Edmond Halley

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<div class="img-caption">Edmond Halley, circa 1687 (National Portrait Gallery, London)</div>
<div class="img-credit">WikiMedia Commons</div>
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<p>By Sarah Keating</p>
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<p>On December 26, 1758, stargazers around the world watched a comet soar through the December skies, proving a prediction made in 1705 by Edmond Halley (1656-1742). A contemporary, collaborator, and friend of Isaac Newton, this confirmation of Halley’s prediction was “the first independent confirmation of a prediction based on Newton’s gravitational theory as postulated in the <em>Principia</em>–a book in which Halley had played a leading part as instigator, editor, and publisher.” (Ronan, 1968, p. 241)</p>
<p>However, Halley’s accomplishments within the field of astronomy were only a small part of his incredible scientific legacy. Halley’s enthusiastic fascination with the mechanics that drive the movements of the Earth and the heavens pulled him deeply into the study of geophysics. “He was an innovative cartographer, student of geomagnetism, inventor of a deep-sea diving bell, author of the first actuarial mortality tables and captain of a bold seagoing scientific expedition.” (Wilford, 1985)</p>
<p>Looking at his accomplishments through a geophysics lens, following is a brief synopsis of Halley’s contributions to our understanding of the world around us.</p>
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<p>Halley was born in London into a middle class family in 1656. His father was a successful soap merchant who recognized and encouraged his son’s interest in science. Halley attended St. Paul’s School, where he demonstrated an early aptitude for mathematics and nurtured a growing love of astronomy. In 1673, Halley enrolled at Queen’s College (Oxford), putting him in contact with some of the greatest scientific minds of his day and kicking off his life’s work as a scientific researcher (Sharp, 2014). Throughout his long career, Halley published regularly. Malin calculates that “of 107 published papers listed by MacPike (1932; p 272-278), 34% were related to geophysics, 36% on astronomy, and 10% on mathematics.” (1993, p 151).</p>
<p>In a 2001 lecture to the Royal Society of London, Alan Cook said, “[Halley was] known in his own day as a distinguished mathematician, a great astronomer, and respected servant of the State. He was renowned throughout Europe, and seen then and since as only second to Newton.” (p. 474).“</p>
<p>Halley was appointed the Savilian Chair of Geometry at Oxford in 1704, and Astronomer Royal in 1720. He married Mary Tooke in 1682 and the couple had three children; two daughters and a son. An enthusiastic scientific researcher to the end of his life, Halley died in 1742 (Complete Dictionary of Scientific Biography, 2008).</p>
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<p><strong>Magnetic Declination</strong></p>
<p>Halley’s interest in <em>magnetic declination</em> (the angle representing the difference between “true north” and magnetic north, at a particular place and time) began with his first recorded calculations at age 16 and continued throughout his life (Malin, 1993). Like many of his contemporaries, Halley was interested in finding a way to determine longitude while at sea and Halley felt that a key might lay in the shifting magnetic fields.</p>
<p>While attending Queen’s College, Halley met Astronomer Royal, John Flamsteed. At this time, Flamsteed was engaged in creating a star map of the north Atlantic skies and Halley was so inspired by this undertaking that he left school without graduating and sailed to St. Helena to survey the stars in the South Atlantic. Throughout this trip, Halley indulged his fascination with the Earth’s shifting magnetic field by taking the opportunity to record magnetic declination at regular intervals throughout his trip.</p>
<p>Halley’s ongoing study of magnetic declination received another boost in 1698 when he was given the captaincy of the Royal Navy ship <em>Paramore, </em>which conducted two studies of the Atlantic from 1698-1700<em>. </em>The purpose of these trips was to “undertake a voyage around the world to improve geographical knowledge, to observe the magnetic variation worldwide and to try out different ways of discovering the longitude.” (Cook, 2001). Traveling from England to Antarctica, Halley collected data that he used to create a detailed map showing magnetic declination across the north and south Atlantic. This chart was the first visualization of a specific set of data ever published.  “The charts contain isogones connecting the points of equal magnetic declination and as they were widely used by British and continental navigators, it was Halley's adoption of this method (often referred to as Halleyan lines) that led to its general use by later cartographers.” (Ronan, 1968)</p>
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<div class="img-caption">"Edmond Halley's <em>New and Correct Chart Shewing the Variations of the Compass </em>(1701)<em>. </em>The first chart to show equal lines of magnetic variation."</div>
<div class="img-credit">WikiMedia Commons (Plate 22 from Mount & Page's 1702 "Atlas Maritimus Novus, or the New Sea-Atlas.")</div>
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<p>These maps were updated and republished every five years, creating a navigation resource for mariners that was used until the advent of modern satellites.</p>
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<p><strong>The Magnetic Core</strong></p>
