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06.08
Edmond Halley, 1656 –
1742
The Man of Magnetism
by John Vardalas, ph.D., IEEE
History Center
When one reads or hears the name
Edmond Halley, the comet of the same name often
comes to mind. Relatively rare, comets have
appeared throughout history, and for millennia,
humanity viewed comets as independent, if not
prophetic, events. In 1682, another comet
appeared to the world. Halley, one of the most
eminent astronomers of the late 17th and early
18th centuries, argued that the comet of 1682
had been the same one that had been recorded in
1066, 1305, and 1380. Rather than on a parabolic
trajectory, this comet, he argued, traveled on a
highly elongated elliptical orbit. Using the new
mathematics and physics developed by his friend
Isaac Newton, Halley predicted that this comet
would appear again to the world in 1758. Halley,
who would become Britain’s Astronomer Royal,
never lived to see his prediction come true. But
Halley’s Comet was born. Not confined to only
astronomy, Halley’s great mind touched many
areas of science and technology. To electrical
engineers, it may come as a surprise that Edmond
Halley was also one of the early explorers into
the realm of electromagnetic phenomena.
It was in the 13th century when
the compass first appeared to Europeans, though
in China it had come about two centuries
earlier. As crude as these early compasses were,
they marked a great technological revolution.
One could argue that the compass was the first
electromagnetic technology. For the first time,
mariners had a tool for navigating on the
undifferentiated ocean, regardless of the
conditions. As explorers ventured further out
into the world’s oceans, they discovered that
the compass did not point to the geographic
North. This difference between geographic North
and magnetic north was called “variation.” [1]
Mariners were further perplexed by the
ever-changing value of the variation as one
moved on the globe. The fact that the compass
behaved oddly could be frightening to sailors
setting out into the unknown. On his first
journey in 1492, fearing a mutiny, Columbus kept
the compass’s odd behavior a secret from his
crew. Even more troubling was the observation
that at a given point on the Earth, magnetic
north would move about over time. During the
17th century, after the pioneering work of
William Gilbert, it was understood that the
earth itself was a giant magnetic dipole with
which the compass interacted. But it was still a
mystery as to why the compass did not point to
North in the same way as one moved across the
globe, particularly in an East-West direction.
Halley’s interest in magnetism
went back to his days as a schoolboy at St.
Paul’s. Born in London in 1656, Edmond Halley
was the eldest son of a prosperous merchant.
Recognizing the potential in the precocious boy,
Edmond’s father sent him to St. Paul’s for a
good education. Halley excelled in his studies,
which were made up of Classics, mathematics, and
some astronomy and navigation. At the age of 16,
while at St. Paul’s, the young Halley made his
first measurement of the magnetic variation,
which he included in a later publication years
later. At the age of 17, he entered Queen’s
College, Oxford, where his focus turned to
astronomy. While at Oxford, he published his
first paper in the Philosophical Transactions,
with John Flamsteed, who had been named
England’s first Astronomer Royal. In 1676, at
the age of 20, Halley dropped out from his
studies at Oxford to undertake an expedition to
the remote island of St. Helena’s in the South
Atlantic. His goal was to create the first star
catalogue of the Southern Hemisphere. The young
Halley must have had good connections, because
his proposed project reached the ear of Charles
II. The King not only induced the East India
Company to provide the transport for Halley, an
assistant, and a considerable cargo of
instruments to St. Helena; Charles II also
ordered the Governor of the island to offer him
any assistance needed. Upon his return from St.
Helena, Oxford University — in an unprecedented
gesture — with the prodding of King Charles II,
granted Halley his M.A., without having to
satisfy the usual residency requirements or
having taken any final examinations. In the
years to follow, Halley would return to the
study of terrestrial magnetism and compass
variation.
Until the experimental work of
Hans Řrsted, Michael Faraday, and James
Maxwell’s brilliant theoretical synthesis,
scientists viewed electricity and magnetism
effects as separate and independent phenomena.
Of the two, magnetism had received the earliest
and most intense scrutiny, from both scientific
and technological perspectives. The imperatives
of maritime trade and naval power drove the
intense interest in magnetic phenomena. The
study of terrestrial magnetism then opened the
door to the science and technology of
electromagnetic phenomena that would follow in
the next two centuries. Halley devoted much of
his time to modeling and mapping the behavior of
the earth’s magnetic field. His grand ambition
was to solve the age-old longitude problem
through a better understanding of the Earth’s
magnetic field.
In 1683, 325 years ago, Halley
produced the first of many papers on the Earth’s
magnetic field. In 1696, he argued that the
Earth was made of any outer shell and a separate
inner core. Each produced its own magnetic
dipole. It was the motion of the inner core that
produced the observed behavior of terrestrial
magnetism. Although Halley’s model was
eventually proven wrong, his belief that the
behavior of the planet’s magnetic field had its
origins deep in the Earth core does resonate
with the explanations that emerged in the 1950s.
