Edmond Halley’s weather map illustrated a theory that accounted for major features of Earth’s atmospheric circulation, including trade winds and monsoon winds. He based his map on common elements that he abstracted from vast, diffuse particulars, including those derived from newly invented meteorological instruments such as the thermometer and the barometer.
Edmond Halley, who was the first to determine the elliptical orbits of comets, especially of the one that bears his name, also developed the first weather map, which he included in his work “Historical Account of the Trade Winds, and Monsoons, Observable in the Seas Between and Near the Tropics, with an Attempt to Assign the Physical Cause of Said Winds.” The paper appeared in the Philosophical Transactions, a scholarly journal of the Royal Society of London, formed in 1662 to advance the sciences, notably their practical applications.
Halley edited and financed the publication of his friend Sir Isaac Newton’s
Philosophiae naturalis principia mathematica (pb. 1687; The Mathematical Principles of Natural Philosophy, 1729; best known as the Principia
Halley’s contributions to meteorology and mapmaking, as well as to many other scientific fields, grew out of his lifelong study of motion: the movement of objects or bodies through time and space, their dimensions or qualities, the effects of their movement, and their changing locations or distances. He often rendered his studies through charts and maps of the earth and sky. He produced terrestrial maps and sky charts, both of which were closely related at the time. Although they differed in method, subject, or purpose, Halley’s maps and charts organized and correlated enormous amounts of information through inductive methods.
In 1676, Halley left Queen’s College, Oxford, and traveled to Saint Helena Island, off the southwest coast of Africa, to produce an astronomical map of the brighter southern stars. English astronomer John Flamsteed
Halley’s skills as an observer and interpreter of natural phenomena were honed from his experience with sea navigation, geography, astronomy, and Newton’s mathematics. His work on planetary wind belts involved the study of weather (a set of atmospheric conditions as they occur) and climate (prevailing atmospheric conditions during a given period of time), thus developing a kind of global meteorology. The term “meteorology” comes from the Greek meteora, meaning “things in the sky,” and was part of the English language by about 1620. For Halley, meteorology studied the result of actions over the entire Earth (and possibly even the entire solar system), events that include solar heating of Earth’s surface, atmospheric pressure, temperature, humidity, wind, cloud type, precipitation, and Earth’s rotation.
Prior to Halley’s time, the ideas of Greek philosopher Aristotle (384-322
Galileo is thought to have initiated the scientific study of weather. In 1593, he invented a thermometer, and in 1638, he conceived of a barometer, with temperature and air pressure being key meteorological components. Like Galileo, Halley believed that accurate scientific knowledge could be obtained only through direct observation, experimentation, and mathematical proof, believing empirical knowledge superior to the traditional knowledge of the ancients, including Aristotle.
For his weather map, Halley drew upon the work of other scientists, including Gerardus Mercator (1512-1594), a Flemish geographer, mathematician, and cartographer known for his method of cylindrical map projection (1568), and Robert Hooke
To create his worldwide weather map of winds, Halley employed technical inventions that grew logically from those currently in use or that could be developed from currently accepted theories. Also, he devised ingenious experiments to extract theories from diffuse, interacting, and highly variable data. Halley’s weather map, printed from a line engraving on copper, measured 19.25 by 5.75 inches, and was a Mercator projection. It focused on the equator and approximately 30 degrees of latitude north and south, ocean areas where wind belts developed best, atmospheric conditions being more uniform over oceans than over continents.
The map extended 90 degrees west of the prime meridian, which passes through Greenwich, England, and 150 degrees east of it. Its system of reference lines combined 15-degree longitude lines with 10-degree latitude lines, producing rectangles that differ in proportion to latitude. The map, representing about half of Earth’s surface, included tapered lines that indicated movement of the trade winds, the steady winds near the equator, and also shorter, thicker arrows that indicated movement of the monsoons. By identifying complex patterns of atmospheric motion that caused those winds, Halley determined, for instance, that the trade winds resulted from the unequal heating of Earth’s surface by the sun, one consequence of the 23.5 degree tilt of Earth’s axis. Warm air moved outward from the tropics, and cold air moved outward from the poles. Halley realized, however, that earth’s rotation from west to east affected the winds moving toward the equator and those moving toward the poles. It caused them to blow from the northeast in the northern hemisphere and from southeast in the southern hemisphere.
In addition, Halley traced the course of the monsoon winds of the Indian Ocean and the western and southern Pacific Ocean. Temperature variations arising from the distribution of landmasses caused the monsoon winds, a seasonal reversal of the trade winds. Monsoons blow from the southwest from April to October and from the northeast between November and March.
Edmond Halley’s weather map, though untitled, became known as “Halley’s Chart of the Trade Winds,” a chart being a map designed for a specific purpose. In this case, Halley’s map aided sea navigation, which was dependent upon ocean winds.
Even though Halley’s theories were tentative and provisional, he was able to visually demonstrate—with his maps—fundamental and comprehensive qualities of physical nature. Mapping winds had never before been done. His weather map initiated scientific weather forecasting well in advance of its sporadic appearance in the eighteenth century and its international establishment in the nineteenth century.
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Armitage, Angus. Edmond Halley. London: Thomas Nelson and Sons, 1966. A biography that focuses on Halley’s many scientific achievements. -
Cook, Alan. Edmond Halley: Charting the Heavens and the Seas. Oxford, England: Clarendon Press, 1998. A comprehensive account of Halley’s life and science. -
Ipsen, David Carl. Edmond Halley: More than a Man with a Comet. Philadelphia: Xlibris, 2004. Ipsen summarizes Halley’s explorations and discoveries. -
MacPike, Eugene Fairfield. Correspondence and Papers of Edmond Halley. London: Taylor and Francis, 1937. A collection of Halley’s correspondence that includes a memoir of Halley by a contemporary.
Robert Boyle; Galileo; Edmond Halley; Robert Hooke; Sir Isaac Newton; Evangelista Torricelli.