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Eclipse Maps
From: The British Library
| By:
Geoff Armitage |
EDITOR'S INTRODUCTION |
Although nowadays we regard eclipses of the sun as natural, albeit spectacular, astronomical events, even as late as the eighteenth century they were thought to be the work of the devil. While some literature exists on the history of eclipses, little has been written on historical attempts to map them. Geoff Armitage, curator at the British Library Map Library, fills in some of this missing history, illuminating the particular genius of Edmond Halley and his mapping of the eclipse of 1715. |
 clipses have been predicted and diagrams drawn of them from at least the time of Aristotle and Claudius Ptolemy, but true eclipse maps, in the sense of geographical maps showing the track of eclipses, are a phenomenon of the eighteenth century onwards. Diagrams of solar eclipses occur in the Renaissance versions of Ptolemy's astronomical work the Almagest and, for example, in Peter Apian's Cosmographicus, first published in 1524. Accurate prediction, however, did not emerge until Edmond Halley (1656-1742) revolutionised astronomy and introduced the eclipse map and many other scientific thematic maps which influenced mapmakers for the rest of the century and beyond. |
Breaking new ground: Edmond Halley and the eclipse of 1715
Edmond Halley was the distinguished British astronomer particularly celebrated for determining the orbits of 24 comets that appeared between 1537 and 1698. He discovered that three of these were in fact the same one, the famous Halley's comet, and Halley predicted its return in 1758 and every 76 years thereafter. He also carried out important work on the southern stars, planetary orbits, Greek geometry and many other scientific subjects. |
Halley's major achievement in astronomical prediction was to improve on the mathematical tables of solar and lunar motion, from which eclipses are predicted and which had not changed since the tenth-century Arabian astronomer Albategnius (al-Battani) corrected Claudius Ptolemy's tables. He was able to do this by discovering that there was a gradual acceleration in the average rate of the moon's motion round the earth, resulting in the alteration of its orbit and average distance from earth as time passed. |
In the century before Halley, eclipse "maps" such as those by John Speed (1626) and Carel Allard (c. 1700) were essentially small diagrams in the margins of larger geographical or celestial maps. Allard's does include a globe on which there are continents and geographical names, but it shows only crudely the area affected by the total eclipse, and at only one point in time. Halley, on the other hand, has deservedly been called the first thematic mapmaker to merit the name cartographer. On the well-known map depicting the predicted path of the total solar eclipse of April 22, 1715, his grasp of graphic representation is shown in the ingenious and deceptively simple depletion of the moon's shadow, or "umbra," as an oval disc which slides across southern England illustrating the track of totality. The map does not, however, show the areas where the penumbra occurred, as some later maps were to do. The use of a very conventional base illustrates Halley's interest in the cosmos as a whole rather than as separate parts, as do the numerous other thematic maps by him. He also produced a "retrospective" map, on a re-engraved plate, shortly after the event, which shows us that, although he misjudged the track of the umbra by about 20 miles and was unsure whether the eclipse would be total over London, he predicted the timing to within four minutes. This map also predicts the track of the next total eclipse, due on May 11, 1724; the fact that it passed over the Paris region may explain why the southward extent was lengthened and the northward extent reduced. The actual timing in various geographical locations was recorded mainly by "the Curious" whom Halley "... desired to observe it and especially the duration of total darkness with all the care they can." |
Total solar eclipses are probably the most spectacular and striking astronomical events. As they are visible in any part of the British Isles on average only about once a century, the last one before the eighteenth century being in 1652, it was important to alert the superstitious and fearful populace, who were also influenced by often dire astrological predictions, "so that the sudden darkness ... may give no surprise to People, who would, if unadvertised, be apt to look upon it as Ominous and to interpret it as portending evil to our Sovereign Lord King George." |