The core is molten and in motion. Complex
magneto-hydrodynamic processes deep within the
earth, which are still not fully understood,
create the behavior of the magnetic field
observed on the Earth’s surface and above. More
important to the science of terrestrial
magnetism was Halley’s extensive work to map the
variations.
For Halley, the behavior of the
variations held the key to solving another great
problem in nautical navigation, the
determination of longitude. Despite its crucial
importance, the practical determination of
longitude at sea had long eluded the best minds.
Latitude was fairly easy to determine. But
without accurate longitude, one could never be
sure where one was on the ocean. Errors in
longitude led to considerable loss of life and
ships. The maritime nation that could master
longitude could more easily consolidate its
command of the sea. The governments of all the
maritime powers offered substantial prizes to
anyone who could solve the longitude problem. In
addition to money, the solution of longitude
also promised great honor and prestige. Halley
was convinced that the east-west changes in
variation could be closely tied to changes in
longitude. The idea was not new. It had been
proposed several times during the course of the
17th century.
Halley’s great contribution was
the invention of the isogonic map. He set out to
map the lines of constant variation over the
Earth’s surface. The hope was that lines of
constant variation could somehow be translated
in a one-to-one manner to longitude. In 1693,
with the full support of the Royal Society,
Halley proposed to the government that it fund a
voyage around the world in order to measure and
map the phenomenon of variation as away of
determining longitude. Queen Mary II approved
all of elements in Halley’s petition. The
outbreak of hostilities with France delayed
Halley’s expedition. Finally, in 1698, Halley set sail
on the Paramore, a 52-ft. vessel built
for the expedition. However, the Admiralty had reduced
the geographic range of Halley’s investigation
to the North and South Atlantic.
Edmond Halley's Second
Expedition (1699)
Halley’s only experience at sea
had been as a passenger, And yet, in an astonishing
move, the Royal Navy gave Halley command of the
Paramore. Halley returned to England
within a year. Shortly after his return, Halley
set out on a second expedition to measure the
magnetic variation. Halley’s charting took him
within 200 miles of the Antarctic. In 1701,
based on all the data gathered, Halley produced
the world’s first isogonic chart of the North
and South Atlantic Oceans. Throughout the first
half of the 18th century, Halley continued to
seek the solution to the longitude problem
through magnetism. Efforts to use magnetic
variation to solve the longitude problem stopped
when reliable and accurate marine chronometers
appeared toward the end of the 18th century.
Nevertheless his chart was a great scientific
achievement. To this day it is still used as a
reference datum when geophysicists want to
validate their magneto-hydrodynamic models of
the Earth’s core.
Edmond Halley's Isogonic Chart
of the Atlantic
A renowned astronomer, Halley
became England’s second Astronomer Royal in
1720. He was actively involved in the
development of diving bell technology. He
developed predictive models of the tides. He did
important work in meteorology. To Halley, we owe
Isaac Newton’s groundbreaking work, the
Principia. Halley encouraged Newton to
organize and publish his ideas. When the Royal
Society found itself unable to fund the
publication of the Principia, Halley, at
his own financial risk, put up the money. Halley
and Newton remained lifelong friends. Halley’s
achievements were indeed many. But to paraphrase
one Halley biographer, while Newton was the man
of gravity, Halley was the man of magnetism.
For more in-depth works on the
life of Edmond Halley and the significance of
his work, the reader is referred to the
following:
Angus Armitage, Edmond Halley,
(London and Edingurgh: Thomas Nelson, 1966)
Alan Cook, Edmond Halley:
Charting the Heavens and the Seas, (Oxford,
Clarendon Press, 1998)
A.R. T. Jonkers, Earth’s
Magnetism in the Age of Sail, (Baltimore and
London: Johns Hopkins University Press, 2003)
Colin Ronan, Edmond Halley:
Genius in Eclipse, (London: MacDonald, 1969)
Julie Wakefield, Halley’s
Quest, (Washington, D.C.: Joseph Henry
Press, 2005)
End notes
-
More correctly stated,
“variation” is the angle between the
horizontal component of the magnetic field
and the local meridian as defined by the
direction of the sun at noon.
John Vardalas, Ph.D., is an
IEEE Postdoctoral Fellow in the Department of
History at Rutgers University in New Brunswick,
N.J. Visit the IEEE History Center's Web page
at:
www.ieee.org/organizations/history_center.
He can be reached at
todaysengineer@ieee.org.
Opinions expressed are the
author's.
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