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    WILLIAM GILBERT, AND TERRESTRIAL
    MAGNETISM IN THE TIME OF
    QUEEN ELIZABETH: A DISCOURSE
    BY SILVANUS P. THOMPSON, F.R.S.




  WILLIAM GILBERT AND TERRESTRIAL MAGNETISM IN THE TIME OF QUEEN
    ELIZABETH.


William Gilbert, the father of electrical science, was born in
Colchester in 1540. Educated at St. John's College, Cambridge, where
he took his degree as Doctor of Medicine in 1569, he settled, after
four years of foreign travel, in London in 1573, and was admitted to
the Royal College of Physicians, of which he became Censor, Treasurer,
and, in 1599, President. He was in February, 1601, appointed personal
Physician to the Queen, whom he attended in her last illness. He came
of a well-known East Anglian family, and held extensive landed estates
in Essex and Suffolk. He survived the Queen only eight months, dying
November 30th, 1603.


Gilbert's monumental work, the _De Magnete_, published in 1600, marks
an era in magnetic science. For some four hundred years the employment
of the magnetic needle in navigation had been known both in Northern
and Southern Europe. While it is possible that the primitive use of
the loadstone may be ascribed to the Baltic, it is certain that the
employment of a pivotted needle, and the addition of a rose of the
winds as a compass card both originated in the Mediterranean. The
pivotted needle is described in the Epistle of Peter Peregrinus,
written in 1269; while the earliest known compass-card marked with
the initials of the names of the winds is that ascribed to Jachobus
Giraldis, of 1426, in the Biblioteca Marciana in Venice. The manner of
use in Elizabethan times of the loadstone and of the compass may be
gathered from Olaus Magnus (_Historia de Gentibus Septentrionalibus_,
1555), from Pedro de Medina (_Arte de Nauegar_, 1545), Martinus Cortes
(_Breve compendio de la sphera_, 1556), Blundevile (_Exercises_, 1594),
Norman (_Newe Attractive_, 1581), Borough (_A discours of the Variation
of the Cumpas_, 1581), Pedro Nuñez (_Instrumenta Artis Navigandi_,
1592), Barlow (_The Navigators Supply_, 1597), Nautonier (_Mécometrie
de l'Eyman_, 1602), and Stevin (_Die Havenvinding_, 1599).

At the time when steering by the compass was introduced into
navigation, the compass pointed in Middle Europe so nearly truly to the
north that with the rough instrumental appliances at hand its deviation
from the true north was seldom noticed, or if noticed ascribed to some
error in the setting of the needle. Later the compass-makers began
to set their needles slightly askew beneath the card, according to
the variation in the place of origin. Norman (1581) states that those
used in the Levant, made in Sicily, Genoa, or Venice, had the needles
straight, while those used in Denmark and Flanders had them set at
three-quarters of a point, or a whole point, to the eastward; while
those made in Spain, Portugal, France, and England, had the needles set
half a point to the east. Those for Russia were set at "three seconds
of a point." Gilbert denounced these devices as tending to obscure
the true facts. Gradually it became recognized, probably after the
voyage of Columbus, when the manifest change in the declination of the
needle nearly caused mutiny of the sailors, that the direction of the
needle differs at different places; and accordingly navigators began to
collect data. The record of the voyage of Columbus states that during
his second voyage in 1496 he used for steering the observations made
on the declination during his first voyage. The "secret" of Sebastian
Cabot, which he declared when dying to be a divine revelation to
him, can have been little else than the idea of using in navigation
the local declinations of the compass. On the other hand, Pedro de
Medina flatly denied the existence of the declination, adding that
if the compass did not show the pole, the fault lay in the defective
construction of the compass itself. Columbus had found a point 2-1/2°
east of Corvo, in the Azores, where there was "no variation," and other
navigators explored the "agonic" lines which crossed the Atlantic and
the Indian ocean. According to Humboldt, Alonzo de Santa Cruz in 1530
constructed the first general variation chart. But along with this
development of practical interest in the subject there grew up a crop
of wild legends to account for the irregularities observed. The reason
why the compass needle pointed north, and the reason why it did not
point truly north, were alike proclaimed to be due to the stars, to
the influence of spirits, or to the existence of loadstone mountains
of uncertain locality and of fabulous power. The old traditions of the
Arabian Nights, dressed in a newer setting, found themselves justified
by the insertion in maps of loadstone rocks, the position of which
changed at the fancy of the chartographer. Ptolemy had located them in
the Manioles; Olaus Magnus declared them to be under the pole; Garzias
ab Horto situated them in the region of Calcutta. The map of Johann
Ruysch, which adorned the edition of Ptolemy, publisht at Rome in 1508,
showed four magnetic islands in the Arctic Circle. Martinus Cortes
placed the loadstone mountains in Sarmatia. Mercator in his great chart
depicted two great rocks rising from the sea to the north of eastern
Siberia, one being drawn on the supposition that at St. Michael the
compass points due north, while the other is further north on the
supposition that the compass points due north at Corvo. The map of
Cornelius Wytfliet, 1597, shows the same phantom islands. Blundevile,
writing in 1594 of the now lost map of Peter Plancius, mentions that
he sets down the pole of the loadstone somewhat to southward of the
islands that lie east of Groynelande.

