from its very subtlety, failed to reveal the cause of his perplexing anomaly. Gilbert failed to discover the distinction between conductors and insulators, and, as a consequence, never found out that similarly electrified bodies repel each other. Had he but suspended an excited stick of sealing-wax, what a promised land of electrical wonders would have unfolded itself to his vision! and what a harvest of results such a reaper would have gathered in! He noticed the effect of distance; for he says, 'The nearer the electric is to the versorium, the quicker is the attraction.' It was reserved, however, for the French mathematician and engineer, Coulomb, to show in 1785 that the law of attraction or repulsion between two electrified particles varies inversely as the square of the distance between them.
From solids, he proceeds to examine the behavior of some liquids, and finds that they too are susceptible of electrical influence. He notices that a piece of excited amber when brought near a drop of water deforms it, drawing it out into a conical shape. He even experiments with smoke, concluding that the small carbon particles are attracted by an electrified body. It was only a few years ago that Dr. Oliver Lodge, extending this observation, proposed to lay the poisonous dust floating about in the atmosphere of lead works by means of large electrostatic machines. He even hinted in his Royal Institution lecture that they might be useful in dissipating mists and fogs, recommending that a trial be made on some of our ocean-bound steamers.
Gilbert next tries heat as an agent to produce electrification. He takes a red-hot coal and finds that it has no effect on his electroscope; he heats a mass of iron up to whiteness and finds that it too exerts no electrical effect. He tries a flame, a candle, a burning torch, and concludes that all bodies are attracted by electrics save those that are afire or flaming, or extremely rarefied. He then reverses the experiment and brings near an excited body the flame of a lamp, and he ingenuously states that the body no longer attracts the pivoted needle. He thus discovered the neutralizing effect of flames, and supplied us with the readiest means we have to-day of discharging non-conductors.
He goes a step further; for we find him exposing some of his electrics to the action of the sun's rays in order to see whether they acquired a charge; but all his results were negative. He then concentrates the rays of the sun by means of lenses, evidently expecting some electrical effect; but finding none, he concludes with a vein of pathos that the sun imparts no power, but dissipates and spoils the electric effluvium.
Professor Righi has shown that a clean metallic plate acquires a positive charge when exposed to the ultra-violet radiation from any artificial source of light, but that it does not when exposed to solar rays. The absence of electrical effects in the latter case is attributed to the absorptive action of the atmosphere on the shorter waves of the solar beam.
Of course, Gilbert permits himself some speculation as to the nature of the agent he was dealing with. He thought of it, reasoned about it, pursued it in every way; and came to the conclusion that it must be something extremely tenuous indeed, but yet substantial, ponderable, material. "As air is the effluvium of the earth," he says, "so electrified bodies have an effluvium of their own, which they emit when stimulated or excited;" and again: "It is probable that amber exhales something peculiar that attracts the bodies themselves."
In 1862, another Gilbert, Sir Wm. Thomson (now Lord Kelvin), writing to his friend. Professor Tait, of Edinburgh, said: "Tell me what electricity is and I'll tell you everything else"; and in April, 1893, the same Lord Kelvin, replying to the writer, added: "I see no reason to say otherwise than what you tell me I said to Professor Tait in 1862." Despite, then, the great work of Clerk Maxwell and the corroborative experiments of Hertz, we must still admit that the ultimate nature of electricity remains wrapped in mystery. It is true, we discard the material effluvium of Gilbert, but only to substitute for it an ethereal ripple, a quiver, a wave motion in the hypothetical ether with which we fill all space.
From 1580 to 1600, we find Gilbert spending in his workship all the leisure he can snatch from his professional duties. He notes down his experiments, his failures as well as his successes, discusses them, reasons on them, and pursues his inquiry further and further. In a word, we find him toiling in his workshop at Colchester as Faraday toiled more than 200 years later in the low, dark rooms of the Royal Institution of Great Britain. Both were actuated by the same calm, persevering, experimental spirit. Gilbert founded and christened the science of electrics; he left it in its infancy, it is true; but with sufficient vitality to enable it to survive the neglect of years, until at last it was taken up and fondly cared for by our Franklins and Faradays.
The science of magnetism is even more indebted to Gilbert than that of electricity. The ancients spoke of the lodestone as the Magnesian stone, from its being found in Magnesia, in Asia Minor. Gilbert constantly uses the adjective magnetica; and it is to his use of that word that we owe the terms magnet, magnetic and magnetism. He showed that a great number of bodies could be electrified; but he maintained that those only could exhibit magnetic properties which contain iron. He satisfies himself of this by rubbing with a lodestone such substances as wood, gold, silver, copper, zinc, lead, glass, etc., and then floating them on corks, quaintly adding. that they show 'no poles, because the energy of the lodestone has no entrance into their interior.'
