Edmond Halley will forever be linked to the comet that bears his name, yet he was also a multitalented mathematician who made important contributions to several fields of science. Able to excel at both pure and applied mathematics, he was a pioneer of social **statistics** and is considered the founder of scientific geophysics. As one of the most respected scientists of his time, he was also a good friend of English mathematician and physicist **Isaac Newton** (1643-1727), and helped publish Newton's greatest work.

### Early success in astronomy

Edmond Halley (pronounced HAL-ee) was born in Haggerston, England, which is outside London and in the borough of Hackney. His father, Edmond Halley, was a rich merchant who sold soap and salt, and owned businesses in London as well as various other rental properties. His mother, Ann Robinson, died in 1672, the year before Halley entered college. Edmond had a younger sister, Katherine, and a younger brother, Humphrey. Halley's father spared no expense on his oldest son's education, and arranged for a tutor to teach Halley at home then sent him to St. Paul's School in London. Halley entered Queen's College, Oxford, at the age of seventeen, where he first formally studied astronomy, a subject in which he had shown an early interest. His father encouraged this interest and purchased Halley several astronomical instruments, one of which was a twenty-four-foot-long telescope.

While a student at Queen's College, Halley began a regular correspondence with John Flamsteed (1646-1719), the Astronomer Royal at the Greenwich Observatory, and the older man guided Halley's progress in astronomy (although they would later have a falling out and Flamsteed would remain Halley's rival until his death). In 1676, Halley was able to join an expedition to Saint Helena to map the stars of the southern hemisphere. St. Helena is an island and a British colony located in the South Atlantic Ocean about one thousand miles off the west coast of Africa. When Halley returned in 1678, he published the first star charts of the southern hemisphere and dedicated it to King Charles II (1630-1685). Impressed with the published work of a twenty-two-year-old, the king issued an order that Oxford should grant Halley his master's degree. A year later, Halley was inducted into the prestigious Royal Society, to which all the leading scientists of England belonged. At the young age of twenty-three, Halley had already established what would be an ever-growing scientific reputation.

### Halley's Comet

Halley's best-known scientific achievement was his theory on the movement of comets. Beginning in 1680 with a trip to Paris to work with Italian French astronomer Giovanni Domenico Cassini (1625-1712), Halley began his painstaking observational work studying a new comet that had appeared that year. This was not to be his hallmark comet, but his detailed observations led him to consider a new theory that comets traveled in elongated or stretched out elliptical (egg-shaped) orbits and made regular or periodic returns past Earth. In other words, that the sightings of comets in the past were of the same comets making their return.

One of the comets he observed and studied intensively was the comet of 1682. This was to become known as Halley's Comet when it reappeared in 1758 (sixteen years after his death) as he predicted. He also predicted that it would reappear roughly every seventy-five or seventy-six years thereafter (1835, 1910, 1986, and so on). To arrive at this prediction, Halley spent years searching historical records and studying the movements of two dozen other comets. After meeting and becoming friends with the great Isaac Newton in 1684, Halley realized that comets were affected by the gravitational influence of planets. It was Newton, of course, who would make the scientific world aware of the universal principle of gravitation with the 1687 publication of his great work, *Philosophiae Naturalis Principia Mathematica* (The Mathematical Principles of Natural Philosophy).

In 1705, after years of mathematical calculations and study, Halley published a paper in which he first outlined his theory of elliptical orbits for comets. He further stated the bold prediction that the comet of 1682 would, as part of its natural, periodic cycle, follow a path that would have it return past Earth for all to see during December 1758. Although this paper and the book that followed aroused some interest among astronomers and scientists, it was not until the comet of 1682 did in fact reappear on December 25, 1758, that the entire scientific world took note. Halley's hope that the world would remember the comet was first discovered by an Englishman came true as the comet soon was named after him. More importantly, his successful prediction was viewed as proof or direct evidence of the correctness of Newton's theory of gravitation. With Halley's Comet, Newtonian mechanics became universally accepted.