Meantime another significant fact had been discovered in 1576 by
Robert Norman, of Limehouse, compass-maker, namely, the tendency of
the magnetized needle to dip its northern end downwards. Noticing this
as a circumstance that occasioned him some trouble in the construction
of his compasses, he thereupon devised a dipping-needle, and measured
the dip, "which for this Cyty of London I finde by exact obseruations
to be about 71 degrees 50 mynutes." He attributed both the declination
and the dip of the needle to the existence of a "poynt respective,"
which the needle respected or indicated, but toward which it was not
attracted. The first authoritative treatise on the variation of the
compass was the tract by William Borough, comptroller to the Navy,
who in 1580 found an eastward declination of 11° 15' at Limehouse.
Borough had himself travelled in northern regions and had found at
Vaigats a westerly declination of 7 degrees, whereas by Norman's
theory of the respective point there should have been an easterly
declination of 49° 22'. The great navigators were continually bringing
home fresh information. Drake, Lynschoten, Cavendish, Hariot all
contributed; as did lesser men such as Abraham Kendall, sailing-master
to Sir Robert Dudley (the _soi-disant_ Duke of Northumberland), and
afterward companion of Drake in his last voyage. Teachers of navigation
such as Simon Stevin of Bruges and Edward Wright, lecturer to the
East India Company, might record and tabulate: but a master-mind was
wanting to forge some larger and consistent doctrine which should
afford a grasp of the whole subject. Such an one arose in Dr. William
Gilbert. Nurtured, as we have seen, in the Cambridge which had so
recently been the home of Linacre and of Kaye--the Kaye who founded
Caius College--Gilbert had, during his subsequent sojourn in Italy,
conversed with all the learned men of his time. He had experimented
on the magnet with Fra Paolo Sarpi: he had, there is reason to think,
met Giordano Bruno: he was the friend and correspondent of Giovanni
Francesco Sagredo. Being a man of means and a bachelor, he spent money
freely upon books, maps, instruments, minerals, and magnets. For twenty
years he experimented ceaselessly, and read, and wrote and speculated,
and tested his speculations by new experiments. For eighteen years he
kept beside him the manuscript of his treatise, which in the year
1600 saw the light under the title of _De Magnete_, to which was added
the sub-title: _magneticisque corporibus, et de magno magnete tellure,
physiologia nova_. That which Gilbert had in fact perceived, and which
none before him had glimpsed even dimly, was that the globe of the
earth itself acted as a great loadstone, and that the tendency of
the needle to point in a polar direction was due to the globe acting
as a whole. So he boldly put into his title-page the statement that
his new philosophy was concerning the great magnet the earth: and
in chapter after chapter he set himself to describe the experiments
upon which he founded his famous induction. The phrase _terrestrial
magnetism_ does not occur in any of the prior treatises, because
the idea had not presented itself. Gilbert piled proof upon proof,
sometimes most cogently, as when he constructed loadstone globes, or
_terrellas_ to serve as magnetic models of the earth; sometimes with
indifferent logic, as when he pointed to the iron ore in the earth
and reasoned that the magnet tended to conform to (_i.e._ turn itself
toward) the homogenic substance of the body from which it had been dug.
The local deviations of the compass he sought to account for by the
irregularities of the earth's crust, and maintained that the compass
tended always, at places off the coast of a continent, to be deflected
somewhat toward that continent. His syllogism was based on the fact
that at that date all the way up the Atlantic seaboard of Europe, from
Morocco to Norway, the variation was eastward. He argued that this was
a universal law. But even within one generation, as may be seen in
_Purchas his Pilgrims_, in the narrative of the voyage of Bylot and
Baffin, the generality of the law was questioned. Gilbert reasoned on
such knowledge as he had, and this did not include any notion of the
secular changes in the declination. In his time, as he tells us, the
variation of the compass at London was 11-1/3 degrees. What he did not
know was that this was a diminishing quantity which in fifty-seven
years would be reduced to zero, to be succeeded by a westward
declination that would last for nearly three hundred years. For the
facts as known in the thirty years succeeding Gilbert's death, see the
remarkable and scarce volume of Gellibrand: _A Discourse Mathematical
on the Variation of the Magneticall Needle_ (1635).