To-day we know that nickel and cobalt behave like iron, whilst antimony, bismuth, copper, silver and gold are susceptible of being influenced by powerful electromagnets, showing what has been termed diamagnetic phenomena. Even liquids and gases, in Faraday's classical experiments, yielded to the influence of his great magnet; and Professor Dewar, in the same Royal Institution, exposed some of his liquid air and liquid oxygen in the presence of the writer to the influence of Faraday's electromagnet and found them to be strongly attracted, thus behaving like the paramagnetic bodies, iron, nickel and cobalt.
Gilbert observes in all his magnets two points, one near each end, in which the force, or, as he terms it, 'the supreme attractional power,' is concentrated. He terms these poles by analogy to the earth; and he will have it understood that these poles are not mathematical points, as the attraction manifests itself 'all over the periphery.' Following the same analogy, he calls the line joining the two poles the axis of the magnet, and the equator the line equally distant from them. With the aid of his steel versorium, he recognizes that similar poles are mutually hostile, whilst opposite poles seize and hold each other in friendly embrace. He also satisfies himself that the energy of magnets resides not only in their extremities, but that it permeates 'their inmost parts, being entire in the whole and entire in each part.' This is exactly what we say; it is nothing else than the molecular theory proposed by Weber, extended by Ewing and universally accepted.
At any rate, Gilbert is quite certain that whatever magnetism may be, it is not, like electricity, a material, ponderable substance; he ascertained this by weighing in the most accurate scales of a goldsmith a rod of iron before and after it had been rubbed with the lodestone, and then observing that the weight is precisely the same in both cases, being 'neither less nor more.' He discovers also that not only the magnet, but all the space surrounding it, possesses magnetic properties; for the magnet 'sends its force abroad in all directions, according to its energy and quality.' This region of influence he calls orbis virtutis, a sphere, or, as we call it, a field of force. With wonderful intuition, he sees this space filled with lines of magnetic virtue passing out radially from his spherical lodestone, and he calls these linesFig. 1. Gilbert's Spherical Lodestone and Field of Magnetic Force.radii virtutis magneticae, rays of magnetic force.
When Faraday spoke of field of force, magnetic field, lines of electric and magnetic induction, some thought the idea new, whereas not only the idea, but also the very terms occur with appropriate illustrations in De Magnete.
Clerk Maxwell was so fascinated with that beautiful concept that he made it the work of his life to study the field of force due to electrified bodies, to magnets and to conductors conveying currents; his powerful intellect visualized those lines and gave them accurate mathematical expression in the great treatise on electricity and magnetism which he gave to the world in 1873.
Gilbert observes that the lodestone may be spherical or oblong; 'whatever the shape, imperfect or irregular, verticity is present, there are poles,' and the lodestones 'have the selfsame way of turning to the poles of the world.' We find Gilbert working even with a ring of iron. He strokes it with a natural magnet and feels certain that he has magnetized it; and he assures us that 'one of the poles will be at the point rubbed and the other will be at the opposite side;' and how does he convince himself that the ring is really magnetized? He cuts it across at the point opposite the one rubbed, opens it out, and finds that the ends exhibit polar properties.
A favorite piece of apparatus with Gilbert was a lodestone ground down into globular form. He called it a terrella, a miniature earth. He used it extensively for reproducing the phenomena described by magnetizers, travelers and navigators as observed in their compass needles. He breaks up terrellas, in order to examine the magnetic condition of their inner parts. There is not a doubtful utterance in his description of what he finds; he speaks clearly and emphatically. "If magnetic bodies be divided, or in any way broken up, each several part hath a north and a south end;" i. e., each part will be a complete magnet.
We find him also comparing magnets by what is known to us as the 'magnetometer method.' He brings the magnetized bars in turn near a compass needle and concludes that the magnet or the lodestone which is able to make the needle go round is the best and strongest. He also seeks to compare magnets by a process of weighing, similar to what is called, in laboratory parlance, the 'test-nail' method. He also inquires into the effect of heat upon his magnets, and finds that 'a lodestone subjected to any great heat loses some of its energy.' He applies a red-hot iron to a compass needle and notices that it 'stands still, not turning to the iron.' He thrusts a magnetized bar into the fire until it is red-hot and shows that it has lost all magnetic power. He does not stop at this remarkable discovery, for he proceeds to let his red-hot bars cool while lying in various positions, and he finds: (1) that the bar will acquire magnetic properties if it lie in the magnetic meridian; and (2) that it will acquire none if it lie east and west. These effects he rightly attributes to the inductive action of the earth.