<p>Halley’s research around magnetic declination unsurprisingly also led him to consider the reason for Earth’s shifting magnetic field. Today, we know that the Earth’s metallic, molten core is constantly in motion, driven by the motion of the Earth and the pull of gravity. This push and pull shifts compass readings both over time and from place-to-place.</p>
<p>Halley was the first to postulate the existence of this metallic core and speculate on it’s influence on the Earth’s magnetic field.</p>
<p>Between 1683 and 1686, Halley published two works on the subject in which he suggested the existence of four magnetic poles. “He kept to his model of two pairs of poles, but placed one in an outer shell of the Earth and the other in a core. He supposed that the core and the shell had separate directions of magnetization and that they could rotate relative one to the other.” (Cook, 2001) Halley speculated that the inner earth was made up a series of rings. Describing the motion of these rings (or arches), Halley himself wrote, “The Concave of each Arch, which is shaded differently from the rest, I suppose to be made up of Magnetical Matter; and the whole to turn about the same common Axis. Only with this difference, that the Outer Sphere still moves somewhat faster than the Inner.” (Halley, 1686).</p>
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<div class="img-caption">"<span style="font-family:Arial">Edmund Halley's model to explain the Earth's magnetic field changes. Color patches represent permanent magnetization."</span></div>
<div class="img-credit">Image and caption courtesy of https://sites.ualberta.ca/~dumberry/axial.html</div>
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<div class="img-caption">Halley's illustration of the Earth's magnetic field</div>
<div class="img-credit">Image courtes of http://www.eoht.info/page/Magnetism</div>
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<p>Although many of the details were incorrect, his well-reasoned theory that the center of the Earth contains a magnetic core that affects the Earth’s magnetic field changed our understanding of the Earth’s interior and paved the way for our modern understanding of the dynamic nature of the Earth’s interior.</p>
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<p><strong>Isaac Newton</strong></p>
<p>Throughout the early 1680s, Halley was working to understand how to predict a comet’s path. As he observed and thought, he began to question Kepler’s belief that comets travel in a straight line (rather than in elliptical orbits like planets) and in 1684 friends recommended he speak with Isaac Newton. During the course of that visit, Halley learned that Newton had completed his proof about gravitation and then set it aside. Halley convinced Newton to publish his findings and became the editor and funder of Newton’s masterpiece <em>Philosophiae Naturalis Principia Mathematia</em>, published in 1687 (Wilford, 1985). “Without Halley, the stimulus, the critic, the supporter, editor and publisher, there would have been no Principia, or at least no published Principia as we now have it. Newton would probably have remained in relative obscurity in Cambridge and be known to us for his mathematics and optics but perhaps not as an outstanding figure in the history of science.” (Cook, 1991)</p>
<p>In an article in <em>The New York Times</em> published as Halley’s Comet approached the Earth in 1985, John Wilford wrote ''Halley the man orbits forever in the shadow of the unmatched Newton, but he was a gifted, original, versatile and productive scientist, and a human being as adventuresome, generous, loving and sweet as Newton was retiring, cold, solitary and austere.''</p>
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<p><strong>Halley’s Comet</strong></p>
<p>Utilizing the calculations Newton presented in <em>Principia</em>, Halley realized that the comet that was observed in 1456, 1531, 1607, and 1682 was actually the same object traveling in an elliptical orbit. Applying Newton’s theories, Halley correctly predicted that the pull of gravity from Jupiter and Saturn would pull at the comet and delay it’s return to late 1758 or early 1759. “Halley’s predication turned out to be correct; the comet did return after 76 years; it was first spotted over Germany of 26<sup>th</sup> December 1758, Thereafter it became universally known as ‘Halley’s Comet’.” (Newton’s Apple).</p>
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<p><strong>Data Visualizations</strong></p>
<p>Throughout his life, Halley demonstrated a keen ability to make sense of great masses of data. He had the ability to see patterns and make inferences from information collated from scientists across the globe. “He collected observations of natural phenomena as widely as possible and presented them in ways that displayed their outstanding features.” (Cook, 2001)</p>
<p>As part of Halley’s voyages aboard the <em>Paramore</em> and his early trip to St. Helena. Halley collected meteorological data focusing on the trade winds and monsoons. Later in life, Halley collected data from mariners across the globe resulting in the first tide and monsoon chart ever published. “His paper on trade winds and monsoons appeared in 1686 in the Philosophical Transactions and contained a chart of the winds across the oceans of the world between latitudes 30" N and 30" S, the winds being indicated by lines thinned at the end from which the wind was blowing. The chart was frequently reproduced in Britain and Holland and was the first to provide meteorological data in a graphic form.” (Ronan, 1968)</p>
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<div class="img-caption">Halley's chart of the Trade Winds, showing wind direction during different seasons.</div>
<div class="img-credit">Image courtesy of the Royal Society Blog, https://blogs.royalsociety.org/publishing/debating-the-winds/</div>