Gilbert's treatise is a skilful literary achievement in which there is
no trace to reveal whether any part was written before the rest. It is
divided systematically into six books. The sixth book only appears to
suffer from some incompleteness. It relates not so much to the magnet
as to the Copernican theory of the universe, which doctrine Gilbert had
eagerly espoused, and which he was the first in England to proclaim.
It is known from a letter to Barlow, printed in 1616, that he intended
to add to it certain chapters descriptive of some of his instruments,
but he had not completed these before his death. The first book treats
of historic accounts of the loadstone, of its origin and properties,
of iron ores in general, and of the fables and vain opinions which in
the handling of Paracelsus and of the schoolmen had grown up around the
magnet. The second book is on the magnetic motions, and primarily on
the attractions and repulsions between loadstones, between loadstone
and iron, and between magnetic needles. In this book occurs the notable
digression upon the subject of amber and the electric forces of amber
and of other substances which when rubbed show, as he discovered,
similar electrical powers. An analysis of this part, and a summary of
Gilbert's electrical discoveries will be found in the Notes printed for
the Gilbert Club to accompany the English translation (1900) of the
_De Magnete_. After this digression Gilbert returns to the attractive
properties of the loadstone, and to the way they are affected by giving
it different shapes. In the course of this enquiry, he announces
his discovery of the augmentation of the power of the loadstone by
arming it with iron caps, an invention which caused Galileo to say: "I
extremely praise, admire, and envy this author for that a conception so
stupendous should come into his mind. I think him moreover worthy of
extraordinary applause for the many new and true observations that he
has made." Gilbert further pointed out that the loadstone is surrounded
by a sort of atmosphere or "orbe of virtue" within which the magnetical
effects can be observed. Book 3, on the directive force of the magnet,
is full of most instructive experiments, in which the terrella figures
largely, relating to the question how one magnet influences another
and tends to make it point toward it. All this was leading up to the
theory of terrestrial magnetism; for we find him naming the parts of
his loadstone globes with poles, equator and meridians. In this book
he dilates on the observation that vertical iron rods, such as the
finial on the Church of St. John at Rimini, spontaneously acquired
magnetic properties. This he traced to the influence of the earth, and
demonstrated the effect by magnetizing iron bars by simply hammering
them on the anvil while they lay in a north and south position. Book 4
deals with the Declination, or, as it was then called, the variation
of the compass. He discusses its observation and measurement, the
influence of islands, the results obtained by travellers to distant
parts, Nova Zembla, the Guinea coast, the Canary Isles, Florida,
Virginia, Cape Race, and Brazil. Then he recounts his experiments with
terrellas having uneven surfaces to represent the irregularities of
the earth's crust. He points out errors arising from the fallacious
practice of setting the needle obliquely under the card. He considers
in separate chapters the variations in Nova Zembla, in the Pacific,
in the Mediterranean, and in the Eastern Ocean. The fifth book is on
the Dip. Gilbert seized with avidity on Norman's discovery of this
effect, and devised an improved form of dipping-needle. He experimented
on the dip of compass-needles placed at different points over his
terrella, and evolved a theory on the proportion which he conceived to
exist between the latitude and the dip. Arguing from all too imperfect
data, he propounded the view that the dip was the same in any given
latitude; and proposed that seamen should ascertain their latitudes
by simply observing the dip. He was aware that local irregularities
might occur, as they do in the declination; but was not deterred by
this knowledge from propounding his theory with much circumstance
and considerable geometrical skill. After the publication of his
book he developed the theory still further and gave it to Blundevile
for publication. At Gilbert's suggestion Briggs of Gresham College
calculated out a table of dip and latitude. It was, however, soon found
that the facts deviated more or less widely from the theory. Further
observations in other lands showed the method to be impracticable; and
Gilbert's hope to give to the mariner a magnetic measure of latitude
remained unfulfilled. Book 5 closes with an eloquent passage in which
Gilbert affirmed the neo-Platonic doctrine of the animate nature of
the universe, and asserted that Thales was right when he held (as
Aristotle relates in the _De Anima_) that the loadstone was animate,
being part of and indeed the choice offspring of its animate mother the
earth. Book 6, as already mentioned, is devoted to Copernican ideas,
and contains Gilbert's one contribution to the science of Astronomy, in
his remark that the fixed stars (previously regarded as fixed in the
eighth of the celestial spheres at one common distance from the central
earth) were in reality set in the heavens at various distances from the
earth.