Total eclipses of the sun often occur in the same geographical area in groups or cycles, and the fact that no less than seven--five of them total eclipses--occurred over the British Isles in the eighteenth century resulted in many opportunities for publishing eclipse maps. The observations by the general public were later communicated to the Royal Society, where they were published in the scientific journal Philosophical Transactions for 1715. This and much other interesting textual information was engraved or letterpress-printed under the map to form a broadsheet or broadside. These were published separately and were the equivalent of modern newspaper reports containing the latest information. This practice dates back to the sixteenth century; an example is the well-known "Hondius Broadside," a world map published by Jodocus Hondius in 1595 to announce Drake's voyage. Broadsides were also used to illustrate marvels of nature and to announce the progress of battles. By the 1700s they contained more sophisticated information, such as a sheet produced by bookseller Thomas Taylor which included diagrams of solar and lunar eclipses with text, an attractive engraved view of people observing the total eclipse and a small map. They were sold at between one penny and sixpence, depending on quality, and in order to maximise sales they were also advertised beforehand in, for example, The London Gazette. |
Halley's competitor: William Whiston
Although Halley takes the credit for the first true eclipse map, the mathematician and astronomer William Whiston (1667-1752) also produced what could loosely be described as a map for the 1715 eclipse. Whiston, who was also an ordained churchman, succeeded Isaac Newton as Lucasian Professor (after Anthony Lucas, Newton's collaborator) at Cambridge University. He made several attempts to win the award for discovering the means of finding longitude at sea by using solar eclipses, which had been the main reason for observing them since the time of Ptolemy. The award was later won by John Harrison with his chronometer. Whiston was also a land surveyor and cartographer, producing a creditable three-sheet trigonometrical chart of the "British" Channel in conjunction with surveyor John Renshaw, as well as other astronomical charts such as the transits of Venus and Mercury across the sun (1735-6) and the solar system (c. 1730). |
Whiston's "geometrical" eclipse map was based on the tables of John Flamsteed (1646-1719), the first Astronomer Royal and an acrimonious competitor of Halley's. It depicts the northern hemisphere of the globe as seen from an oblique angle, with the image of the eclipse superimposed at three points in time. However, the point of the "map" is lost, as no geographical features are shown by which to orientate the track. Whiston himself admitted that "Doctor Halley has given us a particular map of England for the passage of the total shadow over it, but the nature of the construction does not admit of that projection." |
In other words, he was not able to create a map which would show the passage of the eclipse round the earth. Whiston goes on to say that this could be illustrated only by his own invention, the Copernicus, an astronomical instrument which shows the passages of eclipses through history. |
An innovator: Robert Browne
Another British astronomical practitioner to produce a map predicting the track of the 1724 eclipse was Robert Browne (fl. 1705-31), instrument maker and carpenter at St. Katherine's Dock and Mast Yard, Wapping. He was personally known to John Flamsteed, who taught him mathematics and astronomy, and Edmond Halley. Browne submitted a method of calculating longitude by lunar tables, divided the degree into 1,000 for ease of calculation, and observed 1,500 stars and their refractions. However, he was probably not a cartographer, judging by his attempt at mapmaking, which consists of a broadside containing two charts engraved side by side on the same plate. |
The left-hand chart is a geometrical diagram illustrating the appearance of the eclipse from London at different times. The right-hand chart is an attempt at a geographical map showing the track across southern England and France. It is far less accurate than Halley's prediction, aggravated by the lack of coastlines or accurate positioning of major towns with which to plot the track exactly. However, an important innovation appears on this chart in the form of small circular diagrams, about one inch in diameter, used to indicate the appearance of the sun at certain cities in the areas of penumbra. |
The culmination of the Halley tradition: George Witchell and the eclipse of 1764
The British tradition begun by Halley was being perpetuated by George Witchell (1728-85), a mathematician and Master of the Royal Naval Academy at Portsmouth. Witchell was also involved in the calculations of longitude, and in 1775 assisted James Cook, on the return from his second voyage, in checking his chronometers at the academy. His broadside for the eclipse of April 1, 1764, is the closest to the Halley design since the latter's of 1724. Engraved by Barak Longmate Sr. of Soho, London, it is almost a copy of the Halley map. The prediction was calculated from the tables of the French astronomer Abbi de la Caille, who with Cesar Frangois Cassini de Thury, son of the well-known French cartographer Jacques Cassini, revised the arc of the Paris meridian in 1740. The tables were communicated via Thomas Simpson, a mathematics professor at Woolwich Military Academy from 1743 and the author of several papers on astronomy. The prediction of the times is comparatively accurate, the beginning being 1 minute 33 seconds and the end 21 seconds too early, and the predicted track only about six miles too far west. The slight error was attributed by Witchell to his measurement of the diameters of the earth being slightly too large, rather than to an error in the tables. |