### Wide-ranging scientific contributions

Among Halley's other astronomical achievements were his work on the nature and number of stars in the universe, the distance of the Earth from the sun, and how to use the stars to navigate and find longitude at sea. In studying these astronomical questions, his mathematics was always essential. In fact, Halley showed great interest in early mathematics, and when he was appointed Savilian professor of **geometry** at Oxford in 1704, he began a translation of the seven books of the *Conics* by Greek mathematician **Apollonius of Perga** (c. 262-c. 190 b.c.e.). This work took several years, and Halley even produced a reconstruction of the missing Book VIII.

In pure mathematics, Halley published seven papers ranging from higher geometry to **logarithms** and trigonometric functions. He also published papers in which he used mathematics to solve everyday problems, such as calculating a cannon's trajectory (the curved path it follows to its target) and computing the focal length of thick lenses. He also wrote papers on his archaeological (scientific study of the material remains of past human life and activities) research and on the nature of sunlight. He is considered by many to be the founder of scientific geophysics, which is the study of the physics of the Earth. He wrote on solar heating causing trade winds and monsoons, made the first meteorological (weather) chart containing real data, studied the tides, and contributed a theory on Earth's magnetism.

Halley was also a very practical man, and he carried out many experiments having to do with the sea. In addition to designing several different practical instruments, he designed a diving bell and a diver's helmet that were far ahead of anything of the time. He also established the mathematical law connecting barometric pressure with heights above sea level (showing to what degree pressure decreases as one climbs higher). Finally, Halley is recognized as one of the pioneers of keeping and using social statistics, as he used his mathematical skills in 1693 to show how mortality tables could be used as the basis for calculating life insurance payments. It was this practical sense that got him in trouble with church officials and other believers, for he took a mathematical and scientific approach to the question of the age of the Earth and decided that the Biblical estimate was far too low. He also got in trouble by trying to scientifically explain Biblical events, such as the flood in the story of Noah.

### Long and illustrious career

Besides his position at Oxford as Savilian professor of geometry, Halley was made Astronomer Royal in 1720. This appointment demonstrated the high regard in which he was held. In 1682, Halley married Mary Tooke, the daughter of an auditor at the royal bank. They had three children, Katherine, Margaret, and Edmond. His daughters survived him, but his son, a naval surgeon, died a year before Halley. His wife had died five years earlier. Halley was described as a freethinker who had a lively sense of humor and who could be extremely diplomatic and charming when necessary. His colleagues considered him a friendly man who was always ready to offer support to younger scientists. His friendship with Newton is known to have played a major role in the publication of Newton's *Principia,* which many consider to be the greatest scientific work ever published. Were it not for Halley's close collaboration with Newton, as well as his steady encouragement and actual financial assistance, the book that "altered the whole course of physical science" might never have been written. It was Halley who used his own money to pay for the publication of Newton's great work.

### For More Information

- Calder, Nigel.
*The Comet Is Coming!: The Feverish Legacy of Mr. Halley.*New York: Viking Press, 1980. - Girard, Linda Walvoord.
*Earth, Sea, and Sky: The Work of Edmond Halley.*Niles, IL: A. Whitman, 1985. - Heckart, Barbara Hooper.
*Edmond Halley, the Man and His Comet.*Chicago: Children's Press, 1984. - Hibben, Sally. "Edmond Halley." In
*The Great Scientists.*Edited by Frank Magill. Danbury, CT: Grolier Educational Corporation, 1989. - O'Connor, J. J., and E. F. Robertson. "Edmond Halley."
*The MacTutor History of Mathematics Archive.*School of Mathematics and Statistics, University of St. Andrews, Scotland. http://www.groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Halley.html (accessed July 12, 2002). - O'Connor, J. J., and E. F. Robertson. "Friedrich Wilhelm Bessel."
*The MacTutor History of Mathematics Archive.*School of Mathematics and Statistics, University of St. Andrews, Scotland. http://www.groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Bessel.html (accessed July 12, 2002). - Ronan, Colin A. "Edmond Halley." In
*Biographical Dictionary of Mathematicians.*New York: Charles Scribner's Sons, 1991, pp. 960-65.