From this brief analysis it will be seen that Gilbert's claims to
eminence rest not upon any particular discovery or invention, but upon
his having built up a whole experimental magnetic philosophy on a truly
scientific basis, in place of the vague and wild speculations which
had previously been accepted. By his magnificent generalization from
the small scale models to the globe itself, supported from point to
point by experimental researches, he created the science of terrestrial
magnetism. If from the imperfection of the data at his disposal he
fell into sundry errors of detail, he yet founded the method of
philosophizing by which those errors were in due time corrected. And if
for nothing else than his masterly vindication of scientific method,
and his rescue of the subject of magnetism from the pedantry and
charlatanry into which in the preceding ages it had lapsed, his memory
must be held in high honour.

Alas that of the personality of so great a man so little should be
known. A brief but characteristic biography of him is enshrined by old
Fuller in his _Worthies_. The poet Dryden, and the epigrammatist Owen,
celebrated him in still briefer verse. His portrait, which hung for
nigh two hundred years in the Schools Gallery, at Oxford, disappeared a
century ago, leaving only a poor engraving to perpetuate his scholarly
countenance. Doubtless he is one of the four physicians depicted
by the pencil of Camden in his famous cartoon (now in the British
Museum), as walking in the funeral procession of Queen Elizabeth. Of
his handwriting not a vestige was known until about five years ago,
when a signature was unearthed in the Record Office. Subsequently four
signatures were found in the books of St. John's College; and recently
there has come to light a volume of Aristotle bearing Gilbert's own
marginal notes. His will lies at Somerset House, but it is only a copy.
Of his fine collection of minerals and loadstones, which with his maps,
books, manuscripts, and correspondence with Sarpi and Sagredo and
others, he bequeathed to the College of Physicians, nothing remains:
they perisht in the Great Fire of London. In a quiet corner of the City
of Colchester stands the quaint old house where he lived, and where,
according to local tradition, he once received the Queen. And hard by
it is the church of Holy Trinity, in which a mural tablet records his
virtues and marks his last resting place. But his true monument is
the immortal treatise in which he laid the foundations of terrestrial
magnetism and of the experimental science of electricity.

To the names of the men who made great the age of Queen Elizabeth, who
added lustre to the England over which she ruled, and made it famous
in foreign discovery, in sea-craft, in literature, in poetry, and in
drama, must be joined that of the man who equally added lustre in
science, Doctor William Gilbert.


 This discourse on William Gilbert and terrestrial magnetism
   in the time of Queen Elizabeth was delivered by Silvanus
     P. Thompson at the meeting of the Royal Geographical
        Society on March twenty-third MDCCCCIII on the
         occasion of the tercentenary of the death of
             Queen Elizabeth, and is now printed
                    by Charles Whittingham
                      and Company at the
                       Chiswick Press.

[Illustration]




Transcriber's note: The original book used the long "s", which has been
changed to the modern "s" here. Other archaic spellings have not been
changed.

The illustrations are small decorations.