An almost identical map was engraved by John Gibson (fl. 1750-92) for another magazine, The Universal Museum. Witchell's broadside map itself is one of the most attractive, with a good balance of decorative lettering and scrollwork and scientific-looking presentation, along with the almost inevitable Browne-style double circles. |
An unsigned small, crude and basic map of this eclipse was also published in the February 1764 issue of The Gentleman's Magazine, together with a brief history of previous annular eclipses. The source of the prediction data is not given, but the track is far more inaccurate than that of Witchell. It is about 45 miles too far west, and the prediction times are more accurate at the beginning by 54 seconds and less accurate at the end by 7 minutes 31 seconds. |
The great popularizers: Robert Heath and Benjamin Martin
The Smith charts also influenced the mathematician and army captain Robert Heath (d. 1779), who was a great populariser of the study of mathematics in England and the somewhat controversial and opinionated editor of Ladies Diary from 1744 to 1753. Heath also wrote a history of the Scilly Isles, for which he drew a map from an actual survey made in 1744. |
The eclipse map he produced, based on his own tables published in The Royal Astronomer and Navigator (1760) to accompany his well-written popular pamphlet on the eclipse of 1764, used a similar skewed projection to that of Smith. It was engraved by J. Flyn. However, the partial map of the world and the British Isles is less well executed and inaccurate, the predicted path over southeast England being about 150 miles too far west. |
The optician, instrument maker and science populariser Benjamin Martin, the editor and writer of most of The General Magazine of Arts and Sciences, produced eclipse maps in addition to numerous other publications on scientific subjects and maps. He also collaborated with Emanuel Bowen on the Natural History of England (1761), which contained county maps. One of his eclipse maps was published in 1764 with a simplified technical pamphlet. |
This is a Whiston-type geometrical map/diagram of the globe, with the shadow of the eclipse at three points in time but without the geographical content introduced by Thomas Wright. This same map also accompanied an astronomical tract published a year later, together with an inaccurate outline geographical sketch of southeast England and the coast of France. It showed in retrospect the path of the eclipse in complex geometrical detail, contrasting surprisingly with the geographical data. Also in this work is a list of techniques for viewing the eclipse, the preferred method being a mirror attached to a telescope which projects the image onto a screen, and a delightful rustic landscape illustrating the transit of Venus on 3 June 1769. |
Interestingly, Benjamin Martin apparently acquired the globe-making business of John Senex via James Ferguson, who purchased Senex's stock in 1755. As well as making globes and astronomical instruments, Ferguson carried out research into the construction of eclipse maps, although the book he prepared on the subject was never published. |
The golden age
The eighteenth century could be regarded as the golden age of the eclipse map. Invented by Edmond Halley early in the century, maps of the British Isles underwent some changes and innovations and gradually became more accurate, culminating in Witchell's map. However, the style is still distinctively recognisable as that of Halley. Having started out as mainly broadside maps, they found their way into popular literature and journals, and were often extensively pirated. The world maps initiated by Whiston's geometrical diagram underwent a more dramatic evolution, culminating in the highly successful Smith-type skewed projection, which was also frequently copied. The geographical rather than the geometrical types were the most commonly produced, because they could be more easily understood by the public. |
The modern era
During the twentieth century, eclipse maps became more commonly published in newspapers, culminating in extremely accurate computer-generated but rather soulless diagrams. Finally, interesting throwbacks to eighteenth-century broadsides sometimes do turn up, such as a leaflet advertising Southport as "The Eclipse Town 1927," complete with an outline map of England and Wales, prediction times, a picture of a solar eclipse seen from space and a short text on "Nature's phenomenon." This information, however, is outnumbered three to one by three pages of advertisements reminiscent of those on eclipse maps published by John Senex and others in the "century of eclipses." |
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