Gilbert marks these and other experiments with marginal asterisks; small stars denoting minor and large ones important discoveries of his. There are in all 21 large and ITS small asterisks, as well as 84 illustrations in De Magnete. This implies a vast amount of original work, and forms no small contribution to the foundations of electric and magnetic science.
Gilbert clearly realized the phenomena and laws of magnetic induction. He tells us that "as soon as a bar of iron comes within the lodestone's sphere of influence, though it be at some distance from the lodestone itself, the iron changes instantly and has its form renewed; it was before dormant and inert; but now is quick and active." He hangs a nail from a lodestone; a second from the first, a third from the second and so on—a well-known experiment, made every da}-for elementary classes. Nor is this all, for he interposes between his lodestone and a mass of iron thick boards, walls of pottery and marble, and even metals, and he finds that there is naught so solid as to do away with this force or to check it, save a plate of iron. All that can be added to this pregnant observation is that the plate of iron must be very thick in order to carry all the lines of force due to the magnet, and thus completely screen the space beyond.
But Gilbert is astonishing when he goes on to make thick boxes of gold, glass and marble, and suspending his needle within them, declares with excusable enthusiasm that regardless of the box which imprisons
Fig. 2. Gilbert heated and hammered Bars of Iron in the Magnetic Meridian, and allowed them to cool while lying North (Septentrio) and South (Auster).
the magnet, it turns to its predestined points of north and south. He even constructs a box of iron, places his magnet within, observes its behavior, and concludes that it turns north and south, and would do so were 'it shut up in iron vaults sufficiently roomy.' Our experiments show that if the sides of the box are thin, the needle will experience the directive force of the earth; but if they are sufficiently thick—thick as the walls of an ordinary safe—the inside of such a box will be completely screened; none of the earth's magnetic lines will get into it so that the needle will remain indifferently in any position in which it is placed. A few years ago, the physical laboratory of St. Johns College, Oxford, was screened from the obtrusive lines of neighboring dynamos by building two brick walls parallel to each other and eight inches apart and filling in the space with scrap iron. A delicate magnetometer showed that this structure allowed no leakage of lines of force through it but offered an impenetrable barrier to the magnetic influence of the working dynamos.
Gilbert's greatest discovery is that the earth itself is a vast globular magnet. 'Magnus magnes ipse est globus terrestris' are his own words. It has its poles, its axis and equator just as the lodestone or terrella. The pole in our hemisphere he variously calls north, boreal, arctic, whilst that in the other hemisphere he calls south, austral, antarctic. He is quite aware that his theory is a grand generalization; and admits that it is 'a new and till now unheard-of view,' and so confident is he in its worth that he is not afraid to say that 'it will stand as firm as aught that ever was produced in philosophy, backed by ingenious argumentation or buttressed by mathematical demonstration.' Three hundred years have passed away, and Gilbert's theory is accepted by every man of science and is taught in every school of physics. Moreover, save the correction of a few errors of observation, no change of any importance has been made in it.
Gilbert sought to explain the magnetic condition of our globe by the presence, especially in its innermost parts, of what he calls true terrene matter, homogeneous in structure and endowed with magnetic properties, so that every separate fragment of the earth exhibits the whole force of magnetic matter. We attribute terrestrial magnetism to the vast masses of magnetic material which lie near the surface, for at a depth of ten or twelve miles the temperature of the ferruginous masses would deprive them of all magnetic properties. The magnetic condition of the earth is also attributed to the action of electric currents continually flowing through the crust of the earth. Both these theories, as Professor Rücker, of London, said in 1891, are beset with difficulties; at present we must content ourselves with accumulating facts in the hope that a clue to an explanation may hereafter be found.
Gilbert's discovery enabled him to offer a philosophical explanation of the behavior of both compass and dipping needles, as well as of a great many other phenomena. The declination was known before Gilbert's time. Columbus noticed this want of coincidence between the geographical and magnetic meridians in his first voyage to the New World. It was on September 13, 1492, when 200 leagues west of Teneriffe, that his attentive eye observed that the magnet pointed slightly west of north, and that this angular deviation increased during the following days. For a time he kept the secret in his own mind; the pilots, however, soon perceived the variations and grew alarmed, deserted, as they said they were, on the trackless ocean by their only trusty guide. Columbus calmed their fears by saying that the needle did not turn to the polar star, but to some fixed and invariable point near it. This explanation, born of inspiration, quieted the sailors, who marveled much at the Admiral's great astronomical knowledge. Gilbert rightly states that the declination changes with place, but he slips into error when he says: "As the needle hath ever inclined towards east or towards west, so even now does the arc of variation continue to be the same in whatever place or region, be it sea or continent; so, too, will it be forever unchanging."