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<p>As Sir Edward Bullard said in his 1956 article in <em>Nature, </em>“Halley had a real delight in collecting observations, discussing them, and devising visual presentations of them.” (p. 892)</p>
<p>“This was the beginning of what is known as thematic maps, maps that illustrate the geographic distribution of information about climate, vegetation, population, wealth and just about any physical or abstract fact.” (Wilford, 1985)</p>
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<p><strong>Other Firsts</strong></p>
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<li>Halley correctly predicted that the age of the earth was much older than the Church stated, based on studies of water salinity and evaporation rates. This viewpoint brought him into conflict with the church, so he delayed publishing his views until 1715.</li>
<li>Halley was the first to develop a method of using a pendulum to compare gravity in different locations</li>
<li>Halley invented the term “corona” to describe the way rays intersect during an aurora. He was the first to realize that aurora’s were connected to magnetism.</li>
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<li>Newton’s <em>Principia</em>, although brilliant, did contain errors. Most notably pertaining to this conversation about Halley, Newton miscalculated the density of the moon; predicting  that it was three times it’s true density. This error led Halley to propose that the Earth was hollow saying, “Sir Isaac Newton has demonstrated the Moon to be more solid than our Earth, as 9-5; why may we not then suppose four ninths of our globe to be a cavity?” (Kolerstrom, 1992). Halley hypothesized that the earth had an outer shell, plus three equal (and equidistant) inner circles. Each inner circle "floated" on a liquid or vapor of some kind that was occasionally "released" as the aurora boreallis. In the center, was another globe (or "nuceleus"). Halley thought that the outer shell had one set of magnetic poles, and the inner globe/nucelus had another set that were never quite in sync with one another due to the constant motion of the inner earth. Halley felt that these dual poles explained magnetic declination. Halley also believed that an entirely different civilization could live within this hollow earth.</li>
<li>The Great Fire (1666) burned down several of the Halley family’s soap factories, as well as Halley’s school (St. Paul’s)</li>
<li>Halley’s <em>Paramore </em>(1699-1700) made the deepest exploration of the Antarctic ice shelf until James Cook’s voyage in 1769 (Cook, 2001)</li>
<li>Magnetic variations are important, even in 2016! Here’s one reason why: http://ww2.kqed.org/science/2013/12/12/oakland-airport-runways-renamed-a...
<li>Halley’s second in command mutinied during their first voyage of the <em>Paramore. </em>He set sail with a new crew in 1699.</li>
<li>Halley took magnetic declination readings in the English Channel in 1701-1702 but may have actually been spying on French ports for the British government.</li>
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<div class="img-caption">Route of Halley's second Paramore voyage, 1699-1700</div>
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<div class="img-credit">Image courtesy of the blog "Halley's Log", https://halleyslog.wordpress.com/maps/</div>
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<div class="img-caption">Halley’s hollow-earth schema, <em>Philosophical Transactions</em> 95</div>
<div class="img-credit">Image is public domain. Courtesy of http://www.branchcollective.org/?attachment_id=1359.</div>
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<p>Bullard, Edward. (1956). "Edmond Halley: The First Geophysicist." <em>Nature, </em>No. 4539, 891.</p>
<p>Complete Dictionary of Scientific Biography. (2008). "Halley, Edmond." Retrieved on 9/10/16 from http://www.encyclopedia.com/topic/Edmond_Halley.aspx.</p>
<p>Cook, Alan F.R.S. (1991). "Edmond Halley and Newton’s Principia." <em>Notes and Records of the Royal Society of London</em>, Vol 45, No. 2, 129-138.</p>
<p>Cook, Alan F.R.S. (2001). "Edmond Halley and the Magnetic Field of the Earth." <em>Notes and Records of the Royal Society of London</em>, Vol 55, No. 3 (Sept 2001), 473-490.</p>
<p>Halley, Edmond (1686). “An Account of the Cause of the Change of the Variation of the Magnetical Needle; With an Hypothesis of the Structure of the Internal Parts of the Earth: As it was proposed to the Royal Society in one of their late meetings” <em>Philosophical Transactions, </em>Vol. 16, 563-578.</p>
<p>Halley, Edmond (1683). “A Theory of the Variation of the Magnetical COMPASS” <em>Philosophical Transactions, </em>Vol. 13, 208-221.</p>
<p>Kollerstrom, N. (1992). "The Hollow World of Edmond Halley". <em>Journal for the History of Astronomy. </em>Aug. 1, 1992, 23.</p>
<p>Malin, Stuart R. C. (1993). "Edmond Halley-Geophysist." <em>Quarterly Journal of the Royal Astronomical Society,</em> Vol. 34, No. 2/June, 151-155.</p>
<p>Newton’s Apple (blog). "Edmond Halley and his Comet." Retrieved 9/9/16 from <a href="http://www.newtonsapple.org.uk/edmond-hally-and-his-comet/">http...
<p>Ronan, Colin A. (1968). <em>"</em>Edmond Halley and Early Geophysics<em>". Geophysical Journal International</em>, Vol 15, 241-248.</p>
<p>Sharp, Tim. (2014). "Edmond Halley Biography: Facts, Discoveries and Quotes". Retrieved on 9/6/16 from <a href="http://www.space.com/24682-edmond-halley-biography.html">http://...
<p>Wilford, John Noble. (1985). "Sir Edmund Halley: Orbiting Forever in Newton’s Shadow". <em>The New York Times, </em>10/29/1985. Retrieved on 9/10/16 from <a href="http://www.nytimes.com/1985/10/29/science/sir-edmund-halley-orbiting-for...
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