We know, however, that for any given place this angle is continuously, though slowly, changing. Some of these changes require centuries for the completion of their cycle, and are therefore called 'secular'; others require but a year, and are termed 'annual'; whilst others run their course in the space of a day and are known as 'diurnal.' Though these periodic changes in the declination have been established by careful and prolonged observations, we can not say that they are yet satisfactorily accounted for.
The dip of the needle was also familiar to Gilbert, having been first observed in 1576 by Robert Korman. Our philosopher illustrates this phenomenon by balancing a piece of steel so that it remains exactlyFig. 3. Gilbert's Terella showing the Behavior OF A Dipping-needle at its Poles, Equator and other Intervening Places.horizontal when unmagnetized, and by observing that the moment it is stroked by a magnet its north seeking end dips 'as low as the fulcrum on which it is supported permits.' Gilbert moves a needle over his and finds (1) that the dip is 0° on the equator, (2) that it gradually increases with the latitude being 90° at either pole.
He extends this experiment from the terrella to the earth itself, and even devises an instrument for determining the latitude of any place on land or on sea in the thickest weather and in the darkest night, 'without the help of sunne, moone, or starre.' In this, however, he was wrong. For he assumed the isoclinic lines to be circles running parallel to the magnetic equator, which he erroneously supposed to coincide with theequator.
Gilbert recognized that the earth exerts on a freely movable needle a force that gives it direction and not a motion of translation. He illustrates this by floating a needle on a cork and observing that it points N. and S., remaining all the while at any place in the vessel of water in which it may be put. His words, though quaint, are exact: "It revolves on its iron center, and is not borne towards the rim of the vessel." He knew nothing of the mechanical couple in play; but he knew the fact; and with the instinct of a true philosopher, tested it in a variety of ways. With a most luminous insight into terrestrial magnetic phenomena, he observed that near the poles a compass needle tending, as it does, to dip greatly, must necessarily experience only a feeble horizontal directive force. To this he adds that 'at the poles there is no direction,' meaning thereby that a properly balanced compass needle
would remain indifferently in any azimuth in which it might be placed. We express the same by saying that the horizontal component of the earth's force vanishes at the poles.
Gilbert dwells at length on the inductive action of the earth. We have seen him hammering heated bars of iron and then allowing them to cool while lying in the magnetic meridian. He notes that they become magnetized, and does not fail to point out the polarity of each end. He likewise attributes to the influence of the earth the magnetic condition acquired by iron bars that have for a long time lain fixed in the north and south position as bars often are fixed in buildings and in windows, and he ingenuously adds: for great is the effect of long-continued direction of a body towards the poles. To the same cause he attributes the magnetization of iron crosses fixed to steeples, towers, etc.
It must be evident from this brief analysis of De Magnete.
1. That Gilbert was acquainted with all the facts in magnetism known in his days;
2. That he added profusely to the number;
3. That he coordinated these facts and deduced the laws which govern them; and
4. That he was the first to offer a scientific explanation of the behavior of the compass and the dip needle, as well as of numerous other phenomena, correctly attributed by him to the magnetic state of our globe.
Such were some of the 'rowing pins,' as Chancellor Bacon ironically calls them, with which Gilbert built up one of the greatest monuments ever erected by the genius of one man. Had Gilbert done nothing else than propound and establish on the solid basis of observation and experiment his theory that the earth is a great magnet, his name would ever live in the annals of science, surrounded with a halo that even the unjust strictures of Bacon could not dim; but when we consider his spirited advocacy of research at the end of the sixteenth century, and the cardinal advances he achieved in the interpretation of two great branches of knowledge, we can have no hesitation in considering him with Poggendorff, 'the Galileo of Magnetism,' and with Priestley, 'the Founder of Modern Electricity.'
Were we asked to write an inscription for his statue, we should write the simple words:
Gilbert, the Columbus of the Electrical World.
- A town in Essex, fifty miles northeast of London.
- The only English translation of this work which we have is by Mr. P. Henry Mottelay, of New York, published by Wiley & Sons.
- Bacon was raised to the peerage as Baron Verulam, and was subsequently created Viscount St. Albans; where, then, is the propriety of calling him Lord Bacon?
- All things are drawn to electrics.
- To Boyle we are. also indebted for the name barometer.
- According to Humboldt, "the barbarous word magnetismus" was introduced in the eighteenth century.
- Columbus was thus the first to observe that the declination or 'variation of the compass,' as it is called, changes with place.